Group 7

Question 1

What happens to atomic radius as you go down the group?

Answer 1

It increases due to increased shielding

Question 2

What is the trend in boiling point down group 7? Why?

Answer 2

Increases
Because: size of atom increases as more occupied electron shells → stronger van der Waals forces of attraction between
molecules, take more energy to break

Question 3

What is the trend in
electronegativity down
group 7? Why?

Answer 3

Decreases
Because: more occupied electron shells → greater atomic radius and outer electrons are further from the positive charge of the nucleus → lower force of attraction between the nucleus and electron pair in the covalent bond

Question 4

What do you use to test for halide ions?

Answer 4

Acidified AgNO3

Question 5

Why do you add HNO3? Why not HCl?

Answer 5

To remove CO₃2-

Adding HCl would add Cl- ions, giving a false positive result

Question 6

Result and equation for Cl- test?

Answer 6

white ppt

Ag+ + Cl- → AgCl (s)

Question 7

What is the result and

equation for the test for Br-?

Answer 7

Cream ppt

Ag+ + Br- → AgBr (s)

Question 8

What is the result and

equation for the test for I-?

Answer 8

Yellow ppt

Ag+ + I- → AgI (s)

Question 9

What happens to silver chloride when dilute/conc NH3 is added?

Answer 9

AgCl- dissolves in both dilute and conc

AgCl (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Cl

Question 10

What happens to silver bromide when dilute/conc NH3 is added?

Answer 10

AgBr- only dissolves in conc

AgBr (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Br

Question 11

What happens to silver iodide when dilute/conc NH3 is added?

Answer 11

AgI- will not dissolve in either

Question 12

What is the trend in

oxidising ability down the group? Why?

Answer 12

Decreases down group
Because: Cl has fewest occupied electron shells, greatest force of attraction between outer electrons and nucleus, easiest to gain electrons and be reduced → best oxidising agent

Question 13

Write the equation for Cl2 oxidising 2I-

Answer 13

Cl₂ + 2I- → 2Cl- + I₂

Question 14

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

Answer 14

Increases down group
Because: I- has the most occupied electron shells, so outer electrons are further from the nucleus, weakest force of attraction between outer electrons and positive charge of
nucleus → easiest to be oxidised and lose electrons → best
reducing agent

Question 15

Why is chlorine added to drinking water? Why is it safe?

Answer 15

Forms ClO- ions which oxidise (kill) all microorganisms in water. Once it has done its job, little remains, and the health benefits outweigh the risks of use.

Question 16

What are potential risks of adding chlorine to drinking

water?

Answer 16

Chlorine is toxic and damages the respiratory system in large enough quantities; can form
carcinogens with hydrocarbons

Question 17

Why is ozone not used to purify water in the UK?

Answer 17

More expensive than chlorine, evaporates from water more quickly

Question 18

What is the equation for the reaction of Cl2 with water?

Answer 18

Cl₂ (g) + H₂O (l) → HClO (aq) + HCl (aq)

Question 19

What type of reaction is the reaction of chlorine with water?

Answer 19

Disproportionation; chlorine is both oxidised and reduced

Question 20

What are the two forms of the chlorate ion?

Answer 20

ClO- is chlorate (I)

ClO₃- is chlorate (V)

Question 21

What is the equation for making bleach?

Answer 21

Cl₂ + 2NaOH → NaCl + NaClO + H₂O

NaClO is bleach

Question 22

Give the equation for the reaction of chlorine and water in the presence of sunlight

Answer 22

2Cl₂ + 2H₂O → 4HCl + O₂ (g)

Question 23

What is desalination?

Answer 23

Converts saltwater into clean, potable water

Either by reverse osmosis (using a smart membrane) or by vacuum distillation at low pressure and low temperature

Question 24

What are the advantages of desalination?

Answer 24

safe, clean, drinkable water produced in places

where it might not otherwise be available

Question 25

What are the disadvantages of

desalination?

Answer 25

uses lots of energy, reverse osmosis has

low efficiency, can disturb marine ecosystems