Reactions of Carboxylic Acids

Carboxylic acids have many similarities to other acids. For example:

  • They dissolve in water to form an acidic solution. However, as carboxylic acids only partially ionise, they tend to have a higher pH than strong acids like hydrochloric acid.
  • They react with metals to form a salt and hydrogen.
  • They react with carbonates to form a salt, water and carbon dioxide gas.
  • They react with hydroxides to produce salt and water.

All salts formed from the reactions with carboxylic acids end in -anoate. The -COOH functional group determines how carboxylic acids react.

Reactions with Metals

Carboxylic acids react with metals to form a salt and hydrogen gas.

For example, ethanoic acid reacts with magnesium to form a colourless solution of magnesium ethanoate, and hydrogen gas is given off.

Ethanoic acid + Magnesium Magnesium ethanoate + Hydrogen gas

2CH3COOH + Mg (CH3COO)2Mg + H2

Reactions with Hydroxides

Carboxylic acids react with hydroxides to produce a salt and water. This is a neutralisation reaction.

For example, when butanoic acid reacts with sodium hydroxide, it forms a colourless solution of sodium butanoate and water.

Butanoic acid + Sodium hydroxide Sodium butanoate + Water

CH3CH2CH2COOH + NaOH CH3CH2CH2COONa + H2O

Reactions with Carbonates

Carboxylic acids react with carbonates to form a metal salt, water and carbon dioxide gas.

For example, propanoic acid reacts with sodium carbonate to form the salt potassium propanoate, water and carbon dioxide.

Propanoic acid + Sodium carbonate Sodium propanoate + Water + Carbon dioxide

2CH3CH2COOH + Na2CO3  2CH3CH2COONa + H2O + CO2

Making Esters

In the presence of an acid catalyst, carboxylic acids react with alcohols to form esters and water. This reaction is called esterification. Esters are organic compounds with the functional group -COO-. They are often used as organic solvents, and due to their fruity smell, they are also used in many foods and products (e.g. perfumes).

An example of esterification is when ethanoic acid reacts with ethanol to form the ester ethyl ethanoate.

Ethanol + Ethanoic acid Ethyl ethanoate + Water

In the displayed reaction, an ethanol molecule and an ethanoic acid molecule are shown with a green arrow pointing downwards to products: an ethyl ethanoate molecule and a water molecule.

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