4g equimolar mixture of NaOH and Na₂CO₃ contains x g of NaOH and y g of Na₂CO₃. The value of x is ____________ g. (Nearest integer)

Solution

Chemistry ma’am · 4 steps

Equimolar means equal moles, not equal grams, so call the moles n and let the molar masses split the 4 g.

1. Molar masses. NaOH: 23 + 16 + 1 = 40 g mol⁻¹. Na₂CO₃: 46 + 12 + 48 = 106 g mol⁻¹.
2. Equal moles. Let the mixture contain n mol of each compound. Their masses must add up to 4 g.

   40n + 106n = 4 ⇒ n = 4/146 = 0.0274 mol

3. Mass of NaOH. x = 40 × 4/146 = 160/146 = 1.096 g. As a check, y = 106 × 4/146 = 2.904 g, and 1.096 + 2.904 = 4.
4. So. x ≈ 1.1 g, which rounds to 1.

The common slip: 2. Splitting the 4 g equally between the two compounds gives 2. Equimolar fixes equal moles, not equal masses.

The idea to keep. In an equimolar mixture, each component's share of the total mass is its molar mass divided by the sum of the molar masses. The heavier compound takes the bigger share.

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