CHM 101 Sinex Acids and Bases Ch. 19

General Properties ACIDS Taste sour Turn litmus CHM 101 Sinex General Properties ACIDS Taste sour Turn litmus React with active metals – Fe, Zn to form Hydrogen gas React with bases BASES Taste bitter Turn litmus Feel soapy or slippery (react with fats to make soap) React with acids blue to red red to blue

Definitions Acids – produce H+ Bases - produce OH- Acids – donate H+ CHM 101 Sinex Definitions Acids – produce H+ Bases - produce OH- Acids – donate H+ Bases – accept H+ Acids – accept e- pair Bases – donate e- pair Arrehenius only in water Bronsted-Lowry any solvent Lewis used in organic chemistry, wider range of substances

Acid A substance that donates (gives up) H+ ions CHM 101 Sinex Acid A substance that donates (gives up) H+ ions Ex: HCl + H2O H+ + Cl- + H2O High concentration of H+ ions On the pH table: 0 ≈ strong acid 6.9 ≈ weak acid A note about hydronium ion (H3O+): in water H+ H3O+ so they are the same thing!!!

Base A substance that accepts (bonds with) H+ ions CHM 101 Sinex Base A substance that accepts (bonds with) H+ ions Ex: NaOH + H+ Na+ + H2O Low concentration of H+ ions (they all bonded) On the pH table: 14 ≈ strong base 7.1 ≈ weak base

Acids and bases come in pairs CHM 101 Sinex Acids and bases come in pairs General equation is: HX(aq) + H2O(l) ↔ H3O+(aq) + X-(aq) Acid + Base ↔ Conjugate + Conjugate acid base Ex: HCl + NaOH ↔ H2O

Acids and bases come in pairs CHM 101 Sinex Acids and bases come in pairs A “conjugate base” is the remainder of the original acid, after it donates it’s hydrogen ion A “conjugate acid” is the particle formed when the original base gains a hydrogen ion

Water: acid or base? NH3 + H2O ↔ NH41+ + OH1- base acid c.a. c.b. CHM 101 Sinex Water: acid or base? NH3 + H2O ↔ NH41+ + OH1- base acid c.a. c.b. HCl + H2O ↔ H3O1+ + Cl1- acid base c.a. c.b.

Strong and Weak Acids/Bases CHM 101 Sinex Strong and Weak Acids/Bases Strong acids/bases – 100% dissociation into ions HCl NaOH HNO3 KOH H2SO4 Weak acids/bases – partial dissociation, both ions and molecules CH3COOH NH3

Let’s examine the behavior of an acid, HX, in aqueous solution. CHM 101 Let’s examine the behavior of an acid, HX, in aqueous solution. Sinex HX What happens to the HX molecules in solution?

100% dissociation of HX HX H+ Strong Acid X- CHM 101 Sinex 100% dissociation of HX HX H+ Strong Acid X- Would the solution be conductive?

Partial dissociation of HX CHM 101 Sinex Partial dissociation of HX HX H+ Weak Acid X- Would the solution be conductive?

At any one time, only a fraction of the molecules are dissociated. CHM 101 Sinex HX  H+ + X- HX H+ Weak Acid X- At any one time, only a fraction of the molecules are dissociated.

Measuring strength Ionization is reversible: HX + H2O ↔ H+ + X- CHM 101 Sinex Measuring strength Ionization is reversible: HX + H2O ↔ H+ + X- This makes an equilibrium Acid dissociation constant = Ka Ka = [H+ ][X- ] [HX] Stronger acid = more products (ions), thus a larger Ka (Note that the arrow goes both directions.) (Note that water is NOT shown, because its concentration is constant, and built into Ka)

CHM 101 Sinex What about bases? Strong bases dissociate completely. MOH + H2O ↔ M+ + OH- (M = a metal) Base dissociation constant = Kb Kb = [M+ ][OH-] [MOH] Stronger base = more dissociated ions are produced, thus a larger Kb.

Neutralization Reaction CHM 101 Sinex Neutralization Reaction In general: Acid + Base  Salt + Water All neutralization reactions are double displacement reactions. HCl + NaOH  NaCl + HOH HCl + Mg(OH)2  H2SO4 + NaHCO3 