Chemistry Class 11 NCERT Solutions: Chapter 8 Redox Reactions Part 14

Q: 27. Predict the products of electrolysis in each of the following:

(i) An aqueous solution of Equation with silver electrodes

(ii) An aqueous solution Equation with platinum electrodes

(iii) A dilute solution of Equation with platinum electrodes

(iv) An aqueous solution of Equation with platinum electrodes.

Answer:

(i) Equation ionizes in aqueous solutions to form Equation and Equation ions.

On electrolysis, either Equation ions or Equation molecules can be reduced at the cathode. But the reduction potential of Equation ions is higher than that of Equation .

Equation

Equation

Hence, Equation ions are reduced at the cathode. Similarly, Equation metal or Equation molecules can be oxidized at the anode. But the oxidation potential of Equation is higher than that of Equation molecules.

Equation

Equation

Therefore, Ag metal gets oxidized at the anode.

(ii) Pt cannot be oxidized easily. Hence, at the anode, oxidation of water occurs to liberate Equation . At the cathode, Equation ions are reduced and get deposited.

(iii) Equation ionizes in aqueous solutions to give Equation and Equation ions

Equation

On electrolysis, either of Equation ions or Equation molecules can get reduced at the cathode. But

the reduction potential of Equation ions is higher than that of Equation molecules.

Equation

Equation

Hence, at the cathode, Equation ions are reduced to liberate Equation gas.

On the other hand, at the anode, either of Equation ions or Equation molecules can get oxidized. But the oxidation of Equation involves breaking of more bonds than that of Equation molecules. Hence, Equation ions have a lower oxidation potential than Equation . Thus, Equation is oxidized at the anode to liberate Equation molecules.

(iv) In aqueous solutions, Equation ionizes to give Equation and Equation ions as:

Equation

On electrolysis, either of Equation ions or Equation molecules can get reduced at the cathode. But the reduction potential of Equation is more than that of Equation molecules

Equation

Equation

Hence, Equation ions are reduced at the cathode and get deposited. Similarly, at the anode, either of Equation or Equation is oxidized. The oxidation potential of Equation is higher than that of Equation .

Equation

Equation

But oxidation of Equation molecules occurs at a lower electrode potential than that of Equation ions because of over-voltage (extra voltage required to liberate gas). As a result, Equation ions are oxidized at the anode to liberate Equation gas.

Q: 28. Arrange the following metals in the order in which they displace each other from the solution of their salts.

Equation

Answer:

A metal of stronger reducing power displaces another metal of weaker reducing power from its solution of salt.

The order of the increasing reducing power of the given metals is Equation

Hence, we can say that Mg can displace Al from its salt solution, but Al cannot displace Equation .

Thus, the order in which the given metals displace each other from the solution of their salts is given below:

Equation

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