Inorganic 1 Section 2 - Unit 10: Halogens

Question 1

State the equation for the reaction between chlorine and water (1 mark)

Answer 1

• Cl2 + H2O → HOCl + HCl

Question 2

When a pool has a pH of over 7.0, explain how adding chlorine to water affects the equilibrium (2 marks)

Answer 2

• Alkaline ions react with acid

- So equilibrium shifts to the right

Question 3

Explain why chlorine is used to kill bacteria in swimming pools, even though chlorine is toxic (2 marks)

Answer 3

• Only used in small amounts

- Health benefits outweigh the risk

Question 4

Which substance reacts most rapidly to produce a silver halide precipitate with acidified silver nitrate?

Answer 4

• CH3l

Question 5

Explain why chlorine has a lower boiling point than bromine (1 mark)

Answer 5

• Chlorine is smaller than bromine

- Cl2 has weaker intermolecular forces

Question 6

State how you could tell the difference between AgBr and AgI (3 marks)

Answer 6

• Concentrated ammonia
• Cream solid dissolves
• Yellow solid does not dissolve

Question 7

Describe fluorine (1)

Answer 7

• Pale yellow gas

Question 8

Describe chlorine (1)

Answer 8

• Greenish gas

Question 9

Describe bromine (2)

Answer 9

• Red liquid

- Gives off brown/orange poisonous fumes

Question 10

Describe iodine (2)

Answer 10

• Shiny grey solid

- Purple gas

Question 11

Explain why melting and boiling point increases down the halogen group (3 marks)

Answer 11

• Down the group, more electrons
• So larger VDW
• So more energy required to break the forces

Question 12

Role of H₂SO₄ when reacting with NaF and NaCl (1 mark)

Answer 12

• Acid

Question 13

Role of H₂SO₄ when reacting with NaBr and NaI (2 marks)

Answer 13

• Acid in first step

- Then oxidising agent

Question 14

Appearance of HI (1 mark)

Answer 14

• White steamy fumes

Question 15

Appearance of SO₂ (1 mark)

Answer 15

• Colourless acidic gas

Question 16

Appearance of H₂S (1 mark)

Answer 16

• Gas with bad egg smell

Question 17

Equation for reaction of NaF with H₂SO₄ (1 mark)

Answer 17

NaF (s) + H₂SO₄ (l) —> NaHSO₄ (s) + HF (g)

Question 18

Observation for reaction of NaF with H₂SO₄ (1 mark)

Answer 18

White steamy fumes of HF

Question 19

Equation for reaction of NaCl with H₂SO₄ (1 mark)

Answer 19

NaCl (s) + H₂SO₄ (l) —> NaHSO₄ (s) + HCl (g)

Question 20

Observation for reaction of NaCl with H₂SO₄ (1 mark)

Answer 20

White steamy fumes of HCl

Question 21

Explain why redox reactions do not occur with NaF and NaCl with H₂SO₄ (2 marks)

Answer 21

• F- and Cl- are not strong enough reducing agents

- So cannot reduce the S in H₂SO₄

Question 22

Equation for acid-base step of reaction of NaBr with H₂SO₄ (1 mark)

Answer 22

NaBr (s) + H₂SO₄ (l) —> NaHSO₄ (s) + HBr (g)

Question 23

Equation for redox step of reaction of NaBr with H₂SO₄ (1 mark)

Answer 23

2H+ + 2Br- + H₂SO₄ –> Br₂ + SO₂ + 2H₂O

Question 24

Overall equation for reaction of NaBr with H₂SO₄ (1 mark)

Answer 24

2NaBr + 3H₂SO₄ –> 2NaHSO₄ + Br₂ + SO₂ + 2H₂O

Question 25

Observations for reaction of NaBr with H₂SO₄ (3 marks)

Answer 25

- White steamy fumes of HBr - Orange fumes of bromine - Colourless, acidic gas SO₂

Question 26

Equation for acid-base step of reaction of NaI with H₂SO₄ (1 mark)

Answer 26

NaI(s) + H₂SO₄ (l) --> NaHSO₄ (s) + HI(g)

Question 27

State the redox step for the reaction of NaI with H₂SO₄, when SO₂ is given off (1 mark)

Answer 27

2 H+ + 2 I- + H₂SO₄ --> I₂ (s) + SO₂ (g) + 2 H₂O(l)

Question 28

State the redox step for the reaction of NaI with H₂SO₄, when S is produced (1 mark)

Answer 28

6 H+ + 6 I- + H₂SO₄ --> 3 I₂ (s) + S (s) + 4 H₂O (l)

Question 29

State the redox step for the reaction of NaI with H₂SO₄, when H₂S is given off (1 mark)

Answer 29

8 H+ + 8 I- + H₂SO₄ --> 4 I₂ (s) + H₂S(g) + 4 H₂O(l)

Question 30

Observations for reaction of NaI with H₂SO₄ (5 mark)

Answer 30

- White steamy fumes of HI - Black solid and purple fumes of iodine - Colourless acidic gas of SO₂ - Yellow solid of sulfur - H₂S gas with bad egg smell

Question 31

State the equation for the reaction of chlorine with water in sunlight (1 mark)

Answer 31

2Cl₂ + 2H₂O --> 4HCl + O₂

Question 32

State the equation for the reaction of chlorine with water (1 mark)

Answer 32

Cl₂ + H₂O --> HCl (aq) + HClO (aq)

Question 33

State the observation when universal indicator is added to the reaction of chlorine with water (2 marks)

Answer 33

- First turns red due to acidity of both reaction products | - Then turns colourless as the HClO bleaches the colour