1. stirring (agitation) 2. temperature 3. the surface area of the dissolving particles

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1 Chapter A sinkhole forms when the roof of a cave weakens from being dissolved by groundwater and suddenly collapses. One recorded sinkhole swallowed a house, several other buildings, five cars, and a swimming pool! You will learn how the solution process occurs and the factors that influence the process. 1

2 16.1 Solution Formation What factors determine the rate at which a substance dissolves? 16.1 The compositions of the solvent and the solute determine whether a substance will dissolve. The factors that determine how fast a substance dissolves are 1. stirring (agitation) 2. temperature 3. the surface area of the dissolving particles 2

3 16.1 A cube of sugar in cold tea dissolves slowly. Little surface area, cold temperature and no agitation Granulated sugar dissolves in cold water more quickly than a sugar cube, especially with stirring. More surface area and agitation. 3

Anything that increases solute to solvent particle

4 16.1 Granulated sugar dissolves very quickly in hot tea. More surface area and increased temperature. Anything that increases solute to solvent particle contact increases the rate of dissolving. Stirring, heating, pulverizing 4

An unsaturated solution contains less solute than a saturated solution at a 16.

5 16.1 A saturated solution contains the maximum amount of solute for a given quantity of solvent at a given temperature and pressure. An unsaturated solution contains less solute than a saturated solution at a given temperature and pressure In a saturated solution, the rate of dissolving equals the rate of crystallization, so the total amount of dissolved solute remains constant. This is a dynamic equilibrium. 5

6 16.1 The solubility of a substance is the amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution. Solubility is often expressed in grams of solute per 100 g of solvent. Reference table G 6

7 16.1 Some liquids combine in all proportions, while others don t mix at all. Two liquids are miscible if they dissolve in each other in all proportions. Two liquids are immiscible if they are insoluble in each other Oil and water are immiscible. 7

8 16.1 Vinegar and oil are immiscible The mineral deposits around hot springs result from the cooling of the hot, saturated solution of minerals emerging from the spring. 8

9 16.1 Factors Affecting Solubility What conditions determine the amount of solute that will dissolve in a given solvent? 16.1 Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes. 9

10 16.1 Temperature The solubility of most solid substances increases as the temperature of the solvent increases. The solubilities of most gases are greater in cold water than in hot

16.1 A supersaturated solution contains more solute

The crystallization of a supersaturated solution can

11 16.1 A supersaturated solution contains more solute than it can theoretically hold at a given temperature. The crystallization of a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added A supersaturated solution is clear before a seed crystal is added. 11

12 16.1 Crystals begin to form in the solution immediately after the addition of a seed crystal Excess solute crystallizes rapidly. 12

2 Water must be tested continually to ensure that the concentrations of contaminants do not exceed established limits.

13 16.1 Pressure Changes in pressure have little effect on the solubility of solids and liquids, but pressure strongly influences the solubility of gases. Gas solubility increases as the partial pressure of the gas above the solution increases Water must be tested continually to ensure that the concentrations of contaminants do not exceed established limits. These contaminants include metals, pesticides, bacteria, and even the by-products of water treatment. You will learn how solution concentrations are calculated. 13

14 16.2 The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent. A dilute solution is one that contains a small amount of solute. A concentrated solution contains a large amount of solute Molarity (M) is the number of moles of solute dissolved in one liter of solution. To calculate the molarity of a solution, divide the moles of solute by the volume of the solution. Reference Table T 14

15 16.2 To make a 0.5-molar (0.5M) solution, first add 0.5 mol of solute to a 1-L volumetric flask half filled with distilled water Swirl the flask carefully to dissolve the solute. 15

16 16.2 Fill the flask with water exactly to the 1-L mark

17 for Sample Problem 16.2 A solution has a volume of 2.0 L and contains 36.0 g of glucose (C 6 H 12 O 6 ). If the molar mass of glucose is 180 g/mol, what is the molarity of the solution?

18 How many moles for Sample of solute Problem are 16.3 in 250 ml of 2.0 M CaCl 2? How many grams of CaCl 2 is this? 16.2 Making Dilutions What effect does dilution have on the total moles of solute in a solution? Diluting a solution reduces the number of moles of solute per unit volume, but the total number of moles of solute in solution does not change. 18

M 1 and V 1 are the molarity and volume of the initial solution, and M 2 and

19 16.2 The total number of moles of solute remains unchanged upon dilution, so you can write this equation. M 1 and V 1 are the molarity and volume of the initial solution, and M 2 and V 2 are the molarity and volume of the diluted solution. Write this in your reference table T Making a Dilute Solution 19

20 16.2 To prepare 100 ml of 0.40M MgSO 4 from a stock solution of 2.0M MgSO 4, a student first measures 20 ml of the stock solution with a 20-mL pipet She then transfers the 20 ml to a 100-mL volumetric flask. 20

21 16.2 Finally she carefully adds water to the mark to make 100 ml of solution Volume-Measuring Devices 21

22 16.4 How many milliliters for Sample of Problem a solution 16.4 of 4.00M KI are needed to prepare ml of 0.760M KI? ` 22

23 16.2 Percent Solutions What are two ways to express the percent concentration of a solution? 1. as the ratio of the volume of the solute to the volume of the solution or 2. as the ratio of the mass of the solute to the mass of the solution Concentration in Percent (Volume/Volume) 23

24 16.2 Isopropyl alcohol (2-propanol) is sold as a 91% solution. This solution consist of 91 ml of isopropyl alcohol mixed with enough water to make 100 ml of solution. 24

25 A bottle of antiseptic hydrogen peroxide (H2O2) is labeled 3.0% (v/v). How many ml of H 2 O 2 are in a ml bottle of this solution? 16.2 Concentration in Percent (Mass/Mass) 25

the cells from freezing. You will discover how a solute can change the freezing point of a solution. 16.

26 16.3 The wood frog is a remarkable creature because it can survive being frozen. Scientists believe that a substance in the cells of this frog acts as a natural antifreeze, which prevents the cells from freezing. You will discover how a solute can change the freezing point of a solution A property that depends only upon the number of solute particles, and not upon their identity, is called a colligative property. 26

27 16.3 Three important colligative properties of solutions are 1. vapor-pressure lowering 2. boiling-point elevation 3. freezing-point depression 16.3 In a pure solvent, equilibrium is established between the liquid and the vapor. 27

Equilibrium is established at a lower vapor pressure. 16.

28 16.3 In a solution, solute particles reduce the number of free solvent particles able to escape the liquid. Equilibrium is established at a lower vapor pressure The decrease in a solution s vapor pressure is proportional to the number of particles the solute makes in solution. 28

16.3 Three moles of glucose dissolved in

29 16.3 Three moles of glucose dissolved in water produce 3 mol of particles because glucose does not dissociate Three moles of sodium chloride dissolved in water produce 6 mol of particles because each formula unit of NaCl dissociates into two ions. 29

3 Freezing-Point Depression The difference in temperature between the freezing point of a solution and the

30 16.3 Three moles of calcium chloride dissolved in water produce 9 mol of particles because each formula unit of CaCl 2 dissociates into three ions Freezing-Point Depression The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent is the freezing-point depression. What determines the amount by which a solution s freezing point differs from those properties of the solvent? 30

16.3 The magnitude of the freezing-point depression is proportional to the number of solute

The freezing point of water decreases by 1.

This is called the freezing point depression constant for water. 16.

31 16.3 The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity. The freezing point of water decreases by 1.86 C for every mole of particles that the solute forms when dissolved in 1000 g of water. This is called the freezing point depression constant for water The freezing-point depression of aqueous solutions makes walks and driveways safer when people sprinkle salt on icy surfaces to make ice melt. The melted ice forms a solution with a lower freezing point than that of pure water. 31

32 16.3 Boiling-Point Elevation The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent is the boiling-point elevation. The same antifreeze added to automobile engines to prevent freeze-ups in winter, protects the engine from boiling over in summer The magnitude of the boiling-point elevation is proportional to the number of solute particles dissolved in the solvent. The boiling point of water increases by C for every mole of particles that the solute forms when dissolved in 1000 g of water. This is called the boiling point elevation constant for water. 32

You will learn how to calculate the amount the boiling point of the cooking water rises.

33 16.4 Cooking instructions often call for the addition of a small amount of salt to the cooking water. Dissolved salt elevates the boiling point of water. You will learn how to calculate the amount the boiling point of the cooking water rises. My favorite pasta pot is a 3 qt. stockpot. I generally add about ½ tsp. salt to 2 qt. water. At what T will the water boil at standard pressure? 1 tsp salt weighs 20 g. The molar mass of NaCl is g/mol. 33

34 16.4 What are two more ways of expressing the concentration of a solution? The unit molality and mole fractions are two additional ways in which chemists express the concentration of a solution The unit molality (m) is the number of moles of solute dissolved in 1 kilogram (1000 g) of solvent. Molality is also known as molal concentration. 34

35 16.4 To make a 0.500m solution of NaCl, use a balance to measure kg of water and add mol (29.3 g) of NaCl Ethlylene Glycol (EG) is added to water as antifreeze. 35

36 16.6 How many grams of sodium fluoride are needed to prepare a 0.400m NaF solution that contains 750 g of water? 36

37 16.4 Freezing-Point Depression and Boiling-Point Elevation How are freezing-point depression and boiling-point elevation related to molality? The magnitudes of the freezing-point depression (ΔT f ) and the boiling-point elevation (ΔT b ) of a solution are directly proportional to the molal concentration (m), when the solute is molecular, not ionic The constant, K f, is the molal freezing-point depression constant, which is equal to the change in freezing point for a 1-molal solution of a nonvolatile molecular solute. 37

38 The constant, K b, is the molal boiling-point elevation constant, which is equal to the change in boiling point for a 1-molal solution of a nonvolatile molecular solute. 38

39 39

40 16.8 for Sample Problem 16.8 What is the freezing point depression of an aqueous solution of 10.0 g of glucose (C 6 H 6 O 12 ) in 50.0 g H 2 O? 40

41 16.9 for Sample Problem 16.9 What mass of NaCl would have to be dissolved in kg of water to raise the boiling point by 2.00 o C? 41

Name Date Class PROPERTIES OF SOLUTIONS

Name Date Class PROPERTIES OF SOLUTIONS 16.1 PROPERTIES OF SOLUTIONS Section Review Objectives Identify the factors that determine the rate at which a solute dissolves Identify the units usually used to express the solubility of a solute Calculate