Final answer:
Chlorine is able to displace bromide and iodide ions due to its higher electronegativity and stronger oxidizing power. This reactivity is not correlated with the charge density-related acid strength of hydrohalic acids. Acid strength increases down the halogen group primarily due to bond strength, not charge density.
Step-by-step explanation:
The student's question revolves around the displacement of bromide and iodide by chlorine, and the apparent contradiction between this reactivity and the acidity of hydrogen halides.
To clarify, the reactivity of the halogens (fluorine, chlorine, bromine, and iodine) is determined by their electronegativity and their ability to act as oxidizing agents.
Chlorine is more electronegative than bromine and iodine, which makes it a stronger oxidizing agent and capable of displacing bromine and iodine from their ion forms; this doesn't necessarily correlate with the charge density considerations regarding hydrohalic acid strength (HCl, HBr, HI).
Acid strength increases down the group, with HI being the most acidic due to bond strength considerations, not because of charge density. The stability of the halide ions in solution is different from their behavior as part of hydrohalic acids.
When talking about the preparation of hydrogen bromide (HBr) and hydrogen iodide (HI), the use of phosphoric acid is suggested instead of sulfuric acid because the latter is a strong oxidizing agent and would oxidize the bromide and iodide ions, which is not desired in the preparation of HBr and HI.
A typical reaction demonstrating this might be H3PO4 (l) + Br(aq) → HBr(g) + H2PO4 (aq). Finally, although iodine is the least reactive and the weakest oxidizing agent among the halogens, that is a separate issue from its ability to displace other halide ions in solution.
Iodine's relative non-reactivity is not sufficient to overcome chlorine's higher electronegativity and stronger oxidizing power in displacement reactions.