Chemistry 3.2.3 (part 2)

Question 1

What do halides exist as?

Answer 1

Negative ions (X-) e.g. Cl-, F-. Br-.

Question 2

What do halides act as in reactions?

Answer 2

Reducing agents, losing electrons.

Question 3

What affects a halide’s role in a reaction?

Answer 3

The ability of a halide on to act as a reducing agent decreases down group 7. Halide ion size increases and outer electrons are further away from the nucleus.

Question 4

What is the reaction between concentrated sulphuric acid and solid salt NaF and KF?

Answer 4

2NaF + H2SO4 → Na2SO4 + 2HF

2KF + H2SO4 → K2SO4 + 2HF

No redox reactions as F- isn’t a strong enough reducing agent to reduce S in H2SO4.

Question 5

What is the reaction between concentrated sulphuric acid and solid salt NaCl and KCl?

Answer 5

2NaCl + H2SO4 → Na2SO4 + 2HCl

2KCl + H2SO4 → K2SO4 + 2HCl

No redox reactions as Cl- isn’t a strong enough reducing agent to reduce S in H2SO4.

Question 6

What is the reaction between concentrated sulphuric acid and solid salt NaBr and KBr?

Answer 6

2NaBr + H2SO4 → Na2SO4 + 2HBr

2KBr + H2SO4 → K2SO4 + 2HBr

Question 7

What is the reaction between concentrated sulphuric acid and solid salt NaI and KI?

Answer 7

2NaI + H2SO4 → Na2SO4 + 2HBr

2KBr + H2SO4 → K2SO4 + 2HBr

Question 8

What is the half equation of sulphuric acid?

Answer 8

2e- + 2H+ + H2SO4 → SO2 + 2H2O

Question 9

What is the acid-base product of NaF, NaCl, NaBr and NaI + H2SO4?

Answer 9

HF, HCl, HBr, NaI (all misty fumes).

Question 10

What are the redox products of NaBr + H2SO4?

Answer 10

Br2 (brown gas) and SO2 (choking gas).

Question 11

What are the redox products of NaI + H2SO4?

Answer 11

I2 (purple gas/black solid), SO2 (choking gas), S (yellow solid) and H2S (smell of rotten eggs).

Question 12

Which is the strongest reducing agent and weakest reducing agent of H2SO4?

Answer 12

I- is the strongest reducing agent and F- is the weakest reducing agent.

Question 13

Which silver halides are soluble?

Answer 13

AgF is soluble in water but AgCl, AgBr and AgI aren’t so they are ppts. They are ppted when AgNO3 is added to solutions containing them.

Question 14

Why must a silver nitrate solution containing halide ions be acidified?

Answer 14

HNO3 is used to remove carbonates and hydroxides that would form ppt.

Question 15

Why can’t HCl be used to acidify AgNO3?

Answer 15

It contains Cl- ions that would form a ppt.

Question 16

What happens when F- ions are added to AgNO3?

Answer 16

No visible change.

Question 17

What happens when Cl- ions are added to AgNO3?

Answer 17

White ppt forms which dissolves in dilute ammonia.

Ag+(aq) + Cl-(aq) → AgCl(s)

Question 18

What happens when Br- ions are added to AgNO3?

Answer 18

Cream ppt forms which dissolves partially in dilute ammonia and fully in concentrated ammonia.

Question 19

What happens when I- ions are added to AgNO3?

Answer 19

Yellow ppt forms which is insoluble even in concentrated ammonia.

Question 20

What does chlorine form when its dissolved in water?

Answer 20

A mixture of HCl and chloric(I) acid. Here Cl2 is oxidised and reduced (disproportionation). The eqm mixture is called chlorine water (pale green colour).
Cl2(g) + H2O(l) ⇌ HCl(aq) + HClO(aq)

Question 21

What happens when indicator paper is added to a solution of chlorine water?

Answer 21

It turns red since both products are acids. The red colour disappears and turns white because HClO(I) is a bleach.

Question 22

What happens when chlorine is bubbled through water in bright sunlight?

Answer 22

Oxygen is produced when the chlorine oxidises water and itself to chloride ions.
2Cl2 + 2H2O → 4HCl + O2

Question 23

What is chlorine used for?

Answer 23

Sterilise drinking and swimming water as it kills microorganisms. Even though its toxic its safe because its used in small amounts.

Question 24

What happens when chlorine reacts with cold dilute sodium hydroxide

Answer 24

Cl2 + 2NaOH → H2O + NaCl + NaClO
Cl2 + 2OH- → H2O + ClO- (ionic equation)

NaClO is an ingredient in household bleach.