The halogens

Question 1

What is Group 7?

Answer 1

The halogens - the most reactive non-metal group

Question 2

How do the Halogens exist at room temperature and pressue?

Answer 2

As diatomic molecules, X2

Question 3

What do the halogens form in their solid state?

Answer 3

Lattices with simple molecular structures

Question 4

What is the trend in boiling point as you go down the halogen group?

Answer 4

• More electrons
• Stronger London forces
• More energy required to break the intermolecular forces
• Boiling point increases

Question 5

What type of agent is a halogen?

Answer 5

Oxidising agent. It is reduced, and has oxidised another species

Cl2 + 2e- -> 2Cl-

Question 6

What is the trend in reactivity down the halogens?

Answer 6

It decreases

Question 7

What do halogen-halide displacement reactions show?

Answer 7

How the reactivity decreases down the halogen group

Question 8

How are halogen-halide displacement reactions carried out?

Answer 8

A solution of each halogen is added to aqueous solutions of the other 2 halides. If the halogen added is more reactive than the halide present:
- a reaction takes place, the halogen displacing the halide from the solution
- the solution changes colour

Question 9

Why is cyclohexane used in halogen-halide displacement?

Answer 9

Solutions of iodine and bromine in water can appear similar orange-brown colours, depending on concentration. To tell them apart, an organic non-polar solvent such as cyclohexane can be added and shaken with the mixture. The non-polar halogens dissolve more readily in cyclohexane than in water. In cyclohexane their colours are much easier to tell apart

Question 10

Whats the colour of Cl2 in water?

Answer 10

Pale green

Question 11

Whats the colour of Br2 in water?

Answer 11

Orange

Question 12

Whats the colour of I2 in water?

Answer 12

Brown

Question 13

Whats the colour of Cl2 in cyclohexane?

Answer 13

Pale green

Question 14

Whats the colour of Br2 in cyclohexane?

Answer 14

Orange

Question 15

Whats the colour of I2 in cyclohexane?

Answer 15

Violet

Question 16

Whats the reaction between Cl - and Br2?

Answer 16

No reaction

Question 17

Whats the reaction between Cl - and I2?

Answer 17

No reaction

Question 18

Whats the reaction between Br - and Cl2?

Answer 18

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

Orange colour from Br2 formation

Question 19

Whats the reaction between I- and Cl2?

Answer 19

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

Violet colour from I2 formation

Question 20

Whats the reaction between I- and Br2?

Answer 20

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

Question 21

Whats the reaction between Br- and I2?

Answer 21

No reaction

Question 22

What do the results of the halogen-halide displacements show?

Answer 22

• Chlorine has clearly reacted with both Br - and I -
• Bromine has reacted with I - only
• Iodine has not reacted at all

Question 23

In the reaction of chlorine with bromide ions, what is reduced and what is oxidised?

Answer 23

Chlorine is reduced
Bromine is oxidised

Question 24

What is fluorine?

Answer 24

A pale yellow gas, reacting with almost any substance that it comes into contact with

Question 25

What is astatine?

Answer 25

A radioactive halogen that decays rapidly - it is predicted to be the least reactive halogen

Question 26

How is the trend in reactivity of the halogens explained down the group?

Answer 26

- Atomic radius increases - More inner shells so shielding increases - Less nuclear attraction to capture an electron from another species - Reactivity decreases

Question 27

What does the power of oxidising agent do down the halogen group?

Answer 27

Decreases - they become weaker oxidising agents down the group

Question 28

What is a disproportionation reaction?

Answer 28

A redox reaction in which the same element is both oxidised and reduced

Question 29

How does chlorine react with water?

Answer 29

Cl2 (aq) + H2O (l) -> HClO (aq) + HCl (aq)

Question 30

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

Answer 30

Disproportionation reaction

Question 31

What is the reaction of chlorine with cold, dilute aqueous sodium hydroxide?

Answer 31

Cl2 (aq) + 2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)

Question 32

What type of reaction is chlorine with cold, dilute aqueous sodium hydroxide?

Answer 32

Disproportionating reaction

Question 33

How is water purified from its reaction with chlorine?

Answer 33

The bacteria in the water are killed by the chloric acid and chlorate ions produced in the reaction

Question 34

What can chloric acid act as?

Answer 34

A weak bleach

Question 35

What are the risks of chlorine use in water purification?

Answer 35

Chlorine gas in extremely toxic and chlorine can be a respiratory irritant in small concentrations, and large concentrations can be fatal. It can also react with organic hydrocarbons such as methane. This forms chlorinated hydrocarbons which are suspected of causing cancer

Question 36

What are the benefits of using chlorine in water purification

Answer 36

The quality of drinking water would be compromised without use of chlorine. Diseases such as typhoid and cholera might breakout. The benefits of chlorine easily outweigh the risks