Question

Rajat took 100 g of 50% (w/w) sugar solution. He divided the solution into 4 equal parts. He added
5 g of sugar in $1^{st}$ part (A) and 20 g of water in $2^{nd}$ part (B). Then, he mixed these two parts and labelled the solution as ‘C’. The concentration (w/w%) of solution C is

• A. 60%
• B. 40%
• C. 30%
• D. 55%

Answer 1

The correct option is B 40%

100 g of 50% (w/w) sugar solution means 50 g of sugar is dissolved in 50 g of water. After dividing the sugar solution into 4 equal parts, we have 12.5 g of sugar and 12.5 of water in each part.
$1^{st}$ part (A) - Mass of solvent = 12.5 g
Mass of solute = 12.5 + 5 = 17.5 g
Mass of solution = 12.5 + 17.5 = 30 g
$2^{nd}$ part (B) - Mass of solvent = 12.5 + 20 = 32.5 g
Mass of solute = 12.5 g
Mass of solution = 12.5 + 32.5 = 45 g
After mixing part (A) and part (B) to form solution ‘C’, the concentration (w/w%) of solution C can be calculated as follows:
Concentration (w/w%) of solution $=\frac{\text{Mass of solute}}{\text{Mass of solution}}\times 100$
$=\frac{17.5+12.5}{30+45}\times 100=\frac{30}{75}\times 100=40$
Hence, the correct answer is option (b).