Question

3. The density of a 4.53 M NH, solution is 0.9651 g/mL Calculate the molality 4. Calculate the freezing and boiling points of a solution made by mixing 10.5 g magnesium iodide with 150.0 g water. 5. A solution prepared by dissolving 0.56 g of a non-ionic solute in 25.0 g benzene freezes at 4.45°C. What is the molar mass of the solute?

Answer 1

1)density=0.9651 gm/ml

molarity=4.53M

let volume of solution is 1000 ml=1 l

MASS of solution=965.1 gm

moles of solute=4.53

mass of solute=77.01 gm

mass of solvent=888.09 gm=0.88809 kg

molality=4.53/0.88809=5.1 m

2)actually Kf (freezing depression coefficient should be given in the question)

change in freezing point= Kf*m*3

m=10.5/278/0.15=0.25179

3)freezing point of benzene=5.5 degree celcius

freezing point given=4.45 degree celcius

Kf of benzene=4.9

depression in freezing point=1.05

by henry law of depressing freezing points:-

1.05= (0.56/M)/0.025 * 4.90

M=104.533 gm