Group 7 (P1, Chapter 10)

Question 1

How do group 7 exist as molecules?

Answer 1

Diatomically

Question 2

Group 7 are also known as the…

Answer 2

Halogens

Question 3

As you go down the group, the halogens appearances get…

Answer 3

Darker and denser

Question 4

Describe how the four major halogens look

Answer 4

Fluorine - Pale yellow gas
Chlorine - Greenish gas
Bromine - Red-Brown liquid
Iodine - Black solid

Question 5

What happens to the bond strengh down the group, and which element breaks this trend and why?

Answer 5

They get weaker

Fluorine

The small size of fluorine leads to repulsion between non-bonding electrons because they are so close together

Question 6

What happens to electronegativity down the group?

Answer 6

Decreases, increased electron shielding makes electrostatic forces between bonding electrons and the nuclei weaker

Question 7

What happens to atomic radii down the group?

Answer 7

Increases, more main levels of electrons are filled

Question 8

What happens to melting and boiling points down the group? And what does this cause to decrease?

Answer 8

Increases, larger atoms have more electrons and therefore create stronger van der Waals forces between molecules

Volatility, the lower the boiling point the more volatile the element

Question 9

Halogens in regards to oxidising ability

Answer 9

Halogens are oxidising agents, so they are reduced
Halogens usually react to gain a charge of -1
The oxidising ability of the halogens decreases down the group

Question 10

Displacement reactions, give example

Answer 10

More volatile halogens will displace other halogens e.g.
Cl2 (aq) + 2NaBr (aq) —> Br2 (aq) + 2NaCl (aq)
Ionic version: Cl2 (aq) + 2Br- —> Br2 (aq) + 2Cl-

Question 11

Halide ions in regards to oxidising power

Answer 11

Halide ions are reducing agents, they are oxidised

The reducing ability of the halide ions increases down the group

Question 12

What do solid sodium halides react well with?

Answer 12

Sulfuric acid (H2SO4)

Question 13

Sodium chloride + Sulfuric acid

Equation, observations and type of reaction

Answer 13

NaCl (s) + H2SO4 (l) —> NaHSO4 (s) + HCL (g)
Observations; Steamy white HCL fumes
Not a redox reaction
Acid-base reaction

Question 14

Sodium fluoride + Sulfuric acid

Give an equation and a safety risk

Answer 14

NaF (s) + H2SO4 (l) —> NaHSO4 (s) + HF (g)

HF is extremely corrosive

Question 15

Sodium bromide + Sulfuric acid

Answer 15

NaBr (s) + H2SO4 (l) —> NaHSO4 (s) + HBr (g)
Observations: Colourless HBr fumes
Acid-base reaction

Because bromide ions aren’t strong enough reducing agents to reduce sulfuric acid to sulphur dioxide, this second reaction happens

2H+ + 2Br- + H2SO4 (l) —> SO2 (g) + 2H20 (l) + Br2 (l)
Observations: Brown bromine fumes and colourless sulphur dioxide
Because the reactions are exothermic some of the Br vaporises

Question 16

Sodium iodide + Sulfuric acid

Equation, type of reaction and observations

Answer 16

NaI (s) + H2SO4 (l) —> NaHSO4 (s) + HI (g)
Observations: Steamy HI fumes
Acid-base reaction

Because iodide ions are good reducing agents they then reduce the sulphur even further

8H+ + 8I- + H2SO4 (l) —> H2S (g) + 4H20 (l) + 4I2 (s)
Observations: Black iodine solid formed, bad egg smell

Question 17

What can you use to identify metal halides?

Answer 17

Silver ions in aqueous solution

Question 18

Which metal halide doesn’t form a precipitate when it reacts with with silver ions in aqueous solution and why?

Answer 18

Silver fluoride

Because it is soluble in water

Question 19

How do you identify metal halides with silver ions?

Answer 19

1. Add dilute nitric acid (HNO3) to the halide solution to remove any soluble carbonate or hydroxide impurities. The silver would react with these to form silver carbonate or silver hydroxide.
2. Then add a few drops of silver nitrate solution. The halide precipitate will then form.

Question 20

Tests for halide results and further tests

Answer 20

Silver fluoride - No precipitate

Silver chloride - White precipitate, dissolves in dilute ammonia

Silber bromide - Cream precipitate, dissolves in concentrated ammonia

Silver iodide - Pale yellow precipitate, dissolves in concentrated ammonia

Question 21

Chlorine + Water equation and further information (not in sunlight)

Answer 21

Cl2 (g) + H20 (l) —Reversable reaction— HCLO (aq) + HCL (aq)

This is a redox reaction where the oxidation states of some atoms of the same element increase and others decrease. This is called disproportionation.

This reaction takes place when chlorine is used to purify water.

Question 22

Chlorine + water reaction (in sunlight)

Answer 22

2Cl2 (g) + 2H20 (l) —> 4HCL (aq) + O2 (g)
Pale green —> Colourless
This happens because chlorine is rapidly lost due to evaporation. This is why shallow pools need frequent addition of chlorine.

Alternatively, in pools

NaClO (s) + H20 —Reversible reaction— Na+ (aq) + OH- (aq) + HCL0 (aq)
In alkaline conditions the equilibrium moves to to the left and the HCLO is removed as CLO- ions, so it needs to be kept slightly acidic.