Answer to Question #113645 in General Chemistry for Zakari

Question

2. ​Give one difference between the bleaching action of chlorine gas and sulphur(iv) oxide gas

Answer 1

The purpose of bleaching by chemical agents consists in destroying the color-causing groups, or chromophores, in the molecules in the substance using chemical reactions.

The difference between the bleaching action of chlorine gas and sulphur(iv) oxide gas consists in the redox character of the bleaching reaction. The chlorine gas has strong oxidative properties, while sulphur (IV) oxide is a strong reducing agent.

For example, in the processing of the wood pump, chlorine replaces hydrogen in the aromatic rings of lignin, oxidizes the pendant groups and adds across the carbon double bonds in the lignin side chains. Also, chlorine gas reacts with water contained in the sample and produces oxygen. Oxygen molecules react with colored organic compounds, oxidizing them. The products don't have the necessary structural patterns in order to absorb visible light.

On the other hand, sulphur (IV) oxide works through reduction of organic compounds, destroying the conjugated double bonds (converting them to single bonds), important for the visible light absorption.