Halogens

Question 1

What group is the halogens in?

Answer 1

Group 7

Question 2

List 2 properties of halogens?

Answer 2

Low MP and BP

Exist as diatomic molecules.

Question 3

What is the trend in BP going down group 7?

Why?

Answer 3

BP increases down the group because the size of the atom increases as there are more occupied electron shells therefore stronger London forces between the molecules which require more energy to overcome.

Question 4

What is the structure of the halogens?

Answer 4

The halogens are simple molecules structures with weak London forces between the diatomic molecules.

Question 5

What is the trend in reactivity down group 7?

Why?

Answer 5

As you go down group 7, reactivity decreases due to increased atomic radius (greater distance between the nucleus and valence electron), increased shielding (blocks the electrostatic force between the nucleus and electron) and therefore the ability to attract an electron to form a 1- ion decreases.

Question 6

Are halogens oxidising or reducing agents?

Answer 6

Oxidising agents. They get reduced as they gain an electron which oxidises the species from which it takes the electron from.

Question 7

What is the trend in oxidising ability down group 7?

Why?

Answer 7

The ability to oxidise decreases down the group (Cl is the strongest and I the weakest).

This is because Cl has the fewest occupied electron shells, greatest force of electrostatic attraction between the outer electron and the nucleus and can therefore gain the electron the easiest -> is the best oxidising agent.

Question 8

In group 7, what is a reducing agent?

Answer 8

Halide ions are reducing agents e.g. Cl- because they donate electrons (become oxidised )so the other species is gaining the electron therefore being reduced.

Question 9

What is the trend in reducing ability of halides down group 7?

Why?

Answer 9

It increases down the group. Cl- is the weakest, I is the strongest.

This is because I- has the most occupied electron shell therefore the valence electron is furthest from the nucleus, has the weakest electrostatic force of attraction between the positive charge of the nucleus and the valence electron, requiring the least amount of energy to oxidise -> best reducing agent.

Question 10

What is the name of the reaction which halogens take part in?

Describe this reaction?

Answer 10

Displacement reactions.

When a more reactive halogen displaces a less reactive halogen.

Question 11

What is the colour of chlorine water?

Answer 11

Light / pale green

Question 12

What is the colour of bromine water?

Answer 12

Orange

Question 13

What is the colour of iodine water?

Answer 13

Brown

Question 14

What is the colour of chlorine in cyclohexane?

Answer 14

Pale green.

Question 15

What is the colour of bromine in cyclohexane?

Answer 15

Orange

Question 16

What is the colour of iodine in cyclohexane?

Answer 16

Violet

Question 17

Out of Cl-, Br- and I-, which one will displace?

Answer 17

Cl- will displace both Br- and I- because it is oxidised.

Question 18

What is the equation for chlorine displacing bromine?

Answer 18

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

Question 19

What is disproportionation?

Give 2 examples.

Answer 19

When an element is oxidised and reduced at the same time.

e.g. the reaction of chlorine with water

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

or

the reaction of chlorine with cold, dilute aqueous sodium hydroxide.

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

Question 20

Give a use of chloric acid.

Answer 20

Chloric acid - HClO is used to sterilise water. When added to water it further dissociates into ClO- which acts as another strong sterilising agent to clean water making it drinkable by killing the bacteria.

HClO(aq) -> H+ + ClO-(aq)