Reaction with metals
3 marks · NormalCarboxylic acids are classified as weak acids.
Explain what is meant by a 'weak acid'.
Describe what you would observe when sodium carbonate solution is added to ethanoic acid.
State how the reaction of ethanoic acid with sodium carbonate shows its weak acid properties.
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(a) A weak acid is only partially ionised in water.
(b) Effervescence/fizzing is observed due to carbon dioxide gas produced.
(c) The reaction is slower and less vigorous than with a strong acid, showing that ethanoic acid is a weak acid because it releases fewer hydrogen ions in solution.
Common mistakes: Confusing weak with dilute; Forgetting gas production
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Explains weak acid as only partially ionised in water/solution.
B2 (b) · 1 mark · Correctly describes effervescence/fizzing from carbon dioxide.
M1 (c) · 1 mark · Explains that the reaction is less vigorous than with a strong acid, linking this to fewer H+ ions and weak acid behaviour.
Worked solution
a) A weak acid is only partially ionised in water.
b) You would see bubbles/fizzing, showing a gas is evolved (carbon dioxide).
c) The reaction of ethanoic acid with sodium carbonate is slower and gives less fizzing than a reaction with a strong acid because weak acids release fewer hydrogen ions in solution.