Carboxylic acids (Edexcel GCSE Chemistry): Revision Notes
Carboxylic acids
Carboxylic acids are a group of organic compounds that all contain a functional group called the carboxyl group (–COOH). This functional group is what gives carboxylic acids their characteristic chemical properties, such as their acidity.
Naming Carboxylic Acids
The names of carboxylic acids come from the names of their corresponding alcohols by replacing the -e or -ol ending with -oic acid.
For example:
- Ethanol (an alcohol) becomes ethan****oic acid when it is oxidised.
- Methanol becomes methan****oic acid.
- Propanol becomes propan****oic acid.
Structure of Carboxylic Acids
The general formula for carboxylic acids is Cₙ₋₁H₂ₙ₋₁COOH, except for methanoic acid (HCOOH), which is the simplest carboxylic acid.
- The –COOH functional group (also known as the carboxyl group) is what makes these compounds acids. This group contains a carbon atom double-bonded to an oxygen atom (C=O) and also bonded to a hydroxyl group (–OH).
Example: Ethanoic Acid
Ethanoic acid (commonly known as vinegar) is one of the most common carboxylic acids. It is made when ethanol (an alcohol) is oxidised, meaning it gains oxygen to form the carboxyl group.
- The formula for ethanoic acid is CH₃COOH, where the –COOH group is attached to a methyl group (CH₃).
How Are Carboxylic Acids Formed?
Carboxylic acids can be made by oxidising alcohols. Oxidation is a chemical reaction where the alcohol gains oxygen.
This process happens when the –OH group in an alcohol is attached to a carbon atom that is bonded to only one other carbon (this type of alcohol is called a primary alcohol).
To oxidise the alcohol, you need an oxidising agent like potassium dichromate.
For example:
- Ethanol (CH₃CH₂OH) can be oxidised to form ethanoic acid (CH₃COOH).
Properties of Carboxylic Acids
- Acidic: Carboxylic acids are weak acids, meaning they can release hydrogen ions (H⁺) when dissolved in water, which gives them their acidic properties.
- Soluble in water: Smaller carboxylic acids (like methanoic and ethanoic acid) can easily dissolve in water.
- Used in everyday products: Ethanoic acid is commonly found in vinegar, which is used for cooking and cleaning