Final answer:
HBr and HI cannot be prepared with sulfuric acid because it oxidizes bromides and iodides. Phosphoric acid, a weaker oxidizing agent, allows for the preparation of these hydrogen halides, as does the direct reaction between hydrogen and iodine.
Step-by-step explanation:
The student's question appears to contain a typo, but they are likely asking why Hydrogen bromide (HBr) and Hydrogen iodide (HI) can't be prepared from bromides and iodides using sulfuric acid. The problem with sulfuric acid is that it is an oxidizing agent, which means it has the potential to oxidize bromides and iodides, and therefore it is not suitable for the preparation of HBr and HI.
Phosphoric acid, on the other hand, is a weaker oxidizing agent and can be used to prepare these hydrogen halides. For instance, the reaction of phosphoric acid (H3PO4) with a bromide (Br-) will yield Hydrogen bromide (HBr) and dihydrogen phosphate (H2PO4-), as shown in the reaction:
H3PO4 (l) + Br¯(aq) → HBr(g) + H2PO4¯ (aq)
Additionally, the direct reaction of hydrogen with iodine can also be used to produce Hydrogen iodide by achieving chemical equilibrium between the substances.