A certain limiting monobasic carboxylic acid weighing 48.4 g completely dissolved magnesium oxide.

| June 21, 2021 | education

A certain limiting monobasic carboxylic acid weighing 48.4 g completely dissolved magnesium oxide. In turn, magnesium oxide was obtained by calcining magnesium carbonate, the mass of which is 23.1 g, to determine the formula of the carboxylic acid.

The reaction equation for the thermal decomposition of magnesium carbonate:

MgCO3 (t) = MgO + CO2 ↑

Magnesium Carbonate Substance Amount:

v (MgCO3) = m (MgCO3) / M (MgCO3) = 23.1 / 84 = 0.275 (mol).

According to the reaction equation, from 1 mol of MgCO3, 1 mol of MgO is formed, therefore:

v (MgO) = v (MgCO3) = 0.275 (mol).

Let the formula of an unknown limiting monobasic carboxylic acid be: CnH2n + 1COOH, where CnH2n + 1 is an unknown alkyl radical.

The equation for the reaction of this acid with magnesium oxide:

MgO + 2CnH2n + 1COOH = (CnH2n + 1COO) 2Mg + H2O

Amount of acid substance:

v (CnH2n + 1COOH) = m (CnH2n + 1COOH) / M (CnH2n + 1COOH) = 48.4 / (12 * n + 1 * (2n + 1) + 12 + 16 * 2 + 1) = 48.4 / (14n + 46) (mol).

According to the reaction equation, 1 mol of MgO reacts with 2 mol of CnH2n + 1COOH, therefore:

v (CnH2n + 1COOH) = v (MgO) * 2,

48.4 / (14n + 46) = 0.275 * 2,

n = 3, whence the molecular formula of carboxylic acid: C3H7COOH, which corresponds to butanoic (butyric) acid.

Answer: C3H7COOH.



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