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A 1 g sample of a carbonate having the formula M2CO3 is treated with excess hydrochloric acid. If 0.01186 mol of carbon dioxide is evolved, what is the molar mass of M2CO3 in g mol⁻¹?

1. 1186
2. 84.3
3. 118.6
4. 11.86

Correct answer: 84.3

Solution

Each M2CO3 gives one CO2, so moles M2CO3 = 0.01186. Molar mass = 1 g / 0.01186 mol = 84.3 g/mol.

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