1. An aqueous KNO3 solution is made using 72.5 g of KNO3 diluted to a total solu

Question

1. An aqueous KNO3 solution is made using 72.5 g of KNO3 diluted to a total solution volume of 2.00 L. Assume a density of 1.05 g/mL for the solution.

a. Calculate the molarity of the solution.

b. Calculate the molality of the solution.

c. Calculate the mass percent of the solution.

2. Use the expected van’t Hoff factors to calculate the osmotic pressure of a 0.085 M potassium sulfate solution at 298 K.

3. An aqueous solution containing 35.9 g of an unknown molecular (nonelectrolyte) compound in 150.0 g of water has a freezing point of -1.30°C. Calculate the molar mass of the unknown compound.

4. A 10.5 g sample of FeCl3 is dissolved in 1.50 x 102 g of water, with complete dissociation of the iron (III) chloride.

a. Calculate the freezing point of the solution.

b. Calculate the boiling point of the solution.

5. Calculate the vapor pressure of a solution containing 24.5 g of glycerin (C3H8O3) in 135 mL of water at 30.0 °C. The vapor pressure of pure water at this temperature is 31.8 torr. Assume that glycerin is not volatile and dissolves molecularly (i.e. it is not ionic), and use a density of 1.00 g/mL for the water.

6. Calculate the osmotic pressure of a solution containing 18.75 mg of hemoglobin in 15.0 mL of solution at 15.0°C. The molar mass of hemoglobin is 6.5 x 104 g/mol.

Explanation / Answer

1.

Mass of solute = 72.5 g.

MOlar mass of solute = 39 + 14 + 3 (16) = 101 g/mol

Moles of solute = mass / molar mass = 72.5 / 101 = 0.718 mol

Volume of solution = 2.00 L

Density of solution = 1.05 g/mL

So, mass of 1 mL of solution = 1.05 g.

Then,

mass of 2.00 L i.e 2000 mL of solution = 1.05 * 2000 = 2100 g.

Therefore,

mass of solvent = mass of solution - mass of solute = 2100 - 72.5 = 2027.5 g. = 2.0275 kg.

NOW,

(a)

Molarity = moles of solute / volume of solution in L

M = 0.718 / 2.00

M = 0.359 M

(b)

Molality = moles of solute / mass of solvent in kg

m = 0.718 / 2.0275

m = 0.354 m

m = 0.354 mol /kg

(c)

Mass % of solute = mass of solute * 100 / total mass of solution

% by mass = 72.5 * 100 / 2027.5 = 3.56 %

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