The relative vapor density of the saturated dibasic carboxylic acid in air is 4.07. Derive the molecular formula of a carboxylic acid.

Solution: the general formula of diacid is СnH2n (COOH) 2
D = Mr (acid) / 29 = 4.07
⇔ Mr (acid) = 118.03 g / mol
Mr (acid) = 118.03 – 12×2 – 16×4 – 2 = 28 g / mol
⇔ 12n + 2n = 28
⇔ 14n = 28
⇔ n = 2
The acid formula is C2H4 (COOH) 2.
Answer: the formula for the diacid is C2H4 (COOH) 2.

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