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KBr has Neutral pH ?

Posted: Mon Dec 03, 2018 11:27 pm
by Isabel Nakoud 4D
Why does KBr have a neutral pH but KF has a pH greater than 7?

(This question is referring to Homework Problem 12.65 (c) and (d) )

Re: KBr has Neutral pH ?

Posted: Tue Dec 04, 2018 11:33 am
by Sam Kelly 1K
KF dissociates into K+ and F- in solution. K+ would not be a good proton acceptor, since K+ and H+ don't react at all. F- and H+ on the other hand do react, making the weak acid of HF. Since HF is a weak acid, it will only partially dissociate, with only some of it turning back into the individual components F- and H+. The key part here is knowing that weak acids have strong conjugate bases, which tells us that the conjugate base of HF, KF, is strong.

KBr dissociates into K+ and Br-. Br- reacts to make HBr, a strong acid. Since Br- is the conjugate base of HBr, it is weak. K+ is also weak so the two weak components sort of offset and have no real effect on the pH, making it neutral.