unit 1 – section c solubility of solids in water

Unit 1 – Section C

Solubility of Solids in Water

HW

Read & take notes on sectionsC.1 - C.3

Could something dissolved in the water in the Snake River have caused the fish kill?

C.1 Solubility of Solids in Water

Let’s dissolve potassium nitrate in water…

KNO3 is the solute

& H2O is the solvent

C.1 Solubility of Solids in Water(continued)

The KNO3 will dissolve to the point at which the H2O can hold no more. At this point the solvent

is said to be saturated.


The maximum quantity of a substance that will dissolve in a certain quantity at a specific

temperature is called its solubility.


The solubility of most substances will change

depending on the temperature the graphic

representation of this relationship is called the solute’s solubility curve.

C.1 Solubility of Solids in Water(What effects this ?)

Below the curves the area represents an unsaturated solution. There it contains less than it potentially can.

C.1 Solubility of Solids in Water(Continued)

This type of solution is called a supersaturated solution.

C.1 Solubility of Solids in Water(Continued)

Consider a 100mL solution containing 80g of KNO3 at 60°C, you reduce the temperature to 40°C. What do you think would happen?

If all the solute stays in solution. . .

1. a.Mass in ______ g of KNO3 that will dissolve in 100 g of H2O at 60°C?

b. Mass in ______ g of KCl that will dissolve in 100 g of H2O at 60°C?

C.2 Solubility & Solubility Curves(Practice)

2. a.25 g of KNO3 + ____ g will be saturated in 100 g of H2O at 30°C?


2. b.

45 g KNO3 = 25 g KNO3

100 mL H2O X mL H2O


Solve for X . . .

X = 55 mL of H2O

3. a.150 g of KNO3 minus ____ g which will stay in solution in 100 g of H2O at 55°C?

Means _____ g will precipitate out.


3. b.

70 g KNO3 = 150 g KNO3

100 mL H2O X mL H2O


Solve for X . . .

X = 214 mL of H2O at 55°C

C.3 Constructing a solubility curve

HW

Read & take notes on C.4 & C.5

We are interested in finding out how the atoms of the solute and solvent interact?

C.4 Dissolving Ionic Compounds

While an entire H2O molecule is electrically neutral, (the charge of the cation and anion balance) the

electrons are not evenly distributed. This uneven distribution makes it a polar molecule.

Polar H2O molecules are attracted to other polar molecules.

C.4 Dissolving Ionic Compounds(Continued)

This gives H2O the ability to dissolve a great many substances.

H2O molecules are attracted to ions located on the surface of an ionic substance.


H2O’s negative (oxygen) is attracted to the crystals cation.

Dissolving involves competition between 3 types of attraction:


1. Between solute and solvent2. “ solvent particles

themselves.3. And between particles

within the solute crystals.

H2O is highly polar.


Therefore H2O is extremely effective at dissolving charged or ionic substances.

We dissolve 40 g of KCl in 100 g of H2O at 50°C. Then cool the temperature to

25°C.a)What changes do you predict?

C.5 The Dissolving Process

At 50°C?

At 40°C?

At 25°C?

Unsaturated

Supersaturated

Supersaturated

You may change the concentration of a solution by:

C.5 The Dissolving Process(Continued)

Decreasing the volume of H2O, make the remaining solvent more concentrated. (by evaporation)

Increasing the volume of H2O, make the remaining solvent less concentrated. (adding solvent)

Decreasing the volume of H2O, make the remaining solvent more concentrated. (by evaporation)

C.5 The Dissolving Process(Continued)

We dissolve 40 g of KCl in 100 g of H2O at 35°C.

We allow ¼ of the water to evaporate, what will happen?

40 g KCl = X g KCl

100 mL H2O 75 mL H2O X = the amount of KCl that the 75 g of H2O can hold in solution

X = 30 g of KCl can be held in solution.

C.5 The Quizzing Process

HW – Pre-review sections C.6 & C.7 pgs 63-65

and (Especially)

problem out section C.7

Saturated & unsaturated does not adequately describe the properties of a solution.

So we use the term concentration, which refers to how much solute is dissolved in a specific quantity of solution.

C.6 Solution Concentrations

Another way to describe concentration, is with percent value.

C.6 Solution Concentrations(Continued)

Example: 5 g of NaCl dissolved in 95 g of H2O = 5% NaCl solution (by mass)

THINK 5 g

5 g + 95 gParts per 100

For smaller concentrations


Parts per million (ppm)

Parts per billion (ppb)

Example: Maximum nitrates allowed in our drinking water is 10 ppmEasier to write than 0.0010 %

Problem: What is the concentration of a 1% NaCl-H2O solution expressed in ppm?


1% of 1,000,000 =

1,000,000X 0.01

10,000 ppm

C.7 Describing Solution Concentrations

1) 1 tsp of sucrose is dissolved in 1 C of H2O.

a)Solute ?

b)Solvent?

C.7 Describing Solution Concentrations(continued)

2) Concentration of sucrose expressed as % by mass?

a) 17 g of sucrose dissolved in 183 g of H2O?

b) 30 g of sucrose dissolved in 300 g of H2O?


3) Concentration expressed as ppm? i. 0.0020 g of Fe(III) dissolved in 500 g of H2O?

ii. 0.25 g of Ca dissolved in 850 g of H2O?


4) 45 g of KCl in 100 g of H2O at 60°C? a. Concentration of the solution?

b. After adding 155g of H2O?


5) A saturated solution of KNO3 at 25°C?

HW

Read & take notes on C.8 & C.9. Remember to make certain you understand the sections and bring me

questions if you do not.

C.8 Inappropriate Heavy-metal ion concentrations

Many metal ions, Fe(II) (Fe+2), K+, Ca2+

and Mg2+ are necessary for good health.

We get most of what we need from food and in some instances the H2O we drink.

C.8 Inappropriate Heavy-metal ion concentrations (Continued)

Not all metal ions are beneficial, some called heavy-metal ions are harmful to humans. They have greater atomic masses than the essential metallic elements.

Of greatest concern to us is Pb2+ and Hg2+

Because :•Widely dispersed in the environment•Bind to proteins in biological systems


The heavy-metal ions do not get excreted by living organisms (They stay in our bodies ), so they get concentrated upwards in the food chain.


In low concentrations heavy-metals are hard to detect and even more difficult to remove. (We need to eliminate production & use of these

elements), this practice is called green chemistry.

C.8 Heavy-metal ion Pb2+

Many industrial uses:

Until 1970s , Pb(C2H5)4 (tetraethyl lead) was added to gasoline.

Before 1978 Pb paint was used in houses.

C.8 Heavy-metal ion Hg2+

Uses include:

In 18th & 19th centuries , Hg(NO3)2

(mercury (II) nitrate) was used in hat making. Prolonged exposure lead to mercury poisoning (“mad as a hatter”).

Thermometers, medical and weather.

Antiseptics, fungicides and pesticides.

C.9 Inappropriate pH LevelsThe pH scale is an easy way to measure and report the acidic , basic, or chemically neutral character of a solution.

Range 0 – 14

pH < 7.0 = acid

pH > 7.0 = basic

C.9 Inappropriate pH Levels(continued)

Basic solutions (those with pH greater than 7.0) are called alkaline.

Example: NaOH , sodium hydroxide – active ingredient in oven and drain cleaners.


A change of 1 pH unit equals a tenfold (10x) difference in acidity or alkalinity.

Example: lemon juice at pH 2 is 10x more acidic than soda at a pH of 3.


Most acids are made up of molecules that easily give up one or more H+ ions.

Example: the acid in vinegar – acetic HC2H3O2


Most bases are made up of molecules that include OH- ions.

Example: the active ingredients in milk of magnesia Mg(OH)2


Neither acids nor bases ? We call these neutral.

Example: H2O, NaCl and C12H22O11

HW

Notes & Pre-read C.10 & C.12 (Please note we are passing over C.11)

C.10 Inappropriate Molecular Substance Concentrations

Some substances such as (sugar) C12H22O11 and (ethanol) C2H6OH, dissolve in H2O but not as ions – they are called molecular substances. They are non-crystalline.

C.10 Inappropriate Molecular Substance Concentrations (continued)

What determines the solubility of a molecular substances in H2O?

In large part it is determined by the distribution of electrical charges.

C.10 Inappropriate Molecular Substance Concentrations (continued)

The ability of an atom to attract shared electrons when bonding within a compound is known as the element’s electronegativity.

In molecular substances the differences may not be large enough for ions to form, but the electrons may be unevenly distributed.

C.11 Solvents

C.12 Inappropriate dissolved O2 levels?

In most instances solubility increases with temperature, is the same true for gases?

What is the solubility of O2 in 20°C water?

In 40°C water?

C.12 Inappropriate dissolved O2 levels? (continued)

Dissolved gases have an additional factor which must be taken into account, atmospheric pressure.


Gas solubility is directly related to the pressure on that gaseous substance on the liquid.


For sodas CO2 is forced into solution under high-pressure.

C.13 Temperature, Dissolved Oxygen, and Life

As we have learned the temperature of H2O affects how much O2 it can hold in solution.

Different living organisms have different O2 needs.

C.13 Temperature, Dissolved Oxygen, and Life (continued)

How does changing water temperatures affect fish internally?

Remember fish are cold-blooded

1. Body temperature rises.2. Metabolism increases3. Fish eat more, swim more & require more O2

C.13 Temperature, Dissolved Oxygen, and Life (continued)

Additionally there are both lower limits and upper limits to the amount of dissolved O2 a fish can tolerate.

C.14 Determining the Cause of the Fish Kill

Let’s examine the data

HW

On pg 82 Questions 2-4 & 8-10

1. Mass in ______ g of KCl that will dissolve in 100 g of H2O at 70°C?

Q.2 pg 82

3. a.

2 g sucrose = x g sucrose

1 mL H2O 100 mL H2O

b. 2 g sucrose = x g sucrose

1 mL H2O 355 mL H2O c. 2 g sucrose = x g sucrose

1 mL H2O 946 mL H2O

Q.3 pg 82Solve for X . . .

Solve for X . . .

Solve for X . . .

Q.8 & 9 pg 82

35 g

35 g + 115 g

#8

X 100% =

#9

55 g

x gX 100% = 20%

Solve for X . . .

Q 10 pg 820.015 mg/L which is equal to 0.000015 g/L

0.000015 g

0.000015 g + 1000 gX 100% =

0.0000015% Pb concentration

Finally 1,000,000 times 0.00015 equals

0.015 ppm of Pb

unit 1 – section c solubility of solids in water

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