# In the following acid-base reaction, how would you identify the acid, base, and their conjugate acids and bases: NH4+ + HCO3- --> NH3 + H2CO3?

Nov 20, 2015

• Seeing which ion donates a proton (as a Brønsted-Lowry acid) by accepting a pair of electrons (as a Lewis acid)
• Seeing which ion accepts the proton (as a Brønsted-Lowry base) by donating a pair of electrons (as a Lewis base).

Another way to say it is in general, an acid has a proton it can donate, and a base wants a proton.

The change from ${\text{NH}}_{4}^{+}$ to ${\text{NH}}_{3}$ implies a proton was donated from ${\text{NH}}_{4}^{+}$, so simply put, ${\text{NH}}_{4}^{+}$ is the acid, and ${\text{NH}}_{3}$ is the base. Since ${\text{NH}}_{3}$ is the neutral state, ${\text{NH}}_{4}^{+}$ is the conjugate acid.

The change from ${\text{HCO}}_{3}^{-}$ to ${\text{H"_2"CO}}_{3}$ implies a proton was accepted by ${\text{HCO}}_{3}^{-}$, so simply put, ${\text{HCO}}_{3}^{-}$ is the base, and ${\text{H"_2"CO}}_{3}$ is the acid. Since ${\text{H"_2"CO}}_{3}$ is the neutral state, ${\text{HCO}}_{3}^{-}$ is the conjugate base.

Overall, we have:

${\text{NH}}_{4}^{+}$

• Proton donor (Brønsted-Lowry acid)
• Electron acceptor (Lewis acid)

${\text{NH}}_{3}$

• Proton acceptor (Brønsted-Lowry base)
• Electron donor (Lewis base)

${\text{HCO}}_{3}^{-}$

• Proton acceptor (Brønsted-Lowry base)
• Electron donor (Lewis base)

${\text{H"_2"CO}}_{3}$

• Proton donor (Brønsted-Lowry acid)
• Electron acceptor (Lewis acid)

Visually, this is how it is represented: