Question

Pure water is kept in an insulated flask. Some ice cooled to $-{15}^{o}C$ is dropped into the flask.The fraction of water frozen into ice is:

• A. $\frac{6}{29}$
• B. $\frac{3}{35}$
• C. $\frac{6}{35}$
• D. $\frac{2}{35}$

Answer 1

Answer: (C)

$\frac{6}{35}$

Heat required, $(M\times 1\times 15)=(m\times 80)+(m\times 0.5\times 15)$
$\therefore m\times 87.5=M\times 15$
$\therefore \frac{m}{M}=\frac{15}{87.5}=\frac{6}{35}$
where, $\frac{m}{M}$ is the fraction of water frozen into ice.