Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Topic started by: jcais on July 13, 2006, 11:04:48 PM

Title: Conjugate Acid of HPO4-2
Post by: jcais on July 13, 2006, 11:04:48 PM
Hello,

I won't be able to see the teacher until next week. I took a test and got only this problem wrong so it is on my mind. It was
What is the conjugate acid of HPO4-2?

I put H+ because isn't it:
(HPO4)2-  (PO4)3- + H+ in the 3rd ionization?

Maybe I am missing something. Can someone please help me?

Thank you. ???
Title: Re: Conjugate Acid of HPO4-2
Post by: Dan on July 14, 2006, 05:33:14 AM
I think the question is probably referring to

HPO42- + H3O+ <-----> H2PO4- + H2O

ie, HPO42- is acting as a base rather than an acid.

Title: Re: Conjugate Acid of HPO4-2
Post by: sdekivit on July 14, 2006, 01:33:28 PM

What is the conjugate acid of HPO4-2?


an example:

H3PO4 + H2O <--> H2PO4- + H3O+

now we can say that H2PO4- is the conjugated base of H3PO4 and on the other hand we can say that H3PO4 is the conjugated acid of H2PO4-

the definition for the conjugated acid: the acid that will be formed when the base dissociates. Thus in the previous example:

H2PO4- + H2O --> H3PO4  + OH-

but it's actually the same.
now it should be no problem to answer this question ;)