1 g of a carbonate (M₂ CO₃) on treatment with excess HCl produces 0.01 mol of CO₂. The molar mass of M₂ CO₃ is __________ g mol⁻¹. (Nearest integer)

Solution

Chemistry ma’am · 4 steps

Each carbonate unit gives exactly one CO₂, so moles of CO₂ equal moles of carbonate.

1. Write the reaction. The carbonate reacts with acid and releases carbon dioxide. One formula unit of M₂CO₃ carries one carbonate ion, so it gives one CO₂.

   M₂CO₃ + 2HCl → 2MCl + H₂O + CO₂

2. Match the moles. The ratio M₂CO₃ : CO₂ is 1 : 1. So 0.01 mol of CO₂ means 0.01 mol of M₂CO₃ reacted.
3. Find molar mass. Molar mass is mass divided by moles: (1 g)/(0.01 mol) = 100 g mol⁻¹.
4. So. The molar mass of M₂CO₃ is 100 g mol⁻¹.

The common slip: 50. Using the HCl coefficient instead of the 1 : 1 carbonate-to-CO₂ ratio takes 0.02 mol of carbonate and gives 50, not 100.

The idea to keep. In gas-evolution questions, read the mole ratio from the balanced equation first. Then molar mass is just the given mass divided by the moles you found.

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