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 other substances

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