Reactions in Reactions in Aqueous SolutionsAqueous SolutionsChapter 8Chapter 8

Predicting Whether a Predicting Whether a Reaction Will OccurReaction Will Occur

Seem to be several changes that will Seem to be several changes that will cause a reaction to occurcause a reaction to occur Formation of a solidFormation of a solid Formation of waterFormation of water Transfer of electronsTransfer of electrons Formation of a gasFormation of a gas

Reactions in Which a Solid FormsReactions in Which a Solid Forms

Formation of a solid Formation of a solid is called Precipitationis called Precipitation Solid called Solid called

PrecipitatePrecipitate Reaction called Reaction called

Precipitation ReactionPrecipitation Reaction

Formation of solid Formation of solid tells you a chemical tells you a chemical reaction took placereaction took place

What Happens When an Ionic What Happens When an Ionic Compound Dissolves in Water?Compound Dissolves in Water?

When a solid containing When a solid containing ions is dissolved in water, ions is dissolved in water, the ions separatethe ions separate

Call this DissociationCall this Dissociation Ba(NOBa(NO33))2(aq)2(aq) contains no contains no

Ba(NOBa(NO33))2(aq)2(aq) units but units but instead is Bainstead is Ba2+2+ and NO and NO33

-- ionsions

There are 2 NOThere are 2 NO33-- ions for ions for

every Baevery Ba2+2+ ion ion Know it separates b/c Know it separates b/c

conducts electricityconducts electricity When all ions separate When all ions separate

called a strong electrolytecalled a strong electrolyte

What can we do with this info?What can we do with this info?

If we know that ionic compounds break up in If we know that ionic compounds break up in solution can make predictions of what happens solution can make predictions of what happens when 2 solutions dissolvewhen 2 solutions dissolve

KK22CrOCrO4(aq)4(aq) + Ba(NO + Ba(NO33))2(aq)2(aq) forms a yellow solid forms a yellow solid

So what is the product?So what is the product?

Now that we know reactants can guess Now that we know reactants can guess productsproducts

Know a solid compound must have a neutral Know a solid compound must have a neutral charge so anions must combine with cationscharge so anions must combine with cations

Also know (well you do now) that most ionic Also know (well you do now) that most ionic materials contain only 2 types of ionsmaterials contain only 2 types of ions

Below are some examplesBelow are some examples

So with this info there are only a few possible So with this info there are only a few possible combinationscombinations

Know it won’t be KKnow it won’t be K22CrOCrO44 and Ba(NO and Ba(NO33))22

because they were the reactants so this because they were the reactants so this leaves KNOleaves KNO33 and BaCrO and BaCrO44

A chemist knows that KNOA chemist knows that KNO33 is a white is a white

solid and CrOsolid and CrO4 4 is yellow so it must be thisis yellow so it must be this

Where are KWhere are K++ and NO and NO33-- ions? ions?

They are left in solution, so it is KNOThey are left in solution, so it is KNO3(aq)3(aq)

So our reaction readsSo our reaction reads

KK22CrOCrO4(aq)4(aq) + Ba(NO + Ba(NO33))2(aq)2(aq) → → BaCrOBaCrO4(s)4(s) + KNO + KNO3(aq)3(aq)

Which looks like thisWhich looks like this

How were we able to solve How were we able to solve this?this?

We used 2 types of knowledgeWe used 2 types of knowledge Knowledge of factsKnowledge of facts

Color of compoundsColor of compounds

Knowledge of conceptsKnowledge of concepts Solids are always neutral in chargeSolids are always neutral in charge

Using Solubility Rules Using Solubility Rules (or When will something (or When will something dissolve)dissolve)

Soluble Solid – easily dissolves in waterSoluble Solid – easily dissolves in water Insoluble solid and slightly soluble solid – Insoluble solid and slightly soluble solid –

tiny amount dissolves in watertiny amount dissolves in water You will see that the terms “salt” and You will see that the terms “salt” and

“ionic compound” mean the same thing“ionic compound” mean the same thing Some info you will need is on following Some info you will need is on following

slidesslides

8.3 Describing Reactions in Aqueous 8.3 Describing Reactions in Aqueous SolutionsSolutions

KK22CrOCrO4(aq)4(aq) + Ba(NO + Ba(NO33))2(aq)2(aq) → → BaCrOBaCrO4(s)4(s) + KNO + KNO3(aq)3(aq)

This is a “molecular equation” (shows complete This is a “molecular equation” (shows complete formulas)formulas)

Doesn’t give a very clear picture of what happenedDoesn’t give a very clear picture of what happened The “complete ionic equation” doesThe “complete ionic equation” does 2K2K++

(aq)(aq) + CrO + CrO442-2-

(aq)(aq) + Ba + Ba2+2+(aq)(aq) + 2NO + 2NO33

--(aq)(aq) → → BaCrOBaCrO4(s)4(s) + 2K + 2K++

(aq)(aq) + 2NO + 2NO33--(aq)(aq)

In a complete ionic equation all strong In a complete ionic equation all strong electrolytes are shown as ionselectrolytes are shown as ions

Shows which ions participate in reactionShows which ions participate in reaction

Spectator ions like 2KSpectator ions like 2K++(aq)(aq) and 2NOand 2NO33

--(aq)(aq) don’t don’t

participateparticipate They are there as reactants and productsThey are there as reactants and products When only those ions involved are shown it When only those ions involved are shown it

is called a Net Ionic Equationis called a Net Ionic Equation BaBa2+2+

(aq)(aq) + CrO + CrO442-2-

(aq)(aq) → BaCrO→ BaCrO4(s)4(s)

So there are 3 types of So there are 3 types of Equations for Reactions in Equations for Reactions in

Aqueous SolutionsAqueous Solutions

Molecular EquationsMolecular Equations Complete Ionic EquationsComplete Ionic Equations

Net Ionic EquationsNet Ionic Equations

Reactions That Form Reactions That Form Water: Acids and BasesWater: Acids and Bases

Acids (Definition from Arrhenius)Acids (Definition from Arrhenius) Produces H+ ions when dissolved in water Produces H+ ions when dissolved in water

(a proton)(a proton) HCl HCl → H→ H++

(aq)(aq) + Cl + Cl--(aq)(aq)

HNO3 → HHNO3 → H++(aq)(aq) + NO + NO33

--(aq)(aq)

If every molecule dissociates into ions, If every molecule dissociates into ions, called a “strong acid”called a “strong acid”

Bases (Definition from Arrhenius)Bases (Definition from Arrhenius) Produces OH- ions when dissolved in waterProduces OH- ions when dissolved in water NaOHNaOH(s)(s) → Na→ Na++

(aq)(aq) + OH + OH--(aq)(aq)

KOH(s) → KKOH(s) → K++(aq)(aq) + OH + OH--

(aq)(aq)

If every molecule dissociates into ions, If every molecule dissociates into ions, called a “strong base”called a “strong base”

Acids + Bases = NeutralizationAcids + Bases = Neutralization When acids and bases combine the reaction is When acids and bases combine the reaction is

called neutralizationcalled neutralization HCl HCl → H→ H++

(aq)(aq) + Cl + Cl--(aq)(aq) (ACID)(ACID) NaOHNaOH(s)(s) → Na→ Na++

(aq)(aq) + OH + OH--(aq)(aq) (BASE)(BASE)

HH++(aq)(aq)++ Cl Cl--(aq)(aq)++NaNa++

(aq)(aq)++OHOH--(aq)(aq)→H→H22OO(l)(l)++NaNa++

(aq)(aq)++ClCl--(aq)(aq)

So an Acid + Base yields Water and a SaltSo an Acid + Base yields Water and a Salt The Acid and Base have been neutralizedThe Acid and Base have been neutralized The last equation is a Complete Ionic EquationThe last equation is a Complete Ionic Equation Write a Net Ionic Equation for the above reactionWrite a Net Ionic Equation for the above reaction __________________________________________________________________________________

8.5 Reactions of Metals with 8.5 Reactions of Metals with Nonmetals (Oxidation-Reduction)Nonmetals (Oxidation-Reduction) Remember we said atoms will sometimes gain Remember we said atoms will sometimes gain

or lose electrons to become ionsor lose electrons to become ions A reaction that involves a transfer of electrons A reaction that involves a transfer of electrons

is called an is called an Oxidation-Reduction Reaction Oxidation-Reduction Reaction (Redox reactions)(Redox reactions)

2Mg2Mg(s)(s) + O + O2(g)2(g) → 2MgO→ 2MgO(s)(s)

Mg gives up 2e- and OMg gives up 2e- and O22 accepts 2e- accepts 2e- Mg → MgMg → Mg2+2+ + 2e- + 2e- O + 2e- → OO + 2e- → O2-2-

LEOGER = lose e- oxidation; gain e- reductionLEOGER = lose e- oxidation; gain e- reduction OILRIG = oxidation is lose; reduction is gainOILRIG = oxidation is lose; reduction is gain

8.6 Ways to Classify 8.6 Ways to Classify ReactionsReactions Precipitation ReactionPrecipitation Reaction

Whenever a precipitate formsWhenever a precipitate forms Acid-Base ReactionAcid-Base Reaction

Involves H+ ion ending up in HInvolves H+ ion ending up in H22OO Combustion ReactionsCombustion Reactions

Any reaction where something combines with OxygenAny reaction where something combines with Oxygen Synthesis ReactionSynthesis Reaction

A + B A + B →→ AB AB Decomposition ReactionDecomposition Reaction

AB AB →→ A + B A + B Single-Displacement ReactionSingle-Displacement Reaction

AB + C AB + C →→ AC + B AC + B Double-Displacement ReactionDouble-Displacement Reaction

AB + CD AB + CD → AD + CB→ AD + CB