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Regents ChemistryValley Stream South High School

What You Need to know About Solutions

What you need to know and be able to do by the end of this unit?• State the factors that affect the solubility of a substance.• Use the solubility curve (table G) to, determine the saturation point of a substance.• Use the solubility curve (table G) to describe a solution, in terms of its degree of saturation.• Determine the concentration of a solution• Explain the affect of the addition of a nonvolatile solute on the boiling and freezing points of

a solution.

Key Subject Competencies• Define a solution.

o Identify the parts of a solution,o Determine the factors that affect the solubility of a solution.o Distinguish between saturated, unsaturated, and supersaturated solutions.

• Use Table G to determine if a solution is saturated, unsaturated, and supersaturated.o Predict the solubility of an ionic compound by using the solubility table,o Describe a solution in terms of saturated, supersaturated, or unsaturated.o Identify the gases on Table G and explain the effects of temperature on their

solubility,o Explain what is meant by "like dissolves like."

• Use Concentration formula (Table T) to determine moles or Molarity.o Determine percent by mass of a substance,o Determine percent by volume of a substance,o Calculate concentration in pprn.

• Define the term nonvolatile solute.o Explain why the presence of a nonvolatile solute increases the boiling point of a

solution,o Explain why the presence of a nonvolatile solute decreases the freezing point of a

solution,o Understand that the greater the concentration of solute particles, the greater the effect

on the boiling and freezing points of a solution.• Define the term electrolyte.

o Give examples of substances that are electrolytes.o Explain that a solution's ability to conduct electricity depends on the concentration of

ions in the particles.

Vocabulary - * Denotes those terms most frequently appearing on Regents Examinations.

*Boiling point Percent by mass ^Solution

*Molarity ^Saturated ^Supersaturated

Parts per million (ppm) Solute *Unsaturated

*Vapor pressure *Solvent

1. Solution:

2. Solute:

3. Solvent;

4. Solubility:

5. Factors affecting rate/amount of solubility:RATE AMOUNT

a.

b.

6, Types of solutions:a. Saturated:

b. Unsaturated:

c. Supersaturated:

7. Dilute solution:

8. Concentrated solution:

Factors Worksheet

1. In an aqueous solution of potassium chloride., thesolute is

A) Cl B) K C) KC1 D) BhO

2. In an aqueous solution of sodium fluoride; Hiesolvent is

A) F B) Na C) NaF D) HzO

3. At room temperature, the solubility of which solutein water would be most affected by a change inpressure?

A) methanol B) sugarC) carbon dioxide D) sodium nitrate

4. The solubility of a salt in a given volume of waterdepends primarily on the

A) surface area of the salt crystalsB) temperature of the waterC) rate at which the salt and water are stirredD) pressure on the surface of the water

5. What Celsius temperature is equal to 142 K?

6. Base your answer to the following question on the information below.

In a laboratory, a student makes a solution by completely dissolving 80.0 grams ofKN03(s) in 100.0 grams of hot water. The resulting solution has a temperature of 60. °C.

The room temperature in the laboratory is 22°C.

Describe a laboratory procedure that can be used to recover the solid solute from the aqueoussolution.

': Form LsS.lA

SOLUTIONS

Name

Date Period

To explain why substances dissolve

Definition: Solution = homogeneous mixtureik Nature of mixtures

•w" consists of two or more kinds of matter•&- each substance in a mixture retains its own properties

Tt sugar and water - sweet and wet-fc brine (salt water) - salty liquid

~& the composition is variable (not constant)•&• can be separated by physical means

* Distinguishing solutions from mechanical mixtures•& properties of solutions

~k homogeneous mixtures - composed of two or moresubstances and have variable composition BUT theparticles are distributed evenly throughout eachother SO the composition is uniform

~fe the solution appears to be one substance7k consist of a solute dissolved in a solvent

•& solute - substance that IS dissolved by another•£- solvent

•& substance that dissolves anotherik continuous phase - salt dissolved in water appears

to be a liquidSolubility - ability to dissolve in water* Factors that affect solubility

•& Degree of solubility (how much dissolves)7*r nature of solute and solvent

fa in order for a solvent to dissolve a solute, itmust exert forces of attraction on the soluteT*T polar solvents such as water dissolve polar

and ionic solutes because they exertmutual attractions that cause their particlesto intermingle

iK nonpolar solvents such as benzene doNOT dissolve polar and ionic substancesbecause they exert no forces of attractionthat would cause the particles to separateso they can intermingle~k oil and water do NOT mix

fa nonpolar substances such as fat dissolve innonpolar solvents such as benzene becausethe forces of attraction are too weak toprevent the particles from freelyintermingling

fa like dissolves like (See Table F - Table ofSolubilities in Water)

?V Temperature (See Table G - Solubility Curves)fa solubility of solid solutes generally increases as

temperature increasesfa solubility of gaseous solutes generally

decreases as temperature increases

"U

~k Pressure•fa solids and liquids - no effect•fa gases: Henry's Law - mass of a dissolved gas

in a liquid is directly proportional to thepressure of the gas

Rate of solution

Factor

Particle Size

Stirring

Amount ofdissolved solute

Temperature

Affect on Solid Solute

reducing particle size bycrushing increases the rateby increasing surface area

increases the rate byexposing fresh solvent tosolute and increasingkinetic energy

as the amount of dissolvedsolute increases, the ratedecreases

as the temperatureincreases, the rateincreases

Affect on GaseousSolute

not applicable

decreases the rate byIncreasing kineticenergy, thereby reducingsolubility

as the amount ofdissolved soluteincreases, the ratedecreases

as the temperatureincreases, the ratedecreases

Saturation (see Table G)•£• Saturated solution - solution that cannot dissolve any

more solute at a given temperatureT^T added solute will NOT dissolve

A Unsaturated solution - solution that can dissolve moresolute at a given temperatureit added solute will dissolve

& Supersaturated solution - solution that holdsmore solute than it can dissolve at a giventemperature

~V produced by dissolving solute at a high temperatureand allowing it to cool slowly•fa addition of solute causes precipitation of the

excessConcentration - the amount of solute compared to solvent

•& Qualitative descriptionsfa concentrated - large amount of solute compared

to the amount of solventfa example - concentrated orange juice

fa dilute - small amount of solute compared to theamount of solventfa example - weak coffee

: Form N8.1A Solutions: An Introduction

SOLUTIONS Page 2

Answer the questions below by circling the number of the correct response

1. A reason why many salts dissociate in water is that water1, consists of polar molecules, 2. contains ionic bonds, 3, has alinear structure, 4. does not ionize

2. Ammonia gas and hydrogen chloride gas are very soluble in water,which answer best explains the reason for this? 1, water is a goodsolvent for gases, 2. NHs, HCI, and fyO molecules are polar. 3.NHs, and HCI molecules are very compact 4. NHs, HCI, and fyQmolecules are electrically symmetrical,

3. The attraction of water molecules to ions of a solute is1. hydration, 2. dispersion, 3. ionization, 4. crystallization

4. When an ionic solid dissolves in water, which of the followingoccurs? 1. ionization of molecules 2. hydration of molecules3. dissociation of ions 4. formation of ionic bonds with water

5. A reason why many ionic salts dissociate in water is that water1. consists of polar molecules 3. contains ionic bonds2. has a linear structure 4. does not ionize

6. A solution which contains less solute than should normally dissolveis 1. concentrated, 2. unsaturated, 3. saturated,4. supersaturated

7. To a solution of NH4d, a crystal of NH4CI is added. The crystal• falls to the bottom and more solid comes out of the solution. This

indicates the original solution was 1. unsaturated,2, supersaturated, 3. saturated, 4. concentrated

8. A solution in which no more solute can still be added and dissolve is1. supersaturated 3. unsaturated2. saturated 4. concentrated

9. To a solution of NaCI, a crystal of NaCI is added and the crystaldissolves. The solution must have been 1. supersaturated,2. saturated, 3, concentrated, 4. unsaturated

10. A solution which contains a maximum amount of solute that can bedissolved under the existing conditions is 1. saturated,2. unsaturated, 3. dilute, 4. supersaturated

11. Crystals of NaCI, when added to a solution of this salt that is inequilibrium with excess sodium chloride, will 1. dissolve in thesolution, 2. cause additional sodium chloride crystals to separatefrom the solution, 3. form a supersaturated solution, 4. cause nochange in the concentration of the solution

12. A saturated solution of which salt would be the most concentratedat 30°C? (see solubility chart) 1 . NaCI, 2. NaCI03, 3. KCI,4. KCI03

13. Which saturated solution would be most dilute at 0°C?1. Kl 3.2. NaNOs 4.

14. Which compound is most soluble in water?(see solubility chart)1. silver acetate 3. lead nitrate2, silver chloride 4. silver sulfate

1 5. As the temperature increases from 30°C to 40°C, the solubility ofpotassium nitrate in 100 g of water increases by approximately (seesolubility chart)1. 5 grams 3. 15 grams2rlO grams 4. 20 grams

1 6, Which compound is least soluble in 1 00 grams of water at1QOC?(see solubility chart)1. KN03 3. NaCI2. Kl 4. KC|03

17. A small cr/stal of the slightly soluble salt calcium sulfate dissolvesin a solution of calcium sulfate. The original solution must havebeen 1. dilute and saturated, 2. concentrated and saturated,3. dilute and unsaturated, 4. concentrated and unsaturated

18. As the temperature increases and the pressure remains constant,the solubility of a gas in a solution 1. decreases, 2. remains thesame, 3, increases, 4. varies directly

19. As the pressure on a gas increases, temperature remainingconstant its solubility in water 1. decreases, 2. remains the same,3, increases, 4. varies inversely

20. Which silver compound is most soluble in water? (see solubilitychart) 1. AgCl, 2. Agl, 3. AgaSO^ 4. AgNOs

21 . How many grams of KCI are required to saturate 1 000 grams ofH20 at 80°C?(see solubility chart) 1. 390, 2. 500, 2. 800, 4. 1000

Evan P. Silberstein, 2003

Properties of Solutions

Most of the materials that you use every day arenot pure substances. It is more likely that they aremixtures. This topic "will explore an important typeof mixture, the solution. The nature and propertiesof solutions are important concepts used in chem-istry. One reason they are so important is thatmost chemical reactions take place in solutions. Inthis topic you will study the nature and propertiesof solutions and ways to express the concentrationof solutions.

A solution is a homogeneous mixture of sub-stances in the same physical state. Solutions con-tain atoms, ions, or molecules of one substancespread uniformly throughout a second substance.When salt (NaCl) is stirred into water, the individ-ual ions of the salt separate and uniformly spreadthroughout the water, forming a solution.

A solid maybe dissolved in another solid. Brass isa mixture of zinc and copper. When metals aremixed to form a solution., the result is called analloy. Air is an example of a mixture of gases form-ing a solution.

Although solutions exist in all three states, thediscussion in this topic will be limited to liquidsolutions. Perhaps the most common type of solu-tion is one in which a solid or a liquid is dissolvedin a liquid.

The terms solute and solvent are commonlyused to identify the parts of a solution. la generalterms, the soiute is the substance that is being dis-solved, and it is the substance present in thesmaller amount. When solid sodium nitrate dis-solves hi water, the sodium nitrate is the solute.The substance that dissolves the solute is thesolvent, and it is present in the greater amount.Water is, perhaps, the most common solvent. Watersolutions are called aqueous solutions, and thenotation (aq) is used in equations to show that thesubstance is dissolved in water.

NaCKs) -> Na+fa<?) + Cl~(ag)

Once the salt and water are stirred and themixture becomes homogeneous, the dissolvedparticles will not settle. Liquid solutions are clear,and light will pass through a solution withoutbeing dispersed, as shown in Figure 7-1 on the nextpage.

Properties of Solutions 95

Beam oflight

Solution Not a solution

Figure 7-1. Light passing through a solution: The particles ina solution are too small to disperse light.When light passesthrough a liquid with larger particles, such as gelatin in water,you can seethe beam because larger particles disperse light.

Solutions may or may not have color. For exam-ple, solutions of copper salts have a characteristicblue color, while a solution of sodium nitrate is col-orless.

1. Solutions are homogeneous mixtures.

2. Solutions are clear and do not disperse light.

3. Solutions can have color.

4. Solutions will not settle on standing.

5. Solutions will pass through a filter.

You've noticed that some things easily dissolve inwater or other solvents. When you make a cup ofcoffee, certain materials in the coffee grounds dis-solve but other materials don't. Sugar will readilydissolve in the cup of coffee but the spoon you useto stir the solution does not dissolve. How much ofa solute will dissolve in a certain amount of solventat a certain temperature is known as solubility.Materials with a high solubility are said to be solu-ble: materials with a low solubility are said to beinsoluble. "What factors determine the solubility ofa solute hi a solvent?

E OF SOLUTE SOLVENT Whensodium chloride dissolves in water it does sobecause its positively and negatively charged ionsare attracted to the oppositely charged ends of thepolar water molecule. The dissolving process isshown in Figure 7-2. The positively chargedsodium, ions are attracted to the negative pole ofthe water molecules. The attractive forces betweenthe water molecules and sodium ions are greaterthan the attractive'forces between the sodium andchloride ions, hi like manner, the negatively

charged chloride ions are attracted to the positiveend of the water dipole and are dissolved- Ionic and._«..^-,j,j_-..

polar substances dissolve in polar solvents.

7-2, The dissolving process: Ionic and polar solutes dis-solve in polar solvents because unlike charges attract each other.

Nonpolar substances, such as fats, do not dissolvehi water because there aren't strong attractiveforces between the fat molecules and the watermolecules. Fat molecules will dissolve in nonpolarsolvents. The forces that hold the nonpolar mole-cules to each other are quite weak, and the mole-cules simply mix together. The term "like dissolveslike" is often used to describe what solutes will dis-solve in what solvents. Table 7-1 summarizes thisconcept.

SoluteType

nonpolar• polar

ionic

NonpolarSolvent

solubleinsolubleinsoluble

PolarSolvent

insolublesolublesoluble

An interesting and important case of "like dis-solves like" is found in the action of soaps. Greases,which are nonpolar., won't easily wash off ourhands in water, which is polar. Soaps are long car-bon chains that have one end that is polar, allow-ing the soap to dissolve in water. The other end ofthe soap is nonpolar, and grease will dissolve in it.

E As temperature increases, mostsolids become more soluble in water, A few excep-tions exist. Gases react in the opposite manner.As temperature rises, the solubility of all gases inliquids, decreases.

96 Topic 7

Pressure; Ji -s little or no..effecton thesolubility of solid or liquid solutes. Pressure doesaffect the solubility of gases in liquids. As pressureincreases, the solubility of gases in liquidsincreases. When a can of soda is opened, the pres-sure decreases. The carbon dioxide is no longer assoluble at the lowered pressure, and it escapes asbubbles.

1. In a true solution, the dissolved particles (1)arevisible to the eye (2) will settle out on standing(3) are always solids (4) cannot be removed byfiltration

2. When a teaspoon of sugar is added to water andstirred,the sugar (1) melts (2) dissolves(3) condenses (4) evaporates

3. In an aqueous solution of potassium chloride, thesolute is (l)CI-only (2)K+only (3) K+CT (4) H20

4. Which sample of matter is a mixture? (1) H2O(s)(2)H20(€) (3)NaC!(€) (4)NaCI(ag) .

5. Most ionic substances are soluble in water becausewater molecules are (l)nonpolar (2) inorganic(3) ionic (4) polar

6. Nonpolar solvents will most easily dissolve solidsthatare (1) ionic (2) covalent (3) metallic(4) colored

7. An aqueous solution of copper sulfate is poured intoa filter paper cone.What passes through the filterpaper? (1) only the solvent (2) only the solute(3) both solvent and solute (4) neither the solutenor solvent

8. As the temperature rises, the solubility of all gases inwater (1) decreases (2} increases (3) remains thesame (4) depends on the gas

9. A decrease in pressure has the greatest effect on asolution that contains (1) a gas in a liquid(2) a solid in a solid (3) a liquid in a liquid(4) a solid in a liquid

10. Under which conditions are gases most soluble inwater? (1) high temperature and high pressure(2) high temperature and low pressure (3) low tem-perature and high pressure (4) low temperature andidw"pressure

11. What happens when NaCI(j) is dissolved in water?(i)"G~ ions' are attracted YotHe'oxygerTatomTof thewater. (2) Cl~ ions are attracted to the hydrogenatoms of the water. (3) Na* ions are attracted^to thehydrogen atoms of the water. (4) No attractions areinvolved; the crystal just falls apart.

12. Which diagram best illustrates the ion-moleculeattractions that occur when the ions of NaQ{5) areadded to water?

(D

(2)

H-

0.

:o

(4)

Solubility information may be presented in differ-ent ways. Table G of Reference Tables for PhysicalSetting!Chemistry presents quantitative informa-tion showing the relationship of grams of solutethat may be dissolved at various temperatures.Table F provides some general guidelines about thesolubility of ionic substances. You will need to beable to interpret information from both tables.

Table G shows the num-ber of grams of a substance that can be dissolved in100. g of water at temperatures between 0°C and100°C. Each line represents the maximum amountof that substance that can be dissolved at a giventemperature. All of the lines that show an increasein solubility as temperatures increase representsolids being dissolved in water. Although theselines on the graph, show an increase in solubility astemperature increases, a few solids, such as cesiumsulfate, become less soluble as temperatureincreases.

Three lines show decreasing solubility withincreasing temperature. These three lines repre-sent the gases NHg, HC1, and S02. The solubility ofall gases decreases with increasing temperature.

Properties of SoSutions 97

Table G - Solubility Curves

Take a look at Table G in your Reference Tables and also up at the projections on theboard. Together we wfll determine the following:

1. What is the solubility of KI at 20 degrees Celsius per lOOg of water?

a.

2. What is the solubility of KNOs at 50 degrees Celsius per lOOg of water?

a.3. What is the solubility of SC>2 at 10 degrees and 90 degrees Celsius per lOOg of water?

• b.4. What is the solubility of KHs at 10 degrees and 90 degrees Celsius per lOOg of water?

a,

b.

Trends in Table G

1. Temperature versus solubility of a solid

2. Temperature versus solubility of a gas

10

Form WS8 . 1 . 2A

SOLUTIONS

Name

Date Period

The solubility of solid solutes generally increases as temperature increases, whilethe solubility of gaseous solutes generally decreases as temperature increases. Asolution that holds as much solute as can dissolve at a given temperature issaturated. A solution that can dissolve more solute at a given temperature isunsaturated. A solution that holds more solute than can dissolve at a giventemperature is supersaturated. The amount of solute that is needed to form asaturated solution at various temperatures can be graphed. This is what is shownin Table G. The values in Table G are based on solute dissolved in 100 g of water.Since water has a density of 1 g/mL, the graph can be considered to be based on100 mL of water. A 200 mL sample of water would be able to dissolve twice asmuch at each temperature.

Answer the questions below by referring to Table G.

1. The compound which is the most soluble at 20°C is

2. The compound which is the least soluble at 10°C is.

3. The compound which is the least soluble at 80°C is.

Table G SokftlEtty Curves

1-10

4. The number of grams of potassium nitrate needed to saturate 100 mL of water

at 70°C is .

5. The formulas of the compounds which vary inversely with the temperature are

and

0 1& 20 30 40 50 SO 70 80 90 100Temperature ("C)

6. One hundred mL of a sodium nitrate solution is saturated at 10°C. How many additional grams are needed to saturate

the solution at 50°C?

7. One hundred mL of a saturate KC1 solution at 80°C will precipitate 10 grams of salt when cooled to what temperature?

8. The two salts that have the same degree of solubility at 70°C are and

9. The salt with a solubility is least affected by a change in temperature is

10. The salt that has the greatest increase insolubility in the temperature range between 30°C and 50°C is

11. The number of grams of sodium nitrate that must be added to 50jnL,of water to produce a saturated solution at 50°C is

12. A saturated solution of potassium chlorate is made at 10°C by dissolving the correct mass of salt in 100 mL of water.

When the solution is heated to 90°C, how many grams must be added to saturate the solution?

Continue

11

1: Form ws 8 . l. 2A Solubility Curves

SOLUTIONS ' Page 2

13. At what temperature do saturated solutions of sodium chloride and potassium chloride contain the same mass of solute

per 100 rnL of water?

14. A saturated solution of potassium nitrate is prepared at 60°C using 200 mL of water. If the solution is cooled to 30°C,

how many grams will precipitate out of the solution?

15. How many more grams of ammonia can be dissolved in 100 mL of water at 10°C than at 90°C?

16. A saturated solution of sodium nitrate in 100 mL of water at 40°C Is heated to 50°C. The rate of increase in solubility

grams per degree is .

17. Thirty grams of KC1 is dissolved in 100 mL of water at 45°C. The number of additional grams of KC1 that would be

needed to make the solution saturated at 80°C is .


12

Name CONCEPT REVIEW- Solutions

A. What factors determine the amount of solute that will dissolve in a solvent?

B. What factors determine the rate at which a solute dissolves in a solvent?

WHAT IS A SOLUTION?In the space provided, write the letter of the description that best matches the term or phrase1. Solution A. in a solution, the substance in which the solid is dissolved2. Solvent B. describes a solution in which the solvent is water3. Solute C. in a solution, the substance dissolved in the solvent4._ __ Aqueous D. a stable homogenous mixture

What is the solubility of each of thefollowing substances at the temperaturesgiven?

6. KIat20°C

7. HC1 at 50°C

8. NH3at90°C

9. NH4C1 at 85°C

10.NaClatlOO°C

Are the following saturated, unsaturated,or supersaturated?

11. 100gofNaN03at20°C

12. 110eofKIat4040°C

13.30gofKClO3at60°C

14. 10gofNH3at90°C _

15. 55gofNH3 10°C

Table G Solubility Curves

0 10 20 30 40 50 ©0 70 SO 90 100

Temperature (SC)

13

Name

Answer the following questions basedon the solubility curve below.

1. Which salt is least soluble in water

at 20° C?

2. How many grams of potassium

chloride can be dissolved in 200 g

of water at 80° C?

150

3. At 40° C, how much potassium

nitrate can be dissolved in 300 g of

• water? •

4. Which salt shows the least change

in solubility from 0° - 100° C?

5, At 30° C, 90 g of sodium nitrate is

dissolved in 100 g of water. Is this

solution saturated, unsaturated or

supersaturated?

20 30 40 50 60 70 80 90 100

Temperature (0°C)

6. A saturated solution of potassium chlorate is formed from one hundred grams of

'water. If the saturated solution is cooled from 80° C to 50° C, how many grams of

precipitate are formed? ._

7. What compound shows a decrease in solubility from 0°- to 100° C?

8. Which salt is most soluble at 10° C? •

9. Which salt is least soluble at 50° C? '

I 10. Which salt .is least soluble at 90° C?14

NameWorksheet A — Solubility Curves

Solubility Curves- Use Table G to answer the following questions.

1. At what temperature would KNOs and NaNOs have the same solubility?

2. At 40°s how many grams of NaNOs dissolve?

3. What salt will change its solubility the least with an increase in temperature?

4. How is the solubility of a gas affected as temperature increases?

5. How much HC1 will dissolve in Water at thea. boiling point of water

b. freezing point of water^

6. What type of NaNOs solution is present at 30° and 90g of solute?

7. What type of Nt^Cl solution is present at 70°C and 80g of solute?

8. What salt is least soluble at 0°C?

9. How much solute can HC1 and NH3 dissolve at 5°C?

10. What salt increases its solubility the most with an increase in temperature?

15

NameWorksheet BSolutions

1-6 Refer to Reference Table G

1. Which of the salts shown of the graph is the least soluble in water at 10°C?

2. Which of the salts shown on the graph has the greatest increase in solubility as thetemperature increases from 30 to 60°?

3. Which of the salts has its solubility affected the least by a change in temperature?

4. Thirty grams of KC1 are dissolved in lOOg of water at 45°C. Howmanyadditional grams of KC1 are needed 10 make the solution saturated at 80°C?

5. At 20°C a saturated solution of sodium chlorate contains 100 grams of solute inlOOg of water. How many grams of sodium chlorate must be added to saturate thesolution at 5O°C?

6. Identify the following solutions as saturated, unsaturated, or supersaturated.a. 40g of KC1 in lOOg of H20 at SO°Cb. 120g of KN03 in lOOg of H20 at 60°C __^__c. 80g of NaN03 in lOOg of H20 at 10°C __^____ I

7. Soda is produced by dissolving carbon dioxide in water, CC>2(aq).a. When the cap is removed from a soda bottle, CC>2(g) is releases from solution.

State the relationship between gas solubility and pressure

b. When the soda is allowed to warm to room temperature, more CC>2(g) isreleased.

State the relationship between gas solubility and temperature

c. On the graph axis, sketch a curve for gas solubility and temperature: Label axes.

16

Pressure has little or no effect on thesolubility of solid or liquid solutes. Pressure doesaffect the solubility of gases in liquids. As pressureincreases, the solubility of gases in liquidsincreases. When a can of soda is opened, the pres-sure decreases. The carbon dioxide is no longer assoluble at the lowered pressure, and it escapes asbubbles.

Review Questions

1. In a true solution, the dissolved particles (1)arevisible to the eye (2) will settle out on standing(3) are always solids (4) cannot be removed byfiltration

2. When a teaspoon of sugar is added to water andstirred,the sugar (1) melts (2) dissolves(3) condenses (4) evaporates

3. In an aqueous solution of potassium chloride, thesolute is (DCTonly (2)K+only (3) K*cr (4) H20

4. Which sample of matter is a mixture? (1) H2O(5)(3)NaCl(€) (4)

5. Most ionic substances are soluble in water becausewater molecules are (l)nonpolar (2) inorganic(3) ionic (4) polar

6. Nonpolar solvents will most easily dissolve solidsthatare (1) ionic (2)covalent (3) metallic(4) colored

7. An aqueous solution of copper sulfate is poured intoa filter paper cone. What passes through the filterpaper? (1) only the solvent (2) only the solute(3) both solvent and solute (4) neither the solutenor solvent

8. As the temperature rises, the solubility of all gases inwater (1) decreases (2) increases (3) remains thesame (4) depends on the gas

9. A decrease in pressure has the greatest effect on asolution that contains (1 ) a gas in a liquid(2) a solid in a solid (3) a liquid in a liquid(4) a solid in a liquid

1 0. Under which conditions are gases most soluble inwater? (1) high temperature and high pressure(2) high temperature and low pressure (3) low tem-perature and high pressure (4) low temperature andiow'pressure

11. What happens when NaCI(s) is dissolved in water?(1) Cl~ ions are attracted to tHe'oxygen atoms "of thewater. (2) Cl~ ions are attracted to the hydrogenatoms of the water. (3) Na+ ions are attracted to thehydrogen atoms of the water. (4) No attractions areinvolved; the crystal just falls apart.

12. Which diagram best illustrates the ion-rnoleculeattractions that occur when the ions of NaCl(s) areadded to water?

H:o

o:

(1)

(2)

[3)

(4)

Solubility information may be presented in differ-ent ways. Table G of Reference Tables for PhysicalSetting/Chemistry presents quantitative informa-tion showing the relationship of grams of solutethat may be dissolved at various temperatures.Table F provides some general guidelines about thesolubility of ionic substances. You will need to beable to interpret information from both tables.

Table G shows the num-ber of grams of a substance that can be dissolved in100. g of water at temperatures between 0°C and100°C. Each line represents the maximum amountof that substance that can be dissolved at a giventemperature. All of the lines that show an increasein solubility as temperatures increase representsolids being dissolved in water. Although theselines on the graph show an increase in solubility astemperature increases, a few solids, such as cesiumsulfate, become less soluble as temperatureincreases.

Three lines show decreasing solubility withincreasing temperature. These three lines repre-sent the gases NHg, HC1, and SO2. The solubility ofall gases decreases with increasing temperature.


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10 20 30 40 50 60 70 80 90 TOO

Temperature (°C)

Figure 7-3. A solubility curve

Figure 7-3 shows four positions relative to aline of maximum solubility. Position A is below themaximum line of solubility. At this position, thetemperature is 35°C, and 25 g of solute X dissolve.Because at this point the solution holds less solutethan the maximum it can hold,, the solution is saidto be unsaturated. If there is not a temperaturechange, an additional 30 g can be added to bring Xto position B.

Position B is on the line of maximum solubility.A solution that contains a maximum amount ofsolute that will dissolve at a specific temperatureis saturated. At this position, the solution contains55 g of X. The addition of more solid solute will notresult in more being dissolved. Any additional solidthat is added will simply settle to the bottom of thecontainer.

If the temperature is reduced to 20°C, only 35 gof X can dissolve. When the temperature of thesolution at B is reduced, the most likely event isthat the excess 20 g of X will precipitate, and the-solution will remain saturated at point C. Onrather rare occasions, as the temperature decreases,crystals do not form and the substance may be atposition D.

At position D; there is more solid dissolvedthan normal. A solution that holds more solutethan is present in a saturated solution at that

temperature is supersaturated. These solutions arequite .unstable. The addition of a single solid crys-tal of the~substance will cause additional solid toform, and the solution will return to a saturated 'condition. If no temperature change occurred, thesolution would become saturated at point C; with

" 20 g of the substance precipitating. The only way tomake a supersaturated solution is to cool a satu-rated solution in which there are no crystals orimpurities, such as dust, present.

_ t—*•* t -1

, * ' PIGGING DEE^EJR^ - ,

'*. 'There are two~terrnsTthat ate somewhat useful inf **' describing toncenti ations of solutions Dilute solu- •>*? tJons'coritairvrelatively small a mo ants'of dissolved. * solute m a large amount of solvent For examplef5 q \ ^ «l * ft « ^ i I ' f - i - i j ' - l f ^ t 1 ' - ' - 3 ^

of a substance dissolved in 100 "g of H^Q would be a' t> cLjute-solutfon Concentfated/solutions'coiitain rela '

f tivelylatge''amounts(of solute These teifns should ^not be confused \vith5atuiateci and unsatuiatecP

i'lB'Cegramso^fpotassiUiiiVhloiate'dissolvedmJOO'g i' •3 H s ' y j r * ^ T \ -*

* f 'i j. f '- would-be saturated, 80 g*of NaN03 Bissolved in the <

same amount of watei would be concentrated, but.Lfnsatufated - ; ' >

MEMORY JOGGER "Z 1_ --„. -~ ^ p.. j. , _ - . ,,

? Jn'Topic2you jearnedthatdoubie-iepiacement5 reactions" have the gerieial formula '

;LES Table F of Reference Tablesfor Physical Setting!Chemistry contains someguidelines for the solubility of common ionic com-pounds. The table shows that all compounds of theammonium and the nitrate ion are soluble. All ofthe halide ions, such as Cl~, form compounds thatare soluble, but three exceptions are listed. Silverchloride is not soluble, nor are Pb2+ nor Hg22+ chlo-rides, and they are precipitates if they form in. adouble-replacement reaction. This table is useful inpredicting whether or not a precipitate will formwhen two ionic solutions are mixed. A reaction willtake place if one or both of the products is listed asinsoluble.

98 Topic 718

How does the nature of a solute and solvent affect solubility?

1. What is a polar molecule? .

2, What is a non-polar molecule?

3. What do you think is meant by the term, "Like dissolves like?"

19

SOLUBILITY (POLAR VS. NONPOLAR) •Name

Generally, "like dissolves like." Polar molecules dissolve other polar molecules and ioniccompounds. Nonpolar molecules dissolve other nonpolar molecules, Alcohols, whichhave characteristics of both, tend to dissolve in both types of solvents, but will not dissohionic solids.

Check the appropriate columns as to whether the solute Is soluble in a polar or nonpoia"solvent. . • •

SOLUTES

1, NaCI

2. L

3. ethanol

4. benzene

5. Brr

6. KNO,

7, toluene

8. CaCOHX

Water

SOLVENTS

CCL • Alcohol

Chemlstry IF8766 n-"K/-iru-il

How can we determine if a compound is soluble or insoluble?

Define:

1. soluble compound

2. insoluble compound

How can we use table F to find the solubility of a substance?

1, Is NaCl soluble?

2, Is AgBr soluble?

3. Is CaCO3 soluble?

4. Is (NH4)2S soluble?

21

1. Based on Reference Table F3 which of thesesaturated solutions has the lowestconcentration of dissolved ions?

1) NaCI(aq)

3) NiCh(aq)

2) MgCI2(aq)

4) AgCI(aq)

2. According to Reference Table F, which ofthese compounds is most soluble at 298 Karid 1 atm?

I) PbCh

3) PbCrO4

2) AgCl

4) PbCOa

3. According to Reference Table F, whichsubstance is most soluble?

2) CaS04

4)

1) Agl

3) PbCh

4. Based on Reference Table F, which of thefollowing compounds is least soluble inwater?

I) NaCl

3)

2)

4) PbCrCU

5. Based on Reference Table F; which salt isleast soluble?

1} FeCO3

3) BaCk

2) NasCOs

4) CaCh

6. Based on Reference Table F, which of thefollowing saturated solutions Avould be theleast concentrated?

1) sodium sulfate

2) potassium sulfate .

3) copper (II) sulfate

4) barium sulfate

7. According to Reference Table F, whichcompound is most soluble in water?

1) BaC03

3) ZnCOs

2) BaS04

4) ZnSO4

8. Which compound is insoluble in water?

1) calcium bromide

2) potassium bromide

3) silver bromide

4) sodium bromide

9. Which barium salt is insoluble in water?

1) BaCOs 2) BaCh

3) Ba(ClO4)2 4) Ba(NOs)2

10- Which ion, when combined with chlorideions, CI~, forms an insoluble substance inwater?

3) Pb2+

2) Mg2+

4)

22

^ 120

™ no

100

I 90

1 80en

o 70

OJ3 60o3 50>v

£ 40la

" 1 301/1

20

T O

/

D,

CJ/

•

A/

/

y/

•A

//

//

10 20 30 40 50 60 70 80 90 100

Temperature (°C)

Figure 7-3. A solubility curve

Figure 7-3 shows four positions relative to aline of maximum solubility. Position A is below the

rum line of solubility. At this position, theiperature is 35°C, and 25 g of solute X dissolve.

Because at this point the solution holds less solutethan the maximum it can hold, the solution is saidto be unsaturated. If there is not a temperaturechange, an additional 30 g can be added to bring Xto position B.

Position B is on the line of maximum solubility:A solution that contains a maximum amount ofsolute that will dissolve at a specific temperatureis saturated. At this position, the solution contains55 g of X. The addition of more solid solute will notresult in more being dissolved. Any additional solidthat is added will simply settle to the bottom of thecontainer.

If the temperature is reduced to 20°C, only 35 gof X can dissolve. "When the temperature of thesolution, at B is reduced, the most likely event isthat the excess 20 g of X will precipitate, and the'solution will remain saturated at point C. Onrather rare occasions, as the temperature decreases,crystals do not form and the substance may be atposition D.

At position D; there is more solid dissolvednormal. A solution that holds more solute

tiEan is present in a saturated solution at that

temperature is supersaturated. These solutions arequite .unstable. The addition of a single solid crys-tal of the"substance will cause additional solid toform, and the solution will return to a saturated 'condition. If no temperature change occurred, thesolution would become saturated at point C, with

'20 g of the substance precipitating. The only way tomake a supersaturated solution is to cool a satu-rated solution in which there are no crystals orimpurities, such as dust, present.

SuLUBgLETYTABLES Table F of Reference Tablesfor Physical Setting I Chemistry contains someguidelines for the solubility of common ionic com-pounds. The table shows that all compounds of theammonium and the nitrate ion are soluble. All ofthe halide ions, such as Cl~? form compounds thatare soluble, but three exceptions are listed. Silverchloride is not soluble, nor are Pb24" nor Hg22+ chlo-rides, and they are precipitates if they form in adouble-replacement reaction. This table is useful inpredicting whether or not a precipitate will formwhen two ionic solutions are mixed. A reaction willtake place if one or both of the products is listed asinsoluble.

98 Topic? 23

14. Solubility for salt X is shown in the table below.

RECOGNIZING UNSATURATED, SATURATED,AND SUPERSATURATED SOLUTIONS Becausesolutions are clear, it is difficult to simply look at asolution and determine whether it is unsaturated,saturated, or supersaturated.

One method of recognizing the type of solutionnarrows the choices. If a solution contains someundissolved solute, it must be a saturated solution.

The addition of a solute crystal can also beused to determine its condition. If it dissolves, theoriginal solution was unsaturated. If it simply fallsto the bottom, the solution is saturated. If it causesadditional crystals to form, the original solution.was supersaturated.

Review Questions

Use the tables in Reference Tables for PhysicalSetting/Chemistry as needed in answering the follow-ing questions.

13. Which compound's solubility decreases most rapidlyas the temperature changes from 10°C to 70°C?(1)NH4CI (2)NH3 (3)HCI (4) KCI

Temperature

(°O

10

20

30

40

50

60

Solubility

gsalt-Y100gH2O

5

10

15 -

20

30

35

Which graph most closeiy represents the data shownin the table?

Temperature (°C)

(1)

Temperature (°C)

(3)

(3)

Temperature (°C)

{2}

Temperature (°Q

(4)

15. A solution contains 14 g of KCI in 100. g of water at40°C What is the minimum amount of KCI that mustbe added to make this a saturated solution? (1) 14 g(2)19g (3)25g (4)44g

16. Which salt has the greatest change in solubilitybetween 30°C and 50°C? (1)KN03 (2) KCI(3) NaNO3 (4) NaCI

17. Which of the following substances is least soluble in100.gofwaterat50°C? (1) NaCI (2) KCI (3) NH4CI(4) HCI

24Properties of Solutions 99

18. A student obtained the following data in a chemistrylaboratory.

Trial

1234

Temperature

(°Q25324348

Solubility(gKN03/100gH20)

40507060_ —

Based on the reference tables, which of the four trialslisted seems to be in error? (1)1 (2)2 (3)3 (4)4

19. How many grams of the compound potassiumchloride (KCI) must be dissolved in 200. g of water tomake a saturated solution at 60°C?(1)30g (2)45g (3)56g (4) 90 g

20. Which of the following is insoluble? (1) calciumchloride {2} ammonium phosphate (3) bariumsulfate (4) potassium chromate

21. Which of the following is not soluble? (1) sodiumchromate (2) lead(II) iodide (3) lithium hydroxide(4) ammonium sulfate

. If solutions of sodium chromate and potassium car-bonate are mixed and poured into a filter, what willpass through the filter? (1) sodium, chromate, potas-sium,and carbonate ions (2) sodium and carbonateions only (3) potassium and chromate ions only(4) water only

23. Which amount of a compound dissolved in lOO.gofwater at the stated temperature represents a solu-tion that is saturated? (1) 20 g KCI03 at 80°C(2) 40 g KIM03 at 25°C (3) 40 g KCl at 60°C(4)60gNaNO3at40°C

Because solutions are homogeneous mixtures, theircompositions can vary: Sometimes, it is adequateto refer to a solution as dilute or concentrated.However, dilute and concentrated are relativeterms and are not precise regarding the amount ofsolute involved. In most cases it is the specificamount, or concentration, of the solute that isimportant. In this section you will learn several

of expressing the specific concentration ofin a solution.

One of the most important1 methods of stating theconcentration of a solution is in terms of the num-ber of moles of solute in a given volume of solution.The molarity (M) of a solution is the number ofmoles of solute in 1L of solution. The relationshipis listed in Table T of Reference Tables for PhysicalSetting I Chemistry.

, .__ moles of solutemolarity = -pr 7—r~^—~* liters of solution

*?rrai?*i v"''!»:;•?-'I' 'Kf '(vii. —.i<_).w-*tij;.(o iv .iK(.;;::,«•iv& $%& <$&•* fS&e '-*' '-^K' ''• '• !**"•£•'" S JSiT'(1-"'vW ~«i ii;,:" "M"%&zm$£i^&^^

In the previous sample problem, the molarity ofthe solution is 8.0 M. A liter of this solution wouldcontain 8.0 mol of the solute, NaOH. However, inmany problems, the mass of solute is given insteadof the number of moles. To solve this type of prob-lem, convert grams of solute to moles of solute andsolve as above.

100 Topic?25

Form WS8.1.3A

SOLUTIONS

Name

Date Period

A factory releases clean, warm water into a stream. The stream becomes ^ rT^arm wafer fs greatlyseverely polluted as a result. How does this happen? Fish living in the water I , a|Jesse^or S 6

depend on dissolved oxygen in order to breathe. Like other gases, oxygen - - - - - •-°fe-"_. •••"* —^molecules tend to spread out. In order to dissolve them, it is necessary toconfine them. Heat speeds the molecules up and makes them spread outmore-exactly the opposite of what is needed to dissolve them. As a result,heat drives the oxygen out of the water, causing the fish to die. The deadfish begin to decay. Growing decay bacteria deplete the water of oxygeneven further. In this way, clean warm water can pollute a stream. Theprocess of dissolving gases is opposite to the process of dissolving solidsbecause of the differences between gases and solids.

Answer the questions below based on your reading above and on your knowledge of chemistry.

1. A warm can of soda is dropped and bounces down a flight of stairs. When it is opened, carbon dioxide gascoming out of solution causes it to spray all over. Explain the affect of each of the following:

a. The fact that the soda was warm.

b. The fact that the soda was dropped and bounced down a flight of Stan's.

c. The fact that the can was opened.

2. When a gas dissolves, the particles need to be confined. What do the particles of a solid need to do in order to

dissolve? .

3. Sugar is added to a hot cup of coffee and stirred. The sugar dissolves. Explain the affect of each of the

following:

a. The fact that the coffee was hot. .

b. The fact that the coffee was stirred.

Continue

26

: Form WS8.1 .3A

SOLUTIONS

Dissolving Solids and Gases

Page 2

4. Which dissolves faster, a teaspoon of sugar or a sugar cube? Why?

5. A solid is added to water and stirred. Some of it dissolves, but not all. What happens to the rate at which thesolid is dissolving between when it was first added and when it stopped dissolving? Explain. (HINT:

Equilibrium!) .

6. The table below lists four factors that may effect the rate at which solids and gases dissolve. Fill in the table byindicating if the rate of dissolving increases, decreases, or is not effected. Then explain why.

FactorAffect on Rate of Solution for:

Solid Solutes Gaseous Solutes

Crushing

Stirring

Increasing theamount of dissolvedsolute

IncreasingTemperature


27

How concentrated Is a solution?

What does concentration mean?

Distinguish between dilute and concentrated

Define Molarity

What is the Molarity formula?

Solve the following and show all work:

1. What is the molarity of a solution containing 4.0 moles of NaOH in 0,50 L of solution?

2, What is the molarity of a solution containing 82.0g moles of Ca(NO3)2 in 2,0 L ofsolution?

1. What is the molarity of a KP(aq) solution containing 116g of KF in 1.0 L of solution?

28

Wi

!i$its

• . r. ':

'. ii:

m|,f.yi 'i

6;!^!'4;yi

MOLAR1TY (M) Name

Molnritv - motes Of solutetvioiariry - litero{SO|Ution

Solve the problems below.

1. What is the rnoiarity of a solution in- which 58 g of .NaCI are dissolved in 1.0 L ofsolution?

2. What Is the molarity of a solution in which "lO.Og of AgNO3 is dissolved in 500. mlof solution?

-3. How many grams of KNO, should be used to prepare 2.00 L of a 0.500 M solution?

4. To what volume should 5.0 g of KCI be diluted^in order to prepare a 0.25 M solution?

5. How many grams of CuSO4*5H2O are'needed to prepare 100, ml of a 0.10 Msolution?

29

1: Form WS 8 . 2 . 2A

SOLUTIONS

Name

Date Period

One of the most useful measures of concentration in chemistry is molarity (M). Molarity is thenumber of moles of solute per liter of solution. A two molar (2 M) solution contains two moles ofsolute per liter of solution.

Recall that the number of moles is determined by dividing the number of grams by the gram formulamass (GFM). There are a number of formulas for calculation that come from these relationships:

moles = M x L g=M* GFM x L A two molar solution

GFMx L

Below are some sample problems that show how to apply these formulas.

Sample Problem 1Find the molarity of 100. mL of a solution that contains0,25 moles of dissolved solute.

Step 1: Convert all volumes to liters

\mL

Step 2: Substitute values into the definitional equation,, mol Q25molM ~ = — — = 2.5 M

Sample Problem 2Find the molarity of 500. mL of a solution that contains4.9 g of dissolved sulfuric acid (H2SO4).

Step 1: Find the GFMH = 1 x 2 = 2

. S =32 x 1 = 3 2O =16 x 4 = 64


SQO.jnL x -^~—- = 0500ZImL

Step 3: Substitute values into the correct equation

= O.IOMGFMxL

r ASample Problem 3

How many moles of solute are dissolved in 250. mL of a3.0 M solution?


.ImL

Step 2: Substitute values into the correct equationmol = M x L = (3.0»%)(0^50i) = Q.lSmol

Sample Problem 4How many grams of sodium carbonate(Na2CO3) areneeded to prepare 250 mL of a 0.10 M solution?

Step 1: Find the GFMNa = 23C = 120 = 16


Step 3; Substitute values into the correct equation

30

Form W S 8 . 2 . 2 A

SOLUTIONS

Molarity

Page 2

Answer the questions below based on the reading and the sample problems on the previous page.

1. Determine the molarity of 500. mL of a solution with0.35 mol of dissolved solute.

2. A 200. mL sample of a solution contains 4.0 g of NaOH.What is its molarity?

3. How many grams of KNO3 are needed to prepare 25 mLof a 2.0 M solution?

4. How many moles of MgS04 are contained in 50. mL ofa 3.OM solution?

5. How many grams of CaCl2 are dissolved ina 0.75 M solution?

).0 mL of

6. What is the molarity of 300 mL of a solution thatcontains 0,60 mol of dissolved ammonia?

7. What is the molarity of 5.0 L of a solution containing200. g of dissolved CaCO3?

8. How many grams of NaCl are needed to prepare 500.mL of a 0.400 M solution?

9. How many moles of solute are contained in 3.0 L of a1.5 M solution?

10. What is the molarity of 750 mL of a solution thatcontains 40.0 g of dissolved CuS04?


31

Name

Acids are usually acquired from chemical supply houses in concentrated form. Theseacids are diluted to the desired concentration by adding water; Since moles of acidbefore dilution = moles of acid after dilution, and moles of acid = M x V then,M1xV1 = M2xV2, Solve the following problems. ' .

1. How much concentrated 18 M suifuric acid is needed to prepare 250 ml of a6,0 M solution? .

2, How much concentrated 12 M hydrochloric acid is needed to prepare 100 mLof a 2.0 M solution?

.3, .To what volume should 25 ml of 15 M nitric acid be diluted to prepare a 3,0 Msolution?

4. To how much water should 50. jnL of 12 M hydrochloric acid be added to producea 4,0 M solution? . ' .

5. To how much water should -100, ml of 18 M suifuric acid be added to prepare a1.5'M solution?

Chemistrv !F8766 AO

How concentrated is a solution in Parts Per Million?

When do we use pprn? .

What is the ppm formula?

Note: Do not forget to convert between kg, g, or mg.


1. A CuSO4 solution contains 0,050 g of CuSO4 dissolved in 1000 g of a solution. What isthe concentration in ppm?

2. Calculate the grams of fluoride ion in a 1250 grams of a fluoride ion solution having4.0ppm concentration.

3. Approximately 0.0043g of oxygen can be dissolved in 100.0 ml of water at 20°C.Express this in terms of ppm.

33

: Fo rm L s 8 . 2 A

SOLUTIONS

Name

Date Period

to calculate the concentration of a solution, including molarity, percent, and ppm

Concentration•k Definition:

Concentration =

* Molarity

•& definition:

Mass of solute(g)Volume of Solvent or Solution(mL}

moles(solute)

L(solutiori)related equations

if M= gGFM,L

moles = M x £moles

M* GFM

examples

Sample Problem 1Find the molarity of 100 mL of a solution that contains0.25 moles of dissolved solute.

Step 1: Convert all volumes to litersl O Q m L x 1L =0.1L

lUUUniLStep 2: Substitute values into the definitional equation

M= moles = Q..25 moles = 2.5M

L 0.1 L

Sample Problem 2Find the molarity of 250 mL of a solution that contains 4g of dissolved sodium hydroxide (NaOH).

Step 1: Find the GFMNa = 23 x 1O =16 x 1H = 1 x 1

= 23= 16

40~Step 2: Convert all volumes to liters

250 mL x 1L = 0.25 LlOuumL

Step 3: Substitute values into the correct equationM= g = 4g =0,4M

GFM xL 40 g/raole x 0.25 L

Sample Problem 3How many moles of solute are dissolved in 30 mL of a2 M solution?

Step 1: Convert all volumes to liters30 mL x 1L = 0.03 L

1000 mLStep 2: Substitute values into the correct equation

moles = M x L = (2 moles/L)(0.03 L) = 0.06 moles

Sample Problem 4How many grams of silver nitrate (AgNO3) are needed toprepare 200 mL of a 0.1 M solution?

Step 1: Find the GFMAg =108 xN = 14 xO = 16 x

= 108= 14

170Step 2: Convert all volumes to liters

200 mL x 1L = 0.2 L1000 mL

Step 3: Substitute values into the correct equationg = M x GFM x L =(0.1 mole/L)(170g/mole)(0.2 L) *= 3.4 g

Percent solution and parts per million (ppm)•& Percent by mass:

mass (solute)percent mass =

mass (solution)x 100%

Sample ProblemWhat is the percent by mass of a solution containing 2.3 g ofethanol CC3HjOH) dissolved in 10.0 g of water?

Step 1: Find the mass of the solution10.0 g +2.3g =123g

Step 2: Divide the mass of the solute by the mass of the solutionand multiply by 100%

percent mass =J

x 100% - 19%

34

Form Ls8.2A

SOLUTIONS

Quantities in Solutions

Page 2

Of Percent by volume:volume (solute) , n_ri,

percent volume = x 100%volume (solution)

Sample ProblemWhat is the percent by volume of a solution containing18.2 mL of glycerine (C3H6O3) dissolved in 85.0 mL ofwater?

Step 1: Find the volume of the solution.18.2 rnL +85.0mL = 103.2 mL

Step 2: Divide the volume of the solute by the volume ofthe solution and multiply by 100%

percent volume - —'——- x 100% = 17.6%W32mL

Parts per millionmass(solute)

ppm ~mass(solution)

x l,QQO,QOQppm

Sampje ProblemAbout 0.0035 g of hydrogen sulfide are dissolved in10.0 g of water. Express this in parts per million.

Step 1: Find the mass of the solution10.0 g + 0.0035 g= 10.0035 g

Step 2: Divide the mass of the solute by the mass of thesolution and multiply by 1,000,000 ppm.

0-0035* i n r

10.0035^= 350ppm


1. How many grams of H2S04 are contained in 1,00 liter of 0.500 Msulfuric add? (1)22.4 (2)98,0 (3)49.0 (4)196

2. In a 2.0 M solution of KOH, how many moies of KOH are contained in500 milliters of the solution? (1)1 (2)2(3)0.5(4)4

3. If 0.25 mole of sodium chloride is dissolved in a liter of solution, themolarityof the solution would be (1) 1M (2) 0.50 M (3) 0,25 M(4) 0.125 M

4. If 0.5 liter of water is added to 0.5 liter of 2,0 m KBr solution, themolarityof the resulting solution will be (1)1.0 (2)2.0 (3)0.5(4)1.5

5. 29 grams of NaCI are added to enough water to make 1,000. ml ofsolution. What is the molarity of the solution? (1) 1.00 M(2) 0.29 M (3) 0.50 M (4) 5.00 M

6. What is the molarity of a solution of hydrochloric acid that contains3.65 grams of HCI dissolved in 1.0 liter of solution? (1) 0.10 M(2) 0,20 M (3) 0.80 M (4) 0.40 M

7. A1 M solution contains 40 grams of a compound in 500 ml ofsolution. What is the molecular mass of this compound? (1) 20(2) 40 (3) 60 (4) 80

8. A 500 ml solution containing 28 grams of KOH is diluted with waterto 1,000. ml. What is the molarity of the resulting solution? (1)1.0M (2) 2.0 M (3) 0.25 M (4) 0.50 M

9. One liter of a sodium hydroxide solution contains 100 grams ofNaOH. The molarity of the solution is (1J1.0M (2)0.25M(3) 2.5 M (4) 0.50 M

1 0. When 20.0 grams of NaOH is dissolved in 500 ml of solution, theconcentration of the solution is (1)1.0M (2J20M (3) 0.50 M(4) 4.0 M

11. If 49 grams of pure H2S04 are added to enough water to make1 ,000 ml of solution, what is the moiarity of the solution? (1 ) 1 .0 M(2) 0.25 M (3) 0.50 M (4)0.10M

1 2. The number of moles of KCI in 1 ,000 ml of 3 molar solution is(1)1 (2)2(3)3 (4)1.5

13. How many moles of 804 are present in 250 ml of a 2.00 Msolution? (1)0.50 (2)2.00 (3)1.25 (4)8.00

14. If 500 ml of 1 .0 M H2S04 is diluted with H20 to a new volume of1, 000 mL, the molarity of the new solution is (1)1.0 (2)2.0(3) 0,25 (4) 0.50

15. One liter of a solution of nitric acid contains 1 26 grams of solution.The molarity of the solution is (1)1.00 (2)2.00 (3)1.26 (4)0.500

1 6. How much ethanol C^OH must be added to water to make 1 .0liter of 0.5 molar solution of ethanol? (1)0.5 gram (2) 46 grams(3) 23 grams (4) 92 grams

17. What mass of NaOH (formula mass - 40 g,) is needed to prepare500 ml of 0.50 M solution? (1)10. grams (2) 20 grams (3)25grams (4) 40 grams

1 8. Two liters of a solution of sulfuric acid contain 98 grams of H2S04.The molarity of this solution is (1)1.0 (2)2,0 (2)0.50(4)1.5

1 9. How many moles of AgNOs are dissolved in 1 0 ml of a 1 MAgN03? (1) 1 (2) 0.1 (3) 0.01 (4) 0.001


35

Molarity and PPM Worksheet

Show all work. Name:

1. What is the molarity of a solution containing 3 moles of sodium chloride in 0.5 L ofsolution?

2. How many moles of calcium chloride is needed to prepare 0.25M of a 2000mlsolution?

3. What is the molarity of a solution containing 29g of NaCl in 1L solution?

36

4. What is the molarity of a solution containing 57g of MgF2 in 500ml solution?

5. If the amount of dissolved oxygen in water is 0.005g in 75 ml of water. What doesthis represent in ppm?

6. What is the concentration expressed in Parts per million of a solution containing 15.0grams of KN03 in 65.0 grams of EfeO?

37

How do you express concentration of a solution in Percent by Mass?

Percent by Mass is very similar to Percent Composition, We use the same formula, but we arelooking to determine concentration of solutions, not percentages of a molecule.

What is the percent composition formula?

What do we use for Percent by Mass? , . .


1. What is the percent by mass of NaCl if 19.0g of NaCl is Dissolved in enough water tomake 175 g of solution?

2. What is the percent by mass concentration of a solution where 5.0g of salt are dissolvedinSO.Ogof water?

3, What is percent by mass of NaOH if 2.5g is added to 50.0g of water?

38

8. A student obtained the following data in a chemistrylaboratory.

Trial

1234

Temperature(°Q25324343

Solubility(g KNO/1 00 g H^O)

40507060

Based on the reference tables, which of the fourtrialslisted seems to be in error? (1)1 (2)2 (3)3 (4)4

19. How many grams of the compound potassiumchloride (KCI) must be dissolved in 200.g of water tomake a saturated solution at 60°C?(1)30g (2)45g (3)56g (4)90g

20. Which of the following is insoluble? (1) calciumchloride (2) ammonium phosphate (3) bariumsulfate (4) potassium chromate

21. Which ofthefollowing is not soluble? (1)sodiumchromate (2) lead(II) iodide (3) lithium hydroxide(4) ammonium sulfate

If solutions of sodiurn chromate and potassium car-bonate are mixed and poured into a filter, what willpass through the filter? (1) sodium, chromate, potas-sium, and carbonate ions (2) sodium and carbonateions only (3) potassium and chromate ions only(4) water only

23. Which amount of a compound dissolved in lOO.gofwater at the stated temperature represents a solu-tion that is saturated? (1) 20 g KCI03 at 80°C(2) 40 g KNO3 at 25°C (3) 40 g KCI at 60°C(4)60gNaNO,at40°C

Because solutions are homogeneous mixtures, theircompositions can vary: Sometimes, it is adequateto refer to a solution as dilute or concentrated.However, dilute and concentrated are relativeterms and are not precise regarding the amount ofsolute involved. In most cases it is the specificamount, or concentration, of the solute that isimportant. In this section you will learn several

of expressing the specific concentration ofin a solution.

One of the most importanfrmethods of stating theconcentration of a solution is in terms of the num-ber of moles of solute in a given volume of solution.The molarity (M) of a solution is the number ofmoles of solute in 1L of solution. The relationshipis listed in Table T of Reference Tables for PhysicalSetting I Chemistry.

\v — nioles of solutey ~ liters of solution

In the previous sample problem, the molarity ofthe solution is 8.0 M. A liter of this solution wouldcontain 8.0 mol of the solute, NaOH. However, inmany problems, the mass of solute is given insteadof the numher of moles. To solve this type of prob-lem, convert grams of solute to moles of solute andsolve as above.

100 Topic 7 39

It is conunon to find labels that list the concentra-tion of the ingredients by percent mass. Fertilizersoften list the active ingredients as a percentage ofthe entire mass of the fertilizer. Percent mass issimply the mass of an ingredient divided by thetotal mass, expressed as a percent (parts per hun-dred). Percent mass problems are essentially thesame as the percent composition problems found inTopic 3. To calculate the percent mass, use the fol-lowing relationship.

mass of part , „ nftn,percent mass = , *,_ .— x 100%r -mass of whole

When two liquids are mixed to form a solution, it iscommon to express the concentration of the soluteas a percent by volume. A label on a bottle of rub-bing alcohol shows a common example. Usually thelabel will show that the solution is 70% isopropylalcohol by volume. The rest of the solution is

Percent by volume is the ratio of the volume oan ingredient divided by the total volume andexpressed as a percent.

. . volume of solute v ~nnn,percent by volume = —: -,——; x 100%^ * volume of solution


%!'

s per roiUiori is similar to percent compositionecause it compares masses. Parts per million (ppm)

is a ratio between the mass of a solute and thetotal mass of the solution. This method of reportingconcentrations is useful for extremely dilute solu-tions when molarity and percent mass would bedifficult to interpret. For example, chlorine is usedas a disinfectant in swimming pools. Only about2 g of chlorine per 1,000,000 g of swimming poolwater is necessary to keep the pool sanitized.Finding molarity and percent mass would result innumbers too small to be useful. Parts per million isoften used to report a measured amount of air orwater pollutants.

Percent composition uses the amount presentper hundred parts because it is a percent. The onlydifference in finding ppm is that you multiply by1,000,000 ppm instead of 100 percent.

grams of soiute „ -._ „„„ppm = —a——i—T-^. x 1,000,000 ppmgrams GI soiiuion

It is important to be able to calculate the amountof solute to be added to a known volume of solventto make a solution of specified concentration. The

••wing sample problem shows you how to deter-e the amount of solute needed to prepare a

solution of known molarity.

You now know how much solute and solventyou need to actually prepare the solution in thesample problem, but the procedure used in prepa-ration is also essential. The steps outlined beloware specific for the solution used in the sampleproblem, but they apply to the preparation of anysolution of known concentration.

First, add 53.0 g of sodium carbonate to a2.00-L volumetric flask. Then, add some distilledwater and swirl until the solute is dissolved andthoroughly mixed. Finally, nil with distilled waterto the mark on the neck of the flask, and again stirto make sure the solution is homogeneous. The rea-son the water is added in two steps is that it is eas-ier to dissolve the solute if the flask: is not full andthere is room for the water to be adequately stirredor shaken.

102 Topic?41

Review Questions

24. What is the molarity of a Kf(aq] solution containing116 g of KF in 1.00 L of solution? (1J1.00M(2) ZOOM (3) 3.00 M (4}4.00 M

25. What is the molarity of an H2S04 solution if 0.25 !_ oftHe solution contains 0.75 mol of H2SO4? (1) 033 M(2) 0.75 M (3)3.0M (4) 6.0 M

26. What is the total number of moles of the soluteH2S04 needed to prepare 5.0 L of a 2.OM solutionofH2S04? (1)2.5 mol (2) 5.0 rnol (3) 10. mo!(4) 20. mol

27. What volume of a 2.0 M solution is needed to provide0.50 mol of NaOH? (1)0.251 (2) 0.50 L (3J1.0L(4) 2.0 L

28. What is the molarity of a solution that contains 40. gof NaOH in 0.50 L of solution? (1)1.0M (2J2.0M(3) 0.50 M (4) 0.25 M

29. If 100. mL of a 1.0 M solution is evaporated to a vol-ume of 25 ml, what will be the concentration of theresulting solution? (1)0.25M (2) 0.50 M (3J2.0M(4) 4.0 M

30. What is the percent by mass of a solution in which60. g of NaOH are dissolved in sufficient water tomake TOO g of solution? (1)16% (2)40% (3)60%(4) 160%

31. What is the percent by mass of a solution ff60.gofacetic acid are added to 90.g of water? (l) 20%(2) 30% (3) 40% (4) 67%

32. Carbon dioxide gas has a solubility of 0.0972 g/100 gH20 at 40°C Expressed in parts per million,this con-centration is closest to (1) 0.972 ppm (2) 9.72 ppm{3)97.2ppm (4) 972 ppm

33. A substance has a solubility of 350 ppm. How manygrams of the substance are present in 1.0 L of a satu-rated solution? (1) 0.0350 g (2) 0.350 g (3) 3.50 g(4) 35.0 g

Use the reference tables and your knowledge ofchemistry to answer each of the following questions.Be sure to show all work if calculations are needed.

34. What is the percent mass of a saturated solution ofKCI03at20°C?

35. A saturated solution of ammonium chloride in 100. gH20 at 85°C is cooled to 20°C and filtered. What wasthe.mass of the solution af 85°C? What is the mass ofthe liquid that passes through the filter?

42

36. Barium sulfate is listed as insoluble on solubilitytables. It does, however, dissolve to a small extent Itssolubility at 50°C is 0.00034 g in lOO.g of water.Express this solubility in parts per million.

37. The table below gives the solubility of Ca(OH)2(s) inlOO.g of H20 at various temperatures. What is unusualabout the behavior of the solubility of this salt?

Temperature(°O

020406080

Solubility(gCa(OH)/100.g H20)

0.1890.1730.1410.1210.094

The freezing and boiling points of water changewhen nonvolatile solutes are added. When any saltis added to water, the freezing point of the waterdecreases. This helps explain why salt is applied toroads and sidewalks when, they are covered withsnow and ice. The added salt lowers the freezingpoint and helps to melt the snow or ice. Theamount of the lowering of the freezing point isdependent on the nature of the added particle. Onemole of any particles will have the same effect onthe freezing point. One mole of particles lowers thefreezing point of 1000 g of water by 1.86°C.

When one mole of sugar, a molecular substance, isdissolved in water, one mole of particles is pro-duced in solution.

p TT r\x P TT O (rtn\T iw/ ~7 12" 2 11^ ^'

1 mol 1 molWhen one mole of an ionic substance is dis-

solved in water, the results are different. The ionicsubstance separates into individual ions.

NaCl(s) —» Na*(og) + Cl~(a£)1 mol NaCl 1 mol Na^ + 1 mol Cl"

Thus, one mole of sodium chloride produces twomoles of particles and will depress the freezing pointof water twice as much as the mole of sugar. Thegreater the number of ions., the greater the effectthe freezing point. CaCl2 contains three ions, and'one mole of this salt will depress the freezing pointthree times as much as a mole of sugar.


What is the effect of a solute on Boiling Point Elevation and Freezing Point Depression?

Why do we pour salt on the ground in the winter? .

Changes in BP and FP follow these rnles.

Rule#l

Rule #2

Compare how will each of the following arYect the BP or FP of water?

NaCl

MgCl2

A1203

43

: Form N8 . 3A

SOLUTIONS

Name

Date Period

to explain boiling point elevation and freezing point depression

Colligative properties - effect of solute on solvent due to the number of particles~k Nature of colligative properties

-& Not affected by the properties of the solute, but only by the number of particles•& Electrolytes dissociate producing more particles per mole than nonelectrolytes

"& therefor electrolytes produce larger colligative affects than nonelectrolytesif Examples

ik Boiling point elevation - nonvolatile solute reduces the vapor pressure of water, raising theboiling pointif molal boiling point elevation = 0.5 12°C/m

•& Freezing point depression - the presence of solute interferes with crystallization, lowering thefreezing pointif molal freezing point depression = L86°C/m


1. A pupil dissolved 180.00 grams of CgHÔg in 1,000.0 grams ofwater and then heated the solution until it boiled. What was theboiling point of the CgHÔe solution? (air pressure is 1atmosphere) (1)98,96°C (2)100.52°C (3) 99.48°C (4) 101.04°C

2. One mole of an ionic salt will usually depress the freezing point ofwater to a greater extent than one mole of a soluble organicsubstance because the ionic salt(1) will produce more particles in solution(2} is more easily hydrated(3) has a higher melting point(4) has a higher molecular mass

The solutions described in questions 3 - 9 have the sameconcentration of dissolved solute.

3. Which solution would have the lowest freezing point? (1) NaCI(aq)(2) HCl(aq) (3) KCI(aq) (4) CaCI2(aq)

4. Which solution will have the lowest freezing point?(1)CH3COOH (2}C6H1206 (3) C2H5OH (4) H2S04

5. Which water solution will have the lowest freezing point?(1) BaCl2 (2) Nad (3) C3H5(OH)3 (4) CH3COOH

6. Which water solution will have the lowest freezing point?(1}CaCl2 £2}Ci2H22°11 (3) NaCI (4) COCOON

have the highest boiling point?(3) Mg{N03)2(4)

7. Which solution(1)KN03

(2)AI(N03)3

Which solution has the lowest freezing point?(1) acetic acid (3) nitrous acid(2) potassium hydroxide (4) ammonium hydroxide

9. Which water solution(1) CaCI2(2) NaCI

have the highest freezing point?(3)C12H220n(4) CHsCOOH

10, If 46,0 grams of ethanol C2H50H are completely dissolved in1,000. g of water, the freezing point of the solution in Celsius ismostnearly (1)3,72 (2)-1.86 (3)1.86 (4)-3.72

11, The solution with the lowest freezing point would be producedwhen 1.0 gram of CgHÔg is dissolved 'n(1) 18 grams of H20 (3) 180 grams of H20(2) 100 grams of H20 (4) 1,000 grams of H20

12, What is the total number of grams of C^2°Q ât must bedissolved in 1,000 grams of water to raise the boiling point0.52°C? (boiling point elevation constant of H20 = 0.52°C)(1)9 (3)18(2)90 (4)180


44

: Form WS8 . 3 , 1A

SOLUTIONS

Name

Date Period

After a winter storm, people spread salt on the walks to help melt the ice.Salt reduces the freezing point of water. Actually, any soluble solutereduces the freezing point of water by interfering with crystallization. Inthis way, antifreeze keeps the water from freezing in an automobileradiator. This phenomenon is called freezing point depression. Antifreezeis left in the radiator during the summer. It also prevents the radiator fromboiling over by raising the boiling point. Dissolved solute reduces thevapor pressure, raising the boiling point. This is called boiling pointelevation.

The amount the freezing pointis depressed or the boilingpoint is raised depends on theconcentration of dissolvedsolute. The higher theconcentration of dissolved

Va por pressure exerted by waterVapor pressure exerted by solute

These aresaity and

cold!

couldn't ftgbithe barbecue,soi thought," extra.salt ,would-makethem .cnert in.your mouth!

Dad misinterprets freezing point depression.

solute is, the greater the effect on the boiling point or the freezing point is. Only theconcentration of the particles of dissolved solute is important. The nature of thesolute is not A mole of dissolved sugar has exactly the same effect on the freezingpoint and boiling point of 1,000 g of water as a mole of antifreeze because itcontains the same number of particles. Ionic compounds dissociate producing

more particles per mole. One mole of dissolved sodium chloride, for example, produces one mole of aqueous sodium ions andone mole of aqueous chloride ions for a total of two moles [NaCl(s) —*-Na+(ag) -t- Cl~(aq)], One mole of dissolved sodiumchloride, therefore, has twice the effect on the boiling and freezing points of 1,000 g of water as one mole of dissolved sugar.It is not the nature of the solute that matters, but only the concentration of dissolved particles that determines how large thechange in freezing point or boiling point will be. Properties of a solution, such as this, which are dependent only on the numberof particles in solution, and not on their nature are called colligative properties.

Answer the questions below based on your reading and on your knowledge of chemistry.

1. Why are boiling point elevation and freezing point depression considered colligative properties?

2. Why is salt put on icy roads and sidewalks in the winter?

3. How will the boiling points of pure water and sea water compare? Why?

Continue

45

24. What is the molarity of a KF(aq) solution containing116 g of KF in 1.00 L of solution? (1) 1.00 M(2) 2.00 M (3) 3.00 M (4) 4.00 M

25. What is the molarity of an H2SO4 solution if 0.25 L ofthe solution contains 0.75 mol of H2SO4? (1) 0.33 M(2) 0.75 M (3)3.0M (4) 6.0 M

26. What is the total number of moles of the soluteH2S04 needed to prepare 5.0 L of a 2.0 M solutionofH25O4? (1)2.5 mol (2) 5.0 mo! (3) 10. mo I(4) 20. mol

27. What volume of a 2.0 M solution is needed to provide0.50mo!ofNaOH? (1)0.25L (2) 0.50 L (3J1.0L(4) 2.0 L

28. What is the molarity of a solution that contains 40. gof NaOH in 0.50 L of solution? (1)1.0M (2)2.0M(3) 0.50 M (4) 0.25 M

29. If 100. ml of a 1.0 M solution is evaporated to a vol-ume of 25 m L, what will be the concentration of theresulting solution? (1)0.25M (2) 0.50 M (3)2.0M(4) 4.0 M

30. What is the percent by mass of a solution in which60. g of NaOH are dissolved in sufficient water tomakelOOgofsoiution? (1)16% (2)40% (3)60%(4)160%

31. What is the percent by mass of a solution if 60. g ofacetic acid are added to 90.g of water? (1) 20%(2) 30% (3) 40% (4) 67%

32. Carbon dioxide gas has a solubility of 0.0972 g/100 gH20 at 40°C Expressed in parts per million, this con-centration is closest to (1) 0.972 ppm (2)9.72ppm(3)97.2pptn (4) 972 ppm

33. A substance has a solubility of 350 pprn.How manygrams of the substance are present in 1.0 L of a satu-rated solution? (1) 0.0350 g (2) 0.350 g (3) 3.50 g(4) 35.0 g

Use the reference tables and your knowledge ofchemistry to answer each of the following questions.Be sure to show all work if calculations are needed.

34. What is the percent mass of a saturated solution ofKCl03at20°C?

35. A saturated solution of ammonium chloride in lOO.gH20 at 85°C is cooled to 20°C and filtered.What wasthe.mass of the solution at'85°C? What is the mass ofthe liquid that passes through the filter?

36. Barium suifate is listed as insoluble on solubilitytables. It does, however, dissolve to a small extent,solubility at 50°C is 0.00034 g in 100. g of water.Express this solubility in parts per million.

37. The table below gives the solubility of Ca(OH)2(s) in100. g of H20 at various temperatures. What is unusualaboutthe behavior of the solubility of this salt?

Temperaturero0

20406080

Solubility(gCa(OH)/!OO.g H20)

0.1890.1730.1410.1210.094

Ttie freezing and boiling points of water changewhen nonvolatile solutes are added. When any saltis added to water, the freezing point of the waterdecreases. This helps explain why salt is applied toroads and sidewalks when they are covered withsnow and ice. The added salt lowers thepoint and helps to melt the snow or ice. Theamount of the lowering of the freezing point is notdependent on the nature of the added particle. Onemole of any particles will have the same effect onthe freezing point. One mole of particles lowers thefreezing point of 1000 g of water by l.S6°G.

"When one mole of sugafr a molecular substance, isdissolved hi water, one mole of particles is pro-duced in solution.

1 mol 1 molWhen one mole of an ionic substance is dis-

solved in water, the results are different. The ionicsubstance separates into rndividual ions.

NaCKs) -» Na+(ag) + Cl"(aq)1 mol NaCl -> 1 mol Na+ + 1 mol 01"

Thus, one mole of sodium chloride produces twomoles of particles and will depress the freezing pointof water twice as much as the mole of sugar. The ^greater the number of ions, the greater the effectlMthe freezing point. CaC^ contains three ions, and_one mole of this salt will depress the freezing pointthree times as much as a mole of sugar.


The situation, is similar with the boiling point.

*

e mole of particles will elevate the boiling point of)0. g of water by 0.52DC. One mole of dissolved

sugar will elevate the boiling point of 1000. g ofwater by 0.52°C, while one mole of dissolved sodiumchloride will elevate the temperature of the sameamount of water by 1.04°C.

gen, nitrogen, or fluorine, the force of attractionholding them in the liquid phase are hydrogenbonds.

38. Why is salt (NaCl) put on icy roads and sidewalks inthe winter? (1 ) It is ionic and lowers the freezingpoint of water. (2) It is ionic and raises the freezingpoint of water. (3) it is covalent and lowers the freez-ing point of water. (4) It is covalent and raises thefreezing point of water.

39. What occurs as a salt dissolves in water? (T)Thenumber of ions in the solution decreases,and thefreezing point decreases. (2) The number of ions inthe solution decreases,and the freezing pointincreases. (3) The number of ions in the solutionincreases, and the freezing point decreases.(4) The number of ions in the solution increases,and the freezing point increases.

40. Assume equal aqueous concentrations of each of thefollowing substances. Which has the lowest freezingpoint? 0)C2H1206 (2)CH3OH (3) (4) NaOH

41. What occurs when sugar is added to water? (l)Thefreezing point of the water will decrease, and theboiling point will decrease. (2) The freezing point ofthe water will decrease,and the boiling point willincrease. (3) The freezing point of the water willincrease,and the boiling point will decrease.(4) The freezing point of the water will increase,and the boiling point will increase.

42. Which solution has the highest boiling point?Ol)1.0M'KNO3 {2)2.0MKN03 (3) 1.0 M Ca(NO3)2(4}2.0MCa(N03)2

43. Which property of a distilled water solution will notbe affected by adding 50 mLofCH3OH to lOO.mLof the water solution at25°C? (1) conductivity(2) mass (3) freezing point (4) boiling point

Tne molecules in a liquid are held together byrather weak forces. Polar molecules called dipolesare held in the-liquid- phase- by dipole-dipole- forces-.In molecules containing hydrogen and one of oxy-

104 Topic 7

In any sample of a liquid, some of the particlesat the surface have sufficient energy to escape fromtheir neighboring molecules and enter the gasphase. When a substance that is normally a solidor a liquid at room temperature enters the gasphase it is called a vapor. Thus, you will often hearabout water vapor or gasoline vapor, as water andgasoline are normally liquids at room temperature.

As the temperature of a liquid increases, theparticles have more energy, and more particlesescape from the surface. These vapor particles aregaseous particles and exert pressure in the gaseousphase. The pressure that a vapor exerts is called.vapor pressure. Table H of Reference Tables forPhysical Setting/Chemistry is a graph showing thevapor pressure of four substances measured inpressure units of kilopascals (kPa).

Of the substances shown on the graph, propa-none exerts the most pressure, about 93 kPa at atemperature of 50°C. It can be inferred that propa-none has the weakest interrnolecular forces holdingit in the liquid phase, while ethanoic acid lias thegreatest, exerting only about 8 kPa of pressure.

As the temperature of a liquid rises, vapor pres-sure increases. Finally the vapor pressure becomesequal to atmospheric pressure. At this point triegas may vaporize, not only on the surface but atany point in the container. A bubble of vapor belowthe surface has enough pressure that it does notcollapse from the atmospheric pressure pushingagainst it. When a bubble can occur at any point inthe liquid, the process is called boiling. The normalboiling point of a liquid is the temperature atwhich the vapor pressure of the liquid is 101.3 kPa,standard atmospheric pressure. Equivalentpressures are 1 abn, 760 mm Hg, and 760 torr.

47

T^e.heat required to change 1 mol of a substancefrom a liquid at its boiling point to 1 mol of a vaporis termed the heat of vaporization.

The normal boiling point of water is 100.°C. Atthis temperature, the vapor pressure of water is101.3 kPa. The line representing 101.3 kPa onTable H shows the normal boiling point of ethanolto be 78°G. When the pressure is less than101.3 kPa, the boiling point will be less than thenormal value. Water will boil at about 70°C whenthe pressure is about 30 kPa. If the pressure isgreater than normal, liquids will boil at tempera-tures above their normal boiling points. Whenatmospheric pressure is about 145 kPa, waterboils at 110.°C.


44. What is the vapor pressure of water at 105°C?(1)100kPa (2)101.3 kPa (3)110kPa (4}120kPa

uestions

45. As the pressure on a liquid is changed from lOO.kPato 120. kPa, the temperature at which the liq uid willboil (1) decreases (2) increases (3) remains thesame (4) depends on the liquid

46. In a closed system at40°C,a liquid has a vapor pres-sure of 50 kPa.The liquid's normal boiling point couldbe (1)10°C (2)30°C (3)40°C (4) 60°C

47. If the pressure on the surface of water in the liquidstate is 30 kPa, the water will boil at (1)0°C (2)30°C(3)70°C (4)100°C

48. A sample of ethanoic acid at 100°C has a vaporpressure of (1)53kPa (2}100kPa (3)101.3kPa(4)125kPa

49. Which substance has the greatest interrnolecularforces of attraction between molecules?(l)propanone (2) ethanol (3) water(4) ethanoic acid

50. The vapor pressure of ethanol at its normal boilingpoint would be (1)30kPa (2)101.3kPa (3)273kPa(4) 373 kPa

Use the tables in Reference Tables for PhysicalSetting/Chemistry as needed in answering thefollowing questions.

1. When a teaspoon of sugar is added to water in abeaker,the sugar dissolves.The resulting mixture is

(1) a compound

(2) a homogeneous solution

(3) a heterogeneous solution

(4) an emulsion

2. A small quantity of a salt is stirred into a liter of wateruntil it dissolves. In the resulting mixture,the water is

(1) the solvent

(2) the solute

(3) dispersed material

(4) a precipitate

3. A solution

(1) will separate on standing

(2) may have color

(3) can be cloudy

(4) can be heterogeneous

4. Nonpolar solvents will most easily dissolve solidsthat are

(1) ionic

(2) covalent

(3) metallic

(4) heterogeneous

5. What happens when a crystal of a salt is droppedinto an unsaturated solution of the same salt?

(1) Excess solute crystals form.

(2) The crystal dissolves.

(3) The crystal drops to the bottom, unchanged.

(4) The solution becomes colorless.


Name

i

Electrolytes are substances that break up (dissociate or ionize) in water to produce ions.These tons are capable of conducting an electric current.

Generally, electrolytes consist of acids, bases and salts (ionic compounds),Nonelectrolytes are usually covalent compounds, with the exception of acids.

Classify the following 'compounds as either an electrolyte or a nonelectrolyte.

Compound

1, NaCI

2. CH,OH (methyl alcohol)

3-, C,H,(OH), (glycerol)

4. HC!

5. CAH19OA (sugar)

6. .NaOH

7. C,HfiOH (ethyl alcohol)'21 '5

8, CH,COOH (acetic acid)o

9. NH4OH (NH3 + H2O)

10. H2S04

Electrolyte Nonelectrolyte

Chemistry IF8766 49 72 ©Instructional Fair,

Worksheet: Solubility and Electrolytes

• Which of the following substances are likely to be soluble in water?• Write the reaction that happens when each soluble substance in is dissolved in water,• Is the substance an electrolyte?

.. Ba(NOA ll.Hg,(C10A

2. ZnS 12. K3P04

3. (NHACCX

4. Fe203 14.NH4NO3

5. 15.ZnCrO

6. NaCIO, 16.MSO,

7. BaCrO4 17. Aid

8. FeBr, IS.AgI

9. Ag,SO2 4

19. CaBr.

10. Ca(OH), 20. CuS

50

The heat required to change 1 mol of a substancefrom a liquid at its boiling point to 1 mol of a vaporis termed the heat of vaporization.

The normal boiling point of water is 100.°C. Atthis temperature, the vapor pressure of water is101.3 kPa. The line representing 101.3 kPa onTable H shows the normal boiling point of ethanolto be 78°C. When the pressure is less than101.3 kPa, the boiling point will be less than thenormal value. Water will boil at about 70°C whenthe pressure is about 30 kPa. If the pressure isgreater than normal, liquids will boil at tempera-tures above their normal boiling points. Whenatmospheric pressure is about 145 kPa, waterboils at IIO.'C.

Review Questions


44. What is the vapor pressureofwaterat 105°C?(l)lOOkPa (2)1013kPa (3)110kPa (4)120kPa

45. As the pressure on a liquid is changed from lOO.kPato 120. kPa, the temperature at which the liquid willboil (1) decreases (2) increases (3) remains thesame (4) depends on the liquid

46. In a closed system at40°C,a liquid has a vapor pres-sure of 50 kPa.The liquid's normal boiling point couldbe (1)10°C (2)30°C (3)40°C (4) 60°C

47. If the pressure on the surface of water in the liquidstate is 30 kPa,the water will boil at (1)0°C (2}30°C(3)70°C (4)100°C

48. A sample of ethanoic acid at 100°C has a vaporpressureof (1)53kPa {2)100 kPa (3)101.3 kPa(4)125kPa

49. Which substance has the greatest intermolecularforces of attraction between molecules?(l)propanone (2) ethanol (3) water(4) ethanoic acid

50. The vapor pressure of ethanol at its normal boilingpointwouldbe (1)80kPa (2)101.3kPa (3)273kPa(4) 373 kPa

Questions for Regents Practice

Use the tables in Reference Tables for PhysicalSetting/Chemistry as needed in answering thefollowing questions.

1. When a teaspoon of sugar is added to water in abeaker, the sugar dissolves.The resulting mixture is

(1) a compound

(2) a homogeneous solution

(3) a heterogeneous solution

(4) an emulsion

2. A small quantity of a salt is stirred into a liter of wateruntil it dissolves. In the resulting mixture, the water is

(1) the solvent

(2) the solute

(3) dispersed material

(4) a precipitate

3. A solution

(1) will separate on standing

(2) may have color

(3) can be cloudy

(4) can be heterogeneous

4. Nonpoiar solvents will most easily dissolve solidsthat are

(1) ionic

(2) covalent

(3) metallic

(4) heterogeneous

5. What happens when a crystal of a salt is droppedinto an unsaturated solution of the same salt?



(3) Trje crystal drops to the bottom, unchanged.

(4) The solution becomes colorless.


6. The depression of the freezing point is dependent on

(1) the nature of the solute _ _ t

(2) the formula mass of the solute

(3) the concentration of dissolved particles

(4) hydrogen bonding

7. The process of recovering a salt from a solution byevaporating the solvent is known as

(1) crystallization

(2) filtration

(3) reduction

(4) decomposition

8. What happens when a crystal of solute is droppedinto a supersaturated solution of the salt?



(3) The crystal drops to the bottom, unchanged.

(4) The solution begins to boil

9. Under which conditions are gases most soluble inwater?

{1) high temperature and high pressure

(2) high temperature and low pressure

(3) low temperature and high pressure

(4) low temperature and iow pressure

10. As the temperature of a liquid decreases, the amountof a gas that can be dissolved

(1) decreases

(2) increases

(3) remains the same

(4) depends on the identity of the gas

11. As the temperature of liquid water decreases, itsvapor pressure

(1) decreases

(2) increases


(4) disappears

12. The heat energy required to change one mole of aliquid into a vapor at the boiling point is called the

(1) heat of vaporization

(2) heat of formation

(3) heat of solution

(4) heat of fusion

13. Which substance increases in solubility as thetemperature decreases?

(1)KCI03

(2) NH3

(3) KN03

(4) NaC!

14. The diagrams below represent an ionic crystal beingdissolved in water.

Ioniccrystal

Water molecule

According to the diagrams, the dissolving processtakes place by

(1) hydrogen bond formation

(2) metallic bonding

(3) dipole-dipole attractions

(4) molecule-ion attractions

15. If solutions of barium nitrate and sodium sulfate aremixed and then poured into a filter, the solid remain-ing on the filter will be

(1) barium nitrate

(2) sodium nitrate

(3) barium sulfate

(4) sodium sulfate

16. A student tested the solubility of a salt at differenttemperatures and then used the ReferenceTablesforPhysical Setting/Chemistry to identify the saltThe stu-dent's data appears below.

TemperatureC°c)30506276

Solubility Data(g of salt per 10 g of water)

1.22.23.04.0

What is the identity of the salt?

(1) potassium nitrate

(2) sodium chloride

(3) potassium chlorate

(4) ammonium chloride

106 Topic 752

17. If IQO.g of water at 80°C contains 45 _g of KCJ and45 g of NalMO3,the solution is

(1) saturated with respect to both KCI and NaNO3

(2) saturated with respect to KCI and unsaturatedwith respect to NaNO3

(3) unsaturated with respect to both KCI and NaN03

(4) supersaturated with respect to both KCI andNaNO3

18. What happens when Kl(s) is dissolved in water?

(1) l~ ions are attracted to the oxygen atoms ofthe water.

(2) K+ ions are attracted to the oxygen atoms ofthe water.

(3) K+ ions are attracted to the hydrogen atomsof the water.

(4) No attractions are involved; the crystal justfalls apart.

19. A student drops a crystal of NaCI into a beaker ofNaCl(aq) and the crystal dissoIves.The originalsolution must have been

(1) supersaturated

(2) saturated

(3) unsaturated

(4) heterogeneous

20. Which two compounds contain only polarmolecules?

(1)CCI4andCH4

(2)HClandCl2

(3)HClandNH3

(4) CO and CO2

21. A saturated solution of potassium chloride at 10°C isheated to 30°C As the solution is heated in a closedcontainer, the total mass of the solution

(1) decreases

(2) increases


(4) depends on the pressure

22. Water boils at 90°C when the pressure exerted on theliquid equals

(1)82kPa

(2) 90 kPa

(3)l01.3kPa

(4)120kPa

23. Considerthefollowing data for NaCi:

Temperature (°C)Solubility (g/1 00 gH20)

035.7

2036.0

5037.0

TOO39.2

When the salt is added to water,the temperature ofthe solution decreases.Which of the following state-ments is correct?

(1) The process is endothermic, and solubility andtemperature are directly related.

(2) The process is endothermic, and solubility andtemperature are indirectly related.

(3) The process is exothermic, and solubility andtemperature are directly related.

(4) The process Is exothermic, and solubility andtemperature are indirectly related.

24. Which sample of ethanol will have the highest vaporpressure?

(1)10.mLat62°C

(2) 20.0 ml at 52°C

(3)30.mLat42°C

(4) 40 ml at 32°C

25. The vapor pressure of water is 50 kPa.The tempera-ture of this sample of water is

(1)37°C

(2) 62°C

(3) 82°C

(4) 92°C

Show all work for problems 26-30.

26. What is the percent mass of NaOH if.12.5 g is dis-solved in 100, g of water?

27. What volume of 3.0 M HCl contains 0.20 mol of HC1?

28. A swimming pool reading reports that chlorine ispresent at 30 ppm. How many grams of chlorine arepresent per liter of poo! water?

29. What is the molarity of a solution that contains 24 gof NaNO3 in 200 ml of solution?

30. How many grams of KNO3 are present in 250 ml of2.0 M potassium nitrate solution?


31. Describe two methods by which you could removegases that are dissolved in water. [2]

32. Consider the following data for Na75O ,

Temperature {°QSolubility (g/1 00 gH20)

04.76

2062

5050. i

10041

What is the relationship between the temperatureand the amount of dissolved material? Given thatsodium sulfate is a solid, what is unusual about thedata given above? [2]

33. One moleofethanol (C2H5OH) will depress the freez-ing point of 1000. g of water by 1.86°C How manygrams of ethanol would be needed to depress thefreezing point of 1000. g of H20 by 3.72DC? [1]

34. Describe how to prepare 500. ml of 4.0 MShow any calculations. [2]

Use the following figure to answer questions 35and 36.

IT-B~o

noTOO

90

80

70

60

50

40

30

20

10^

A

^

/

•

B

/

//

//

C

A/

D

//

F

//

/

/

E

35. The figure represents the line showing the solubilityof substance X. A solution of substance X is repre-sented by point D. What are two ways that this solu-tion can be made saturated? [2]

36. Point B represents a supersaturated solution.Consider the equation:

When a crystal is placed into the supersaturatedsolution, additional crystals form and fail to the bot-tom of the beaker, and the solution returns to a satu-rated condition. Which of the two positions shownon the line of saturation would best representthesolution when the crystals first settled to the bot-tom? Explain the reason for your answer. [2]

37. Substance X is a molecular substance that is solublein water. It costs $.90/ton.Substance Y is an ionic sub-stance that costs $ 1 .00/ton. Both have the same envi-ronmental impacts,are easy to handle,andarenontoxic. Using your knowledge of chemistry, whichwould be a better choice to use to melt snow onwalks or driveways? Justify your answer. [2]

38. if 0,169 g of carbon dioxide can be dissolved in 100.gof H2O at 20°C, what is the concentration in parts per

. million? [1]

10 20 30 40 50 60 70 80 90 100

Temperature(°C)

TQS Topic 7 54

Name

Across2, Solution containing the

maximum amount of solutepossible at that temperature

4. Two liquids which can mix aresaid to be _____ ,

i.i

15

12 13

14

17

11

10

16

6, The presence of anonvolatile solute will

the boiling •point of a solvent,

9. " A homogeneous •mixture

10. Substance present inlarger amount in amixture

13. Moles of a soluteper kilogram ofsolvent

14. Solution containing arelatively large amount ofsolvent

15. Jhe solubility of gases' as temperatureincreases,

17. State in which the rate ofdissolving is equal to the rate of precipitation

. 18. The presence of a nonvolatile solute will the freezing point of a solvent,19. These substances dissociate or ionize in.water and are then able to conduct an

electric current, •

19

Down1. Properties that depend on the number of particles in solution3. Solution in which more solute can be dissolved5, Solution containing a relatively large amount of dissolved solute7. Substance present in smaller amount in a mixture8. The solubility of most solids as temperature increases.

II1, Maximum amount of solute that can dissolve in a stated amount of solute at a given

temperature12, Moles of solute per liter of solution16. Solutions in which water is the solvent are called , .

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