Carboxylic acids · Year 13
In Year 13 you get fluent with: carboxylic acids: the –COOH group and their names; carboxylic acids as weak acids.
Carboxylic acids are a homologous series with the –COOH group: methanoic, ethanoic, propanoic and butanoic acid. They are made by oxidising alcohols, and vinegar is a solution of ethanoic acid. They are weak acids: they only partly ionise in water, but they still react with metals, bases and carbonates like other acids.
Key facts
- Carboxylic acids contain –COOH: methanoic, ethanoic, propanoic and butanoic acid. They are weak acids and react with carbonates to give carbon dioxide.
- Oxidising an alcohol gives the carboxylic acid with the same number of carbon atoms: ethanol gives ethanoic acid.
- Vinegar is a dilute solution of ethanoic acid.
Worked examples
Example 1
Draw ethanol and ethanoic acid and name their functional groups.
Answer: ethanol: –OH (hydroxyl); ethanoic acid: –COOH (carboxyl)
Example 2
What is the name of chem HCOOH?
Answer: methanoic acid
Example 3
What is the name of chem C2H5COOH?
Answer: propanoic acid
Example 4
Which gas is made when ethanoic acid reacts with sodium carbonate?
Answer: carbon dioxide
Example 5
A student adds sodium carbonate to ethanoic acid and to ethanol. What would be seen?
Answer: fizzing (carbon dioxide) only with ethanoic acid
Example 6
Why is ethanoic acid called a weak acid?
Answer: it only partly ionises in water