Group 7 Reactions

Question 1

Are all nitrates soluble or insoluble

Answer 1

Soluble

Question 2

How to identify the halide

Answer 2

Add a few drops of dilute nitric acid and a few drops of silver nitrate solution and see what colour it turns due to coloured precipitates forming

Question 3

What colour does precipitate is formed when silver nitrate is added to chlorine

Answer 3

White

Question 4

What colour precipitate is formed when silver nitrate is added to bromine

Answer 4

Cream

Question 5

What colour precipitate is formed when silver nitrate is added to iodine

Answer 5

Yellow

Question 6

How to distinguish between the three similar colours further

Answer 6

Silver chloride dissolves in dilute ammonia, silver bromide dissolves in concentrated ammonia and silver iodide does not dissolve

Question 7

How does sulphuric acid react with halide salts

Answer 7

Acts as either an oxidising agent by removing electrons from halide ions converting them into the diatomic gas (for bromine and iodine) or as an acid where it gives hydrogen ions to the halide and displaces its salt (for fluorine and chlorine as these are strong oxidising agents)

Question 8

What is formed when hydrogen halides react with ammonia gas

Answer 8

React to produce corresponding ammonium salt(white solid) and white smoke eg HCl+NH3—> NH4Cl

Question 9

Formula for bleach

Answer 9

NaClO

Question 10

Reaction between chlorine and cold aqueous sodium hydroxide

Answer 10

Cl2 + 2NaOH ——>NaClO(bleach) + NaCl + H2O

Question 11

Reaction between chlorine and hot aqueous sodium hydroxide and why it’s different

Answer 11

3Cl2 + 6NaOH —->NaClO3 + 5NaCl + 3H2O
Chlorine oxidised further from 0 to +5 instead of on cold where it is to +1

Question 12

Are hydrogen halide gases soluble

Answer 12

Yes

Question 13

Reaction of chlorine with cold water

Answer 13

Cl2 + H2O ——>ClO-(chlorate(I) ions) + Cl- + 2H+

Question 14

Reaction of sodium fluoride and chloride with sulfuric acid and why it stops there

Answer 14

NaF/Cl + H2SO4——-> NaHSO4 + HF/Cl (misty fumes)
- the hydrogen halide does not further reduce the sulfuric acid as it is not a strong enough reducing agent

Question 15

How to identify hydrogen halides

Answer 15

Misty fumes

Question 16

How to identify sulfur dioxide

Answer 16

Choking fumes

Question 17

Two step reaction of sodium bromide with sulfuric acid and why are there two steps

Answer 17

NaBr + H2SO4 ——-> NaHSO4 + HBr
2HBr + H2SO4 ——-> Br2(reddish-brown gas) + SO2 + 2H2O
-two steps as hydrogen bromide is a strong enough reducing agent to reduce the sulfuric acid to form sulfur dioxide (choking gas)

Question 18

Three step reaction of sodium iodide with sulfuric acid and why three steps

Answer 18

NaI + H2SO4 ——> NaHSO4 + HI
2HI + H2SO4 ——> SO2 + I2 + 2H2O
6HI + SO2 ——> H2S + 3I2 + 2H2O
-iodide ions have strongest reducing power so can further reduce the sulfur dioxide

Question 19

How to identify hydrogen sulfide and what is its formula

Answer 19

H2S, toxic gas which smells of rotten eggs

Question 20

Reactions of hydrogen halides with water

Answer 20

-form strong acids as they dissociate to release their halide ions and hydrogen ions and these hydrogen ions form a hydronium ion with water resulting in strong acidic solution
Eg HCl + H2O ——> Cl- + H3O+

Question 21

What are hydrogen halides in solution

Answer 21

Strong acids

Question 22

Colour of halogens in water

Answer 22

Fluorine-pale yellow
Chlorine- greenish yellow
Bromine- reddish brown
Iodine- brown

Question 23

Colour of halogens in organic solvent

Answer 23

Fluorine- yellow
Chlorine- green
Bromine- orange-yellow
Iodine- purple

Question 24

Why does HBr form misty fumes when in moist air

Answer 24

Dissolves in water in air to form droplets of hydrobromic acid