Q16 of 28 Page 187

When zinc and copper (II) sulphate are heated together, the following redox reaction occurs:

Zn + CuSO4→ ZnSO4 + Cu


(s) (aq) (aq) (s)


i) What does the word redox stand for?


ii) Show how electrons are transferred in the reaction.


iii) Write the ionic equation for the redox reaction.

(i) Redox stands for those reactions in which oxidation and reduction takes place simultaneously.

(ii) The scheme of elctron transfer in this reaction could be understood from the following equation : -


Zn → Zn2+ + 2e-


The stable ionic species the force of attraction between which forms the compound CuSO4 are Cu2+ and SO42-.


Now the electrons which are liberated by Zn are accepted by Cu2+ which is then displaced from the compound to form the elemental copper and the sulphate anion left (SO42-) then combines with Zn2+ already present in the solution to form ZnSO4.


(iii) The ionic equation for the redox reaction is : -


Zn(s) + Cu2+SO42-→ Zn2+ SO42- + Cu(s)


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When lead powder is added to copper chloride solution, a displacement reaction occurs and solid copper is formed.

i) Write the equation for the reaction.


ii) Why does the displacement reaction occur?

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If a substance gains oxygen during a reaction, it is being oxidized. If it loses oxygen, it is being reduced. Oxidation and Reduction always take place together, so that if one substance is oxidized, another is reduced. Using this idea, say which substance is oxidised and which substance is reduced in each reaction.

i) Mg + O2→ 2MgO


(s) (g) (s)


ii) ZnO + C →Zn + CO


iii) Fe2 O3+ 3CO →2Fe + 3CO2


iv) Cr2O3 + 2Al → + 2Cr + Al2O3

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i) What is the PH of the solution?


ii) What is the POH of the solution?


iii) Is the given solution, acidic or basic?.