Question

Given the balanced ionic equation:

3Pb2+ + 2Cr ==> 3Pb + 2Cr3+
What is the number of moles of electrons gained by 3.0 moles of lead ions?
(1) 5.0 mol (3)3.0 mol
(2) 2.0 mol (4) 6.0mol

Answer 1

answer:  6......................

Answer 2

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

Explanation :

The given balanced ionic 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 and 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