Question

How would you identify the acid, base, conjugate acid and conjugate base in the following reaction: HCN + SO4^(2-) --> HSO4^(-) + CN^(-)?

Answer 1

Acid, hydrogen cyanide, "Prussic" acid; base, sulfate ion. The conjugate species is idenitified by proton addition OR removal.

Explanation:

Acid, `H-C-=N`; conjugate base, `N-=C^-`, cyanide anion.

Base, `SO_4^(2-)`, sulfate ion; conjugate acid. `HSO_4^-`.

The conjugate acid is simply the starting material PLUS a proton; the conjugate base is simply the starting material MINUS a proton. Both mass and charge are conserved. SO the conjugate base of sulfuric acid, `H_2SO_4`, is `HSO_4^-`, and the conjugate base of this anion is `SO_4^(2-)`.

What is the conjugate acid of sulfuric acid, `H_2SO_4`? I assure you that it exists.