JEE Main 2023 · 11 April · evening · Single correct · +4 / −1
A solution is prepared by adding 2 g of "X" to 1 mole of water. Mass percent of "X" in the solution is :
- (a) 20%
- (b) 10%
- (c) 2%
- (d) 5%
Answer and solution
Answer (b) 10%
Solution
Chemistry ma’am · 3 steps
Turn 1 mole of water into grams first. Then divide the mass of X by the total mass.
- Water in grams. The molar mass of H₂O is 2 + 16 = 18 g mol⁻¹. So 1 mole of water weighs 18 g.
- Mass of solution. The solution contains both solute and solvent: 2 g + 18 g = 20 g.
Mass % of X = 2/20 × 100 = 10%
- So. The mass percent of X is 10%, which is option (b). Dividing by 18 g of water alone would give about 11.1%, which is not the mass percent.
The idea to keep. Mass percent always divides by the mass of the whole solution, solute plus solvent. If an amount is given in moles, convert it to grams before you add.
Answer from the NTA final answer key. Solution by PrepWiser.