A mixture of 10 g of sodium bicarbonate and sodium carbonate was heated until the mass became constant. The total mass decreased by 1.55 g. Calculate the mass fraction of sodium carbonate in the initial mixture.
- 42%
- 58%
- 31%
- 69%
📝 Detailed explanation
Only NaHCO₃ decomposes: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂.Mass loss (H₂O + CO₂) = 1.55 g.
Molar mass of (H₂O + CO₂) = 18 + 44 = 62 g/mol.
n(products) = 1.55 / 62 = 0.025 mol.
n(NaHCO₃) = 0.025 * 2 = 0.05 mol.
Mass NaHCO₃ = 0.05 * 84 = 4.2 g.
Mass Na₂CO₃ = 10 - 4.2 = 5.8 g.
Mass fraction = 5.8 / 10 = 0.58 or 58%.