3.1.3 Group 7

Question 1

How do halogens exist at RTP

Answer 1

Diatomic molecules

Question 2

Describe and explain the trend in boiling points in group 7

Answer 2

Increases down the group due to more electrons and stronger London forces so more energy is required to break IMF

Question 3

Redox reactions in group 7

Answer 3

Each halogen atom reduced, gain electron to form 1- halide ion
Oxidising agent

Question 4

Trend in reactivity of halogens

Answer 4

Decreases down the group

Question 5

Describe halogen-halide displacement reactions

Answer 5

Solutions of halogen and halide ions combined, if reaction takes place the solution changes colour
When chlorine and bromide are combined, bromine forms and an orange colour is produced
When chlorine and iodide are combined, iodine forms and a violet colour is produced
When bromine and iodide are combined, iodine forms and a violet colour is produced

Question 6

Explain the trend in reactivity of halogens

Answer 6

As you go down the group, atomic radius increases, shielding increases due to more inner shells and there’s less nuclear attraction to capture an electron from another species
Therefore, reactivity decreases

Question 7

Disproportionation definition

Answer 7

Redox reaction in which same element is oxidised and reduced

Question 8

Disproportionation as shown in the reaction of chlorine and water

Answer 8

Cl2 (aq) + H2O (l) -> HClO (aq) + HCl (aq)
One chlorine atom is oxidised and one is reduced

Question 9

Disproportionation as shown in the reaction between chlorine and cold, dilute aqueous sodium hydroxide

Answer 9

Chlorine has low solubility in water so addition of NaOH means more chlorine dissolves
Cl2 (aq) + 2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)
One chlorine atom is reduced, one chlorine atom is oxidised

Question 10

Risks of chlorine use

Answer 10

It’s a toxic gas that is a respiratory irritant in small conc, fatal in large conc
Chlorine in drinking water can react with hydrocarbons (eg methane) and the product can cause cancer

Question 11

Benefits of chlorine use

Answer 11

Poor quality of drinking water would cause break out in diseases such as typhoid and cholera

Question 12

Uses of disproportionation reaction of chlorine

Answer 12

Used to purify water, chloric acid kills bacteria and acts as a weak bleach, chlorate ions kill bacteria