Strong/Weak Acids and Bases

Strong acids. Two types of strong acids, with examples you should memorize, are

1. The hydrohalic acids HCl, HBr, and HI

2. Oxoacids in which the number of O atoms exceeds the number of ionizable protons by two or more, such as HNO₃, H₂SO₄, and HClO₄; for example, in the case of H₂SO₄, 4 O’s − 2 H’s = 2

Weak acids. There are many more weak acids than strong ones. Four types are

1. The hydrohalic acid HF

2. Acids in which H is not bonded to O or to a halogen, such as HCN and H₂S

3. Oxoacids in which the number of O atoms equals or exceeds by one the number of ionizable protons, such as HClO, HNO₂, and H₃PO₄

4. Carboxylic acids (general formula RCOOH, with the ionizable proton shown in red), such as CH₃COOH and C₆H₅COOH

Strong bases. Water-soluble compounds containing O²⁻ or OH⁻ ions are strong bases. The cations are usually those of the most active metals:

1. M₂O or MOH, where M = Group 1A(1) metal (Li, Na, K, Rb, Cs)

2. MO or M(OH)₂, where M = Group 2A(2) metal (Ca, Sr, Ba) [MgO₂ and Mg(OH)₂ are only slightly soluble in water, but the soluble portion dissociates completely.]

Weak bases. Many compounds with an electron-rich nitrogen atom are weak bases (none is an Arrhenius base). The common structural feature is an N atom with a lone electron pair (shown in blue):

1. Ammonia (H₃)

2. Amines (general formula RH₂, R₂H, or R₃), such as CH₃CH₂H₂, (CH₃)₂H, and (C₃H₇)₃