3.2 REACTIVITY TRENDS

Question 1

Reducing agents (group 2).

Answer 1

Reducing agents (group 2):
-another species will gain 2 electrons and be reduced (metal loses 2 electrons, oxidised)
-group 2 called reducing agents as they reduce another species

Question 2

Group 2 redox with oxygen.

Answer 2

All group 2 elements react with oxygen to form metal oxides

Question 3

Group 2 redox with water.

Answer 3

Group 2 react with water to form alkaline hydroxide and hydrogen. Reactions become more vigorous going down group

Question 4

Solubility of hydroxides.

Answer 4

The solubility of hydroxides decreases down the group, so results in solutions that contain more OH- ions and are more alkaline

Question 5

Group 7.

Answer 5

Group 7:
-reactivity decreases down the group = atom bigger, shielding increases, outweighs nuclear charge, harder to gain electron
-displacement reactions prove reactivity trend
-boiling point decreases down the group = London forces get stronger as the molecule gets bigger
-simple molecules = London forces diatomic

Question 6

Halide and halogen reactions.

Answer 6

Halide and halogen reactions:
Cl2 + KBr = pale green (with and without cyclohexane)
Cl2 + KI = orange (with and without cyclohexane)
Br2 + KI = brown (without cyclohexane) violet (with cyclohexane)

Ag + Cl = AgCl (white)
+ Br = AgBr (cream)
+ I = AgI (yellow)

Question 7

Halogen reactions.

Answer 7

Halogen reactions:
Cl- + Br2 and Cl- + I2 and Br- + I2 = no reaction
Br- + Cl2 = orange from Br2 formation
I- + Cl2 and I- + Br2 = violet from I2 formation

Question 8

What is the boiling point trend down group 7?

Answer 8

Down group 7, there are more electrons for each element, meaning there are stronger London forces and more energy is required to break those London forces. This results in the boiling point increasing down the group

Question 9

What is the reactivity trend down group 7?

Answer 9

Down group 7, the atomic radius increases and due to there being more inner shells, shielding increases. This causes the nuclear attraction to decrease and thus the ability to capture an electron from another species. This means reactivity decreases down the group

Question 10

What is disproportionation?

Answer 10

Disproportionation is when the same element in a reaction is both oxidised and reduced in a reaction (element must appear as 2 separate compounds)

Question 11

Qualitative analysis.

Answer 11

Qualitative analysis:
Cl- = dissolve in dilute nitric acid, then a white precipitate forms with silver nitrate solution (precipitate dissolves in dilute ammonia solution)
Br- = dissolve in dilute nitric acid, then a cream precipitate forms with silver nitrate solution (precipitate insoluble in dilute ammonia solution but soluble in concentrated ammonia solution)
I- = dissolve in dilute nitric acid, then a yellow precipitate forms with silver nitrate solution (precipitate insoluble)
SO4^2- = dissolve in dilute nitric acid, then white precipitate forms with barium nitrate/barium chloride solution
CO3^2- =add dilute acid, then pass CO2 gas through limewater which turns cloudy