Group 7 halogens qp

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 / an imbalance in
electron density in one molecule
1
Induces a dipole in a neighbouring molecule.
1
(These) temporary dipoles attract / temporary attraction between δ+ and δ–
1

Question 2

Which pair of solutions, when mixed, reacts to form a dark brown solution?
A NaF(aq) + Cl2(aq)
B NaCl(aq) + Br2(aq)
C NaBr(aq) + Cl2(aq)
D NaI(aq) + Br2(aq)

Answer 2

D

Question 3

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

1 2H2SO4 + 2NaBr → Na2SO4 + SO2 + Br2 + 2H2O
orange/brown fumes/solution

Question 4

A solution that is thought to contain chloride ions and iodide ions is tested.
1. Dilute nitric acid is added to the solution.
2. Aqueous silver nitrate is added to the solution.
3. A pale yellow precipitate forms.
4. Excess dilute aqueous ammonia is added to the mixture.
5. Some of the precipitate dissolves and a darker yellow precipitate
remains.
Give a reason for the use of each reagent.
Explain the observations.
Give ionic equations for any reactions.

Answer 4

) HNO3 removes (hydroxide/carbonate) ions that may give other
ppts with AgNO3
1
AgNO3 produces ppts with chloride/iodide/halide not chlorine/iodine/halogen
1
Ag+ (aq) + Cl− (aq) → AgCl(s) OR Ag+ (aq) + I-(aq) → AgI(s) allow Ag+
(aq) + X− (aq) → AgX(s)

1
NH3 dissolves AgCl (leaving yellow AgI)
allow chloride/iodide salt/ppt
1
AgCl(s) + 2NH3(aq) → Ag(NH3)2 + (aq) + Cl− (aq)
allow with Ag+
(aq)

Question 5

Silver nitrate is added to the solution.
Suggest why an excess is used.

Answer 5

To ensure that all the halide ions (chloride and iodide) are removed from
the solution / to ensure that all the halide ions precipitate out of solution