Question

Calculate the molality of a solution that contains $51.2g$ of naphthalene $\left(C_{10}{H}_8\right)$ in $500mL$ of carbon tetrachloride. The density of $C{Cl}_4$ is $1.60g/mL$.

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

Answer 1

Answer: (B)

$0.500m$

Given,
$W_B=$ mass of naphthalene $=51.2g$

$M_B=$ molar mass of naphthalene $\left(C_{10}{H}_8\right)=12\times 10+8=128g$

$W_A=$ density $\left(d\right)\times$ volume $\left(V\right)$

$(\because d=\frac{W}{V})$

$W_A=1.60gm{L}^{-1}\times 500mL=800g$

$\because m=\frac{W_B}{M_B}\times \left(\frac{1000}{W_A\left(kg\right)}\right)$

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

Hence, option B is correct.