Disproportionation reactions of chlorine.
A reaction in which an element is both oxidised and reduced.
In the example shown to the right:
- hydrogen peroxide decomposes into water and oxygen
- the oxygen undergoes oxidation in forming oxygen gas
as its oxidation number increases from -1 → 0 - the oxygen undergoes reduction in forming water
as its oxidation number is reduced from –1 → -2
1. Reaction of chlorine with water.
Cl2 (g) + H2O (l) → HCl (aq) + HClO (aq)
Chlorine water Cl2 (aq)
- Chlorination is the process of adding chlorine to drinking water to kill parasites, bacteria, and viruses.
- It does mean that it is the major contaminant in drinking water
- It also removes colour and whitens.
2. Reaction of chlorine cold dilute NaOH.
Cl2 (g) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)
- Sodium chloride, sodium chlorate(I) and water are formed
- the chlorine undergoes oxidation in forming sodium chlorate(I)
as its oxidation number increases from 0 → +1 - the chlorine undergoes reduction in forming sodium chloride
as its oxidation number is reduced from 0 → -1
Sodium chlorate(I) solution is also known as sodium hypochlorite.
- It is a solution of chlorate(I) or hypochlorite ion ClO – (aq)
- It is commonly known as ‘bleach’.
- It is a so-called ‘broad-spectrum disinfectant’ that is effective in
killing viruses, bacteria, and fungi - It is used to disinfect swimming pools
- It is used for clean up patio surfaces comprising of cement and brick
- It has many applications in agriculture, food and beverage industries
- It is used as an oxidising agent in organic manufacturing industries
3. Reaction of chlorine hot conc. NaOH.
3Cl2 (g) + 6NaOH (aq) → 5NaCl (aq) + NaClO3 (aq) + 3H2O (l)
- Sodium chloride, sodium chlorate(V) and water are formed
- the chlorine undergoes oxidation in forming sodium chlorate(V)
as its oxidation number increases from 0 → +5 - the chlorine undergoes reduction in forming sodium chloride
as its oxidation number is reduced from 0 → -1
Sodium chlorate(V) is a white solid – also known as ‘chlorate of soda’.
- It is a powerful oxidizing agent and is used in the manufacture of matches and soft explosives
- Most is used to produce chlorine dioxide (ClO2) for bleaching paper pulp
- It is also used as a herbicide – but is banned in some countries because is hazardous to people and harmful to the environment
Expect to see a similar disproportionation reaction between hot KOH and iodine.
3I2 (aq) + 6KOH (aq) → 5KI (aq) + KIO3 (aq) + 3H2O (l)