PAG 1 - reactivity trend - for group 7 - spec

Question 1

Safety

Answer 1

It is important in this practical activity to ensure the safe use and careful handling of liquids, including careful mixing of reagents. In particular, solutions of the group 7 elements are toxic, irritating or harmful.

Eye protection must be worn.

Question 2

Aims

To use displacement reactions to identify the trend in reactivity of the group 7 (IUPAC group 17) elements.

A more reactive halogen can (??)

Answer 2

Aims

To use displacement reactions to identify the trend in reactivity of the group 7 (IUPAC group 17) elements.

A more reactive halogen can displace a less reactive halogen from solutions of its salts.

Question 3

For example, chlorine is more reactive than iodine. A solution of chlorine can displace iodine from potassium iodide solution:

chlorine + potassium iodide → potassium chloride + iodine

Cl2(aq) + 2KI(aq) → 2KCl(aq) + I2(aq)

The reaction mixture turns __ and __ solution forms.

Answer 3

For example, chlorine is more reactive than iodine. A solution of chlorine can displace iodine from potassium iodide solution:

chlorine + potassium iodide → potassium chloride + iodine

Cl2(aq) + 2KI(aq) → 2KCl(aq) + I2(aq)

The reaction mixture turns darker and iodine solution forms.

Question 4

Method

Answer 4

use a dropping pipette to add a few drops of potassium chloride solution, KCl(aq), to a column of three wells in a spotting tile
repeat step 1 with two more columns of wells, using potassium bromide solution, KBr(aq), then potassium iodide solution, KI(aq)
use a dropping pipette to add a few drops of chlorine solution, Cl2(aq), to a row of three wells in the spotting tile
repeat step 3 with two more rows of wells, using bromine solution, Br2(aq), then iodine solution, I2(aq)

Question 5

Results

Observe and record what happens in each well at step 3 or 4 in a suitable table. This table shows some sample results.

Answer 5

KCl(aq) KBr(aq) Kl(aq) Number of reactions seen
Cl2(aq) Not done Solution darkens Solution darkens 2
Br2(aq) No visible reaction Not done Solution darkens 1
I2(aq) No visible reaction No visible reaction Not done 0

Question 6

Analysis?

Answer 6

Count the number of reactions seen with each halogen solution.

Question 7

Suggest an explanation for why three combinations of halogen and salt solution were not done.

Answer 7

A halogen cannot displace itself from a solution of one of its salts, so these combinations were not done.

Question 8

Astatine is placed below iodine in group 7. Predict whether astatine will displace iodine from potassium iodide solution.

Answer 8

Astatine is less reactive than iodine, so it will not displace iodine from potassium iodide solution.

Question 9

a) Write an ionic equation for the reaction between chlorine solution and bromide ions from potassium bromide solution.
b) Write two half equations for this reaction.
c) Explain why this displacement reaction is also a redox reaction.

Answer 9

a) Write an ionic equation for the reaction between chlorine solution and bromide ions from potassium bromide solution.

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

b) Write two half equations for this reaction.

Cl2(aq) + 2e- → 2Cl-(aq)

2Br-(aq) → Br2(aq) + 2e-

c) Explain why this displacement reaction is also a redox reaction.

Chlorine gains electrons and is reduced to chloride ions. At the same time, bromide ions lose electrons and are oxidised to bromine.

Question 10

Harms and precautions of chlorine solution, bromine solution, iodine solution

Answer 10

Chlorine solution= Chlorine gas is produced, which is toxic if inhaled. Make sure the lab is well ventilated and avoid inhaling the gas.

Bromine solution= Toxic bromine vapour is produced. Solution irritates the skin. Make sure the lab is well ventilated and avoid inhaling the vapour. Wear gloves.

Iodine solution= Harmful to the skin. Stains clothes.
Wear gloves. Avoid contact with clothing.