AAMC 5 question about salts?

[AOT11]

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I was down to A and C. The answer is A. Why is it basic? Shouldn't the NH4+ make it acidic?

 

[grapepopsicle]

In the reaction shown it's basic, because hydrogen phosphate deprotonates water, making dihydrogen phosphate. With these types of questions you can really only go on the information they give.

 

[nabilesmail]

In the reaction shown it's basic, because hydrogen phosphate deprotonates water, making dihydrogen phosphate. With these types of questions you can really only go on the information they give.

By deprotonating water doesn't that make WATER acidic since it is losing a proton?

 

[sotto voce]

I was down to A and C. The answer is A. Why is it basic? Shouldn't the NH4+ make it acidic?

The answer is A. The question asks about the acidity of the salt. Notice that the salt takes a proton from water, hence the salt is basic. You're left with the hydroxide ion.

Actually, I didn't know that the acidity/basicity of the salt matters when you're doing something like this. I always just leave out pure solids and liquids in the equilibrium expression. Nevertheless, the salt is basic.