3.2.3 Group 7 (inorganic chemistry)

Question 1

Reducing abilities of halides

Answer 1

-Behave as reducing agents in chemical reactions
-Reducing strength increases going down the group
-Ionic radius increases
-Attraction between outer electron and nucleus decreases

Question 2

Half equations for I-
Observations

Answer 2

2I- –>I2 + 2e-
Black solid / Brown solution

Question 3

Half equations for Br-
Observations

Answer 3

2Br- –>Br2 + 2e-
Brown fumes

Question 4

Products of H2SO4 reactions with halides
Observations from these products

Answer 4

2e- + 2H+ + H2SO4 –> SO2 + 2H2O
Acidic choking gas
Br- or I-

6e- + 6H+ + H2SO4 –> S + 4H2O
Yellow solid
I-

8e- + 8H+ + H2SO4 –> H2S + 4H2O
Foul smelling gas
I-

Question 5

Bromide and H2SO4

Answer 5

2Br- + 2H+ + H2SO4 –> Br2 + SO2 + 2H2O

Question 6

Iodide and H2SO4
observed - acidic choking gas

Answer 6

2I- + 2H+ + H2SO4 –> I2 + SO2 + 2H2O

Question 7

Iodide and H2SO4
observed - yellow solid

Answer 7

6I- + 6H+ + H2SO4 –> 3I2 + S + 4H2O

Question 8

Iodide and H2SO4
observed - foul smelling gas

Answer 8

8I- + 8H+ + H2SO4 –> 4I2 + H2S + 4H2O

Question 9

NaF reaction with H2SO4
observations

Answer 9

NaF + H2SO4 –> NaHSO4 + HF
misty fumes of HF gas

Question 10

NaCl reaction with H2SO4
observations

Answer 10

NaCl+ H2SO4 –> NaHSO4 + HCl
misty fumes of HCl gas

Question 11

Halide tests

Answer 11

1. dissolve sample in water
2. add acidified AgNO3 solution

F- = no precipitate
Ag+(aq) + F-(aq) –>AgF(aq)
Cl- = white ppt
Ag+(aq) + Cl-(aq) –>AgCl(aq)
Br- = cream ppt
Ag+(aq) + Br-(aq) –>AgBr(aq)
I- = yellow precipitate
Ag+(aq) + I-(aq) –>AgI(aq)

3.add dilute NH3
White ppt of AgCl dissolves
AgCl + 2NH3 –> Ag(NH3)2 + Cl-

4. add concentrated NH3
   Cream precipitate of AgBr dissolves
   AgBr + 2NH3 –> Ag(NH3)2 + Br-

Question 12

Halogen displacement reactions
Oxidising abilities

Answer 12

-oxidising abilities decrease going down the group
-atomic radius increases going down the group
-shielding increases
-lower attraction between nucleus and outer e-

• a more reactive halogen will displace a less reactive halogen ( a weaker oxidising agent)

Question 13

Halide ion and Halogen reactions

Answer 13

Question 14

Why is chlorine added to water

Answer 14

Sterilises water by killing bacteria

Question 15

Why is it added in low concentrations

Answer 15

Chlorine is toxic

Question 16

Equation when chlorine is added to water

Answer 16

Cl2 + H2O –> HCl + HClO

Question 17

What type of reaction is it when chlorine is added to water

Answer 17

-Chlorine has been oxidised from 0 to +1 in HClO
-Chlorine has been reduced from 0 to -1 in HCl
-The same species has been both oxidised and reduced
-This is a disproportionation reaction