3.1.3 The halogens (and halides)

Question 1

describe the trend in melting and boiling points of the halogens

Answer 1

The m.p. and b.p. increase going down the group as shown by F2 and Cl2 being gases, Br2 being a liquid and I2 and At2 being solids at rooms temperature.

Question 2

Explain the trend in melting and boiling points of halogens

Answer 2

They increase down the group because the london forces between the molecules get stronger down the group becuase there are more electrons and so more energy is require to break them.

Question 3

describe the trend in reactivity of halogens

Answer 3

Reactivity decreases down the group, as it becomes more difficult for the atom to gain an electron.

Question 4

explain what is meant by halogen displacement

Answer 4

more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide

Question 5

what are the colours of the halogens in water

Answer 5

Cl2 = chlorine = colourless
Br2 = bromine = yellow
I2 = iodine = brown

Question 6

what are the colours of halogens in cyclohexane

Answer 6

Cl2 = colourless
Br2 = orange
I2 = purple

Question 7

what is the colour of the cyclohexane layer after the addition of KBr to a chlorine solution

Answer 7

orange

Question 8

what is the colour of the cyclohexane layer after the addition of KI to a chlorine solution

Answer 8

pink

Question 9

what is the colour of the cyclohexane layer after the addition of KCl to a Bromine solution

Answer 9

orange

no change

Question 10

what is the colour of the cyclohexane layer after the addition of KI to a bromine solution

Answer 10

purple

Question 11

what is the colour of the cyclohexane layer after the addition of KCl to a iodine solution

Answer 11

purple

no reaction

Question 12

what is the colour of the cyclohexane layer after the addition of KI to a iodine solution

Answer 12

purple

no reaction

Question 13

explain the trend in reactivity of halogens

Answer 13

Going down the group the atomic radius increases, there are more inner shells so more shielding and less nuclear attraction to gain an electron so reactivity decreases

Question 14

Benefits and risks of using chlorine

Answer 14

helps make water safe to drink as it kills bacteria but chlorine is a toxic gas that causes respitory irritant in small concentrations and can be fatal in large ones.
Chlorine can react with hydrocarbons to produce chlorinated hydrocarbons which are suspected of causing cancer. However the overall risk to health of not adding chlorine outweighs the risk of chlorinated hydrocarbons.

Question 15

how are halide ions tested for

Answer 15

Add silver nitrate to a solution containing a halide. Then add ammonia (NH3)

Question 16

what happens when silver nitrate is added to chloride

then follow on with any other addatives and consequences

Answer 16

a white precipitate is formed.
If dilute NH3 is then added the precipitate will disolve

Question 17

what happens when silver nitrate is added to bromide

then follow on with any other addatives and consequences

Answer 17

a cream precipitate is formed
This precipitate will dissolve in concentrated NH3

Question 18

what happens when silver nitrate is added to iodide

follow on with any other addatives and consequences

Answer 18

a yellow precipitate is formed
This precipitate will not dissolve in either dilute nor concentrated NH3