Question

Which of the following solution can be used to prepare 1 M solution of sodium hydroxide solution?

• A. 500 ml solution containing 10 g of NaOH
• B. 500 ml solution containing 20 g of NaOH
• C. 1 L solution containing 10 g of NaOH
• D. 1 L solution containing 20 g of NaOH

Answer 1

The correct option is B

500 ml solution containing 20 g of NaOH

Gram molecular mass of NaOH = 40 g
Molarity of a solution =
$\frac{\text{Number of moles of solute}}{\text{Volume of the solution (litres)}}$
For 1 M solution of NaOH, 1 mole (40 g) of NaOH is added to 1 litre (1000 ml) solution.
Ratio of mass of NaOH (in gram) to volume of solution (in ml) = $\frac{40}{1000}=\frac{1}{25}$
Option having mass to volume ratio of $\frac{1}{25}$ is the answer.
For option, 500 ml solution containing 20 g of NaOH
Ratio of mass to volume = $\frac{20}{500}=\frac{1}{25}$
Therefore, 20 g of NaOH dissolved in 500 ml will give 1 M solution of sodium hydroxide.