2.3 Group 7, halogens

Question 1

What is the trend in electronegativity down group 7?

Answer 1

• Decreases
• The outer electron gets further away from the nucleus, due to shielding.
• Reduces the attraction so harder to attract bonding electrons.

Question 2

What is the trend in boiling point down group 7?

Answer 2

• Increases
• Larger atoms have more electrons
• More VDWS
• So need more energy to overcome them

Question 3

What is the trend in oxidising ability down group 7?

Answer 3

• Decreases
• Higher up halogens displace those lower down
• They have a higher electronegativity so have a higher affinity to taking electrons

Question 4

How to prove the oxidising ability trend?

Answer 4

Use displacement reactions between halide ions in an aqueous solution.

Question 5

What is the trend in reducing ability down group 7?

Answer 5

• Increases
• Larger ions going down, so can lose their outer electrons more easily
• Due to weaker attraction and bigger AR

Question 6

How to prove the reducing ability trend?

Answer 6

Sodium Halide + Sulfuric Acid

Question 7

NaCl + H₂SO₄ =

Answer 7

NaHSO₄ + HCl

Question 8

NaBr + H₂SO₄ =

Answer 8

1. NaHSO₄ + HBr
2. 2Br¯ = Br₂
3. 2Br¯ + 2H⁺ + H₂SO₄ = SO₂ + 2H₂O + Br₂

Question 9

NaI + H₂SO₄ =

Answer 9

1. NaHSO₄ + HI
2. 2I¯ = I₂
3. 2I¯ + 2H⁺ + H₂SO₄ = SO₂ + 2H₂O + I₂
4. 6I¯ + 6H⁺ + H₂SO₄ = S + 4H₂O + 3I₂
5. 8I¯ + 8H⁺ + H₂SO₄ = H₂S + 4H₂O + I₂

Question 10

What does chlorine as a reducing agent produce?

Answer 10

Nothing, no reduction

Question 11

What does bromine as a reducing agent produce?

Answer 11

SO₂, gas with choking smell

Question 12

What does iodine as a reducing agent produce?

Answer 12

S, yellow solid
SO₂, gas with choking smell
H₂S, gas with rotten egg smell

Question 13

What are the tests for halides? (2 types)

Answer 13

• Silver nitrate

- Ammonia

Question 14

Outline the silver nitrate test

Answer 14

1. Add nitric acid (to acidify carbonate ions)
2. Add silver nitrate
3. AgX precipitate form

Question 15

AgCl colour

Answer 15

white

Question 16

AgBr colour

Answer 16

cream

Question 17

AgI colour

Answer 17

yellow

Question 18

In what type of ammonia does Cl¯ dissolve in?

Answer 18

dilute

Question 19

In what type of ammonia does Br¯ dissolve in?

Answer 19

concentrated

Question 20

In what type of ammonia does I¯ dissolve in?

Answer 20

none, doesn’t dissolve

Question 21

Chlorine + water (no UV) =

Answer 21

Cl₂(g) + H₂O(l) ⇌ HClO (aq) + HCl (aq)

forms chlorate ions (+1 ox state) [Cl₂ oxidised]
forms chloride ions (-1 ox state) [Cl₂ reduced]

Question 22

What is a disproportionation reaction?

Answer 22

A reaction where a substance is simultaneously oxidised and reduced, giving two different products.

Question 23

Chlorine + water (in sunlight) =

Answer 23

2Cl₂(g) + 2H₂O(l) → 4HCl (l) + O₂(l)

Question 24

Chlorine + Sodium Hydroxide =

Answer 24

Cl₂(g) + 2NaOH(aq) → NaClO (aq) + NaCl (aq) + H₂O(l)

forms chlorate ions (+1 ox state) [Cl₂ oxidised]
forms chloride ions (-1 ox state) [Cl₂ reduced]

Question 25

Why is chlorine used in water treatment?

Answer 25

Produces chlorate ions which kills bacteria by oxidation.

Question 26

What conditions is the Cl₂ + NaOH reaction under?

Answer 26

Cold, dilute NaOH

Question 27

What is the use of NaClO

Answer 27

Used in bleach