CHAPTER 15CHAPTER 15

SolutionsSolutions

SoluteSoluteA solute is the dissolved substance in a solution.

A solvent is the dissolving medium in a solution.

SolvenSolventt

Salt in salt water Sugar in soda drinks

Carbon dioxide in soda drinks

Water in salt water Water in soda

Concentrated vs. DiluteConcentrated vs. Dilute

Saturation of SolutionsSaturation of Solutions

A solution that contains the maximum A solution that contains the maximum amount of solute that may be dissolved amount of solute that may be dissolved under existing conditions is under existing conditions is saturatedsaturated. .

A solution that contains less solute than a A solution that contains less solute than a saturated solution under existing saturated solution under existing conditions is conditions is unsaturatedunsaturated. .

A solution that contains more dissolved A solution that contains more dissolved solute than a saturated solution under the solute than a saturated solution under the same conditions is same conditions is supersaturatedsupersaturated..

Saturation and EquilibriumSaturation and Equilibrium

Solubility Rules

Reference Tables

Solubility Values

• Solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature

• The rate at which a substance dissolves does not alter the substances solubility

Factors that Affect Solubility

• Temperature

– Solubility of solids increases with temperature

– Solubility of gases decreases with temperature

• Pressure

– has no real effect on the solubility of liquids and solids in liquid solvents

– Increasing pressure increases the solubility of gases in liquids

Solubility Curves

• Each line represents a solute

• Higher curves mean that the solute is more soluble, lower curves are less soluble

• ABOVE the curve is SUPERsaturated, on the curve is saturated, and UNDER the curve is UNsaturated

Solubility ChartSolubility Chart

Solubility TrendsSolubility Trends The solubility of MOST solids increases The solubility of MOST solids increases

with temperature. with temperature.

The rate at which solids dissolve increases The rate at which solids dissolve increases with increasing surface area of the solid. with increasing surface area of the solid.

The solubility of gases decreases with The solubility of gases decreases with increases in temperature. increases in temperature.

The solubility of gases increases with the The solubility of gases increases with the pressure above the solution.pressure above the solution.

Therefore…Therefore…Solids tend to dissolve best when:

o Heated o Stirred o Ground into small particles

Gases tend to dissolve best when:o The solution is cold

o Pressure is high

Review Questions

Problem 18

A physical change occurs when

– A a peach spoils

– B a bracelet turns your wrist green

– C a copper bowl tarnishes

– D a glue gun melts a glue stick

Problem 19

What substance has a melting point of -94°C and a boiling point of 65°C?

– a. Ethanol

– b. Chlorine

– c. Hexane

– d. Methanol

Problem 20

22.4 liters of a gas has a mass of 36.5 grams. What is the identity of the gas?

– a. Chlorine

– b. Hydrogen chloride

– c. Nitrogen

– d. Hydrogen

Day 2

Molarity and Dilutions

Heat of SolutionHeat of SolutionThe Heat of Solution is the amount of heat energy absorbed (endothermic) or released (exothermic) when a specific amount of solute dissolves in a solvent.

•Endothermic: absorbs heat so it feels cool

•Exothermic: releases heat so it feels hot

MolarityMolarity

The concentration of a solution measured in moles of solute per liter of solution.

mol of solute = M L of solution

Example

What is the molarity of 2.5 mol KCl in 1.0L solution?

M= mol L

M= 2.5mol 1L

M= 2.5M

Example 2

What is the molarity of 0.96g MgCl2 in 500mL of solution?

M= mol L

0.96g MgCl2 1mol MgCl2 = .01 mol MgCl295g MgCl2

M= .01 mol MgCl2.500L

M= .02M

ExampleHow many moles of solute are contained in

15.25mL of a 2.1M solution of CaCl2?

M = mol L

# of mol = molarity x L of solution

# of mol = 2.1M (.01525L)

# of mol = .032 mol CaCl2

Practice Problems

Practice 1

What is the molarity of 1.35 mol H2SO4 in 245mL solution?

M= 5.51M

Practice 2

What is the molarity 9.33g Na2S in 450 mL solution?

M= 0.27M

Practice 3

How many moles of solute are contained in 125mL of a 0.050M

solution of Ba(OH)2?

.00625mol

Practice 4

How many grams of solute are contained in 64.3mL of a 0.0238M

solution of KOH?

.0859g

Practice 5

How many grams of solute are contained in 142mL of a 1.4M solution

of K2SO4?

34.6g

Dilutions

• Because the # of moles of solute does not change during a dilution

Moles of solute in the stock solution = moles of solute after dilution

M1V1=M2V2

M1V1 is the molarity and volume of the stock solution and M2V2 is the molarity and volume of the diluted

solution

Example

• How many milliliters of 2.55M NaOH is needed to make 125ml 0.75M NaOH?

M1V1 = M2V2

V1= M2V2

M1

V1=(.75)(125) 2.55

V1= 36.76L

Practice Problems

Practice 1

How would you prepare 500mL of 3 M HCl using 6 M HCl from the

stockroom?

250mL

Practice 2

How much 12 M HCl must be used to prepare 500 ml of a 1 M HCl

solution?

41.67mL

Homework

Molarity and Dilution Problems

Review Questions

Problem 21

• Which of the following substances best illustrates polar covalent bonding?

– a. HCl

– b. NaBr

– c. CsF

– d. Cl2

Problem 22

• The methane, CH4, gas molecule exhibits what type of geometric shape?

– a. trigonal planar

– b. tetrahedral

– c. bent or V-shaped

– d. trigonal pyramidal

Problem 23

• Which substance would have London dispersion forces as the main type of intermolecular forces of attraction?

– a. H2O

– b. F2

– c. HCl

– d. NaCl

Problem 24

• Which of the following compounds is an exception to the octet rule?

– a.BH3

– b.CH4

– c.NH3

– d.H2O