a new chapter: 17 Acids & Bases The basics: it’s just equilibrium same K expressions, with new names: K a, K b same equilibrium calculations What’s new: the concept of K w p-functions (pH, pK a, pK w ) pH scale

What do you recall about Acid /Base Chemistry?

Acid /Base Chemistry in the Garden Soil Acidity determines Flower color Plant pigments: anthocyanin Anthocyanin, red form Acid form: AH Anthocyanin, blue form Base form, A-

The chemist-gardener: how to make your hydrangeas Pink or Blue Pink form = protonated anthocyanin, acid form AH Need acid: gardeners use ferrous sulfate Reaction:

The chemist-gardener: how to make your hydrangeas Pink or Blue Blue form = deprotonated anthocyanin, base form A- Need base: gardeners use lime Reaction:

The chemist-gardener: how to choose reagents for your garden Think about it: why use ferrous sulfate? why not use HCl? Reaction differences:

Equilibrium Constants in Acid Base Chemistry K a : acid dissociation constant describes how much H+ (H 3 O+) formed General Acid Reaction:

Equilibrium Constants in Acid Base Chemistry K b : base dissociation constant describes how much OH- formed

Equilibrium Constants in Acid Base Chemistry The magnitude of K eq ( so either K a or K b ) determines the strength of acid or base HCl is a strong acid: so K a is very large, K a = 10 8, what is [H 3 O+]? Ferrous ion, Fe(2+) is a weak acid: so K a is small, K a = Now what is [H 3 O+]?

Takes Two to Tango! Acid Base Conjugate Species AH + H 2 OA - + H 3 O+ acid conjugate base conjugate acid

Takes Two to Tango! Acid Base Conjugate Species B + H 2 OBH + + HO- base conjugate acid conjugate base

Takes Two to Tango! Acid Base Conjugate Species B + AHBH + + A- base conjugate acid conjugate base