# Conjugate pairs

1. Jan 17, 2016

### TT0

1. The problem statement, all variables and given/known data
Which pairing is not a set of conjugates?

A. OH1– and H2O
B. HC2H3O2 and C2H3O21–
C. HCl and Cl1–
D. NH3 and NH41+
E. H2SO4 and SO42–

2. Relevant equations
-

3. The attempt at a solution
I couldn't choose because conjugates, from what I learnt, is basically an acid or a base and its equivalent with more or less protons. All of the pairs have protons as their only difference. The only special case is E with 2 proton difference, but I know H2SO4 is sulfuric acid and when it has donated its protons it will become SO42–. So it seems to me E would also be conjugate. However, the answer is E. Could someone explain to me why E is not a pair of conjugates?

2. Jan 17, 2016

### Staff: Mentor

That's imprecise. Acid and its conjugate base differ by exactly one proton.

Please remember, that sulfuric acid dissociates stepwise:

H2SO4 ↔ HSO4- + H+

and

HSO4- ↔ SO42- + H+

Can you show now conjugate pairs in this process?

3. Jan 17, 2016

### TT0

I see thanks Borek