A-Level Chemistry AQA Notes

Google rating

4.8

Trustpilot rating

4.7

View All Resources

Group 7, The Halogens

Down the group electronegativity decreases, as atomic radius and shielding increases, reducing the force on electrons. So oxidising ability also decreases.
Down the group boiling point increases, as the molecules have a greater surface area and electrons for stronger London forces
A more reactive halogen will displace the halide ion of a less reactive halogen from solution

NaX (s) + H2SO4 (l) → NaHSO4 (s) + HX (g)

Halide ions react with silver nitrate solution to form a silver halide precipitate

Ag^+ (aq) + X^- (aq) → AgX (s)

Dilute nitric acid removes any soluble impurities that could interfere with the test to identify halide ions

Silver Halide	Colour of Precipitate	Addition of Dilute Ammonia	Addition of Concentrated Ammonia
AgCl	White	Dissolves to give a colourless solution	Dissolves to give a colourless solution
AgBr	Cream	Does not dissolve	Dissolves to give a colourless solution
Agl	Yellow	Does not dissolve	Does not dissolve

Use of Chlorine and Chlorate

Chlorine can dissolve in water to form hydrochloric acid and chloric(I) acid (disproportion reaction).

Cl2 (g) + H2O (l) → HCl (aq) + HClO (aq)
Oxidation States: 0 -1 +1

Chloric(I) acid is an oxidising agent that kills bacteria and sanitises water
2Cl2 (g) + 2H2O (l) → 4HCl (aq) + O2 (g)
Cl2 (g) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)
Sodium chlorate(I) has a bleaching action which allows it to be an active ingredient in household bleach.
The advantages of using chlorine to treat water is that it prevents the spread of waterborne disease and sanitises water. However, it is added without direct customer consent, chlorine is a respiratory irritant and it could react to form chlorinated hydrocarbons, implicated in cancers

Google rating

4.8

Trustpilot rating

4.7