Chapter 14: Solutions Concentration formulas Freezing pt. depression Boiling pt. elevation Ch. 14...

Chapter 14: Solutions

Concentration formulas

Freezing pt. depression

Boiling pt. elevation

Ch. 14

Making a solution

Concentration formulas

Molarity Molality

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?

•  Solvation: 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 solventsolute will dissolve in solvent.

Affect on dissolvingAffect on dissolving

1Stirring/ Stirring/ agitationagitation

2 Temperature Temperature

3Surface area Surface area of soluteof solute

Stir/agitate Solute dissolves fasterfaster

Increase temp Solute dissolves fasterfaster

Increase surface area Solute dissolves fasterfaster

Su

rfac

e ar

ea

Solubility – amount of solute that solute that dissolvesdissolves in solventin solvent at a given temp. temp. and pressureand pressure

Varying solubility of solution

1UnsaturatedUnsaturated solution

2SaturatedSaturated Solution

3Super-Super-

saturatedsaturated solution

Less soluteLess solute than saturated solution

Contains maximummaximum amount of solute at given temp and pressure

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

Factors affecting solubility

Simulation: Solubility and temp

Factors affecting solubility

1Temper-Temper-

atureature

•Increase tempIncrease temp

• increase increase solubility ofsolubility of solids solids

•Allows supersaturated soln. to be made

• decrease decrease solubility ofsolubility of gases gases

•CrystallizationCrystallization of supersaturated soln. initiated by

•seed crystalseed crystal •If container is scratchedscratched

Factors affecting solubility

Factors affecting solubility

2 PressurePressure

•Negligible for solubility of L and SL and S

•Increase pressure gas increase solubility gas

•(Henry’s Law)

Section 2 Concentrations of Solutions

Objective:

Using Molarity (M)

1. Mass of solute in grams

2. Amount of solute in mol

3. Volume of solute in L

4. Molar concentration, M

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:

Section 3: Colligative properties

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

Freezing point (FP)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 lower lower Freezing pointFreezing point than the pure solvent

Boiling point (BP)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 a higher higher boiling pointboiling point than the pure solvent

Factors affecting Colligative PropertiesFactors affecting Colligative Properties

1.1. Increase amt. of solute, increase Increase amt. of solute, increase magnitude…magnitude…

a. VP lowering

b. FP depression

~1 mol solute lowers FP by 1.86°C1.86°C

c. BP elevation

~ 1 mole solute increases BP by 0.512°C0.512°C

2. Solutes that dissociate2. Solutes that dissociate have greater effects than nondissociating (nonpolar) solutes

Factors affecting Colligative PropertiesFactors affecting Colligative Properties

3 particles 6 particles 9 particles

Affect colligative property least

Affect colligative property most

Calculations with Colligative properties

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

solution and FP of pure solvent

ΔΔTTff = (K = (Kff)()(mm))

FP dep. example problems

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

ΔΔTTff = (K = (Kff)()(mm))

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?

ΔΔTTff = (K = (Kff)()(mm))

Calculations with Colligative properties

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

and BP of pure solvent

ΔΔTTbb = (K = (Kbb)()(mm))

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?

ΔΔTTbb = (K = (Kbb)()(mm))

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

ΔΔTTbb = (K = (Kbb)()(mm))