Chapter 20, Problem 74A

a.

Interpretation Introduction

Interpretation:

The cathode and anode needs to be identified.

Concept introduction:

Rusting of iron is a redox reaction which is somewhat pseudo electrolytic. It involves the formation of electrodes at different sites of rusting.

Answer to Problem 74A

The site from where magnesium is getting corroded acts as anode and the site of rust deposition acts as cathode.

Explanation of Solution

At the site where metal gets corroded oxidation of metal is taking place so it acts as anode while at the site where metal is deposited it is getting reduced so it acts as cathode.

b.

Interpretation Introduction

Interpretation:

The process of magnesium protecting the steel needs to be explained.

Concept introduction:

The preference of a metal being oxidized at the anode or reduced at the cathode depends on its reduction potential.

Answer to Problem 74A

Magnesium acts as a sacrificial anode by getting oxidized instead of the steel therefore protecting it from corrosion.

Explanation of Solution

Magnesium has a highly negative reduction potential as compared to iron or steel therefore it gets higher preference for oxidization at the anode and thus saves the steel from getting corroded.