ACID BASE EQUILIBRIA ACID-BASE THEORIES (4 theories)

ARRHENIUS THEORY-H + AND OHˉ An acid is any substance that ionizes (partially or completely) in water to give hydrogen ions Means associate with solvent to give hydronium ions HA +H 2 O ↔ H 3 O+ + Aˉ

A base ionizes in water to give hydroxyl ions. Weak (partially ionizes) bases ionizes as follows: B + H 2 O ⇋ BH + + OHˉ For strong bases e.g.: (NaOH) M(OH) n →M^n+ + nOHˉ this theory is obviously restricted to water as a solvent only

Franklin’s theory Recognizes the ionization of a solvent to give a cation and an anion E.g: 2H 2 O ⇋ H 3 O + + OHˉ 2NH 3 ⇋ NH 4 + NH 2 ¯ Acid = a solute that yields the cation of the solvent Base = a solute that yields the anion of the solvent Eg of strong acid is NH 4 Cl in liquid ammonia Eg of strong base is NaNH 2 in ammonia

Brønsted-Lowry theory Taking and giving protons States that an acid is any substance that can donate a proton and a base is any substance that can accept a proton.

Give example of Bronstead-Lowry theory, pp220.

Half reaction Acid = H + + base Acid and base of a half-reaction are called conjugate pairs. There must be a combination of two half reaction

LEWIS THEORY Taking and giving electrons It states that: an acid is a substance that can accept an electron pair and a base is a substance that can donate an electron pair. Assumes a donation (sharing) of electrons from a base to an acid.

Give example of Lewis acid-base.

ACID-BASE EQUILIBRIA IN WATER When acid or base is dissolved in water, it will dissociate Amount of ionization depends on the strength of the acid Strong electrolyte completely dissociated Weak electrolyte dissociated partially

Example: a)Hydrochloric acid (strong acid) a)Acetic acid (weak acid) Equilibrium constant is the thermodynamic activity constant

Pure water ionizes slightly (autoprotolysis) Equilibrium constant is thermodynamic autoptorolysis, self-ionization, constant

H + will be used instead of H 3 O + for simplification Molar concentration will be replaced by [] K a and K w are molar equilibrium constants [H + ]=1.0×10 -7 M = [OH - ]

Give example 7.1