Final answer:
The conjugate base of HBr, when it reacts with water, is the bromide ion (Br−). HBr donates an H+ ion to become Br−, which is a very weak base and does not significantly change the solution's pH.
Step-by-step explanation:
The conjugate base of an acid is what remains after the acid donates an H+ ion in a reaction. In the case of hydrobromic acid (HBr) reacting with water, HBr acts as a Brønsted-Lowry acid by donating an H+ to the water molecule, forming H3O+ (hydronium ion) and leaving behind the bromide ion (Br−), which is the conjugate base of HBr.
Since HBr is a strong acid, its conjugate base, Br−, is a very weak base and does not significantly affect the pH of the solution. The reaction can be represented as:
HBr (aq) + H2O (l) ⇒ H3O+ (aq) + Br− (aq)
In this reaction, water is also acting as the conjugate acid, H3O+, when it gains a proton.