Reactions of acids
5 marks · HardA piece of magnesium ribbon is added to dilute ethanoic acid in a test tube.
Describe what you would observe during the reaction.
Write a balanced chemical equation for this reaction.
State one way you could test the gas given off and describe the result you would expect.
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.
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(a) Fizzing/effervescence, magnesium dissolves/disappears, colourless gas evolves.
(b) \ce{Mg(s) + 2CH3COOH(aq) -> (CH3COO)2Mg(aq) + H2(g)}
(c) Test with a lighted splint; the gas burns with a squeaky pop.
Common mistakes: Not mentioning fizzing or 'pop' test; Writing an incomplete or unbalanced equation
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Observation of fizzing or effervescence/gas produced.
B1 (a) · 1 mark · States that magnesium gradually dissolves/disappears or the solution becomes warm/colourless.
B1 (b) · 1 mark · Correct formulae for reactants and products.
B1 (b) · 1 mark · Correct balancing of the equation.
B1 (c) · 1 mark · Describes testing gas with a lighted splint and gives correct result ('squeaky pop').
Worked solution
a) You would observe fizzing or effervescence as the magnesium reacts, with bubbles of gas produced. Over time, the magnesium gradually disappears and the solution may become warm and colourless.
b) The balanced chemical equation is:
c) You can test the gas by holding a lighted splint near it. If hydrogen is present, it burns with a squeaky pop.