When zinc metal is added to an aqueous solution of copper sulphate, which substance is displaced from the solution?

Introduction / Context:
This question examines your understanding of displacement reactions in inorganic chemistry, specifically the reaction between zinc metal and copper sulphate solution. Such reactions illustrate the reactivity series of metals and show how a more reactive metal can displace a less reactive metal from its compound in solution.

Given Data / Assumptions:

• Reactants: zinc metal (Zn) and aqueous copper sulphate solution (CuSO4).
• We are asked which substance is displaced from the solution when zinc is added.
• We assume standard conditions and that the reaction occurs.
• We use the usual reactivity series where zinc is more reactive than copper.

Concept / Approach:
The reactivity series shows that a more reactive metal can displace a less reactive metal from its salt solution. Zinc is placed above copper in the reactivity series. When zinc is added to a solution of copper sulphate, zinc will displace copper from the solution, forming zinc sulphate and depositing copper metal. The sulphate ion remains in solution and is not displaced. Hydrogen and oxygen are not involved as displaced elements in this reaction.

Step-by-Step Solution:
Step 1: Write the word equation for the reaction: Zinc + Copper sulphate → Zinc sulphate + Copper. Step 2: Write the balanced chemical equation: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s). Step 3: In copper sulphate, copper is present as Cu2+ ions and sulphate as SO4 2− ions. Step 4: Zinc atoms lose electrons and enter the solution as Zn2+ ions, while Cu2+ ions gain electrons and are deposited as copper metal. Step 5: As a result, copper is removed from the solution and zinc takes its place in the sulphate salt. Step 6: Therefore, copper is the substance displaced from the solution.

Verification / Alternative check:
Observation in the laboratory supports this explanation. When zinc is placed in blue copper sulphate solution, the blue colour gradually fades because Cu2+ ions are being removed, and a red brown deposit of copper metal appears on the zinc surface or at the bottom of the vessel. The solution gradually becomes colourless as it becomes zinc sulphate solution. These visual changes confirm that copper is the species displaced.

Why Other Options Are Wrong:
Hydrogen is not part of copper sulphate and therefore cannot be displaced in this reaction. Zinc is not displaced; it is the metal that enters the solution and replaces copper, so it is the displacing metal, not the displaced substance. The sulphate ion remains in solution associated with zinc and is not displaced as a separate substance. Oxygen is not an individual reactant or product here, so it is also incorrect.

Common Pitfalls:
Students sometimes confuse which metal is more reactive and may think copper displaces zinc. Remember that in the reactivity series zinc lies above copper, so zinc is more reactive. Another mistake is to misinterpret the word displaced and think of any species that changes form in the reaction, rather than focusing on the less reactive metal ion being removed from its compound.

Final Answer:
When zinc is added to copper sulphate solution, the substance displaced from the solution is copper.