Carboxylic Acids
7 marks · HardA student is investigating the behaviour of ethanoic acid with different substances in the laboratory.
State the main component of vinegar.
Give one observation when magnesium metal is added to ethanoic acid.
Write a balanced chemical equation for the reaction of ethanoic acid with magnesium.
Explain why ethanoic acid reacts more slowly with magnesium than hydrochloric acid.
Name the salt formed in the reaction between ethanoic acid and magnesium.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Ethanoic acid
(b) Fizzing/effervescence; production of hydrogen gas
(c) Mg(s) + 2CH3COOH(aq) → (CH3COO)2Mg(aq) + H2(g)
(d) Ethanoic acid is a weak acid and only partially ionises in water, providing fewer H+ ions to react with magnesium, so the reaction is slower than with hydrochloric acid, which is a strong acid and fully ionises.
(e) Magnesium ethanoate
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies ethanoic acid as the main component of vinegar.
B1 (b) · 1 mark · States correct observation (e.g., fizzing, effervescence, hydrogen gas evolved).
M1 (c) · 1 mark · Shows correct reactants/products; correct formulae.
A1 (c) · 1 mark · Equation is correctly balanced.
M1 (d) · 1 mark · States ethanoic acid is a weak acid/partially ionised; hydrochloric acid is a strong acid/fully ionised.
A1 (d) · 1 mark · Links partial ionisation/lower concentration of H+ to slower reaction rate.
B1 (e) · 1 mark · Correctly names the salt as magnesium ethanoate.
Worked solution
a) The main component of vinegar is ethanoic acid.
b) Adding magnesium to ethanoic acid causes fizzing or effervescence, due to hydrogen gas being produced.
c) Ethanoic acid reacts more slowly with magnesium than hydrochloric acid because ethanoic acid is a weak acid, only partially ionising in solution and providing fewer H+ ions, so the reaction occurs more slowly. Hydrochloric acid is a strong acid and provides a higher concentration of H+ ions.
e) The salt formed is magnesium ethanoate.