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

Concentration formulas MolarityMolality EquationM = mole of solute. Liter of solution m = mole of solute. kilogram of solvent EffectsDepends 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 solute will dissolve in solventSolution formation depends on how much solute will dissolve in solvent. Affect on dissolving 1 Stirring/ agitation 2Temperature 3 Surface area of solute faster Stir/agitate  Solute dissolves faster faster Increase temp  Solute dissolves faster faster Increase surface area  Solute dissolves faster

Surface area

solute that dissolvesin solventtemp. and pressure Solubility – amount of solute that dissolves in solvent at a given temp. and pressure

Varying solubility of solution 1Unsaturated solution 2Saturated Solution 3 Super- saturated solution Less solute Less solute than saturated solution maximum Contains maximum amount of solute at given temp and pressure more solute theoretically hold Contains more solute than it can theoretically hold at given temp. and pressure

Factors affecting solubility Simulation: Solubility and temp

Factors affecting solubility 1 Temper- ature Increase tempIncrease temp increase solubility of solids increase solubility of solids Allows supersaturated soln. to be made decrease solubility of gases decrease solubility of gases CrystallizationCrystallization of supersaturated soln. initiated by seed crystalseed crystal scratchedIf container is scratched

Factors affecting solubility

2Pressure L and SNegligible for solubility of L 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 g of potassium hydroxide in some water and then diluting the solution to a volume of mL? Given: Unknown: Don’t forget to use moles!

2. Determine the molarity of a solution prepared by dissolving g of citric acid, C 3 H 5 O(COOH) 3 in water and then diluting the resulting solution to mL. Given: Unknown:

3. What is the molarity of a salt solution made by dissolving 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 g of acetic acid, HC 2 H 3 O 2, dissolved in enough acetone to make mL of solution? Given: Unknown:

5. An analytical chemist wants to make 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, C 6 H 12 O 6 would be required to prepare 5.000x10 3 L of a 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 (C 6 H 12 O 6 ). 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) Solute disrupts formation of orderly pattern; as a result, more kinetic energy must be withdrawn from a solution to cause solidification. lower Freezing point * Solution that contains a solute has a lower Freezing point 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. * higher boiling point * Solution that contains a solute has a higher boiling point than the pure solvent

Factors affecting Colligative Properties 1.Increase amt. of solute, increase magnitude… a.VP lowering b.FP depression 1.86°C ~1 mol solute lowers FP by 1.86°C c.BP elevation 0.512°C ~ 1 mole solute increases BP by 0.512°C

2. Solutes that dissociate 2. Solutes that dissociate have greater effects than nondissociating (nonpolar) solutes Factors affecting Colligative Properties 3 particles 6 particles9 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 ΔT f = (K f )(m) FP dep. example problems

FP dep example 1: What is the freezing point depression ( ΔT f ) of a m solution made with water? ΔT f = (K f )(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? ΔT f = (K f )(m)

Calculations with Colligative properties Boiling point elevationBoiling point elevation (BP elev.) –difference in temp between BP of a solution and BP of pure solvent ΔT b = (K b )(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? ΔT b = (K b )(m)

ΔT b BP elev. Example 2: Determine BP elevation ( ΔT b ) of a m CaCl 2 solution? ΔT b = (K b )(m)