# Conjugate Acids and Conjugate Bases

## Key Questions

#### Explanation:

And here's another way to look at it.

A conjugate acid contains one more H atom and one more + charge than the base that formed it.

A conjugate base contains one less H atom and one more - charge than the acid that formed it.

Let us take the example of bicarbonate ions reacting with water to create carbonic acid and hydronium ions.

HCO₃⁻ + H₂O → H₂CO₃ + OH⁻
base + acid → Conj A + Conj B

We see that HCO₃⁻ becomes H₂CO₃. It has one more H atom and one more + charge (-1 + 1 = 0). So H₂CO₃ is the conjugate acid of HCO₃⁻.

The H₂O becomes OH⁻. It has one less H atom and one more – charge. So OH⁻ is the conjugate base of H₂O.

• Acid strength is determined by the amount of that acid that actually ionizes. Acids are molecular covalent compounds which you don't expect to ionize (release an ${H}^{+}$ and leave behind the conjugate base, or $C {l}^{-}$ for example).

The strongest acids ionize 100%. There are 6 that most consider to be the "STRONG" acids: HCl, HI, HBr, HNO_3$, {H}_{2} S {O}_{4}$ and HClO_4#. These split apart 100%.

All other acids are weak acids and ionize to a much lesser amount. For example, acetic acid, like most weak acids, ionizes, 5%.

• All acids have a conjugate base. All bases have a conjugate acid. Acids "donate" ${H}^{+}$ when they react. This is most easily seen when they dissociate in water:

${H}_{2} S {O}_{4}$ + ${H}_{2} O$ => $H S {O}_{4}^{-}$ + ${H}_{3} {O}^{+}$

In this example, sulfuric acid (${H}_{2} S {O}_{4}$) is an acid because it "donates" ${H}^{+}$ to the water. It becomes the hydrogen sulfite ion ($H S {O}_{4}^{-}$) which is the conjugate base of sulfuric acid.

The same idea applies to a base:

$N {H}_{3}$ + ${H}_{2} O$ <=> $N {H}_{4}^{+}$ + $O {H}^{-}$

Ammonia ($N {H}_{3}$) is a base because is "accepts ${H}^{+}$ from water to come its conjugate acid, the ammonium ion ($N {H}_{4}^{+}$).

This video gives an overview of acids and bases; the second half is about conjugate pairs:

Simple, easy to understand can be on this site http://www.chemteam.info/AcidBase/Conjugate-Pairs.html