Group 7 exam questions

Question 1

Chlorine has a low boiling point because the forces between the molecules
are weak.
Explain how these forces arise between molecules of chlorine

Answer 1

(Random) movement of electrons in one molecule (creates a dipole) /
a (temporary) dipole is formed in one molecule
Induces a dipole in a neighbouring molecule.
temporary attraction between δ+ and δ–

Question 2

Give an equation for the reaction of chlorine with water.
Give a reason why chlorine is added to drinking water.

Answer 2

Cl2 + H2O ⇌ HCl + HClO
kills bacteria

Question 3

This question is about Group 7 chemistry.
(a) Give an equation for the reaction of solid sodium bromide with
concentrated sulfuric acid to form bromine.
State one observation made during this reaction.

Answer 3

3H2SO4 + 2NaBr → 2NaHSO4 + SO2 + Br2 + 2H2O

HBr is formed and this breaks down into the sulfur dioxide and bromine gas

OR break it down into two equations:
H2SO4 (l) + NaBr (s) → HBr (g) + NaHSO4 (s)

2HBr (g) + H2SO4 (l) → Br2 (g) + SO2 (g) + 2H2O (l)

observation made: orange/ brown fumes

Question 4

Chlorine reacts with cold, aqueous sodium hydroxide in the manufacture of
bleach.
Give an equation for this reaction.

Answer 4

Cl2 + 2 NaOH → NaCl + NaClO + H2O

Question 5

Chlorine is used to treat water even though it is toxic to humans.
Give one reason why water is treated with chlorine.
Explain why chlorine is added to water even though it is toxic.
Give an equation for the reaction of chlorine with cold water.

Answer 5

Reason: sterilise water /kill bacteria

Explanation: health benefit outweighs risk / only used in small
quantities/low concentrations

Equation:
Cl2 + H2O ⇌ HCl + HClO