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