KBr is neutral, but why KF is basic?

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KBr is neutral, but why KF is basic?

Postby Chem_Mod » Sun Aug 21, 2011 12:20 pm

K+ is not an acid and Br- is not a base, so the solution is neutral. But KF is basic, why is it not also neutral since they both have K+ and Br and F are in the same group? Also for compounds such as AlCl3 and Cu(NO3)2, how do I determine that it is Al(H2O)6 or Cu(H2O)6 when I am writing out the chemical equation?

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Re: KBr is neutral, but why KF is basic?

Postby Chem_Mod » Sun Aug 21, 2011 12:20 pm

F- is an exception in that it is the only halogen that affects the pH of a solution. If one thinks about the series H-F, H--Cl, H---Br, H----I and recalls that H-F is the weakest acid (strongest bond) then it makes sense that F- will pick up H+ from water to form H-F and OH- and hence raise the solution pH. For the metal complexes, Al3+ and Cu2+ form octahedral complexes with water, the main point is that a highly charged cation can remove H+ from H2O to form OH-.


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