Final answer:
NH4+ and Br- react to form ammonium bromide, NH4Br, an acidic salt, due to the reaction being a double replacement and the NH4+ acting as a Brønsted-Lowry acid.
Step-by-step explanation:
When NH4+ and Br- react together, they form ammonium bromide, NH4Br. This reaction is an example of a double replacement reaction, where the cations and anions exchange partners. Ammonium (NH4+) ion is the cation derived from a weak base (ammonia, NH3), while bromide (Br-) ion is the anion derived from a strong acid (HBr).
The ammonium ion (NH4+) acts as a Brønsted-Lowry acid because it donates a proton, and the bromide ion (Br-) would theoretically accept a proton in the reverse reaction, acting as a Brønsted-Lowry base. However, since bromide is the conjugate base of a strong acid, it is a very weak base and does not usually accept a proton. Consequently, the reaction produces NH4Br, which is an acidic salt due to the nature of the NH4+ ion.