Air was drawn through a solution containing 40 g of solute (non-volatile, non-electrolyte) in 100 g — Solutions and Colligative Properties Chemistry Question
Question
Air was drawn through a solution containing 40 g of solute (non-volatile, non-electrolyte) in 100 g of water and then through water. The loss of mass of water was 0.05 g and the total mass of water absorbed in sulphuric acid tube was 2.05 g. The molecular mass of the solute is
💡 Solution & Explanation
According to the Ostwald-Walker method, loss in mass of solvent is proportional to $(P^\circ - P)$ and the total mass absorbed by the sulphuric acid tube is proportional to $P^\circ$. Thus, relative lowering is $(P^\circ - P) / P^\circ = 0.05 / 2.05 = 1 / 41$. From $(P^\circ - P) / P = n / N$, we have $1 / 40 = n / N$. Therefore, $1 / 40 = (40 / M) / (100 / 18) \Rightarrow 1 / 40 = (40 \times 18) / (100 \times M) \Rightarrow 1 / 40 = 7.2 / M \Rightarrow M = 40 \times 7.2 = 288.0$ g/mol. Therefore, correct answer is B.