Halogens

Physical Properties

State at stpAtomic radius

(nm)BptoC

F2Pale yellow

gas0.071 -188

Cl2Pale green

gas0.099 -35

Br2 Red liquid 0.114 59

I2 Purple solid 0.133 184

Which Halogen is the best Oxidising Agent?

• Potassium halide solutions• Cl-(aq) Brl-(aq) l-(aq)

• Halogen dissolved in water• Cl2(aq), Br2(aq) I2(aq)

• Write brief plan of investigation• Make predicted results table• Write up results & conclusion

Displacement Reactions

Cl-(aq) Br-

(aq) I-(aq)

Cl2 (aq)

Yellow/ orange solution

Brown solution & black ppt

Br2 (aq) No changeBrown

solution & black ppt

I2 (aq) No change No change

Chlorine displaces Br2 & I2

Cl2 + 2KBr → 2KCl + Br2

Cl2 + 2Br- → 2Cl- + Br2

Cl2 + 2KI → 2KCl + I2

Cl2 + 2I- → 2Cl- + I2

Cl2 is the oxidising agent

Cl2 + 2e- → 2Cl-

Bromine displaces I2

Br2 + 2KI → 2KBr + I2

Br2 + 2I- → 2Br- + I2

Br2 is the oxidising agent

Br2 + 2e- → 2Br-

Halogens as Oxidising Agents

Br2 + 2I- → 2Br- + I2

Cl2

Br2

I2

Cl2 + 2Br- → 2Cl- + Br2

Cl2 + 2I- → 2Cl- + I2

Strongest oxidising agent

Oxidising Agents Accept Electrons-

Halogens as Oxidising Agents

F2 > Cl2 > Br2 > I2

Fluorine would displace all other halogens

F2 + 2CI- → 2F- + Cl2

Increase in oxidising power

Oxidising Agents Accept Electrons

X2 + 2e- → 2X-

Halides as Reducing AgentsThe halide ions act as reducing agents

2X- → X2 + 2e-

Reducing Agents Donate Electrons

F-

Cl-

Br-

I- Strongest reducing agent

Which Halide is the best Reducing Agent?

• Solid sodium halides

• NaCl (s) NaBr(s) NaI(s)

• Concentrated H2SO4

• Predictions

• What products could be formed?

Possible Products

X- →

The halide ions act as reducing agents

The sulphuric acid acts as an oxidising agent

H2SO4 →

X2 ?

-1 0

+6

SO2 ? S ? H2S ?+4 0 -2

Halide Products Observations

NaCl

NaBr

NaI

Results

HalideReaction Products

Observations

NaCl HCl Steamy fumes

NaBr

HBr

Br2

SO2

Steamy fumes

Brown Fumes

Colourless gas

NaI

HI

I2

SO2

S

H2S

Steamy fumes

Black solid, purple fumes

Colourless gas

Yellow solid

Smell of bad eggs

1. Acid – Base Reactions

• All halides can act as bases

• Bases accept H+ ions

NaX + H2SO4 → HX + NaHSO4

Base + acid → Hydrogen halide + salt

NaF + H2SO4 → HF + NaHSO4

Hydrogen halide produced via acid-base reaction with ALL halides

2. Redox Reactions

• Products of this stage depend on the reducing ability of the halide

Reducing Agents Donate Electrons

F-

Cl-

Br-

I- Strongest reducing agent

Sodium Bromide NaBr

• Br- quite a good reducing agent

H2SO4 → SO2

2Br- → Br2

2Br- + 2H+ + H2SO4 → SO2 + 2H2O + Br2

2H+ + 2e- + H2SO4 → SO2 + 2H2O

2Br- → Br2 + 2e-

Sodium Iodide NaI

• I- very good reducing agent

H2SO4 → SO2

2I- → I2

2I- + 2H+ + H2SO4 → SO2 + 2H2O + I2

2H+ + 2e- + H2SO4 → SO2 + 2H2O

2I- → I2 + 2e-

Sodium Iodide NaI

• I- very good reducing agent

H2SO4 → S

2I- → I2 + 2e-

6I- + 6H+ + H2SO4 → S + 4H2O + 3I2

6H+ + 6e- + H2SO4 → S + 4H2O

6I- → 3I2 + 6e-

x 3

Sodium Iodide NaI

• I- very good reducing agent

H2SO4 → H2S

2I- → I2 + 2e-

8I- + 8H+ + H2SO4 → H2S + 4H2O + 4I2

8H+ + 8e- + H2SO4 → H2S + 4H2O

8I- → 4I2 + 8e-

x 4