Define disproportionation .

A disproportionation reaction is one in which the same element is simultaneously oxidised and reduced . The reaction of chlorine with alkali is a classic example.

Write the ionic equation for the reaction of Cl 2 with cold dilute NaOH and identify which species is oxidised and which is reduced.

Cl 2 (aq) + 2OH - (aq) → Cl - (aq) + ClO - (aq) + H 2 O (l) Cl 2 is oxidised to ClO - (oxidation number 0 → +1) and reduced to Cl - (oxidation number 0 → −1). This is a disproportionation reaction.

True or False? When Cl 2 reacts with hot alkali at 70°C, the chlorine is oxidised to chlorate(I) ions (ClO - ).

False. In hot alkali (70°C), chlorine is oxidised to chlorate(V) ions (ClO 3 - , oxidation number +5), not ClO - (+1). Cold alkali produces ClO - .

Cl 2 reacts with water reversibly: Cl 2 (aq) + H 2 O (l) ⇌ .......... (aq) + .......... (aq).

Cl 2 reacts with water reversibly: Cl 2 (aq) + H 2 O (l) ⇌ HCl (aq) + HClO (aq).

How does chlorine make drinking water safe?

Chlorine reacts with water in a disproportionation reaction to form chloric(I) acid (HClO) , which sterilises water by killing bacteria. HClO can further dissociate to form ClO - (aq), which is also a sterilising agent.

True or False? In the reaction of Cl 2 with cold NaOH, the oxidation number of Cl in ClO - is +1.

True. In ClO - , oxygen is −2 and the overall charge is −1, so chlorine must be +1 . This represents the oxidation of Cl 2 (oxidation number 0) in the disproportionation reaction.

In the reaction of Cl 2 with hot alkali, chlorine is oxidised to .......... (oxidation number +5) and reduced to .......... (oxidation number −1).

In the reaction of Cl 2 with hot alkali, chlorine is oxidised to ClO 3 - (oxidation number +5) and reduced to Cl - (oxidation number −1).

Write the equation for the further dissociation of HClO in water.

HClO (aq) → H + (aq) + ClO - (aq) Both HClO and ClO - act as sterilising agents, making chlorine an effective treatment for drinking water.

Write the ionic equation for the reaction of Cl 2 with hot NaOH (70°C).

3Cl 2 (aq) + 6OH - (aq) → 5Cl - (aq) + ClO 3 - (aq) + 3H 2 O (l) This is a disproportionation reaction in which Cl 2 is both oxidised (to ClO 3 - , +5) and reduced (to Cl - , −1).

A LevelChemistryCambridge (CIE)Flashcards11. Group 17The Reactions of Chlorine

The Reactions of Chlorine (Cambridge (CIE) A Level Chemistry): Flashcards

Exam code: 9701

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FrontThe Reactions of Chlorine
Define disproportionation.

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Cards in this collection (9)

Define disproportionation.
A disproportionation reaction is one in which the same element is simultaneously oxidised and reduced. The reaction of chlorine with alkali is a classic example.
Write the ionic equation for the reaction of Cl₂ with cold dilute NaOH and identify which species is oxidised and which is reduced.
Cl₂ (aq) + 2OH^- (aq) → Cl^- (aq) + ClO^- (aq) + H₂O (l)
Cl₂ is oxidised to ClO^- (oxidation number 0 → +1) and reduced to Cl^- (oxidation number 0 → −1). This is a disproportionation reaction.
True or False?
When Cl₂ reacts with hot alkali at 70°C, the chlorine is oxidised to chlorate(I) ions (ClO^-).
False.
In hot alkali (70°C), chlorine is oxidised to chlorate(V) ions (ClO₃^-, oxidation number +5), not ClO^- (+1). Cold alkali produces ClO^-.
Cl₂ reacts with water reversibly: Cl₂ (aq) + H₂O (l) ⇌ .......... (aq) + .......... (aq).
Cl₂ reacts with water reversibly: Cl₂ (aq) + H₂O (l) ⇌ HCl (aq) + HClO (aq).
How does chlorine make drinking water safe?
Chlorine reacts with water in a disproportionation reaction to form chloric(I) acid (HClO), which sterilises water by killing bacteria. HClO can further dissociate to form ClO^- (aq), which is also a sterilising agent.
True or False?
In the reaction of Cl₂ with cold NaOH, the oxidation number of Cl in ClO^- is +1.
True.
In ClO^-, oxygen is −2 and the overall charge is −1, so chlorine must be +1. This represents the oxidation of Cl₂ (oxidation number 0) in the disproportionation reaction.
In the reaction of Cl₂ with hot alkali, chlorine is oxidised to .......... (oxidation number +5) and reduced to .......... (oxidation number −1).
In the reaction of Cl₂ with hot alkali, chlorine is oxidised to ClO₃^- (oxidation number +5) and reduced to Cl^- (oxidation number −1).
Write the equation for the further dissociation of HClO in water.
HClO (aq) → H⁺ (aq) + ClO^- (aq)
Both HClO and ClO^- act as sterilising agents, making chlorine an effective treatment for drinking water.
Write the ionic equation for the reaction of Cl₂ with hot NaOH (70°C).
3Cl₂ (aq) + 6OH^- (aq) → 5Cl^- (aq) + ClO₃^- (aq) + 3H₂O (l)
This is a disproportionation reaction in which Cl₂ is both oxidised (to ClO₃^-, +5) and reduced (to Cl^-, −1).

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