Colligative Properties Name

Colligative Properties Name:

Colligative properties: physical properties of a solution that depend upon the amount of solute in the solvent.

a. Vapor Pressure Lowering: Some solutes attract the water molecules so the vapor pressure is lowered. The more solute, the lower the VP

b. Boiling Point Elevation: Since Boiling Point is dependent of VP, and a solute lowers the VP, then the Boiling Point increases.

^Tb= kb x m for ionic solutions ^Tb= kb x m x i

o kb= freezing point constant for solvent. Water is .512 C/m see text for more

i= number of ions formed when an ionic compound dissociates. NaCl---> Na+ + Cl- i= 2

m= molality

c. Freezing Point Lowering: A solute in a solvent interfers with crystal structure so the solvent freezes at a lower temperature.

all equations are analogous to ^Tb.

o Kf for water is -1.86 C/m

Problems:

1. Calculate the boiling temperature for a solution which contains 1.5mole of sodium iodide, NaI, dissolved in 1.25 kg of water.

2. Calculate the freezing point of a solution composed of 23.4 grams of Calcium Fluoride dissolved in 175 grams of water.

3. Calculate the molality of an aqueous solution(not ionic), that has a boiling point of 105.0oC. 4. At what temperature will a 3.0m solution of sodium fluoride freeze?

5. Calculate the boiling temperature for a solution which contains .325 mole of calcium phosphate dissolved into 240.0 grams of water.

6. What is the value of i for the following solutes? a. Na2SO4 b. KOH c. Al2(SO4)3 d. CH3OH

7. A solution is made by dissolving 25.0 grams of sodium sulfate in .500 kg of water. What are the boiling point and Freezing points of this solution.

8. What is the GFM of a substance that lowers the freezing point of water by 1.12o when 20 grams are put into 200 grams of water. ( not ionic)

9. What is the GFM of a substance that raises the boiling point to 103oC when 3.5 grams are put into 150 grams of water? ( not ionic )