Chapter 16Acids and Bases

PropertiesArrhenius Definitions

Bronsted-Lowry Definitions

Properties of Acids

Properties of Bases

Svante Arrhenius Acids and Bases• BASES: yield OH- ions in

water, substances that increase the OH- ion concentration when dissolved in water

• ACIDS: yield H+ ions in water, substances that increase the H+ ion concentration when dissolved in water

Bronsted-Lowry Definition• Broadens substances that be

categorized as Acid or Base• Involves the TRANSFER of H+

ions

Water to Hydronium• Chemists use H+ and H3O+ interchangeably • Considered the “acidic” form of water• Amphoteric = react as an acid or base• Amphiprotic = can donate and accept H+ ion

Watch This Tutorial

HCl (aq) + H2O (l) Cl- (aq) + H3O+ (aq)

ACID

BASE

CONJUGATE BASE

CONJUGATE ACID

• ACID = proton donor • BASE = proton acceptor

Practice Naming/Writing Conjugate Pairs

ACID + BASE CONJUGATE BASE + CONJUGATE ACID

HCl H2O H3O+ Cl-

H2O NH3 OH- NH4+

H2SO4 NH3 HSO4- NH4

+

Strengths of Acids and Bases

• The stronger an acid, the weaker it’s conjugate base.

• INVERSE relationship• Table p. 657

1. STRONG acids completely ionize in water, have neglible conjugate bases.

2. WEAK acids partially ionize in water, have weak base conjugates.

3. NEGLIBLE acids incapable of protonation (do not dissociate), thus have strong base conjugates.

• In every acid-base reaction, equilibrium favors transfer of proton from the stronger acid to the stronger base to form the weaker acid and the weaker base.

Acid-Base Equilibrium

• In any acid-base reaction, the equilibrium will favor the reaction that moves the proton to the stronger base.

QUESTION?Predict whether equilibrium lies to the left or to the right.

LEFT would be Kc < 1

RIGHT would be Kc > 1

ANSWER:Examine the two bases on table (forward and reverse rxns)

H2O and Cl-

H2O is a stronger base than Cl-, forward rxn favored, Equilibrium lies to rightKc > 1

HCl (aq) + H2O (l) Cl- (aq) + H3O+ (aq)

In any acid-base reaction, the equilibrium will favor the reaction that moves the proton to the stronger base.

HC2 H3O2 (aq) + H2O (l)H3O

+ (aq) + C2H3O2- (aq)

QUESTION?Predict whether equilibrium lies to the left or to the right.

LEFT would be Kc < 1

RIGHT would be Kc > 1

• Acetate is a stronger base than H2O, so the equilibrium favors the left side (K < 1)