When bleach is treated with an acid, evolution of chlorine gas ensues

Preparation of Chlorine Gas from Bleach

Demonstration The evolution of chlorine gas was rapid

in the presence of acid

Chlorine gas was unable to be collected “over water” like oxygen gas since chlorine gas will react with water

Chlorine reacted with the red dye in the paper, bleaching it to a lighter color

Purpose

To prepare chlorine gas

To collect chlorine gas by upward displacement of air

To demonstrate the presence of chlorine gas

Concepts

1. Bleach

2. Redox Reactions

3. Oxidizing Agents

1. Bleach Commercial laundry bleach is a solution of

sodium hypochlorite in water

NaClO(s)

When dissolved in water the sodium hypochlorite dissociates into hydrated sodium and hydrated chlorite ions

The hypochlorite ion is responsible for laundry

bleaching: it gobbles up electrons

water Na+(aq) + ClO-(aq)

2. Redox Reactions

In a redox reaction, one substance loses electrons while another substance gains electrons

“Redox” is a conventional term which is a combination of the words “reduction” AND “oxidation”

The substance that loses electrons is said to be oxidized and/or the reducing agent

The substance that gains electrons is said to be reduced and/or the oxidizing agent

3. Oxidizing Agents Oxidizing agents have many uses

bleaches: hypochlorite batteries: zinc and sulfuric acid antiseptics: hydrogen peroxide

Oxidizing agents work by gaining electrons from other substances

and/or

donating oxygen to othersubstances

Conclusions When hypochlorite bleaches

something, its chlorine atoms are being reduced to chloride ions

The hypochlorite in bleach can be rapidly decomposed in the presence of an acid

Chlorine gas is the product of the decomposition of hypochlorite ion

Comments Redox reactions are extremely common

chemical reactions photography germicides hair bleaching batteries biochemical reactions

In bleaching, the bleach is an oxidizing agent and the stain is a reducing agent