AP | A-Level | IB | NCERT 11 + 12 – FREE NOTES, RESOURCES AND VIDEOS!
CIE® A-Level
YouTube Channel
YouTube Channel
@chemistry.student
*Revision Materials* 1 Atomic Structure 2 Atoms, molecules and stoichiometry 3 Chemical Bonding 4 States of matter 5 Chemical energetics 6 Electrochemistry 7 Equilibria 8 Reaction kinetics 9 The Periodic Table, chemical periodicity 10 Group 2 11 Group 17 12 Nitrogen and sulfur 13 Organic 14 Hydrocarbons 15 Halogen compounds 16 Hydroxy compounds 17 Carbonyl compounds 18 Carboxylic acids and derivatives 19 Nitrogen compounds 20 Polymerisation 21 Organic synthesis 22 Analytical techniques 23 Chemical energetics 24 Electrochemistry 25 Equilibria 26 Reaction kinetics 27 Group 2 28 Chemistry of transition elements 29 Organic 30 Hydrocarbons 31 Halogen compounds 32 Hydroxy compounds 33 Carboxylic acids and derivatives 34 Nitrogen compounds 35 Polymerisation 36 Organic synthesis 37 Analytical techniques

11 Group 17

11.1 Physical properties of the Group 17 elements 11.2 The chemical properties of the halogen elements and the hydrogen halides 11.3 Some reactions of the halide ions 11.4 The reactions of chlorine

The Reactions of Chlorine

Specification Reference Inorganic Chemistry, Group 17 11.4

Quick Notes

  • Chlorine undergoes disproportionation when it reacts with cold or hot NaOH.
    • Disproportionation = the same species is both oxidised and reduced in the reaction.
  • With cold NaOH, chlorine forms Cl− and ClO− (bleach). CIE A-Level Chemistry diagram of chlorine reacting with cold dilute NaOH to form bleach (NaClO).
  • With hot NaOH, chlorine forms Cl− and ClO3−. CIE A-Level Chemistry diagram of chlorine reacting with hot concentrated NaOH to form chlorate(V) ions.
  • Chlorine reacts with water to produce HClO (chloric(I) acid) and Cl−, which kill bacteria. CIE A-Level Chemistry diagram of chlorine reacting with water to form HCl and HClO.
  • HClO and ClO− are used to kill bacteria in water treatment.

Full Notes

Disproportionation Reactions of Chlorine with Sodium Hydroxide

Chlorine reacts differently with cold and hot aqueous sodium hydroxide.

Cold, Dilute NaOH

CIE A-Level Chemistry diagram of chlorine reacting with cold dilute NaOH to form bleach (NaClO).

This is a disproportionation reaction because the Cl2 is simultaneously oxidised (to ClO−, +1) and reduced (to Cl−, –1) at the same time.

CIE A-Level Chemistry diagram showing disproportionation of chlorine in NaOH forming Cl- and ClO-.

Use: Sodium chlorate(I) (NaClO) is the active ingredient in bleach and disinfectants.

Hot, Concentrated NaOH

CIE A-Level Chemistry diagram of chlorine reacting with hot concentrated NaOH to form chlorate(V) ions.

Here, chlorine is oxidised further to ClO3− (+5 oxidation state) and reduced to Cl−. This is also a disproportionation reaction, occurring under hotter conditions.

Chlorine in Water Purification

Chlorine dissolves in water and reacts to form chloric(I) acid (HClO) and hydrochloric acid (HCl):

CIE A-Level Chemistry diagram of chlorine reacting with water to form HCl and HClO.

HClO (chloric(I) acid) is a strong oxidising agent and kills bacteria.

The HClO and HCl both dissociate in water, forming ClO− (chlorate(I) ion) and Cl−. This can be represented in an ionic equation form.

CIE A-Level Chemistry ionic equation showing dissociation of HCl and HClO in water treatment.

Summary