Question

Calculate the molality of a solution that contains $51.2 \,g$ of naphthalene. $(C_{10}H_8)$, in $500\, mL$ of carbon tetrachloride. The density of $CCI_4$ is $1.60\,g/mL$

• A. 0.250, $m$
• B. 0.500 $m$
• C. 0.750 $m$
• D. 0.840 $ m$
• E. 1.69 $m$

Answer 1

Answer: (B)

Given,

$W_{B}=$ mass of naphthalene $=51.2\, g$

$M_{B}=$ molar mass of naphthalene $\left( C _{10} H _{8}\right)$

$=12 \times 10+8=128\, g$

$W_{A}=$ density $(d) \times$ volume $(V)\left(\because d=\frac{w}{V}\right)$

$ W_{A} =1.60\,gmL ^{-1} \times 500\,ML =800\, g$

$ \because m =\frac{W_{B}}{M_{B}} \times\left(\frac{1000}{W_{A}( kg )}\right) $

$ m =\frac{51.2 \times 1000}{128 \times 800}=0.5\,m $