Please Pick Up

• Electrolytes, Acids and Bases Problem Set• General Solubilities of Common Compounds

in Water• Guidelines for Identifying Electrolytes and

Nonelectrolytes• Guidelines for Writing Net Ionic Equations• Ionization Constants for Acids and Bases

Aqueous EquilibriaAcids and Bases

Edward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

04/18/23

Electrolytes

• Reading Assignment: • Zumdahl: Chapter 4.9, 7.1

• The degree that a compound dissociates into ions is a measure of its strength, not its concentration.• Strong electrolytes - dissociate virtually

100% into ions, at all concentrations• Weak electrolytes - dissociate less than

50% into ions• Non-electrolytes - do not form ions when

dissolved in a solvent.

04/18/23

Strong Electrolytes

• Strong Acids

• HCl, HBr, HI, HNO3, H2SO4, HClO4, etc.

• Strong Bases• Group IA hydroxides: NaOH, KOH

• Ca(OH)2, Sr(OH)2, Ba(OH)2

• Most ionic compounds

04/18/23

Strong Electrolytes

• Soluble Salts• Binary compounds of metal cations with

nonmetal anions• Compounds of metal cations with

polyatomic anions• Ammonium cation with nonmetal or

polyatomic anions.

Which of these are soluble, strong electrolytes?

KCl, Zn(NO3)2, CuSO4, NH4I

04/18/23

Strong Electrolytes

• Slightly soluble salts• Compounds which have a solubility

product constant (Ksp) are strong electrolytes, but are not very soluble.

• AgCl, BaSO4, Mg(OH)2, etc.

04/18/23

Weak Electrolytes

• Weak acids, weak bases, and other soluble compounds which do not ionize extensively.

• A weak electrolyte will usually have a dissociation constant associated with it such as Ka or Kb.

04/18/23

Weak Electrolytes

• Weak Acids

• HCOOH, CH3COOH, HF, HCN, HNO2, H3PO4, H2S, HS–, H2CO3, HCO3

–, etc.

• Weak Bases

• NH3, CH3NH2, N2H4, etc.

04/18/23

Non-electrolytes

Compounds which dissolve but do not form a significant number of ions.

Most covalent compounds: compounds of two or more nonmetals excluding those which are strong or weak electrolytes.• water, sugar, methanol, ethylene glycol,

etc.

04/18/23

Solubility is related to theconcentration of the solute

in the solvent

Dissociationis related

to the ability ofthe compoundto form ionsin solution

04/18/23

Solubility is related to theconcentration of the solute

in the solvent

Dissociationis related

to the ability ofthe compoundto form ionsin solution

Categorize each of thefollowing compounds

in terms of its solubilityand tendency to form ions.

oilNaClsugar

acetic acidCa(OH)2

04/18/23

Electrolytic Character SolubilityExamples

• Oil -- not very soluble, doesn’t ionize• NaCl -- very soluble and very conductive• Sugar -- very soluble but non-conducting• Acetic acid -- very soluble but poorly

conducting• Calcium hydroxide -- slightly soluble but

the amount that dissolves, completely ionizes in water

04/18/23

Solubility is related to theconcentration of the solute

in the solvent

Dissociationis related

to the ability ofthe compoundto form ionsin solution

solubleslightlysoluble

strong

weak

non-electrolyte

04/18/23

Electrolytic Character SolubilityExamples

• Sugar -- very soluble but non-conducting• Acetic acid -- very soluble but poorly

conducting• Calcium hydroxide -- slightly soluble but

the amount that dissolves, completely ionizes in water

• Oil -- not very soluble, doesn’t ionize

04/18/23

Solubility is related to theconcentration of the solute

in the solvent

Dissociationis related

to the ability ofthe compoundto form ionsin solution

solubleslightlysoluble

strong

weak

non-electrolyte

oil

NaCl Ca(OH)2

sugar

acetic acid CO2

The solubility of a compound does not predictits electrolytic character.

04/18/23

Equation Notation

Each compound in solution is considered in its “predominant” form with proper annotation:

HCl(aq) H+(aq) + Cl– (aq)

KOH (aq) K+(aq) + OH– (aq)

• Strong Electrolytes as completely dissociated.

04/18/23

Equation Notation

Each compound in solution is considered in its “predominant” form with proper annotation:• Weak Electrolytes and Non-electrolytes as

molecular compounds

HF(aq) H+(aq) + F– (aq)

CH3OH (aq) H+(aq) + CH3O– (aq)

04/18/23

Group Activity

Identify the predominant form and write a dissociation reaction for the following compounds• nitric acid• hydrofluoric acid• potassium chlorate• aqueous ammonia• sodium hydroxide

04/18/23

Equilibrium Arrows

HNO3(aq) H+(aq) + NO3–

(aq)

HF(aq) H+(aq) + F– (aq)

KClO3(aq) K+(aq) + ClO3–

(aq)

NH3(aq) + H2O (l) NH4+(aq) + OH–

(aq)

NaOH (aq) Na+(aq) + OH– (aq)

04/18/23

Acidity versus Neutralizing Ability

HCl(aq) H+(aq) + Cl– (aq)

CH3COOH (aq) H+(aq) + CH3COO– (aq)

HCl(aq) + OH– (aq) H2O (l) + Cl– (aq)

CH3COOH(aq) + OH–(aq) H2O (l) + CH3COO– (aq)

0.1 M hydrochloric acid is more acidic than 0.1 M acetic acid, but the same volume of each can neutralize the same amount of

base.

04/18/23

Acid - Base Theories

Theory Acid Base

Arrhenius H+ donor OH– donor

Brønsted-Lowry

H+ donor H+ acceptor

Lewis e– pairacceptor e– pair donor

04/18/23

Conjugate Acids and Bases

The reaction of an acid and a base produces a conjugate acid and a conjugate base.

HCl(aq) + OH– (aq) H2O(l) + Cl– (aq)

acid base conjugateacid

conjugatebase

04/18/23

Conjugate Acid-Base Pairs

Acid ConjugateBase

Base ConjugateAcid

HCl HCl

NH3

HCO3–

HCO3– HCO3

–

HCO3–CO3

2– CO32–

H2CO3 H2CO3

NH3 NH4+NH4

+

Cl– Cl–

04/18/23

Group Activity

Write an equation that demonstrates the acidic character of carbonic acid when it reacts with water.• Assign appropriate equilibrium arrows for

the reaction.• Identify the acid and base.• Identify the conjugate acid and conjugate

base.

04/18/23

Acid Character of Carbonic Acid

H2CO3(aq) + H2O(l) H3O+(aq) + HCO3–(aq)

acid base conjugateacid

conjugatebase

Which is the acid, which is the base?

Which way does the equilibrium arrow point?

What are the products of this reaction?

04/18/23

Group Activity

Determine how the bisulfide ion (HS–)• can behave as an acid in water.• can behave as a base in water.

Write an equation for each reaction as it demonstrates its acid or base character.

If possible, assign appropriate equilibrium arrows for each reaction.

04/18/23

Acid-Base Character of Bisulfide Ion

HS–(aq) + H2O(l)

acid base

H3O+(aq) + S2–(aq)

HS–(aq) + H2O(l)

base acid

OH–(aq) + H2S(aq)

conjugateacid

conjugatebase

conjugatebase

conjugateacid

04/18/23

Group Activity

For each of the following species determine• if it can behave as an acid.• if it can behave as a base.

Write an equation for each species as it demonstrates its acidic or basic character.

If possible, assign appropriate equilibrium arrows for each reaction.

04/18/23

Determine the Acid-Base Character

H2CO3

OH–

K+

F–

HS–

H2O

NH4+

SO42–

Which of these species can act as an acid,which can act as a base, which can act as both?

Write an equation that shows each characterand justify your answer.

04/18/23