Chapter 13Chapter 13Section 1Section 1

Dissociation, Ionization, Dissociation, Ionization, Electrolytes & Electrolytes &

Net Ionic EquationsNet Ionic Equations

SOLUTION VOCABULARYSOLUTION VOCABULARY

SolutionSolution - - A homogeneous mixture of two A homogeneous mixture of two or more substances in a single phase or more substances in a single phase (solute dissolved in a solvent)(solute dissolved in a solvent)

DissociationDissociation occurs when an occurs when an ionic compound ionic compound dissolves to form its constituent ions.dissolves to form its constituent ions...

IonizationIonization occurs when ions are formed from the occurs when ions are formed from the separation of particles in a separation of particles in a molecular molecular compoundcompound

Dissociation

• Dissociation is separation of ions that occurs when an ionic compound dissolves.

s aq + aq2H O –NaCl( ) Na ( ) Cl ( )

s aq + aq2H O 2 –2CaCl ( ) Ca ( ) 2Cl ( )

1 mol 1 mol 1 mol

1 mol 1 mol 2 mol

Compounds in Aqueous Solution

Dissociation of NaClDissociation of NaCl

Dissociation Dissociation

•Sample Problem A

Write the equation for the dissolution of aluminum sulfate, Al2(SO4)3 , in water. How many moles of aluminum ions and sulfate ions are produced by dissolving 1 mol of aluminum sulfate? What is the total number of moles of ions produced by dissolving 1 mol of aluminum sulfate?

DissociationDissociationSample Problem A Solution•Given: amount of solute = 1 mol Al2(SO4)3

solvent identity = water•Unknown: a. moles of aluminum and sulfate ions

b. total number of moles of solute ions produced•Solution

s aq + aq2H O 3 2–2 4 3 4Al (SO ) ( ) 2Al ( ) 3SO ( )

+ 3 2–2 4 3 41 mol Al (SO ) 2 mol Al 3 mol. SOa

+ 3 2–42 mol Al 3 mol SO 5 mol of solute i. sb on

IonizationIonization Ions can be formed from solute molecules by the

action of the solvent in a process called ionization.

• When a molecular compound dissolves andand ionizes in a polar solvent, multiple ions are formed where none existed before the molecule dissolve.

• Hydrogen chloride, HCl, is a molecular compound that ionizes in aqueous solution.

• HCl contains a highly polar bond.

aq + aq2H O –HCl H ( ) Cl ( )

Molecules in Aqueous Solution

IonizationIonizationThe Hydronium IonThe Hydronium Ion

The “Acid” ionThe “Acid” ion• Some molecular compounds ionize in an aqueous

solution to release H+.

• The H+ ion attracts other molecules or ions so strongly that it does not normally exist alone.

aq + aq2H O –3HCl H O ( ) Cl ( )

• The H3O+ ion is known as the hydronium ion.

Why is the formation of ions Why is the formation of ions important?important?

Electrolytes:Electrolytes: • Electrolytes are substances that yield ions and conduct an electric current in solution. ((95% of all chemical reactions occur 95% of all chemical reactions occur when the chemicals are in solutionwhen the chemicals are in solution.).)

• The strength with which substances conduct an electric current is related to their ability to form ions in solution.

• Strong and weak electrolytes differ in the degree of ionization or dissociation.

Types of solutionsTypes of solutionsStrong ElectrolytesStrong Electrolytes a compound that a compound that

completely or largely dissociates in an completely or largely dissociates in an aqueous solution. Solutions with strong aqueous solution. Solutions with strong electrolytes conduct electricity very well.electrolytes conduct electricity very well.

Weak ElectrolyteWeak Electrolyte a compound that a compound that dissociates only to a small extent in dissociates only to a small extent in aqueous solution. Solutions of weak aqueous solution. Solutions of weak electrolytes do not conduct electricity as electrolytes do not conduct electricity as well as solutions with strong electrolytes. well as solutions with strong electrolytes.

Strong and Weak Electrolytes Strong and Weak Electrolytes and Nonelectrolytesand Nonelectrolytes

• A strong electrolyte is any compound whose dilute aqueous solutions conduct electricity well; this is due to the presence of all or almost all of the dissolved compound in the form of ions.

• To whatever extent they dissolve in water, they yield only ions.

• HCl, HBr, HI• All soluble ionic compounds

Strong and Weak Strong and Weak Electrolytes and Electrolytes and NonelectrolytesNonelectrolytes

[HF] >> [H+] and [F–]

• A weak electrolyte is any compound whose dilute aqueous solutions conduct electricity poorly; this is due to the presence of a small amount of the dissolved compound in the form of ions.

• Some molecular compounds form aqueous solutions that contain not only dissolved ions but also some dissolved molecules that are not ionized.

aq + aq–3HF H O ( ) F ( )

Strong and Weak Strong and Weak Electrolytes and Electrolytes and NonelectrolytesNonelectrolytes

• Write equations for the dissolution of soluble ionic compounds in water.

• Predict whether a precipitate will form when solutions of soluble ionic compounds are combined, and write net ionic equations for precipitation reactions.

• Compare dissociation of ionic compounds with ionization of molecular compounds.

Compounds in Aqueous Solution

DissociationDissociationNet Ionic EquationsNet Ionic Equations

• A net ionic equation includes only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution.

• Ions that do not take part in a chemical reaction and are found in solution both before and after the reaction are spectator ions.

Net Ionic EquationsNet Ionic Equations

Overall ionic equation

aq + aq + aq + aq

s + aq + aq

2 3– 4 2–

3– 4

Cd ( ) 2NO ( ) 2NH ( ) S ( )

CdS( ) 2NO ( ) 2NH ( )

aq + aq s 2 2–Cd ( ) S ( ) CdS( ) net ionic equation

Cd(NO3)2 + (NH4)2S

Writing a Net Ionic EquationWriting a Net Ionic Equation

•Sample Problem BSample Problem B

Identify the precipitate that forms when aqueous solutions of zinc nitrate and ammonium sulfide are combined. Write the equation for the possible double-displacement reaction. Then write the formula equation, overall ionic equation, and net ionic equation for the reaction.

Net Ionic EquationNet Ionic Equation

Sample Problem B Sample Problem B SolutionSolution• Given: identity of reactants: zinc nitrate and

ammonium sulfide • Unknown:

a. equation for the possible double-displacement reaction

b. identity of the precipitate

c. formula equation

d. overall ionic equation

e. net ionic equation

Net Ionic EquationNet Ionic Equation

• Solution:

aq + aq ? + ?3 2 4 2 4 3Zn(NO ) ( ) (NH ) S( ) ZnS( ) 2NH NO ( )

aq + aq s + aq3 2 4 2 4 3Zn(NO ) ( ) (NH ) S( ) ZnS( ) 2NH NO ( )

Table 1 reveals that zinc sulfide is not a soluble sulfide and is therefore a precipitate. Ammonium nitrate is soluble according to the table.

The formula equationThe formula equation

Net Ionic EquationNet Ionic Equation

The overall ionic equation

aq + aq + aq + aq

s + aq + aq

2 – 2–3 4

–4 3

Zn ( ) NO ( ) NH ( ) S ( )

ZnS( ) NH ( ) NO ( )

aq + aq s 2 2–Zn ( ) S ( ) ZnS( )

The ammonium and nitrate ions appear on both sides of the equation as spectator ions.

The net ionic equationThe net ionic equation

Net Ionic EquationNet Ionic Equation