3.1.3: The halogens

Question 1

What group elements are referred to as halogens?

Answer 1

7

Question 2

List 2 properties of halogens

Answer 2

● Low melting and boiling points

● Exist as diatomic molecules

Question 3

What is the trend in boiling point down group 7? Why?

Answer 3

Increases down the group because:
-size of atom increases as more occupied electron shells → stronger London forces of attraction between molecules, take more energy to break

Question 4

What is the trend in reactivity down group 7? Why?

Answer 4

Reactivity decreases because:
● Atomic radius increases
● Electron shielding increases
● Ability to gain an electron and form 1- ions
decreases

Question 5

What is the trend in oxidising ability down the group? Why?

Answer 5

Decreases down group (Cl strongest, I weakest)
This is because Cl has the fewest occupied electron shells,
greatest force of attraction between outer electrons and
nucleus and thus is the easiest to gain electrons and be
reduced → best oxidising agent

Question 6

What is the trend in reducing ability of the halides down the group?
Why?

Answer 6

Increases down the group (Cl- weakest, I- strongest)
This is because I- has the most occupied electron shell so outer electrons are further from the nucleus, weakest force of attraction between outer electrons and positive charge of nucleus and thus is the easiest to be oxidised and lose electrons → best reducing agent

Question 7

When a more reactive halogen displaces a less reactive halide, what is the reaction called?

Answer 7

Displacement reaction

Question 8

What is the colour of chlorine in water?

Answer 8

pale green

Question 9

What is the colour of bromine in water?

Answer 9

orange

Question 10

What is the colour of iodine in water?

Answer 10

brown

Question 11

What is the colour of chlorine in cyclohexane?

Answer 11

pale green

Question 12

What is the colour of bromine in cyclohexane?

Answer 12

orange

Question 13

What is the colour of iodine in cyclohexane?

Answer 13

violet

Question 14

Out of the 3 halides Cl-, Br- & I-, which one of these can be oxidised by chlorine?

Answer 14

Br- & I- ions

Question 15

Write the equation for chlorine oxidising bromide ions

Answer 15

Cl₂ (aq) + 2Br- (aq) → 2Cl- (aq) + Br₂ (aq)

Question 16

Write the equation for Cl2 oxidising 2I-

Answer 16

Cl₂ (aq) + 2I- (aq) → 2Cl- (aq) + I₂ (aq)

Question 17

Out of the 3 halides Cl- , Br- & I- , which one of these can be oxidised by bromine?

Answer 17

I- ions

Question 18

Write the equation for bromine oxidising iodide ions

Answer 18

Br₂ (aq) + 2I- (aq) → 2Br- (aq) + I₂ (aq)

Question 19

Out of the 3 halides Cl- , Br- & I- , which one of these can be oxidised by iodine?

Answer 19

Does not oxidise Cl- or Br-

Question 20

Define disproportionation

Answer 20

The oxidation and reduction of the same

element in a redox reaction

Question 21

What is the equation for the reaction of Cl2 with water?

Answer 21

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

Question 22

What type of reaction is the reaction of chlorine with water?

Answer 22

Disproportionation; chlorine is both

oxidised and reduced

Question 23

Why is chlorine added to drinking water?

Answer 23

It kills the bacteria in the water and

makes it safer to drink

Question 24

What are the two forms of the chlorate ion?

Answer 24

ClO- is chlorate (I)

ClO₃- is chlorate (V)

Question 25

What is the equation for forming bleach?

Answer 25

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