Questions: Halogen and Interhalogen Chemistry

Question 1

Which reaction occurs when chlorine water is added to a solution of potassium bromide?

• A. No reaction, since both are halogens
• B. Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂
• C. Br₂ + 2Cl⁻ → 2Br⁻ + Cl₂
• D. Cl₂ + 2K⁺ → 2KCl

Answer: (B)

Cl₂ is a stronger oxidizing agent than Br₂ (E° about +1.36 V versus +1.07 V), so chlorine oxidizes bromide to bromine and is itself reduced to chloride.

Question 2

The F–F bond in F₂ is weaker than the Cl–Cl bond in Cl₂.

• T. True
• F. False

Answer: True

The F–F bond energy is about 158 kJ/mol and the Cl–Cl bond energy is about 242 kJ/mol. The short F–F distance crowds the lone pairs on the two atoms, and their repulsion weakens the bond.

Question 3

What is the molecular shape of ClF₃?

• A. Trigonal planar
• B. Trigonal pyramidal
• C. T-shaped
• D. Tetrahedral

Answer: (C)

Chlorine has three bonding pairs and two lone pairs, a trigonal bipyramidal electron arrangement. The lone pairs occupy equatorial positions, leaving a T-shaped molecule.

Question 4

Explain why fluorine is such a strong oxidizing agent even though its electron affinity is lower than that of chlorine.

Model answer: Two factors favor fluorine: the weak F–F bond makes F₂ easy to split, and the small F⁻ ion is very strongly hydrated. Together these outweigh fluorine's slightly smaller electron affinity, giving F₂ the highest standard reduction potential of the halogens (about +2.87 V).

Oxidizing power in water depends on the whole cycle of bond breaking, electron gain and hydration, not on electron affinity alone. This kind of cycle analysis explains many group trends.