ACID-BASE THEORY

Arrhenius Acids and Bases Acids dissociate in water to give H+ ions. Bases dissociate in water to give OH- ions. Strong acids and bases are 100% dissociated. HI(aq) H+(aq) + I- (aq)

the only recognized type BRONSTED - LOWRY THEORY conjugate base conjugate acid acid base HA + B- A- + BH lose H+ gain H+ acid = proton (H+) donor Everything is defined in terms of the proton, the only recognized type of acid in B-L theory. base = proton (H+) acceptor

Figure: 01-07-038UN Caption: In addition to the Arrhenius acids and bases, the Brønsted–Lowry definition includes bases that have no hydroxide ions, yet can accept protons. Consider the following examples of acids donating protons to bases. NaOH is a base under either the Arrhenius or Brønsted–Lowry definition. The other three bases are included under the Brønsted–Lowry definition but not under the Arrhenius definition because they have no hydroxide ions.

Na2CO3(aq) + 2HCl(aq)  H2CO3(aq) + 2NaCl(aq) Conjugate acids and Conjugate bases HCl(aq) + KOH(aq)  HOH(aq) + KCl(aq) acid base conj. acid conj. base Na2CO3(aq) + 2HCl(aq)  H2CO3(aq) + 2NaCl(aq) base acid conj. acid conj. base Na2CO3(aq) + 2HCl(aq)  H2O(l) + CO2(g) + 2NaCl(aq) acid base conj. acid conj. base

Acid and Base Strength Strong acids and bases completely dissociate in water Weak acids and bases partially dissociate in water Acid dissociation constant Ka larger Ka = stronger weak acid Base dissociation constant Kb larger Kb = stronger weak base stronger acid = weaker conjugate base weaker acid = stronger conjugate base

100% ionized (completely dissociated) in water. HCl  H+ + Cl- Strong Acids: 100% ionized (completely dissociated) in water. HCl  H+ + Cl- Strong Acids: Perchloric HClO4 Chloric HClO3 Hydrobromic HBr Hydrochloric HCl Hydroiodic HI Nitric HNO3 Sulfuric H2SO4

100% ionized (completely dissociated) in water. Strong Bases: 100% ionized (completely dissociated) in water. Strong Bases: alkali and heavy alkaline earth hydroxides LiOH, NaOH, KOH, RbOH, and CsOH Ca(OH)2, Sr(OH)2, and Ba(OH)2

1. 3Ba(OH)2(aq) + 2H3PO4(aq)  1. Ba(OH)2(aq) + H3PO4(aq)  Ba3(PO4)2(aq) + H2O(l) Ba3(PO4)2(aq) + 6H2O(l) 2. HC2H3O2(aq) + NaOH(aq)  NaC2H3O2(aq) + H2O(l) 3. H2SO4(aq) + KOH(aq)  3. H2SO4(aq) + 2KOH(aq)  K2SO4(aq) + 2H2O(l) K2SO4(aq) + H2O(l) 4. H2CO3(aq) + 2NaOH(aq)  4. H2CO3(aq) + NaOH(aq)  Na2CO3(aq) + 2H2O(l) Na2CO3(aq) + H2O(l)

Strong Acids: 100% ionized (completely dissociated) in water. HCl  H+ + Cl- Note the “one way arrow”. Weak Acids: Only a small % dissociated in water. HC2H3O2 ⇆ H+ + C2H3O2- Note the “2-way” arrow.

electron-pair acceptor LEWIS ACID - BASE THEORY more general than Bronsted - Lowery theory BASE Substances other than proton donor and acceptors are recognized as acids and bases. B: electron-pair donor A ACID electron-pair acceptor Lewis base Lewis acid

Lewis base Lewis acid Figure: 01-07-055UN Caption: The Lewis acid–-base definitions allow reactions having nothing to do with protons to be considered as acid–base reactions. Below are some examples of Lewis acid–base reactions. Notice that the common Brønsted–-Lowry acids and bases also fall under the Lewis definition, with a proton serving as the electrophile. Curved arrows are used to show the movement of electrons, generally from the nucleophile to the electrophile. Lewis base Lewis acid