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The Redox Nature of Displacement

Why does a piece of shiny silver-coloured zinc turn into a red-brown sludge when dropped into blue copper sulfate solution? This happens because of an invisible swap of electrons between the elements involved.

A displacement reaction occurs when a more reactive element takes the place of a less reactive element in one of its compounds.
These are a sub-type of redox reaction because both oxidation and reduction happen simultaneously.
For a displacement to occur, the added metal must be higher in the reactivity series. The higher a metal is, the greater its tendency to form a positive ion (cation).

The Electron Transfer Mechanism

In a displacement reaction, electrons are transferred directly from the more reactive metal to the ions of the less reactive metal.
To remember which process is which, use the OIL RIG mnemonic: Oxidation Is Loss, Reduction Is Gain of electrons.
The more reactive metal atoms lose electrons to become positive ions. This loss of electrons is oxidation. Because this metal causes the other species to be reduced, it acts as the reducing agent.
The less reactive metal ions (which are dissolved in the solution) gain those electrons to become neutral solid atoms. This gain of electrons is reduction. By taking electrons, these ions act as the oxidising agent.
These reactions are typically exothermic, releasing heat energy to the surroundings.

Visual Indicators of Displacement

When zinc is added to copper(II) sulfate (), the blue colour of the solution gradually fades.

Students often state that "copper is reduced" instead of "copper ions are reduced". You must specify that the metal ION gains electrons, not the neutral atom.

When asked to explain why a displacement is a redox reaction, examiners expect you to explicitly identify which specific atom loses electrons (oxidation) and which specific ion gains electrons (reduction).

Always remember to include the charges on your ions when writing half-equations (e.g., writing $Cu^{2+} + 2e^-$ instead of just $Cu + 2e^-$ ), as forgetting the charges will lose you marks.

When explaining the reactivity series, use the exact Edexcel phrase: more reactive metals have a "greater tendency to form their positive ion".

A reaction in which a more reactive element takes the place of a less reactive element in one of its compounds.

A reaction where both reduction and oxidation occur at the same time.

The loss of electrons by a substance.

The gain of electrons by a substance.

The species that loses electrons, thereby reducing another species.

The species that gains electrons, thereby oxidising another species.

A mnemonic used to remember electron transfer: Oxidation Is Loss, Reduction Is Gain.

A chemical equation that shows only the reacting particles that undergo a change in oxidation state or physical state.

Ions that do not change their physical state or charge during a reaction and are excluded from ionic equations.

An equation that describes only the oxidation or reduction component of a reaction, explicitly showing the movement of electrons.

A positively charged ion, formed when an atom loses electrons.

A reaction that releases energy to the surroundings, usually in the form of heat.

An insoluble solid that emerges from a liquid solution during a reaction.

A substance dissolved in water, indicated by the state symbol (aq).

A list of metals ordered by their reactivity (their tendency to lose electrons and form positive ions).