The Chemistry of the Halogens

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Chemical Concepts Demonstrated

Oxidation/reduction chemistry of halogens and their halides
Relative strengths of oxidizing and reducing agents

Demonstration

Prepare three solutions each of NaI (aq), NaBr (aq), and NaI (aq).

Cl₂(aq) is added to one of the NaI(aq) solutions and Br₂(aq) to another. CH₂Cl₂ is added to each of the test tubes. The tubes are stoppered and shaken.
Cl₂(aq) is added to one of the NaBr(aq) solutions and I₂(aq) to another. CH₂Cl₂is added to each of the test tubes. The tubes are stoppered and shaken.
Br₂(aq) is added to one of the NaCl(aq) solutions and I₂(aq) to another. CH₂Cl₂is added to each of the test tubes. The tubes are stoppered and shaken.
0.1M Fe³⁺ is added to each of the remaining halide solutions. CH₂Cl₂is added to each of these test tubes. The tubes are stoppered and shaken.

Observations

The halogen has been extracted into the bottom organic phase.

1. The metallic color of iodine can be seen in both tubes in the first set of reactions.
2. The reddish color of bromine can be seen in the first test tube but not in the second.
3. The yellow color of chlorine can NOT be seen in either of the test tubes.
4. Only iodine has been extracted from the halide solutions reacted with Fe³⁺.

Explanations (including important chemical equations)

1. Cl₂(aq) + 2 NaI(aq) → 2 NaCl (aq) + I₂(aq)

Br₂(aq) + 2 NaI(aq) → 2 NaBr(aq) + I₂(aq)

2. Cl₂(aq) + 2 NaBr(aq) → 2 NaCl (aq) + Br₂(aq)

I₂(aq) + 2 NaBr(aq) → 2 NaI(aq) + Br₂(aq)

3. Br₂(aq) + 2 NaCl(aq) → 2 NaBr(aq) + Cl₂(aq)

I₂(aq) + 2 NaCl(aq) → 2 NaI(aq) + Cl₂(aq)

4. Fe³⁺ (aq) + NaI (aq) ---> Fe²⁺ (aq) + I₂(aq)

X₂ (aq) + 2 Y (aq) → 2 X (aq) + Y₂ (aq)

X₂ must be a stronger oxidizing agent than Y₂, and Y must be a stronger reducing agent than X in order for the reactions to occur.
Cl₂ is a stronger oxidizing agent than Br₂. Br₂ is a stronger oxidizing agent than I₂. ( Cl₂ > Br₂> I₂)
I^- is a better reducing agent than Br^-. Br - is a better reducing agent than Cl^-. (I^-> Br^-> Cl^-)
Fe³⁺ is a stronger oxidizing agent than I₂, but not as strong as Br₂. ( Cl₂ > Br₂> Fe³⁺ >I₂)