Chemical reactionsChemical reactions

ClassificationsClassificationsReactions in solutionReactions in solution

Ionic equationsIonic equations

Learning objectivesLearning objectives

Distinguish between chemical and physical changeDistinguish between chemical and physical changeDescribe concepts of oxidation and reductionDescribe concepts of oxidation and reductionClassify reaction according to types of reactants and Classify reaction according to types of reactants and productsproductsDistinguish among strong, weak and non-electrolytesDistinguish among strong, weak and non-electrolytesIdentify common acids and bases by from chemical Identify common acids and bases by from chemical formulaformulaPredict formation of precipitates by application of Predict formation of precipitates by application of solubility rulessolubility rulesWrite total and net ionic equations from balanced Write total and net ionic equations from balanced molecular equationsmolecular equations

One approach to classificationOne approach to classification

Oxidation – reduction: focusing on Oxidation – reduction: focusing on electronselectrons

Oxidation is loss of electronsOxidation is loss of electrons

Reduction is gain of electronsReduction is gain of electrons

Oxidation is always accompanied by Oxidation is always accompanied by reductionreduction

The total number of electrons is kept constantThe total number of electrons is kept constant

Oxidizing agents oxidize and are Oxidizing agents oxidize and are themselves reducedthemselves reduced

Reducing agents reduce and are Reducing agents reduce and are themselves oxidizedthemselves oxidized

Redox in chemistryRedox in chemistry

All reactions involve rearrangement of All reactions involve rearrangement of atoms and moleculesatoms and molecules

Some reactions involve rearrangement of Some reactions involve rearrangement of atoms and molecules atoms and molecules and and electronselectrons– Photosynthesis, respiration, combustion...Photosynthesis, respiration, combustion...

These are called These are called redoxredox reactions reactions

Any reaction involving elements Any reaction involving elements mustmust be be redoxredox

Combination reactionsCombination reactions

Element + element Element + element compound ( compound (redoxredox))– S + OS + O22 → SO→ SO22

– Metal + nonmetal Metal + nonmetal binary ionic compound binary ionic compound– Nonmetal + nonmetal Nonmetal + nonmetal binary covalent compound binary covalent compound

Compound + element Compound + element compound ( compound (redoxredox))– CO + OCO + O22 → CO → CO22

Compound + compound Compound + compound compound compound– SOSO22 + H + H22O →HO →H22SOSO33

Decomposition reactionsDecomposition reactions

Compound Compound element + element ( element + element (redoxredox))– HgO HgO →→ Hg + O Hg + O22

Compound Compound element + compound ( element + compound (redoxredox))– PClPCl55 → PCl → PCl33 + Cl + Cl22

Compound Compound compound + compound compound + compound– CaCOCaCO33 → CaO + CO → CaO + CO22

Single replacement (displacement)Single replacement (displacement)

Element displaces another element from Element displaces another element from compound (compound (redoxredox))– Zn + CuSOZn + CuSO44 → → ZnSOZnSO44 + Cu + Cu

Double replacement (displacement)Double replacement (displacement)

Compounds exchanging partnersCompounds exchanging partners– Usually ionic compounds in solutionUsually ionic compounds in solution

Identify ions and swap themIdentify ions and swap themKKClCl + Ag + AgNONO33 → K → KNONO33 + Ag + AgClCl(s)(s)

Very often a solid is producedVery often a solid is produced

Acid – base neutralization:Acid – base neutralization:special case of double replacementspecial case of double replacement

KOH(aq) + HKOH(aq) + HNONO33(aq) = K(aq) = KNONO33(aq) + H(aq) + H22O(l)O(l)

Product is liquid water not a solidProduct is liquid water not a solid

BASE ACID SALT WATER

CombustionCombustion

Element or compound reacting with Element or compound reacting with oxygenoxygen ( (redoxredox))– CHCH44 + O + O22 →→ CO CO22 + H + H22OO

Associated with production of heat and lightAssociated with production of heat and light

Often involves hydrocarbons (COften involves hydrocarbons (CxxHHyy))

COCO22 and H and H22O are productsO are products

Sorting solution reactions: Sorting solution reactions: dissolved speciesdissolved species

Electrolytes: Electrolytes: – Ionic compounds produce ions in solution Ionic compounds produce ions in solution

(NaCl, NH(NaCl, NH44NONO33 etc.) etc.)

Non-electrolytes: Non-electrolytes: – Covalent compounds do not produce ions in Covalent compounds do not produce ions in

solution (CHsolution (CH33OH, COH, C66HH1212OO66 etc.) etc.)

Electrolytes: distinguishing by Electrolytes: distinguishing by strengthstrength

StrongStrong electrolytes are characterized by electrolytes are characterized by complete dissociation in watercomplete dissociation in water

WeakWeak electrolytes dissociate to a much smaller electrolytes dissociate to a much smaller extent.extent.

Strong, weak or non electrolyte?Strong, weak or non electrolyte?

AllAll soluble salts are strong electrolytes soluble salts are strong electrolytes

Strong acids and bases are strong Strong acids and bases are strong electrolyteselectrolytes

Weak acids and bases are weak Weak acids and bases are weak electrolyteselectrolytes

Insoluble compounds are non-electrolytesInsoluble compounds are non-electrolytes

Molecular compounds are non-electrolytesMolecular compounds are non-electrolytes

Classification of electrolytesClassification of electrolytes

Strong Strong electrolyteselectrolytes

Weak Weak electrolyteselectrolytes

Non-Non-electrolyteselectrolytes

ACIDS:ACIDS:

HCl, HBr, HIHCl, HBr, HI

HClOHClO44, HNO, HNO33, H, H22SOSO44

ACIDS:ACIDS:

HF, HHF, H33POPO44,,

CHCH33COCO22HH

Molecular Molecular covalent covalent compounds:compounds:

HH22O,O,

CHCH33OH,OH,

CC1212HH2222OO1111

(sucrose)(sucrose)

Most organic Most organic compoundscompounds

SALTS:SALTS:

KBr, NaKBr, Na33POPO44

SALTS:SALTS:

NoneNone

BASES:BASES:

NaOH, Ba(OH)NaOH, Ba(OH)22

BASES:BASES:

NHNH33

Four classes of substance with Four classes of substance with solution reactionssolution reactions

Solubility in water

Ionic or covalent

Insoluble substance

Strong electrolyte

Nonelectrolyte

Acid or base

Weak or strong

Weak electrolyte

Yes No

Yes

No

ioniccov

weak strong

Recognizing acids and basesRecognizing acids and bases

Acids usually have H at the beginning of Acids usually have H at the beginning of the formula – the formula – HHClCl

Bases usually have OH in the formula – Bases usually have OH in the formula – NaNaOHOH– Not in organic compounds though - CHNot in organic compounds though - CH33OHOH

Focus on double replacementFocus on double replacement

Driven by removal of ions from solutionDriven by removal of ions from solution1.1. Formation of an insoluble solid (precipitate)Formation of an insoluble solid (precipitate)

2.2. Formation of non-ionized molecules (acid – base)Formation of non-ionized molecules (acid – base)

3.3. Formation of a gasFormation of a gas

1. Predicting precipitation reactions1. Predicting precipitation reactions

Does one of the new cation-anion Does one of the new cation-anion combinations produce insoluble salt? combinations produce insoluble salt?

How do I know?How do I know?– Initial combinations are all solubleInitial combinations are all soluble– Use solubility rules to investigateUse solubility rules to investigate– If yes, a precipitate is producedIf yes, a precipitate is produced

Solubility roolsSolubility rools

Group I and ammonium compounds are Group I and ammonium compounds are generally solublegenerally soluble

Nitrates and acetates are generally solubleNitrates and acetates are generally soluble

Chlorides, bromides and iodides are generally Chlorides, bromides and iodides are generally soluble {except Pb(II), Ag(I) and Hg(I)}soluble {except Pb(II), Ag(I) and Hg(I)}

Carbonates and phosphates are generally Carbonates and phosphates are generally ininsoluble (except group I)soluble (except group I)

Hydroxides and sulphides are generally Hydroxides and sulphides are generally ininsolublesoluble (except groups I and II)(except groups I and II)

3. Production of a gas3. Production of a gas

If product is a gas that has a low solubility If product is a gas that has a low solubility in water, reaction in solution is driven to in water, reaction in solution is driven to produce the gasproduce the gas

Tums reliefTums relief

Any carbonate with an acidAny carbonate with an acidNaHCONaHCO33(s) + HCl(aq) = NaCl(aq) + H(s) + HCl(aq) = NaCl(aq) + H22O(l) + O(l) +

COCO22(g)(g)

Writing balanced molecular equations Writing balanced molecular equations for double replacement reactionsfor double replacement reactions

Use correct formulaeUse correct formulae– Metal ion charge predicted Metal ion charge predicted

from group numberfrom group number– Use table for correct Use table for correct

formula and charge for formula and charge for polyatomic ionspolyatomic ions

Identify as solid (s), gas Identify as solid (s), gas (g), liquid (l) or dissolved (g), liquid (l) or dissolved (aq)(aq)

Balance: atoms (groups) Balance: atoms (groups) on left = atoms (groups) on left = atoms (groups) on righton right

Balancing double replacement equationsBalancing double replacement equations

It’s very much a matter of It’s very much a matter of states – states – show show them!them!Pb(NOPb(NO33))22(aq)(aq) + 2KI + 2KI(aq)(aq) = 2KNO = 2KNO33(aq)(aq) + PbI + PbI22(s)(s)

Balance polyatomic ions as units:Balance polyatomic ions as units:– PbPb2+2+, K, K++, I, I--, NO, NO33

--

Left hand sideLeft hand side Right hand sideRight hand side1 Pb2+ 1 Pb2+

2 NO3- 2 NO3

-

2 K+ 2 K+

2 I- 2 I-

Molecular equation for reaction of Molecular equation for reaction of NaNa22SOSO44 + Ba(NO + Ba(NO33))22

Total ionic equationsTotal ionic equations

Dissolved substances:Dissolved substances:– Strong electrolytes show as ionsStrong electrolytes show as ions– Weak or non- electrolytes show as molecular formulaWeak or non- electrolytes show as molecular formula

All others show as All others show as molecular formulamolecular formula

Pb(NOPb(NO33))22(aq) + 2KI(aq) = 2KNO(aq) + 2KI(aq) = 2KNO33(aq) + PbI(aq) + PbI22(s)(s)

PbPb2+2+(aq) + 2NO(aq) + 2NO33--(aq) + 2K(aq) + 2K++(aq) + 2I(aq) + 2I--(aq) = 2K(aq) = 2K++(aq) + 2NO(aq) + 2NO33

--(aq) (aq)

+ + PbIPbI22(s)(s)

Net ionic equationsNet ionic equations

Spectator ions are those ions that do not Spectator ions are those ions that do not undergo a change; they do not participate undergo a change; they do not participate in the chemical change and are the same in the chemical change and are the same on both sides of the equationon both sides of the equation

Remove all Remove all spectatorspectator ions from the ions from the equationequation

PbPb2+2+(aq) + (aq) + 2NO2NO33--(aq)(aq) + + 2K2K++(aq)(aq) + 2I + 2I--(aq) = (aq) = 2K2K++(aq)(aq) + +

2NO2NO33--(aq)(aq) + PbI + PbI22(s)(s)

Net ionic equationsNet ionic equations

PbPb2+2+(aq) + 2I(aq) + 2I--(aq) = PbI(aq) = PbI22(s)(s)

Mass and charge must still balance, although Mass and charge must still balance, although overall charge may not be neutral in a net ionic overall charge may not be neutral in a net ionic equationequation

Net ionic equation for reaction of Net ionic equation for reaction of NaNa22SOSO44 + Pb(NO + Pb(NO33))22