Chlorine & Chlorate(I)
Chemistry: AQA A Level, topic 3.3.3
Reactions of Chlorine
Chlorine reacts with water in different ways depending on the conditions. The different products have some practical uses.
With water
- The equation for this reaction is:
- Cl2(g) + H2O(l) ⇌ HCl(aq) + HClO(aq) ⇌ 2H+(aq) + ClO−(aq) + Cl−(aq)
- This reaction is used in water treatment to kill bacteria.
With water and in sunlight
- The same reaction happens with water. But in sunlight, a further reaction can happen.
- In sunlight, the chlorate(I) ion produced will decompose to produce hydrochloric acid and oxygen. The equation for this reaction is:
- 2HClO(aq) ⇌ 2HCl(aq) + O2(g)
- So the overall equation can be written as:
- 2Cl2(g) + 2H2O(l) ⇌ 4HCl(aq) + O2(g)
Practical Uses of Chlorine
The reactions of water and chlorine have some practical uses.
Water treatment
- Chlorine is added to the water supply to try to make it safe to drink.
- But the treatment has risks:
- Chlorine gas is toxic.
- Liquid chlorine on the skin or eyes causes burns.
- Water contains trace organic compounds. Chlorine will chlorinate hydrocarbons and many of these chlorinated hydrocarbons are carcinogenic.
Benefits of water treatment
- Water treatment kills harmful bacteria.
- The increased cancer risk is small, but a cholera epidemic would kill thousands.
- Some people complain about this forced mass medication, but this prevents thousands of deaths every year and on balance is good for society.
Making bleach
- When Cl2 is added to sodium hydroxide, you get sodium chlorate(I) and sodium chloride.
- This is an example of a disproportionation reaction.
- This means chlorine is both oxidised and reduced at the same time.
- Cl2 has oxidation state 0, Cl- has oxidation state -1 and chlorate(I) has oxidation state +1.
Test yourself on Chlorine & Chlorate(I)
Compared to the standard reaction of water and chlorine, the reaction of water and chlorine in sunlight is what?