Uses of Chlorine and Chlorate(I)
Quick Notes
- Chlorine reacts with water to form chloride ions (Cl−) and chlorate(I) ions (ClO−).
- This is a disproportionation reaction: Cl in Cl2 is both oxidised (to ClO−) and reduced (to Cl−).
- Reaction of chlorine with water (disinfectant HClO formed):
- In sunlight, chlorine with water produces oxygen:
- Chlorine is used in water treatment because HClO acts as a disinfectant, killing bacteria.
- Despite its toxicity, the benefits of chlorine in water treatment outweigh its risks.
- Chlorine reacts with cold, dilute NaOH to form NaClO (sodium chlorate(I)), which is used in bleach:
Full Notes: Uses of Chlorine and Chlorate(I)
Reactions of Chlorine with Water
Chlorine reacts with water to form chloride (Cl−) and chlorate(I) (ClO−) ions.
Chloric(I) acid (HClO) is formed, which acts as a disinfectant by oxidising bacteria.
Reaction of chlorine with water:
HClO kills bacteria and helps prevent disease and the reaction is reversible (an equilibrium is set up in water).
The reaction is a disproportionation reaction as chlorine (Cl2) is both oxidized and reduced.
Oxidation states: 0 in Cl2, +1 in ClO−, −1 in Cl−.
In sunlight, chlorine decomposes water differently:
O2 is released, reducing the concentration of disinfectant species in water.
Use of Chlorine in Water Treatment
Chlorination kills harmful microorganisms (e.g., cholera, typhoid). HClO is a strong oxidising agent that damages bacterial cell walls and inhibits algae growth, improving water quality.
Advantages:
- Kills disease-causing bacteria and viruses.
- Prevents algae formation.
Disadvantages:
- Chlorine gas is toxic and harmful if inhaled.
- Chlorine reacts with organic compounds in water to form harmful chlorinated hydrocarbons, some of which are carcinogenic.
- Possible taste/odour concerns.
Overall: Public-health benefits typically outweigh risks; chlorination remains widely used.
Reaction of Chlorine with Sodium Hydroxide
With cold, dilute sodium hydroxide, chlorine forms sodium chlorate(I) (NaClO) — the active ingredient in household bleach (a powerful oxidising agent).
Reaction of chlorine with NaOH:
NaClO oxidises bacterial components (disinfection) and removes colour from dyes (bleaching).
Summary
| Process | Key equation / idea | Why it’s useful |
|---|---|---|
| Chlorine with water (disproportionation) | Cl2 + H2O ⇌ HCl + HClO | HClO disinfects by oxidising microorganisms |
| Effect of sunlight | 2Cl2 + 2H2O → 4HCl + O2 | Produces O2; lowers effective disinfectant level |
| Chlorine with cold, dilute NaOH | Cl2 + 2NaOH → NaCl + NaClO + H2O | NaClO is bleach; strong oxidising disinfectant |
| Risk–benefit balance | Toxic gas; potential by-products | Clean, disease-free water generally outweighs risks |