Question

Given the balanced ionic equation:

3Pb2+(aq) + 2Cr(s) ---> 3Pb(s) + 2Cr3+(aq)

what is the number of moles of electrons gained by 3.0 moles of lead ions?

1. 5.0 mol
2. 2.0 mol
3. 3.0 mol
4. 6.0 mol


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Answer 1

Answer : The correct option is, (4) 6.0 mol

Explanation :

The given balanced chemical equation is,

`3Pb^(2+)+2Cr\rightarrow 3Pb+2Cr^(3+)`

In this reaction, lead undergoes reduction and chromium undergoes oxidation.

Oxidation reaction : It is the reaction in which a substance looses its electrons. In this oxidation state increases.

Reduction reaction : It is the reaction in which a substance gains electrons. In this oxidation state decreases.

Half reactions of oxidation-reduction are :

Oxidation :
`2Cr\rightarrow 2Cr^(3+)+6e^-`

Reduction :
`3Pb^(2+)+6e^-\rightarrow 3Pb`

From the reduction reaction, we conclude that 6 moles of electrons gained by the 3 moles of lead ions.

Hence, the correct option is, (4) 6.0 mole