When potassium bromide (KBr) is dissolved in pure water, it disassociates into potassium ions (K+) and bromide ions (Br–). Both of these ions are the conjugates of strong acids and strong bases. Potassium comes from the strong base KOH, and bromide comes from the strong acid HBr.
The key point here is that neither potassium ions nor bromide ions react with water to produce H+ or OH– ions. This means they do not affect the concentration of hydrogen or hydroxide ions in the solution. In other words, KBr is a neutral salt and does not affect the balance of acids and bases in the water.
As a result, when KBr is added to pure water, the pH remains essentially unchanged at around 7, which is the neutral point. The solution retains the same properties that it had before the addition of KBr, and thus, the pH does not change.