Question

Calculate the percentage composition of the solute in % (w/w) present in a solution obtained by mixing 400 g of a 25% (w/w) solution and 500 g of a 40% (w/w) solution.

• A. 33.33%
• B. 45.38%
• C. 75.65%
• D. 60.84%

Answer 1

The correct option is A 33.33%

25% (w/w) means 25 g of solute is present in 100 g of the solution.
40% (w/w) means 40 g of solute is present in 100 g of the solution.
Mass of solute in 400 g solution of 25% = $25\times \frac{400}{100}$ = 100 g
Mass of solute in 500 g solution of 40% = $40\times \frac{500}{100}$ = 200 g
Therefore, total mass of solute = 100 + 200 = 300 g
Total mass of the solution = 400 + 500 = 900 g
% (w/w) of solute = $\frac{\text{mass of the solute}}{\text{total mass of the solution}}\times 100$
= $\frac{300}{900}\times 100$ = 33.33%