Question

What are Bronsted acids and bases?

Answer 1

In short, acids are proton donors and bases are proton acceptors.

Take the following reaction for example:

$HCl+N{H}_3\leftrightharpoons N{H}_4^{+}+C{l}^{-}$

Hydrochloric acid (HCl) is the Brønsted-Lowry acid because it donates a hydrogen ion. Ammonia $\left(N{H}_3\right)$ is the Bronsted-Lowry base because it accepts the hydrogen ion.

Based on the reaction above, the ammonium ion

$\left(N{H}_4^{+}\right)$is the conjugate acid of the base ammonia and the chloride ion $\left(C{l}^{-}\right)$ is the conjugate base of hydrochloric acid.

Here's a tip to let you know which substance is the conjugate acid and which substance is the conjugate base:

A conjugate base has one less $\left(H^{+}\right)$ proton than the acids you started with.

A conjugate acid has one more$H^{+}$ proton than the base you started with.

Here's a general depiction of conjugate acid-base pairs:

HA represents an acid

B represents a base

$A^{-}$represents the conjugate base since this substance has one less proton than the acid, HA.

$H{B}^{+}$represents the conjugate acid since this substance has one more proton than the base, B.