First slide

Questions based on phase change

Question

Pure water cooled to - 15°C is contained in a thermally insulated flask. Some ice is added into the flask. The fraction of water frozen into ice is :

Moderate

A

$\frac{3}{35}$
B

$\frac{6}{35}$
C

$\frac{2}{35}$
D

$\frac{6}{29}$

Solution

Here if m is the mass of ice and M is the mass of water, then
80 m = m × 0.5 × 15 + (M-m) × 1 × [0-(-15)]
= m × 7.5 +15 M - 15m
or $\frac{m}{M} = \frac{6}{35}$
$∴$ Correct choice is (2).

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