Chapter 24: Problem 88

Although carboxylic acids and alcohols both contain an \(-\mathrm{OH}\) group, one is acidic in water and the other is not. Explain the difference.

Short Answer

Expert verified

The difference in acidity between carboxylic acids and alcohols stems from their structural differences. Carboxylic acids contain a carboxyl group (R-COOH), which undergoes a reaction in water to form hydronium ions (H3O+) and carboxylate ions (RCOO-), making the solution acidic. In contrast, alcohols have a hydroxyl group (R-OH) connected to a carbon atom and do not dissociate in water or lose a proton, thus not making the solution acidic. The presence of the carbonyl group (C=O) in carboxylic acids allows for resonance stabilization of the carboxylate ion, making the hydroxyl group more acidic than the one in alcohols.

Step by step solution

Identify the structure of carboxylic acids and alcohols.

Carboxylic acids contain a carboxyl group, which consists of one carbonyl group (C=O) connected to a hydroxyl group (-OH). Their general formula is R-COOH, where R represents an alkyl group. Alcohols, on the other hand, have a hydroxyl group (-OH) connected directly to a carbon atom in the molecule. The general formula of an alcohol is R-OH, where R represents an alkyl group.

Understand the behavior of carboxylic acids in water

When carboxylic acids dissolve in water, they undergo a reaction to form a hydronium ion (H3O+) and a carboxylate ion (RCOO-). This reaction is an acid-base reaction, where the carboxylic acid donates a proton (H+) to a water molecule. The equilibrium lies to the left, so only a small amount of the carboxylic acid will ionize in water. Nonetheless, the presence of hydronium ions makes the solution acidic. The reaction is as follows: \( RCOOH + H_2O \rightleftharpoons RCOO^- + H_3O^+ \)

Understand the behavior of alcohols in water

When alcohols dissolve in water, they do not dissociate or give away a proton. Because the hydroxyl group is attached directly to a carbon atom, which is less electronegative, it is more difficult for the alcohol to lose a proton in an acid-base reaction. As a result, alcohols do not increase the concentration of hydronium ions (H3O+) in the solution, and thus, the solution is not acidic.

Explain the difference in acidity

The difference in acidity between carboxylic acids and alcohols stems from their structural differences. In carboxylic acids, the presence of the carbonyl group (C=O) makes the adjacent hydroxyl group more acidic due to resonance stabilization of the resulting carboxylate ion. In alcohols, no such resonance stabilization occurs. As a result, the hydroxyl group in carboxylic acids is more acidic than the one in alcohols, leading to the observed difference in acidity in water.

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Although carboxylic acids and alcohols both contain an \(-\mathrm{OH}\) group, one is acidic in water and the other is not. Explain the difference.

Short Answer

Step by step solution

Identify the structure of carboxylic acids and alcohols.

Understand the behavior of carboxylic acids in water

Understand the behavior of alcohols in water

Explain the difference in acidity

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