Types of Chemical Reactions > Single Displacement Reaction

The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by formation of its own ions, is called displacement reaction.

• A more reactive metal can replace a less reactive metal from its compound in solution.
• Zinc, iron, and lead can displace copper from copper sulphate or copper chloride solutions.
• During displacement, the displaced metal appears in elemental form, while the replacing metal forms its salt.
• In the reaction Fe + CuSO₄ → FeSO₄ + Cu, the iron nail turns brownish due to deposited copper, and the blue solution fades.
• Heat may be released during displacement reactions, indicating that the reaction is exothermic.

A single displacement reaction, also known as a single replacement reaction, occurs when a more reactive element replaces a less reactive element in a compound. The products of these reactions can be predicted using the reactivity series, which arranges elements in decreasing order of their reactivity. Elements at the top of the reactivity series are more reactive and can displace elements positioned below them.

A + BC → AC + B

Here, A (a metal) replaces B (another metal) in the compound BC, forming AC while B is released as a free element.

$$Y+XZ\to XY+Z$$

In this reaction, Y (a nonmetal) replaces Z (another nonmetal) in the compound XZ, forming XY, while Z is released as a free element.

For example, in the reaction between potassium (K) and magnesium chloride (MgCl₂), potassium, being more reactive, displaces magnesium from its salt, forming potassium chloride (KCl) and releasing magnesium (Mg) as a free element.

2K + MgCl₂ → 2KCl + Mg

1. Aim: To observe a single displacement reaction, where a more reactive metal displaces a less reactive metal from its compound.

2. Requirements

• Apparatus: test tubes, beaker, dropper, magnesium strip, zinc metal.
• Chemicals: Copper(II) nitrate [Cu(NO₃)₂] solution, hydrochloric acid (HCl), zinc (Zn), and magnesium (Mg).

3. Procedure

Experiment 1: Reaction of Magnesium with Copper(II) Nitrate

• Take an aqueous solution of Cu(NO₃)₂ in a test tube.
• Place a magnesium (Mg) strip into the solution.
• Observe that copper (Cu) precipitates while magnesium nitrate [Mg(NO₃)₂] forms in solution.

Mg(s) + Cu(NO₃)₂(aq) → Mg(NO₃)₂(aq) + Cu(s)

Experiment 2: Reaction of Zinc with Hydrochloric Acid

• Take dilute hydrochloric acid (HCl) in a test tube.
• Add a small piece of zinc (Zn) to it.
• Observe the formation of bubbles of hydrogen gas (H₂) and the formation of zinc chloride (ZnCl₂) in solution.

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

4. Conclusion: A single displacement reaction occurs when a more reactive metal replaces a less reactive element in a compound. These reactions follow the reactivity series, where more reactive metals displace less reactive ones, producing new compounds and free elements.