Carboxylic Acid

A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

Carboxylic Acid
• Draw the structures of methanoic acid, ethanoic acid and propanoic acid.
• Describe the reactions of carboxylic acids.

1. Carboxylic acids react with carbonates to produce carbon dioxide.
   
2. Carboxylic acids react with alcohols to make esters.
   
3. Carboxylic acids dissolve in water to produce acidic solutions.

• Explain why carboxylic acids are weak acids.
Hydrochloric acid is a strong acid as it fully ionises. Hydrochloric acid has a low pH.
Carboxylic acid are weak acids as they do not fully ionise. Carboxylic acids have a higher pH.

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Carboxylic Acid Reactions

1. Reaction with sodium hydroxide
   Ethanoic acid + sodium hydroxide → sodium ethanoate + water
   CH₃COOH + NaOH → CH₃COONa + H₂O
   
2. Reaction with sodium carbonate
   Ethanoic acid + sodium carbonate → sodium ethanoate + carbon dioxide + water
   2CH₃COOH + NaCO₃ → 2CH₃COONa + CO₂ + H₂O
   
3. Reaction with sodium hydrogen carbonate
   Ethanoic acid + sodium carbonate → sodium ethanoate + carbon dioxide + water
   CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O
   
4. Reaction with aqueous ammonia
   Ethanoic acid + ammonia → ammonium ethanoate
   CH₃COOH + NH₃ → CH₃COONH₄
   
5. Reaction with sodium metal
   Ethanoic acid + sodium → sodium ethanoate + hydrogen
   2CH₃COOH + 2Na → 2CH₃COONa + H₂
   
6. Reaction with phosphorus pentachloride
   CH₃COOH + PCl₅ → CH₃COCl + HCl + POCl₃
   

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Ethanol and Ethanoic Acid
Ethanol is produced from ethene, a chemical produced from the fractional distillation of crude oil and involving cracking using a catalyst at high temperature and pressure. Ethanol can be made in two ways:
1. Hydration of Ethene
Ethene + steam → ethanol
C₂H₄ + H₂O → C₂H₅OH
2. Fermentation of Glucose
Fermentation of sugar from standard crops like sugar cane and corn, under warm and anaerobic conditions.
sugar (glucose) → ethanol + carbon dioxide
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
This process uses yeast as an enzyme.

Ethanoic Acid
Ethanol + oxygen → ethanoic acid + water
C₂H₅OH + O₂ → CH₃COOH + H₂O
Ethanoic acid is also known as acetic acid or vinegar.

Carboxylic Acids - Reactions
• Ethanoic acid is a typical acid. It will turn litmus paper and universal indicator red.
Ethanoic acid reacts with metal to form hydrogen gas.
• Magnesium + ethanoic acid → magnesium ethanoate + hydrogen
Mg(s) + 2CH₃COOH(aq) → (CH₃COO)₂Mg(aq) + H₂(g)
• Ethanoic acid reacts with bases to form water in a neutralisation reaction.
Ethanoic acid + sodium hydroxide → sodium ethanoate + water
2CH₃COOH(aq) + NaOH(aq) → CH₃COO₂Na(aq) + H₂O(l)
• Ethanoic acid reacts with carbonates to form water and carbon dioxide.
Ethanoic acid + sodium carbonate → sodium ethanoate + water
2CH₃COOH(aq) + Na₂CO₃(aq) → 2CH₃COO₂Na(aq) + CO₂(g) + H₂O(l)

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