chemical reactions
DESCRIPTION
Chemical reactions. Classifications Reactions in solution Ionic equations. Learning objectives. Distinguish between chemical and physical change Describe concepts of oxidation and reduction Classify reaction according to types of reactants and products - PowerPoint PPT PresentationTRANSCRIPT
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
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