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Pieces of zinc react with copper sulfate solution - Edexcel - GCSE Chemistry: Combined Science - Question 5 - 2019 - Paper 1
Question 5
Pieces of zinc react with copper sulfate solution. Zinc sulfate solution is colourless. Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s) (a) Describe what you would see when ... show full transcript
Worked Solution & Example Answer:Pieces of zinc react with copper sulfate solution - Edexcel - GCSE Chemistry: Combined Science - Question 5 - 2019 - Paper 1
Step 1
Describe what you would see when an excess of zinc is added to copper sulfate solution and the mixture left until the reaction is complete.
Answer
When excess zinc is added to the copper sulfate solution, the initially blue color of the solution will start to fade. This happens as the zinc reacts with the copper sulfate, displacing the copper ions from the solution. As the reaction proceeds, the solution becomes more pale and eventually may turn colorless when all of the copper ions have been replaced by zinc ions. Additionally, you would observe a reddish-brown precipitate of copper forming at the bottom of the container as copper is deposited.
Step 2
Explain, in terms of electrons, which particles have been oxidised and which particles have been reduced in this reaction.
Answer
In this redox reaction, zinc (Zn) is oxidised as it loses electrons to form zinc ions (Zn²⁺). The reaction can be represented as:
ightarrow ext{Zn}^{2+} + 2 ext{e}^-$$ Conversely, copper ions (Cu²⁺) in the copper sulfate solution are reduced as they gain the electrons lost by zinc, forming solid copper (Cu). This reduction can be represented as: $$ ext{Cu}^{2+} + 2 ext{e}^- ightarrow ext{Cu}$$ Thus, zinc is oxidised and copper ions are reduced in the reaction.