Displacement reactions involving solutions of salts
3 marks · NormalSilver is displaced from a solution of silver nitrate by magnesium metal. Write balanced ionic half-equations for the oxidation and reduction steps in this reaction.
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Oxidation: Mg(s) \rightarrow Mg^{2+}(aq) + 2e^-; Reduction: 2Ag^+(aq) + 2e^- \rightarrow 2Ag(s)
Also accept: Oxidation: \ce{Mg(s) -> Mg^{2+}(aq) + 2e^-}; Reduction: \ce{2Ag^+(aq) + 2e^- -> 2Ag(s)}
Common mistakes: Incorrect number of electrons; Mixing up which is oxidation or reduction
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Marking points
M1 · 1 mark · Correctly writes the oxidation half-equation for magnesium losing electrons.
M2 · 1 mark · Correctly writes the reduction half-equation for silver ions gaining electrons; must balance electron transfer.
A1 · 1 mark · Both equations are fully balanced with correct states and charges.
Worked solution
Magnesium is oxidised: Mg(s) loses 2 electrons.
Silver ions are reduced: 2Ag^+(aq) gain 2 electrons to form 2Ag(s).