Reactions in Aqueous Solutions

7.1 Predicting Whether a Reaction Will Occur?Driving Forces

Formation of solidFormation of waterTransfer of electronsFormation of a gas

7.2 Reactions in Which a Solid Forms?Driving forces

Precipitation – formation of solidE.g Ba(NO3)2(aq) + K2CrO4(aq) yellow solid

yellow sol. colorless

What happens When an Ionic Compound Dissolves in Water?Ba(NO3)2(aq) => barium nitrate (white solid)

has been dissolved in waterContaining Ba2+ (aq) and 2 NO3

-(aq) ions

Strong electrolytes: A unit of substance that dissolves in water produces separate ionsE.g K2CrO4(aq) contains K+, K+ and CrO4

2- ions=> strong electrolyte

Strong ElectrolytesBa(NO3)2(aq) + K2CrO4(aq) yellow solid

How to Decide What Products Form

NONO33-- CrOCrO44

2-2-

KK++ KNOKNO33

BaBa2+2+ Ba(NOBa(NO33))22

Write out all possible formula that can be formed

Using Solubility RulesGeneral Rules for Solubility of ionic compounds (salts) in

water at 25oCMost nitrate (NO3

-) salts are solubleMost salts of Na+, K+ and NH4

+ are solubleMost chloride, bromide, iodide (Cl-, Br- and I-) salts are

soluble. Notable exceptions are AgCl, PbCl2 and Hg2Cl2.Most sulfate salts are soluble. Notable exceptions are

BaSO4, PbSO4 and CaSO4Most hydroxide (-OH) compounds are slightly soluble.

The important exception are NaOH and KOH. Ba(OH)2 and Ca(OH)2 are only moderately soluble

Most sulfide (S2-), carbonate (CO32-) and phosphate (PO4

3-) salts are slightly soluble

* The term insoluble and slightly soluble really mean the same thing

Identifying Precipitates in Reactions Where a Solid FormsStep 1: Write the reactants as they actually

exist before any reaction occursStep 2: Consider the various solids that

could form.Step 3: use solubility rules to decide

whether a solid formsE.g AgNO3(aq) + KCl(aq) white solid

ExamplesUsing solubility rules to predict the product

of ReactionsKNO3(aq) + BaCl2(g) Na2S(aq) + Cu(NO3)2(aq) KOH(aq) + Fe(NO3)2(aq)

Describing Reactions in Aqueous SolutionsMolecular equation: shows overall

reaction but not necessary the actual forms of the reactants and products in solution

Complete ionic equation: represents all reactants and products that are strong electrolytes as ions. All reactants and products are included.

The net ionic equation includes only those components that undergoes a change. Spectator ions are not included

ExamplesFor each of the following reactions, write

molecular equation, the complete ionic equation and the net ionic equationAqueous sodium chloride is added to aqueous

silver nitrate to form solid silver chloride plus aqueous sodium nitrate

Aqueous nickel (II) nitrate is added to aqueous potassium carbonate to form solid nickel (II) carbonate and aqueous potassium nitrate

7.4 Reactions That Form Water: Acids and BasesArrhenius acids: a substance that produces

H+ ions (protons) when it dissolved in waterStrong acids: strong electrolytesCommon strong acids: HCl, HBr, HI, H2SO4,

HClO4, HNO3

dissolved in H2O

HCl(aq) -------------- H+(aq) + Cl-(aq)

7.4 Reactions That Form Water: Acids and BasesArrhenius Bases: substance that produces –

OH ion (hydroxide ions) in waterStrong bases: Strong electrolytesCommon strong bases: KOH, LiOH, NaOH,

Ba(OH)2 and Sr(OH)2

dissolved in H2O

NaOH(aq) ----------------- Na+(aq) + -OH(aq)

Writing Equations for Acid-Base ReactionsNitric acid is a strong acid. Write the

molecular, complete ionic and net ion equations for the reaction of aqueous nitric acid and aqueous potassium hydroxide.

Hydrobromic acid is a strong acid. Write the molecular, complete ionic and net ion equations for the reaction of aqueous hydrobromic acid and aqueous barium hydroxide

7.5 Reactions of Metals with Nonmetals (Oxidation Reduction)Oxidation – Reduction or Redox reaction:

process of transferring electrons from one to the other

Step in determination Redox ReactionDetermine the charges of each atomOxidation: loss of electron(s); charge becomes

more positiveReduction: gain of electron(s); charge becomes

less positiveE.g 2 Na(s) + Cl2(g) 2 NaCl(s)

ExamplesFor each of the following reactions, show

how electrons are gained and lost2 Al(s) + 3 I2(g) 2 AlI3(s)

2 Cs(s) + F2(g) 2 CsF(s)

2SO2(g) + O2(g) 2SO3(g)

7.6 Ways to Classify ReactionsConsider the driving forces

Formation of solid Precipitation reaction Double replacement

Formation of water Acid – base reaction

Transfer of electrons Oxidation – Reduction reaction

7.7 Other Ways to Classify ReactionsCombustion

Organic Compound + O2(g) + heat CO2(g) + H2O(g)

CombinationElement + element compound

DecompositionCompound element + element

ExamplesClassify each of the following reactions in

as many ways as possible2 K(s) + Cl2(g) 2 KCl(s)

BaCl2 (aq) + Na2SO4(aq) BaSO4 (s) + 2 NaCl(aq)

HNO3(aq) + NaOH(aq) H2O(l) + NaNO3(aq)

2C2H2 (g) + 5O2 (g) 4 CO2 (g) + 2H2O(l)

PbO2 (s) Pb(s) + O2 (g)

Fe2O3(s) + 2 Al(s) Al2O3(s) + 2 Fe(s)