Chapter 16: Solutions

Concentration formulas

Freezing pt. depression

Boiling pt. elevation

Ch. 16

Making a solution

Concentration formulas

_____________ __________

Equation M = mole of solute . Liter of solution

m = mole of solute . kilogram of solvent

Effects Depends on temp. Does not depend on temp.

How do you make a solution?

•  _________: process of surrounding solute particles with solvent particles to form a solution

•  Heat of solution: overall energy change that occurs during the solution formation process

Speed of dissolving• Solution formation depends on how much

solute will dissolve in solvent.

Affect on dissolving

1__________________

2 __________

3 __________

Stir/agitate Solute dissolves faster

Increase temp Solute dissolves faster

Increase surface area Solute dissolves faster

Su

rfac

e ar

ea

Solubility – amount of solute that dissolves in solvent at a given _____________________________

Varying solubility of solution

1 _________ solution

2 ___________ Solution

3___________

_____ solution

Less solute than saturated solution

Contains maximum amount of solute at given temp and pressure

Contains more solute than it can theoretically hold at given temp. and pressure

Factors affecting solubility

Simulation: Solubility and temp

Factors affecting solubility

1Temper-

ature

• Increase temp

• __________solubility of solids

• Allows supersaturated soln. to be made

• _________ solubility of gases

• Crystallization of supersaturated soln. initiated by • ____________ • If container is scratched

Factors affecting solubility

Factors affecting solubility

2 Pressure

• Negligible for solubility of L and S

• Increase pressure gas increase solubility gas

• _______________

Section 2 Concentrations of Solutions

Objective:

Using Molarity (M)

1. Mass of solute in grams

2. Amount of solute in ____

3. Volume of solute in __

4. Molar concentration, __

Change to moles!!

1. What is the molarity of a solution prepared by dissolving 37.94 g of potassium hydroxide in some water and then diluting the solution to a volume of 500.0 mL?

Given:

Unknown:

Don’t forget to

use moles!

2. Determine the molarity of a solution prepared by dissolving 141.6 g of citric acid, C3H5O(COOH)3 in water and then diluting the resulting solution to 3500.0 mL.

Given:

Unknown:

3. What is the molarity of a salt solution made by dissolving 280.0 mg of NaCl in 2.00 mL of water?

Given:

Unknown:

mg… tricky?How do you get grams?

Here’s a hint: 1g = 1000 mg

4. What is the molarity of a solution that contains 390.0 g of acetic acid, HC2H3O2, dissolved in enough acetone to make 1000.0 mL of solution?

Given:

Unknown:

5. An analytical chemist wants to make 750.0 mL of a 6.00 M solution of sodium hydroxide. What mass of NaOH will the chemist need to make this solution?

Given:

Unknown:

6. What mass of glucose, C6H12O6 would be required to prepare 5.000x103 L of a 0.215 M solution?

Given:

Unknown:

Can you figure this

out?

7. A solution has a volume of 2.0 L and contains 36.0 g of glucose (C6H12O6). If the molar mass of glucose is 180 g/mol. What is the molarity of the solution?

Given:

Unknown:

8. A solution has a volume of 250 mL and contains 0.70 mol NaCl. What is its molarity?

This is

CAKE!

Given:

Unknown:

Making Dilutions

• M1 V1 = M2 V2

•Question If you have 6M HCl acid, you want 500ml of 2M HCl acid, How can you prepare this?

Section 3: Colligative properties

• Property that depends on amount of solute in solution, and not on identity of solution.

Freezing point (FP)• Solute disrupts formation of orderly pattern; as a

result, more kinetic energy must be withdrawn from a solution to cause solidification.

* Solution that contains a solute has a ____________ than the pure solvent

Boiling point (BP)

• Since adding a solute to a solvent decreases VP, additional kinetic energy must be added to raise VP and initiate boiling.

* Solution that contains a solute has __________ than the pure solvent

Factors affecting Colligative Properties

1. Increase amt. of solute, increase magnitude…

a. VP lowering

b. FP depression

~1 mol solute lowers FP by 1.86°C

c. BP elevation

~ 1 mole solute increases BP by 0.512°C

2. Solutes that dissociate have greater effects than nondissociating (nonpolar) solutes

Factors affecting Colligative Properties

3 particles 6 particles 9 particles

Affect colligative property least

Affect colligative property most

Calculations with Colligative properties

• Freezing pt. depression (FP dep) – difference in temperature between FP of

solution and FP of pure solvent

ΔTf = (Kf)(m)

FP dep. example problems

FP dep example 1: What is the freezing point depression (ΔTf) of a 0.100 m solution made with water?

ΔTf = (Kf)(m)

FP dep. Example 2: A solution made with ethanol is made to lower the freezing point by 6.10˚C. What is the molality of the solution?

ΔTf = (Kf)(m)

Calculations with Colligative properties

• Boiling point elevation (BP elev.)– difference in temp between BP of a solution

and BP of pure solvent

ΔTb = (Kb)(m)

BP dep. example problems

BP elev. Example 1: What molality of NaCl solution would have to be used raise the boiling point of water by 2.00˚C?

ΔTb = (Kb)(m)

BP elev. Example 2: Determine BP elevation (ΔTb) of a 0.857 m CaCl2 solution?

ΔTb = (Kb)(m)