A solution is prepared by adding 1 mole ethyl alcohol in 9 mole water. The mass percent of solute in the solution is ________ (Integer answer) (Given : Molar mass in g mol⁻¹ Ethyl alcohol : 46 water : 18)

Solution

Chemistry ma’am · 3 steps

Turn both mole counts into grams first, because mass percent only understands mass.

1. Moles to grams. Ethyl alcohol: 1 × 46 = 46 g. Water: 9 × 18 = 162 g.
2. Total mass. The solution weighs 46 + 162 = 208 g. The denominator is this total, not the water alone.

   Mass % = 46/208 × 100 = 22.1

3. So. The mass percent of ethyl alcohol is about 22.1%, which rounds to 22.

The common slip: 28. Dividing by the mass of water alone, 46/162 × 100, gives 28. The denominator must be the whole solution, 208 g.

The idea to keep. Mass percent is solute mass over solution mass, times 100. Whenever the data comes in moles, convert each component to grams with its molar mass before you divide.

Answer from the NTA final answer key. Solution by PrepWiser.