Question

When 'x' x \(10^{-2}\) mL methanol (molar mass = 32 g; density = 0.792 \(g/cm^3\)) is added to 100 mL water (density = 1 \(g/cm^3\)), the following diagram is obtained.

x =…………(nearest integer) [Given: Molal freezing point depression constant of water at 273.15 K is 1.86 K kg \(mol^{-1}\)]

Answer 1

Correct answer is : 543

\(\Delta T _ f=273.15 - 270.65 = 2.5 \,K\)

\(\Delta T_f = K_fm \Rightarrow 2.5 = 1.86 \times \frac {n}{0.1}\)

\(\Rightarrow n = 0.1344\, moles\)

\(\Rightarrow w = 0.1344 \times 32 = 4.3 \,g\)

Volume \(=\frac {4.3}{0.792} = 5.43 \, ml = 543 \times 10 ^{-2}\,ml\)