Brønsted-Lowry Acid: Substance that can donate H + Brønsted-Lowry Base: Substance that can accept H + Chemical species whose formulas differ only by one proton are said to be conjugate acid–base pairs.

Weak Acid Ionization Constants 7.1 x 10 –4 4.5 x 10 –4 3.0 x 10 –4 1.7 x 10 –4 8.0 x 10 –5 6.5 x 10 –5 1.8 x 10 –5 4.9 x 10 – x 10 –10 HF HNO 2 C 9 H 8 O 4 (aspirin) HCO 2 H (formic) C 6 H 8 O 6 (ascorbic) C 6 H 5 CO 2 H (benzoic) CH 3 CO 2 H (acetic) HCN C 6 H 5 OH (Phenol) F – NO 2 – C 9 H 7 O 4 – HCO 2 – C 6 H 7 O 6 – C 6 H 5 CO 2 – CH 3 CO 2 – CN – C 6 H 5 O – ACID CONJ. BASEK a pK a =-logK a

Oxoacids with different central atoms that are from the same group of the periodic table and that have the same oxidation number, acid strength increases with increasing electronegativity. Brønsted-Lowry Acid Strength

1. For binary acids in the same group acidity increases with increasing size of A. 2. For binary acids in the same row acidity increases with increasing electronegativity of central atom in A. 3. In most cases acidity increases as the ability of the conjugate base to disperse negative charge increases. The lower the charge- to-radius ratio of the conjugate base the more stable it is and the stronger its conjugate acid. Brønsted-Lowry Acid Strength

Oxoacids with same central atom, acid strength increases with increasing size.

The size of the conjugate base anion may be modulated by the inductive and resonance effects.