Question

What is the molality m, of methanol in a solution prepared by dissolving $160$ g of methanol in $200.0$ g of water?

• A. 1.0 m
• B. 5.0 m
• C. 10.0 m
• D. 25.0 m

Answer 1

The correct option is D 25.0 m

The molar mass of methanol is 32 g/mol.
The number of moles of methanol present in 160 g of methanol are $\frac{160g}{32g/mol}=5mol$.
The mass of water is 200.0 g or 0.200 kg.
$Molality=\frac{\text{Number of moles of methanol}}{\text{Mass of water (in kg)}}=\frac{5mol}{0.200kg}=25.0m$