Question

Calculate the mass of sodium chloride required to prepare its 20% (mass %) solution in hundred grams of water.

• A. 12.5 g
• B. 25 g
• C. 50 g
• D. 20 g

Answer 1

The correct option is B 25 g

Mass of the solution = mass of solute + mass of solvent
Given that the mass percent of sodium chloride solution is 20%.
Let the mass of sodium chloride which is required to prepare this solution be $x$ grams.
Given that the mass of water is 100 g.
So,
$20=\left[\frac{x}{(x+100)}\right]\times 100$
$\frac{20}{100}=\left[\frac{x}{(x+100)}\right]$
$\frac{1}{5}=\frac{x}{(x+100)}$
$x+100=5x$
$5x-x=100$
$4x=100$
$x=25$
Thus, 25 g of sodium chloride is required.