Polyprotic Acids and Salts

Diprotic and Polyprotic Acids

• Yield more than one hydrogen ion per molecule

• Ionize in a stepwise manner (one proton at a time)

• H2CO3(aq) ↔ H+(aq) + HCO3

-(aq) Ka1

• HCO3-(aq) ↔ H+

(aq) + CO32-

(aq) Ka2

Diprotic and Polyprotic Acids

Diprotic and Polyprotic Acids

• 1st Ka > 2nd Ka > 3rd Ka ……

Calculate….

• Calculate the concentrations of all the species present at equilibrium in a 0.10 M oxalic acid solution C2H2O4

Calculate….

• Compare the pH of a 0.040 M HCl solution with that of a 0.040 M H2SO4 solution.

Salts

• Ionic compounds formed by the reaction between an acid and a base

• Strong electrolytes that completely dissociate into ions in water

Salt Hydrolysis

• Describes the reaction of a cation or anion of a salt with water

Neutral Salts

• Salts containing an alkali metal ion or alkaline earth metal ion and the conjugate base of a strong acid.

• Do not undergo hydrolysis

• Neutral pH

Neutral Salts

• Cations – Li+, Na+, K+, Mg2+, Ca2+

• Anions – Cl-, Br-, NO3-

Basic Salts

• Salts derived from a strong base and a weak acid

• CH3COONa(s) → Na+(aq) + CH3COO-

(aq)

• CH3COO-(aq) + H2O ↔ CH3COOH(aq) +OH-

(aq)

Calculate….

• What is the pH of a 0.15 M sodium acetate solution? What is the percent hydrolysis?

• %hydrolysis = [hydrolized]/[initial] x 100%

Acidic Salts

• Salts derived from a strong acid and a weak base

• NH4Cl(s) → NH4+

(aq) + Cl-(aq)

• NH4+

(aq) + H2O ↔ NH3(aq) + H3O+(aq)

Salts in which both the cation and the anion hydrolyze

• Salts derived from weak acids and weak bases

• If Kb > Ka , basic

• If Kb < Ka , acidic

• If Ka = Kb , nearly neutral

Analyze….

• Predict whether the following solutions will be acidic, basic or nearly neutral

• NH4I

• NaNO2

• NH4F

Analyze….

• HCO3-(aq) + H2O↔ H3O+

(aq) + CO32-

(aq) Ka

• HCO3-(aq) + H2O↔ OH-

(aq) + H2CO3(aq) Kb

Kb > Ka , hydrolysis will outweigh ionizationTherefore, NaHCO3 will be basic.

¿preparado? Teneís un QUIZ

• Cerrad vuestros libros y cuadernos, por favor

QUIZ

• 1. Calculate [H3O+],[HCO3-], [CO3

2-] and [OH-] in a 0.025 M H2CO3 solution. Ka1= 4.3 x 10-7, Ka2= 5.6 x 10-11.

• 2. Calculate the pH of a 0.42 M NH4Cl solution. Kb,NH3 = 1.8 x 10-5.