Net Ionic EquationsNet Ionic Equations

PrecipitatesPrecipitates►A precipitate is the solid substance A precipitate is the solid substance

that separates from solutionthat separates from solution►Precipitates can also form from Precipitates can also form from

reactionsreactions►Reactions that produce a precipitate Reactions that produce a precipitate

are called are called precipitation reactionsprecipitation reactions ►Most ionic compounds dissolve in Most ionic compounds dissolve in

waterwater►Solutes that produce ions in solution Solutes that produce ions in solution

are called are called electrolyteselectrolytes because because their solutions can conduct electricitytheir solutions can conduct electricity

Electrolytes:Electrolytes:

An ionic compounds An ionic compounds dissociatesdissociates as as it dissolves in waterit dissolves in waterIons separate from the solid

and become hydrated or surrounded by water molecules.

The ions move freely and the solution is able to conduct electricity.

Ionic compounds that dissociate completely are strong electrolytes

Nonelectrolytes:Nonelectrolytes:►Most solutions of molecular Most solutions of molecular

compounds do not conduct compounds do not conduct electricity and are called electricity and are called nonelectrolytesnonelectrolytes

The molecules of a nonelectrolyte separate but stay intact. The solution is nonconducting because no ions are generated.

Some ionic compounds have low solubilities in water but are still strong electrolytes because what does dissolve is 100% dissociated.

Electrolytes:Electrolytes:►The dissociation of ionic The dissociation of ionic

compounds may be described with compounds may be described with chemical equationschemical equations

►The hydrated ions, with the symbol The hydrated ions, with the symbol ((aqaq), have been written separately), have been written separately

►Since physical states are often Since physical states are often omitted, you might encounter the omitted, you might encounter the equation as:equation as:

)(SO )(Na 2 )(SONa -2442 aqaqs

-2442 SO Na 2 SONa

Know your Solubility Rules!Know your Solubility Rules!► Ionic compounds often react when Ionic compounds often react when

their aqueous solutions combinetheir aqueous solutions combineWhen a solution of Pb(NO3)2 is mixed with a solution of KI the yellow precipitate PbI2 rapidly forms.

► A precipitation reaction may be A precipitation reaction may be represented with a represented with a molecularmolecular, , ionicionic, or , or net ionic equationnet ionic equation::Molecular:Molecular:Ionic:Ionic:

Net Ionic:Net Ionic:

► The most compact notation is the net The most compact notation is the net ionic equation which eliminates all the ionic equation which eliminates all the non-reacting non-reacting spectator ionsspectator ions from the from the equationequation

)(2KNO)(PbI)2KI()()Pb(NO 3223 aqsaqaq

)(2NO)(2K)(PbI

)(2I)(2K)(2NO)(Pb-3

--3

2

2 aqaqs

aqaqaqaq

)(PbI )(2I)(Pb 22 saqaq

Know your Solubility Know your Solubility Rules!Rules!

Types of chemical equationsTypes of chemical equations►Here is a typical molecular equation:Here is a typical molecular equation:Cd(NOCd(NO33))22(aq) + Na(aq) + Na22S(aq) S(aq) CdS(s) + 2NaNO CdS(s) + 2NaNO33(aq)(aq)

►We can write this as an ionic equation (all We can write this as an ionic equation (all compounds that are (aq) are written as ions):compounds that are (aq) are written as ions):

CdCd2+2+(aq) + 2NO(aq) + 2NO33––(aq) + 2Na(aq) + 2Na++(aq) + S(aq) + S2–2–(aq) (aq)

CdS(s) + 2Na CdS(s) + 2Na++(aq) + 2NO(aq) + 2NO33––

(aq)(aq)

►To get the NET ionic equation we cancel out all terms To get the NET ionic equation we cancel out all terms that appear on both sides:that appear on both sides:

Net: CdNet: Cd2+2+(aq) + S(aq) + S2–2–(aq) (aq) CdS(s) CdS(s)

AgAg++ + Cl + Cl-- AgCl (s) AgCl (s)

Criteria for balanced net ionic Criteria for balanced net ionic equations:equations:

1)1) Material balance – the same number Material balance – the same number of each type of atom on each side of of each type of atom on each side of the arrowthe arrow

2)2) Electrical balance – the Electrical balance – the netnet electrical electrical charge on the left side of the arrow charge on the left side of the arrow must equal the must equal the netnet electrical charge electrical charge on the right side of the arrowon the right side of the arrowRemember that the charge on an ion must be included when it

is not in a compound. Adding the charges on all the ions on one side of the arrow gives the net electrical charge.

NaOH(aq) + MgClNaOH(aq) + MgCl22(aq) (aq)

Mg(OH) Mg(OH)22(s) + (s) +

NaCl(aq) NaCl(aq) Next, balance the equationNext, balance the equation

First write the skeleton equationFirst write the skeleton equation

2222

Second write the Ionic equation:Second write the Ionic equation:2Na2Na++(aq) + 2OH(aq) + 2OH--(aq) + Mg(aq) + Mg2+2+(aq) + 2Cl(aq) + 2Cl--(aq) (aq)

Mg(OH) Mg(OH)22(s) (s) + 2Na+ 2Na++(aq) + 2Cl(aq) + 2Cl--(aq)(aq)

Third cancel the spectator ions and write theThird cancel the spectator ions and write theNet ionic equation:Net ionic equation:

2OH2OH--(aq) + Mg(aq) + Mg2+2+(aq) (aq) Mg(OH) Mg(OH)22(s)(s)

Practice EquationsPractice EquationsWrite balanced net ionic equations:Write balanced net ionic equations:1)1) CuSOCuSO44(aq) + BaCl(aq) + BaCl22(aq) (aq)

1)1) Fe(NOFe(NO33))33(aq) + LiOH(aq) (aq) + LiOH(aq)

2)2) NaNa33POPO44(aq) + CaCl(aq) + CaCl22(aq) (aq)

3)3) NaNa22S(aq) + AgCS(aq) + AgC22HH33OO22(aq) (aq)

Net: SONet: SO442–2–(aq) + Ba(aq) + Ba2+2+(aq) (aq) BaSO BaSO44(s)(s)

Net: FeNet: Fe3+3+(aq) + 3OH(aq) + 3OH––(aq) (aq) Fe(OH) Fe(OH)33(s)(s)

Net: 2PONet: 2PO443–3–(aq) + 3Ca(aq) + 3Ca2+2+(aq) (aq) Ca Ca33(PO(PO44))22(s)(s)

Net: SNet: S2–2–(aq) + 2Ag(aq) + 2Ag++(aq) (aq) Ag Ag22S(s)S(s)

Net Ionic Equation Solutions