Group 7, the halogens

Question 1

How does electronegativity change as you go down group 7

Answer 1

It decreases as you go down because the other atom gets further away from the halogens nucleus

Question 2

How does melting and boiling point change as you go down group 7

Answer 2

They increase as you go down the group as the larger atoms have more electrons so stronger VDW forces

Question 3

How does oxidising agent ability change as you go down group 7

Answer 3

As you go down the group, oxidising ability decreases as halogens want to gain an electron but the bigger the atom, the further from the nucleus

Question 4

How do halogens react with metal halides

Answer 4

More reactive halogens will displace less reactive halogens e.g.
Cl2 + 2NaBr —> 2NaCl + Br2

Question 5

What is the oxidising agent in this reaction
Cl2 + 2NaBr —> 2NaCl + Br2

Answer 5

Chlorine is the oxidising agent as it has gained an electron

Question 6

How does reducing agent ability of halide ions change as you go down the group

Answer 6

As you go down the group, the atom becomes larger and so it is easier for it to lose an electron so reducing agent ability of halides increases down the group

Question 7

What is the general equation for a sodium halides reaction with H2SO4

Answer 7

NaX + H2SO4 —> HX + NaHSO4

Question 8

How can halide ions be identified

Answer 8

Add dilute nitric acid
Add silver nitrate

Question 9

How can halide ions be identified

Answer 9

Add dilute nitric acid
Add silver nitrate
A precipitate will be formed

Question 10

What will you witness if NaBr reacts with H2SO4

Answer 10

Steamy fumes

Question 11

What will you witness if NaI reacts with H2SO4

Answer 11

Steamy fumes
Black solid of iodine
Small amounts of yellow sulphur

Question 12

What are the equations for NaBr and H2SO4

Answer 12

NaBr + H2SO4 —> HBr + NaHSO4
2H+ + 2Br- + H2SO4 —> SO2 + 2H2O +Br2

Question 13

What is the equation for NaI and H2SO4

Answer 13

NaI + H2SO4 —> HI + NaHSO4
8H+ + 8I- + H2SO4 —> H2S + 4H2O + 4I2

6H+ + 6I- + H2SO4 —> S + 4H2O + 3I2

2H+ + 2I- + H2SO4 —> SO2 + 2H2O + I2

Question 14

What colour will a chloride ion produce in the halide test

Answer 14

White ppt

Question 15

What colour will a bromide ion produce in the halide test

Answer 15

Cream ppt

Question 16

What colour will an Iodide ion produce in the halide test

Answer 16

Yellow ppt

Question 17

How does the solubilities of the silver halides change in ammonia

Answer 17

Silver chloride - dissolves in dilute ammonia
Silver bromide - dissolves in concentrated ammonia
Silver iodide - Insoluble in ammonia

Question 18

What colour will an fluoride ion produce in the halide test

Answer 18

Nothing will happen

Question 19

Why is silver nitrate used as the halide test

Answer 19

It is sensitive enough to detect fairly small concentrations of halide ions

Question 20

Why is dilute nitric acid put into the halide test before the silver nitrate

Answer 20

Prevents unreacted hydroxide ions reacting with the silver ions to give a confusing precipitate

Question 21

Why is ammonia used in the halide test

Answer 21

Colours are similar and can be difficult to distinguish between so ammonia sorts them out objectively

Question 22

How does chlorine react with water in the dark

Answer 22

Cl2 + H2O —> HClO + HCl (these will dissociate producing chloride and chlorate ions)

Question 23

How does chlorine react with water in sunlight

Answer 23

2Cl2 + 2H2O —> 4HCl + O2 (produces chloride ions and oxygen)

Question 24

What are the advantages and disadvantages of adding chlorine to water

Answer 24

+
Kills bacteria
Inhibits algal growth
-
Toxic and harmful
Forms chlorinated hydrocarbons

The positives outweigh the negatives

Question 25

How is chlorine used in water treatment

Answer 25

Swimming pools and drinking water

Question 26

What is the reaction equation between chlorine and cold, dilute NaOH

Answer 26

Cl2 + 2NaOH —> NaClO + NaCl + H2O

Question 27

What is NaClO used for

Answer 27

Bleach