Reactions of chlorine
| English | Chinese | Pinyin |
|---|---|---|
| chlorate | 氯酸盐 | lǜ suān yán |
| disproportionation | 歧化 | qí huà |
| water purification | 水净化 | shuǐ jìng huà |
| bacteria | 细菌 | xì jūn |
The chemistry that cleans water
- Chlorine reacts with sodium hydroxide in two ways.
- In both, chlorine is disproportionated.
- A little chlorine also makes water safe to drink.
Chlorine reaction route
Follow chlorine from water treatment to redox reactions.
Chlorine reacts with water to form a mixture used to disinfect water supplies.
It forms chloric(I) acid, which kills microbes.
With sodium hydroxide
- Cold, dilute NaOH → chloride + chlorate 氯酸盐(I):
$$\text{Cl}_2 + 2\text{NaOH} \rightarrow \text{NaCl} + \text{NaClO} + \text{H}_2\text{O}$$
- Hot, concentrated NaOH → chloride + chlorate(V):
$$3\text{Cl}_2 + 6\text{NaOH} \rightarrow 5\text{NaCl} + \text{NaClO}_3 + 3\text{H}_2\text{O}$$
- In both, chlorine's oxidation number goes both up and down from 0 — disproportionation 歧化.
Chlorine is added to pool water to kill microbes
Chlorine with cold, dilute sodium hydroxide forms:
Cl₂ + 2NaOH → NaCl + NaClO + H₂O (chlorate(I)); hot concentrated NaOH gives chlorate(V) instead.
These reactions of chlorine with NaOH are disproportionation because chlorine:
Some chlorine goes to −1 (chloride) and some to +1 or +5 (chlorate) — the same element both up and down.
In the reaction of chlorine with sodium hydroxide, chlorine is both oxidised and reduced.
That is what makes it a disproportionation reaction.
Match each chlorine reaction to its product/role.
Each item links the term to its correct meaning.
Water purification 水净化
- A little chlorine is added to water:
$$\text{Cl}_2 + \text{H}_2\text{O} \rightleftharpoons \text{HOCl} + \text{HCl}$$
- The active species HOCl and ClO⁻ kill bacteria 细菌, making the water safe to drink.
Chlorine displaces bromine: the solution turns orange
Chlorine makes water safe to drink because:
Cl₂ + H₂O ⇌ HOCl + HCl; the HOCl and ClO⁻ kill bacteria.
Chlorine in water treatment
- Chlorine reacts with water to form chloric(I) acid, which kills microbes.
- The benefit (safe drinking water) is judged to outweigh the risks of using a toxic gas.
You've got it
- chlorine + cold dilute NaOH → NaCl + NaClO (chlorate I); + hot conc NaOH → NaCl + NaClO₃ (chlorate V)
- both are disproportionation (Cl goes up and down from 0)
- chlorine purifies water: $\text{Cl}_2 + \text{H}_2\text{O} \rightleftharpoons \text{HOCl} + \text{HCl}$; HOCl kills bacteria