Question

The freezing point of a solution prepared from 1.25 g of non-electrolyte and 20 g of water is 271.9K. If molar depression constant is 1 86 $K m^{-1}$ then molar mass of the solute will be

• A. 105.7
• B. 106.7
• C. 115.3
• D. 93

Answer 1

Answer: (D)

93

Answer 2

$\Delta T _{ f }=\frac{1000 K _{ f } \times W _{2}}{ Mw _{2} \times W _{1}}$ $[\Delta T =273-271.9=1.25]$ $1.25=\frac{1000 \times 1.86 \times 1.25}{ Mw _{2} \times 20}$ $Mw _{2}=93$