Question

In the solution of ${\mathrm{Na}}_2{\mathrm{SO}}_4$ the weight of ${\mathrm{Na}}^{+}$ is $92\mathrm{g}$. What is the molality of ${\mathrm{Na}}^{+}$ per kg of water?

• A. $2$
• B. $4$
• C. $6$
• D. $8$

Answer 1

The correct option is B

$4$

The explanation for the correct options (B) $4$

Step 1:

• Given the weight of sodium is $92\mathrm{g}$.
• The molecular weight of sodium is $23\mathrm{g}/\mathrm{mol}$.

Step 2:

• $\mathrm{Molality}=\frac{\mathrm{weight}}{\mathrm{molecular}\mathrm{weight}}$
• As given in the formula
• $\begin{array}{rcl}\mathrm{Molality}& =& \frac{92}{23}\\ & =& 4\mathrm{molal}\end{array}$

Hence, option (B) is correct., the molality of ${\mathrm{Na}}^{+}$ per kg of water is $4\mathrm{molal}$.