unit 9 solution chemistry, a introduction dissolution of ionic crystals in water dissolution of...

Unit 9 Solution Chemistry, a Introduction Dissolution Of Ionic Crystals In Water Dissolution Of Molecular Substances In Water Electrical Conductivity Electrolytes vant Hoff Factor Units of Concentration Diluting and Concentrating Solutions Solution Chemistry, b Works best when seen as a slide show. Click the Slide Show button on the lower right.

Matter Homogeneous Heterogeneous Compounds Elements Pure substances Mixtures solutions

We will focus our attention primarily on solid-liquid solutions. In this case the solid is the solute, or substance being dissolved by the liquid, or solvent. The liquid is generally water. An example would be dissolving salt in water. The composition of a solution can vary and its components can be physically separated, but each part is identical to every other part of the mixture (a salt solution tastes salty throughout). Allowing a salt solution to evaporate will leave the dry salt residue.

A solution with a relatively high amount of solute is said to be more than one that is more. One holding the maximum quantity of solute is said to be. concentrated dilute saturated

Dissolution Of Ionic Crystals In Water 1. First the water molecules draw near the Na + and Cl - ions in the crystal lattice. Then the negative part of the H 2 O dipole pulls on the sodium ion. In a similar fashion the attraction of the positive end of the water dipole pulls on the chloride ion. The ions actually separate from the crystal lattice. Chemist6ry. Zumdahl. Copyright2000 by Houghton Mifflin

Sugars are molecular substances that, like ionic compounds, dissociate from their crystal lattice. However, there is a big difference. Sugar does not dissociate into ions. The individual sugar molecule remains intact. Water surrounds each sugar molecule after it is separated from the crystal. C 6 H 12 O 6 (s) C 6 H 12 O 6 (aq) H2OH2O C 12 H 22 O 11 Dissolution Of Molecular Substances In Water C 12 H 22 O 11

The passage of electricity occurs when a voltage is applied to an electrical conductor such as metal. The electrical current results from the movement of electrons through the conductor. Electrical Conductivity Gold bar

In addition, electrical current will result when a voltage is applied through certain solutions. The NaCl solution will conduct a current because it contains ions. The ions in the solution environment are mobile and respond to a voltage. The sugar solution will not conduct a current because there are no free ions only neutral molecules (water and sucrose).

For this reason NaCl is called an electrolyte, a substance that conducts electricity when dissolved in water. Sugar is a nonelectrolyte because it does not conduct a current when dissolved in water. Pure water is a very low conductor due to some ionization.

No ions or free electrons in solution No No ions formed when dissolved No No ions or free electrons in solution No No ions formed when dissolved No No ions or free electrons in solution No No ions formed when dissolved No Very few free ions in solution Slight Dissociates into ions only slightly when dissolved Slight Ions immobile in crystal lattice No Dissociates into ions when dissolved Yes Mobile Ions in liquidYes Dissociates into ions when dissolved Yes Mobile Ions in solution Yes Dissociates into ions when dissolved Yes Electrons through metal conductor YesNot solubleNo Electrons through metal conductor YesNot solubleNo Reason Conductivity?Reason Electrolyte? Substance C 6 H 12 O 6 (l) C 6 H 12 O 6 (aq) C 6 H 12 O 6 (s) AgCl(aq) NaCl(s) NaCl(l) NaCl(aq) Ag(l) Ag(s)

The degree that substances dissociate when dissolved in water is called the vant Hoff Factor, i. For sodium chloride it is 2 because one mole of sodium ion, Na +, and one mole of chloride ion, Cl -, forms for every mole of NaCl dissolved. Q Specify the vant Hoff Factor for each of the following: calcium bromide cesium oxide ethanol CaBr 2 Ca 2+ (aq) + 2Br - (aq) = Cs 2 O 2Cs + (aq) + O 2- (aq) = C 2 H 5 OH(l) C 2 H 5 OH (aq) = 3 3 1

Units of Concentration When interested in experiments with a salt such as CuSO 4 we weigh out the portion we need, usually in grams.. www.sperlescales.com

Many chemical reactions, however, are carried out by mixing chemicals that are already dissolved in water. In that case, the CuSO 4 is not weighed as crystals since it is immersed in water. To solve problems when chemicals react in an aqueous environment we use the idea of concentration instead of mass. www.comeau.ca/beaker.jpg Units of Concentration

Chemists measure the concentration of solutions several ways. In chemistry we will frequently use the unit called molarity, which is the ratio of moles of solute per liter of solution: molarity, M= In dilute solutions, the concentration of solute is relatively low compared to a concentrated solution. Units of Concentration

The diagrams and descriptions following show how to prepare one liter of a 1 molar (1.000 M), solution of NaCl. This is the recipe: 1. Weigh out 1.000 mole of NaCl, or 58.44 g. 2. Carefully pour it into a specially marked 1.000-liter volumetric flask. 3. Add about 200 mL distilled water. 4. Shake until dissolved. 5. Add distilled water to the 1.000-liter mark. Note: this step is done after the initial mixing. Adding a solute to water changes the volume in different ways. 6. Mix thoroughly. Units of Concentration

1. Weigh out 1.000 mole of NaCl, or 58.44 g. 2. Carefully pour it into a specially marked 0.500-liter volumetric flask. 3. Add about 200 mL distilled water. 4. Shake until dissolved. 5. Add distilled water to the 0.50-liter mark. 6. Mix thoroughly. Q Suppose you needed to prepare 500 mL of a 2.000 M NaCl solution. How would you carry out this procedure? What would you need? Units of Concentration

Solving problems involving molarity will at times require simple plug-in-the-formula procedures, at other times lengthier dimensional analysis sentences. Q What is the molarity of a 500-mL solution containing 1.75 mole of sodium hydroxide? Molarity = moles solute/liter of solution = mol NaOH0.300 = 1.75 mol/0.500 L = 3.50 mol/L Q How many moles of sodium hydroxide are needed to make 750. mL of a 0.400 M solution? Units of Concentration

Q What is the molarity of a 250.-mL solution containing 56.0 g of sodium hydroxide? Q What volume solution will be prepared if 42.0 g of sodium hydroxide are used to make a 0.42 M solution? = mol/L NaOH5.60 = L NaOH2.50 Units of Concentration

More Practice 1.Calculate the molarity of a solution that contains 5.78 grams of calcium chloride dissolved to get a 500.0-mL solution. (ans. 0.104 M) 2.How many grams of solute are in 250.0 mL of a 1.500 M hydrochloric acid solution? (ans. 13.7 g) 3.How many liters of solution can be prepared if 35.8 grams of sodium chloride are used to make a 0.500 M solution? (ans. 1.22 L)

Diluting and Concentrating Solutions

suegregg.com Step 1 Preparing a special solution Diluting and Concentrating Solutions

Step 2 Diluting and Concentrating Solutions

Step 3 Serves eight Diluting and Concentrating Solutions

Dilution is a process where water is added to an existing solution. The solutes concentration thereby decreases. The problems associated with this topic use the molarity formula. Keep in mind, though, that the total number of moles of solute is the same after the water is added. Diluting and Concentrating Solutions

Dilution diminishes the concentration because the particles are separated. Add water Add 50 mL CuSO 4 Diluting and Concentrating Solutions

Dilution reduces the concentration of the solute proportionally. 0.40 L water Diluting and Concentrating Solutions

Diluting solutions follows a numerical format moles 1 = moles 2 moles 1 = M 1 L 1 moles 2 = M 2 L 2 Then M 1 L 1 = M 2 L 2 Diluting and Concentrating Solutions

Q Water is added to a beaker containing 200. mL of 0.750 M HCl. The new concentration is 0.500 M. a) What is the volume of the solution after dilution? M l L 1 = M 2 L 2 200. mL 0.750 M HCl 0.500 M HCl L 2 0.750 x 0.200 = 0.500 x L 2 0.300 L = L 2

b) How much water had to be added to the original solution to dilute it to 0.500 M? 200. mL 0.750 M HCl 0.500 M HCl L 2 L 2 L 1 0.300 L 0.200 L = 0.100 L

1. Add your concentrated solution to the volumetric flask 2. Dilute with water 3. Invert several times How chemists dilute solution

In some cases, more of a solute is added to a solution to make it more concentrated. Q A person adds 0.50 mole of sugar crystals to a 1.00-liter solution containing already 1.00 mole of sugar. The new sugar completely dissolves and makes the solution volume increase to 1.05 liter. What is the concentration of the new solution? New molarity = 1.00-liter 1.05-liter 1.00 mole sugar add 0.50 mole of sugar moles 1 + moles added Total volume 1.00 mol + 0.50 mol 1.05 L 1.43 mol/L

www.oxbowhay.com/images/ Medicinal Casey Recommended Daily Intake: 50cc/kg Body weight (divided between 3-5 feedings per day/) Example: 2 lb. (0.9 kg) guinea pig would be fed a total 45 cc per day when mixed at a 1:1 ratio, adjust feeding amounts accordingly if more water is added, to account for dilution effect

Chemists use fancy equipment to do dilutions

The process of dilution can be harmful, such as the dilution of harsh reagents in our ground water.

Microbiologists go to great lengths to make serial dilutions to study enzyme activity and other metabolic phenomena

More Practice 1.250. mL of a 0.300 M glucose (C 6 H 12 O 6 ) solution is diluted with water to a concentration of 0.200 M. a) What is the volume of the new solution? (ans. 375 mL) b) How much water had to be added to the original solution? (ans. 125 mL) 2.Water was added to 1,250 mL of a 0.682 M potassium sulfate solution. The final volume was 1,860 mL. Determine the final concentration of the solution. (ans. 0.458 M)

Other Concentration Units

Besides molarity we will present two other units of solution concentration. One is called weight fraction or percentage with the symbol w/w: Q A sample of 0.892 g of potassium chloride is dissolved in 54.600 g of water. a) What is the fraction (w/w) of KCl in this solution? b) What are the units for this number? Mass of solution Mass of solute 0.892 g + 54.600 g 0.892 g 55.492 g 0.892 g = 0.0161 Generally unitless but in this case it is g KCl/g solution ==

Other Concentration Units Density is a measure of the compactness of substances. A relative measure of density is given in this table: SubstanceDensity (g/mL) Air0.001 Balsa wood0.16 Water1.00 Table salt2.16 Iron7.9 Gold19.32

Q A solution is prepared by dissolving 3.76 g of calcium nitrate in 37.60 g of water. The total volume of the solution is 39.4 mL. a) Calculate the density of the solution. b) Calculate the molarity of the solution. Volume of solution Mass of solution 39.4 mL 37.60+3.76 g Ca(NO 3 ) 2 = 1.05 g/mL = mol/L Ca(NO 3 ) 2 0.582 =

More Practice 1.Calculate the fraction by mass (w/w) of 3.76 grams of KNO 3 in 95.0 grams of water. (ans. 0.0381) 2.If a chemist dissolves 6.88 g of glucose, C 6 H 12 O 6, in 100.0 g of water the total volume is 102.0 mL. Calculate the density of this solution. (ans. 1.05 g/mL)

unit 9 solution chemistry, a introduction dissolution of ionic crystals in water dissolution of...

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