Group 7

Question 1

Reducing ability of halides

Answer 1

Increases down the group, ionic radius increases, weaker attraction between outer electrons and nucleus.

Question 2

Halide reactions

Answer 2

H2SO4 + (Br- or I-) –> SO2 (acidic gas)
H2SO4 + I- –> S yellow solid
HzSO4 + I- —> H2S - bad egg smell

Question 3

halide half equations

Answer 3

2I- –> I2 + 2e- (appears as a black solid)
2Br- –> Br2+ 2e- (appears as brown fumes)

Question 4

Reduction half equations

Answer 4

2e- +2H+ +H2SO4 –> SO2 +2H2O
6e- +6H+ +H2SO4 –> S +4H2O
8e- +8H+ +H2SO4 –> H2S + 4H2O

Question 5

Flouride and Chloride are too weak as reducing agents to reduce H2SO4 sp they undergo basic acid reactions

Answer 5

F- + H+–> HF (observation= misty fumes of HF gas)
Cl- + H+ –> HCl (misty fumes of HCl gas)
Solid reaction: 2NaCl +H2SO4 –> Na2SO4 + 2HCl
Forms white solid

Question 6

Halide tests

Answer 6

1. dissolve sample in water if not already aqueous
2. Add HNO3 (to remove any possible CO£2- imurities)
3. Add AgNO3
   F- no precipitate
   Cl-= White precipitate
   Br-= Cream precipitate
   I-= yellow precopitate
4. Add dilute NH3
   Cl- white precipitate dissolves
   Br-= Cream precipiate insoluble
   I-= yellow precipitate insoluble
5. Add concentrated NH3
   Br-= cream precipitate dissolves
   I-= yellow precipitate insoluble.

Question 7

Ionic equations for halide tests

Answer 7

Precipitates:
Ag+(aq) +F-(aq)–> AgF
Ag+(aq) +Cl- (aq)–> AgCl
Ag+(aq) + Br- (aq) –> AgBr
Ag+(aq) +I- (aq)–> AgI
NH3:
AgCl +2NH3 –> Ag(NH3)2+ + Cl-
AgBr +2NH3 –> Ag(NH3)2+ + Br-

Question 8

Halogen displacement reactions

Answer 8

trend in oxidising ability- Decreases down group, larger radius, weaker attraction between nucleus and incoming electron.

Question 9

Displacement reaction examples

Answer 9

Chlorine + sodium bromide –> Bromine + sodium chloride
Cl2 +2Br- –> 2Cl- + Br2
Chlorine + sodium Iodide –>Iodine + sodium chloride
Cl2 +2I- –> 2Cl- + I2

Question 10

Br- and Cl2

Answer 10

B2 formed- solution turns brown

Question 11

CL2 AND I-

Answer 11

I2 formed- black solid

Question 12

Br2 and I-

Answer 12

I2 formed- black solid.

Question 13

Chlorine

Answer 13

Sterilises water by klling bacteria. used because benefits outweigh risks, used in small concentrations so not toxic
Chlorine and water: Cl2 + H2O ⇌ HClO + HCl
This is a disproportionation, the same element gets reduced and oxidised