Question

1 kg of $NaOH$ solution contains 4 g of $NaOH$. The approximate concentration of the solution is:

• A. 0.1 molar
• B. 0.1 molal
• C. decinormal
• D. about 0.1 N

Answer 1

The correct option is B 0.1 molal

Molality is a measure of the concentration of a solute in a solution in terms of the amount of substance in a specified amount of mass of the solvent. The molality $\left(b\right)$, of a solution, is defined as the amount of substance (in mol) of solute, $n_{solute}$ divided by the mass (in kg) of the solvent, $m_{solvent}$.

No. of moles of solute $\left(NaOH\right)$ $n_{solute}=\frac{4}{40}=0.1$ moles

Mass of solvent $\left(NaOH\right)$ in kg $m_{solvent}=1$ kg Molality of solution will be $b=\frac{0.1}{1}=0.1$ molal