Carboxylic AcidsCambridge IGCSE Chemistry: Revision notes
Section 1
What Defines a Carboxylic Acid?
Carboxylic acids are a homologous series with the general formula , defined by the -COOH (carboxyl) functional group.
You should be able to name and draw the structural and displayed formulae of carboxylic acids containing up to four carbon atoms (e.g. methanoic acid, ethanoic acid, propanoic acid, butanoic acid).
Section 2
How Is Ethanoic Acid Formed?
Ethanoic acid, the most important carboxylic acid at this level, can be formed by oxidation of ethanol:
- Using acidified aqueous potassium manganate(VII) as the oxidising agent (in the laboratory)
- By bacterial oxidation during vinegar production (the natural route that turns wine/cider into vinegar)
Both methods convert the -OH group of ethanol into the -COOH group of ethanoic acid.
Ethanol + oxygen (from acidified potassium manganate(VII)) -> ethanoic acid + water.
Section 3
How Does Ethanoic Acid React Like Other Acids?
Ethanoic acid shows the typical reactions of an acid, reacting with metals, bases and carbonates to form salts. Salts of ethanoic acid are called ethanoates.
| Reactant | Products |
|---|---|
| Metal (e.g. magnesium) | Salt (magnesium ethanoate) + hydrogen |
| Base (e.g. sodium hydroxide) | Salt (sodium ethanoate) + water |
| Carbonate (e.g. sodium carbonate) | Salt (sodium ethanoate) + water + carbon dioxide |
You need to be able to name and give the formulae of the salts produced.
Remember that carboxylic acids are weak acids (partially dissociated), unlike hydrochloric acid, but they still undergo the same characteristic acid reactions with metals, bases and carbonates.
Section 4
How Do Carboxylic Acids React with Alcohols?
A carboxylic acid reacts with an alcohol, using an acid catalyst, to form an ester (plus water). This is called esterification.
You should be able to name and draw the displayed formulae of unbranched esters made from alcohols and carboxylic acids each containing up to four carbon atoms.
Ethanoic acid + ethanol --acid catalyst--> ethyl ethanoate + water.
Must Know
- Carboxylic acids have general formula with the -COOH functional group
- Ethanoic acid is formed by oxidation of ethanol, using acidified potassium manganate(VII) or by bacterial oxidation (vinegar production)
- Ethanoic acid reacts with metals, bases and carbonates to form ethanoate salts
- Reaction with a carbonate also produces carbon dioxide and water
- A carboxylic acid + an alcohol, with an acid catalyst, produces an ester + water (esterification)
- Be able to name/draw esters made from alcohols and carboxylic acids up to four carbons
That's the notes covered.
Carry on to the next subtopic.