CBSE Class 12 Chemistry 2014 Delhi Set 1 Solved Paper

Question : 11

Total: 30

Calculate the mass of compound (molar mass = 256gmol−1 ) to be dissolved in 75g of benzene to lower its freezing point by 0.48K(Kf=5.12K‌kg. mol−1 ).

Solution:

Let Xg of the compound is to be dissolved. Number of moles of compound,
n=

molar mass

given mass

256

Mass of Benzene =75g=0.075Kg
Molality =

moles of solute

mass of solvent in kg

256×0.075

19.2

Freezing point depression ΔTf=0.48 K
Molar depression of freezing point constant =5.12 K kg∕ mol
It is defined as the total number of molecules of reactants.
⇒Tf=Kf0.48
=5.12 W=1.8 g
Hence, 1.8 g solute has been dissolved.

Go to Question:

Prev Question

Next Question