Group 7, The Halogens

Question 1

A student was reacting different halide ions with silver nitrate solution and studying the precipitates formed. Why did the student not bother testing fluoride ions?

Answer 1

Silver fluoride is soluble and so you don’t get a precipitate

Question 2

What colour precipitate is produced when you react silver nitrate solution with iodide ions?

Answer 2

Pale yellow

Question 3

What colour precipitate is produced when you react silver nitrate solution with chlorine ions?

Answer 3

White

Question 4

What colour precipitate is produced when you react silver nitrate solution with bromine ions?

Answer 4

Cream

Question 5

Give a simple ionic equation to show the reaction between silver nitrate solution and chlorine ions

Answer 5

Ag+(aq) + Cl-(aq) –> AgCl(s)

Question 6

Give a simple ionic equation to show the reaction between silver nitrate solution and bromine ions

Answer 6

Ag+(aq) + Br-(aq) –> AgBr(s)

Question 7

Give a simple ionic equation to show the reaction between silver nitrate solution and iodide ions

Answer 7

Ag+(aq) + I-(aq) –> AgI(s)

Question 8

Give the reaction of chlorine with water to form chloride and chlorate ions

Answer 8

Cl2 + H2O HCl + HClO (chloric acid)

Question 9

What type of reaction is that of chlorine with water? (ox, reduc etc)

Answer 9

Disproportionation

Question 10

How could you test for the presence of chlorine?

Answer 10

Blue litmus turns red in the presence of chlorine (bleaches it)

Question 11

Give the reaction of chlorine with water to form oxygen

Answer 11

2Cl2 + 2H2O –> 4HCl + O2

Question 12

Give a use of chlorine in water

Answer 12

Forms bleach which sterilises water for swimming and drinking

Question 13

Give a reaction to show the formation of bleach

Answer 13

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

Question 14

Describe and explain what you would observe if you added chlorine water to KBr

Answer 14

An orange solution is formed
Cl has displaced Br as it is a better oxidising agent, and so oxides Br- to Br2

Question 15

Describe and explain what you would observe if you added chlorine water to KI

Answer 15

A brown solution is formed
Cl2 can oxidise the I- to I2

Question 16

Describe and explain what you would observe if you added bromine water to KI

Answer 16

A brown solution is formed
Br2 can oxidise the I- to I2

Question 17

Give an ionic equation to show the reaction between bromine water and KI

Answer 17

Br2 + 2I- –> 2Br- + I2

Question 18

What kind of reaction is shown between the reaction of chlorine water and KBr

Answer 18

Displacement reaction
Also a redox reaction

Question 19

What kind of reaction is shown between the reaction of chlorine water and KBr

Answer 19

Displacement reaction
Also a redox reaction

Question 20

Describe and explain the trend in oxidising ability down the halogen ions

Answer 20

Decreases as you go down
Get larger - more shielding and so weakened nuclear attraction, resulting in the ion being less able to attract an electron (be reduced)

Question 21

What type of reaction is the formation of bleach (ox/redox)?

Answer 21

Disproportionation

Question 22

Why is dilute nitric acid added to a solution of halides in order to determine what ions are present?

Answer 22

to remove any other ions that could give undesired precipitates with silver nitrate