Question

In an experiment, 18.04 g of mannitol were dissolved in 100 g of water. The vapour pressure of water was lowered by 0.309 mm Hg from 17.535 mm Hg. Calculate the molar mass of manitol.

• A. 150.0 g/mol
• B. 184.3 g/mol
• C. 140.4 g/mol
• D. 123.21 g/mol

Answer 1

The correct option is B 184.3 g/mol

Using the relation

$\frac{p-p^o}{p^o}=\frac{\frac{W_2}{M_2}}{\frac{W_1}{M_1}+\frac{W_2}{M_2}}$

$\frac{0.309}{17.535}=\frac{\frac{18.04}{M_2}}{\frac{100}{18}+\frac{18.04}{M_2}}$

On solving the equation, we get $M_2=184.3g/mol$