Conjugate acids and bases

When a substance loses ONE hydrogen ion, the species produced is called a “conjugate base” What’s the conjugate base of H 2 SO 4 HSO 4 - Its important to notice that it only loses one proton (hydrogen ion)

Similarly when a species gains one proton it is referred to as the conjugate acid. What is the conjugate acid of ammonia? NH 4 +

Acid base reactions generally involve the transfer of a proton They contain two acid base pairs Consider ethanoic acid dissolving in water CH 3 COOH + H 2 O  H 3 O + + CH 3 COO - Identify the 2 acid-base pairs

CH 3 COOH / CH 3 COO - acid / conjugate base H 2 O / H 3 O + base/ conjugate acid Notice that every acid has a conjugate base and every base has a conjugate acid They come in pairs!

Acid Base HCl Hydrochloric acidCl − Chloride ion H 2 SO 4 Sulfuric acidHSO 4 − Hydrogen sulfate ion HNO 3 Nitric acidNO 3 − Nitrate ion H 3 O + Hydronium ionH 2 O Water HSO 4 − Hydrogen sulfate ionSO 4 2− Sulfate ion H 3 PO 4 Phosphoric acid H 2 PO 4 − Dihydrogenphosphate ion CH 3 COOH Acetic acidCH 3 COO − Acetate ion H 2 CO 3 Carbonic acid HCO 3 − Hydrogen carbonate ion NH 4 + Ammonium ionNH 3 Ammonia HCO 3 − HydrogencarbonateCO 3 2− Carbonate ion H 2 O Water (neutral, pH 7)OH − Hydroxide ion

Even though we haven’t defined strong and weak acids (or bases), its still worth mentioning that Strong acids have weak conjugate bases And weak acids have strong conjugate bases Eg HCl is a strong acid Cl - is such a weak conjugate base that we don’t really consider it to be a base at all!