Identify the conjugate acid of ${\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NH}}_2$.

Identify the conjugate acid-base pairs in the following equations:

${\mathrm{HCO}}_3^{-}\left(\mathrm{aq}\right)+{\mathrm{S}}^{2-}\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{HS}}^{-}\left(\mathrm{aq}\right)+{\mathrm{CO}}_3^{2-}\left(\mathrm{aq}\right)$

${\mathrm{CH}}_3\mathrm{COOH}\left(\mathrm{aq}\right)+{\mathrm{HPO}}_4^{2-}\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{CH}}_3{\mathrm{COO}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}_2{\mathrm{PO}}_4^{-}\left(\mathrm{aq}\right)$.

${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COOH}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\rightleftharpoons {\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{COO}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}_3{\mathrm{O}}^{+}\left(\mathrm{aq}\right)$

Which species represent a conjugate acid-base pair?

Which species behave as Bronsted-Lowery acids in the following reversible reaction?

${\mathrm{H}}_2{\mathrm{PO}}_4^{-}\left(\mathrm{aq}\right)+{\mathrm{CN}}^{-}\left(\mathrm{aq}\right)\rightleftharpoons \mathrm{HCN}\left(\mathrm{aq}\right)+{\mathrm{HPO}}_4^{2-}\left(\mathrm{aq}\right)$

Which of the following is/are formed when a metal oxide reacts with a dilute acid?

I. A metal salt

II. Water

III. Hydrogen gas.