Question

How many grams of methyl alcohol should be added to $10$ litre tank of water to prevent its freezing at $268\, K$ ? $\left(K_{f} \, for\, water\, is \,1.86 K\, kg \, mol^{-1} \right)$

• A. 880.07 g
• B. 899.04 g
• C. 886.02 g
• D. 868.06 g

Answer 1

Answer: (D)

868.06 g

Answer 2

$\Delta T_{f} =K_{f} m$
where m = molality
273 - 268= 1.86 x $\frac{w}{M\times V}$
$5=1.86 \times\frac{w}{32\times10}$
$W=\frac{5\times32\times10}{1.86}$
$=860.2 \approx 868.06 g$