Conjugate Acids and Bases?

Question

I'm having a really hard time figuring out conjugate acids and bases. This is the problem:

Write in the boxes formulas for the conjugate acids and conjugate bases of the following substances. If there is none, write 'NONE'.

HPO4 ^2-

HCO3 ^-

H2O (which I know can be either an acid or a base)

Cl^-

NH4 ^+

I don't know very much about chemistry, but I really want to learn how to work these. Any help you could give will be greatly appreciated.

Answer 1

The conjugate acid-base pair concept is part of the Lowery-Bronsted definition of acids and bases. In this definition, an acid is a proton donor and a base is a proton acceptor. What this creates is a pair, because as soon as a base accepts a proton, it has a proton it can lose, making it an acid.

Lets take your first one. If HPO4^2- accepts a proton, we get its conjugate acid
HPO4^2- + H^1+ <=> H2PO4^1-

in this case, H2PO4^1- is the conjugate acid of HPO4^2- because it was formed by HPO4^2- gaining a proton which H2PO4^1- could lose, and HPO4^2- is the conjugate base of H2PO4^1- because it is formed by H2PO4^1- losing a proton giving HPO4^2- which could gain another proton.

Lets see if it is simpler with Cl^- If Cl^- gains a proton it is acting as a base in the Lowery-Bronsted sense because it is forming HCl which would be the conjugate acid to the conjugate base Cl^-

So what I am saying is that a conjugate acid-base pair are related by gaining a proton to form the conjugate acid and losing a proton to form the conjugate base.

Answer 2

complicated step. search into bing and yahoo. this will help!