The mass fraction of carbon in the saturated monobasic carboxylic acid is 54.6%. Find the formula for this acid.

The mass fraction of carbon in the carboxylic acid is not too high, hence we can conclude that the carbon chain in the acid is short. Let us find the mass fractions of carbon in the first members of the homologous series of monobasic saturated carboxylic acids:

1) Formic acid (HCOOH):

w (C) = 12 / (1 * 2 + 12 + 16 * 2) = 0.26 = 26% – does not match;

2) Acetic acid (CH3COOH):

w (C) = (2 * 12) / (1 * 4 + 12 * 2 + 16 * 2) = 0.4 = 40% – does not match;

3) Propionic acid (C2H5COOH):

w (C) = (3 * 12) / (1 * 6 + 12 * 3 + 16 * 2) = 0.4865 = 48.65% – does not match;

4) Butanoic acid (C3H7COOH):

w (C) = (4 * 12) / (1 * 8 + 12 * 4 + 16 * 2) = 54.5% – matches.

Answer: butanoic acid