Slides - Chapter 16

Properties of

Solutions

A Summary of Water’s Properties

 Surface Tension

 Hydrogen bonds create a skin on the surface of

water that causes water to form beads

 Low vapor pressure (High Boiling Point)

 Hydrogen bonds hold water molecules together

so they don’t escape easily

 Low density of ice

 Ice forms a open hexagonal framework due to

Solutions

 Solutions are made by dissolving a

substance (solute) in a solvent (usually water)

 Solute particles are very small in size

(<1 nm) and can be ionic or molecular

 Solute is distributed evenly- homogeneous

Solvation

 Solvation is the general process of

dissolving a solute in a solvent

 Positive and negative ions of the

solute separate and are surrounded by water molecules

 Insoluble compounds have strong

6

What affects the rate at which something dissolves?

Factors that affect the rate: 1. Agitation/Stirring/Shaking

2. Temperature

3. Surface Area

How do each of these affect the rate at which something dissolves?

Discuss. Describe what is

What is solubility?

 Solubility refers to how much of

a solute can be dissolved in solvent

 A saturated solution contains the

maximum amount of dissolved solute

8

What is supersaturation?

 Supersaturation occurs when a

saturated solution made at a high temperature is cooled, keeping

the solute in solution

 Supersaturated solutions are

Starter

 Using what you know about the solubility of gases in a liquid, think of ways to create the

highest shooting bottle with Diet Coke and

10

How does temperature affect solubility?

 Increased kinetic energy causes

an increase in particle collisions

 Solubility of most solids

increases with increase in solvent temperature

 Solubility of gases decreases

How does pressure affect gas solubility?

 Gas solubility increases as the

pressure of the gas increases

 Henry’s Law:

12

What affects solubility?

Factors that affect solubility: 1. Type of Compound

2. Temperature

3. Pressure (for gases in aqueous

Concentrations of

Solutions

Starter

 What is the freezing temperature

of water?

 What is the melting temperature

of ice?

 Are the two temperatures the

same or different?

 What is happening on the

Molarity (M)

 Molarity (M) is the most common

form of expressing solution concentration

 Based on the total solution

Sample Problem #1

 If 3.00 moles of HCl is mixed

with 6.00L of water, what is the molarity of this solution?

Sample Problem #2

 If 51.0g of ammonia (NH₃) is

dissolved in 6.00 L of water,

Sample Problem #3

 If you have 2.00 L of a 3.00M

solution, what will be the

molarity of the new solution be if you dilute the solution to

4.00 L?

Making Dilutions

 Most solutions are stored as

concentrated stock solutions

 Fresh solution made using

dilution

2 2

1

1

V

M

V

Starter

 60g of CaCl₂ is dissolved

in 100g of water. Is the solution unsaturated, saturated, or

supersaturated? Explain.

 You are given an

unknown solution with 92g dissolved in 100g of water at 25oC. How could you determine what is

dissolved?

Dilution Practice

 Write a procedure to prepare 10 mL of

a 0.147M solution from a stock solution that is 0.869M.

 Indicate how much stock solution and

water you need.

 Make your solution

 Bring your cuvette to Mr. Cheng for

22

Colligative Properties

Something to think about

 What has to happen in order for

24

What are colligative properties?

 Colligative properties are

properties of a solution that

depend on the number of solute particles, not the type of solute particles

 Vapor pressure lowering

 Boiling point elevation

What is vapor pressure lowering?  A solution that

contains a nonvolatile solute (such as salt) has a lower vapor pressure than the pure solvent

 Shells of water of

26

What is boiling point elevation?

 Boiling point elevation is the temperature

difference between the boiling point of a solution and the pure solvent

 More kinetic energy is required to boil a solution

due to the vapor pressure lowering and water wanting to “cling” to the solute particles

 Remember: A lower vapor pressure means a

What is freezing point depression?

 Freezing point depression

is the temperature difference between the freezing point of a solution and the pure

solvent

 Presence of a solute

interferes with solid

Freezing Solutions

 Pure solvent crystals freeze

leaving a highly more concentrated liquid

 Solid solvent with pockets of

highly concentrated solution result.

 All the sweet liquid comes out,

and all you have left is ice with very little sugar leftover

 Solvent (water) freezes with a

highly concentrated solution

How is water affected?

 Boiling point of water

increases 0.512C per mol of solute particles in 1000 g water

 Freezing point of water

decreases 1.86C per mol of solute particles in 1000 g water

How do the number of

particles affect these factors?

 Refer to Figure 16.14 in your textbook  When ionic solids (or any electrolyte)

dissolve in water, they split into multiple parts

 Consider a mole of sugar (sucrose) and a

mole of NaCl

 Sucrose does not break apart (1 particle) and

NaCl forms 2 particles (Na+ and Cl-)

 NaCl will increase the boiling point or

depress the freezing point TWICE as much sucrose

Review Questions

 A mole of which of the following

will raise the boiling point of water the most?

A) NaCl

B) Sugar

Review Questions

 True or False: Hydrogen bonding

is responsible for why water is a polar molecule

Review Questions

 True of False: When sugar is

Electrolytes

 Electrolytes conduct electric

current when dissolved

 Strong electrolytes completely

dissociate

 Weak electrolytes partially dissociate

 Nonelectrolytes do not conduct

Review Questions

 True or False: Falling from 20

Surface Tension

 A water molecule

in the middle of a solution is pulled in all directions.

 A water molecule

Review Questions

 Why does water expand when it

Review Questions

 As the pressure over a liquid

increases, the solubility of a gas in the liquid

A) Increases

B) Decreases

C) Stays the same