Question

A solution made by dissolving 40 g $NaOH$ in 1000 g of $H_{2}O$ is :

• A. 1 molar
• B. 1 normal
• C. 1 molal
• D. none of these

Answer 1

The correct option is C 1 molal

No. of moles $n=\frac{mass}{molarmass}$

No. of moles of $NaOH$ is $n=\frac{40}{40}=1mole$

Mass of solvent in kg is $m=\frac{1000}{1000}=1Kg$

Molality of solution is $\frac{n}{m}=\frac{1}{1}=1Molal$

1 molal aqueous solution means 1 mole of solute in $1kg$ or $1000g$ of water.

Hence, option C is correct.