Question

Vapour pressure of solution of $5$ g of non electrolyte in $100$ g of water a particular temperature is $2985N/m^2$ if the vapour pressure of pure water at this temperature is $3000N/m^2$ the molecular mass of the solute is

• A. 60
• B. 120
• C. 180
• D. 360

Answer 1

Answer: (C)

180

Mole fraction of solute $X_2=\frac{△P}{P_1}=\frac{3000-2985}{3000}=0.005$

$X_2=\frac{\frac{m_2}{M_2}}{\frac{m_1}{M_1}}$

$\therefore 0.005=\frac{\frac{5}{M_2}}{\frac{100}{18}}$

$M_2=180$

Molar mass of solute is 180 gm/mol

Hence the correct option is [C}