Chemistry Class 12 NCERT Solutions: Chapter 3 Electrochemistry Part 3

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Q: 12. What is the quantity of electricity in coulombs needed to reduce mol of ? Consider the reaction:


The given reaction is as follows:

Therefore, to reduce mole of the required quantity of electricity will be:

Q: 13. Write the chemistry of recharging the lead storage battery, highlighting all the materials that are involved during recharging.


A lead storage battery consists of a lead anode, a grid of lead packed with lead oxide as the cathode, and a solution of sulphuric acid as an electrolyte.

When the battery is in use, the following cell reactions take place:

At anode:

At cathode:

The overall cell reaction is given by,

When a battery is charged, the reverse of all these reactions takes place.

Hence, on charging, present at the anode and cathode is converted into and respectively.

Q: 14. Suggest two materials other than hydrogen that can be used as fuels in fuel cells.


Methane and methanol can be used as fuels in fuel cells.

Q: 15. Explain how rusting of iron is envisaged as setting up of an electrochemical cell.


In the process of corrosion, due to the presence of air and moisture, oxidation takes place at a particular spot of an object made of iron. That spot behaves as the anode. The reaction at the anode is given by,

Electrons released at the anodic spot move through the metallic object and go to another spot of the object.

There, in the presence of ions, the electrons reduce oxygen. This spot behaves as the cathode. These ions come either from , which are formed due to the dissolution of carbon dioxide from air into water or from the dissolution of other acidic oxides from the atmosphere in water.

The reaction corresponding at the cathode is given by,

The overall reaction is:

Also, ferrous ions are further oxidized by atmospheric oxygen to ferric ions. These ferric ions combine with moisture, present in the surroundings, to form hydrated ferric oxide i.e., rust.

Hence, the rusting of iron is envisaged as the setting up of an electrochemical cell.

Exercise: 2

Q: 1. Arrange the following metals in the order in which they displace each other from the solution of their salts. and


The following is the order in which the given metals displace each other from the solution of their salts.

Q: 2. Given the standard electrode potentials,

Arrange these metals in their increasing order of reducing power.


The lower the reduction potential, the higher is the reducing power. The given standard electrode potentials increase in the order of

Hence, the reducing power of the given metals increases in the following order: