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AqueousReactions
Unit # 4:Aqueous Reactions and Solution Stoichiometry
CHM 1045: General Chemistry and Qualitative Analysis
Dr. Jorge L. AlonsoMiami-Dade College –
Kendall CampusMiami, FL
Textbook Reference: •Module # 6 and 4 (V-VII)•Chapt 4 (Brown & LeMay)•Chapter # 3-6 to 3-8, 4 & 11-1 to 11-3
AqueousReactions
Solutions
• Solutions (soln) are homogeneous mixtures of two or more pure substances.
• The solvent (solv) is present in greatest abundance.
• All other substances are solutes (solu).
Volumetric flask
{PrepASolu}
H2O
Cu(NO3)2
Molarity (M) = Moles of solute
Liters of solution
Most useful measure of concentration of solutions:
AqueousReactions
Solubility of Chemical Substances
Covalent Compounds: mostly insoluble gases, except O & N containing organic (C) liquids (polar: acids, bases, alcohols, etc.)
Ionic Compounds: many are soluble.SOLUBILITY RULES: for Ionic Compounds (Salts)1. All salts of alkali metals (IA) are soluble.2. All NH4
+ salts are soluble.
3. All salts containing the anions: NO3-, ClO3
-, ClO4-, (C2H3O2
-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+, and Pb2+ salts.
5. All SO42- are soluble except for Pb2+, Ba2+, and Sr2+.
6. All O2- are insoluble except for IA metals Ca2+, Ba2+, and Sr2+ salts.{Soluble metal oxides form hydroxides: CaO Ca 2+ + 2OH-}
7. All OH- are insoluble except for IA metals, NH4+ & slightly soluble Ca 2+ Ba2+ & Sr2+
8. All salts containing the anions: CO32-, PO4
3-, AsO43-, S2- and SO3
2- are insoluble except fro IA metals and NH4
+ salts. 9. For salts containing the anions not mentioned above (e.g., CrO4
2-, Cr2O72-, P3-,
C2O42- etc.) assume that they are insoluble except for IA metals and NH4
+ salts, unless, otherwise informed.
H2O
Elements: mostly insoluble solids, liquids & gases.
Ionic Compounds:Except
HAPExcept
PBS
AqueousReactions
The Solution Process: Ionic vs. Molecular
(1) Ionic Compounds: undergo dissociation - process by which many ionic substances dissolve in water, the solvent pulls the individual ions from the crystal and solvates them.
{*NaCl + H2O }
++
_
Polar water molecule
H2O
NaCl(s)
Electrolytes vs Nonelectrolytes?
H2O Na+(aq) + Cl-(aq)
Dissociation
AqueousReactions
Do soluble substances conduct electricity in water?
{ElectrVsNonE} • Electrolytes substances that dissociate in water and conduct electricity (many ionic salts)
C6H12O6(s) C6H12O6 (aq)
NaCl(s) Na+(aq) + Cl-(aq)
H2O
H2O
H2O
{DoesWaterConduct?} H2O(l) H+(aq) + OH-
(aq)
A nonelectrolytes may dissolve in water, but they do not dissociate into ions, thus do not conduct electricity. These are most commonly polar molecular (covalent) compounds.
Glucose molecules Dissolved Glucose molecules
AqueousReactions
Electrolytes: Strong and Weak• A strong electrolyte dissociates
completely when dissolved in water.
HCl (g) H2O H+(aq) + Cl-(aq)
• A weak electrolyte only dissociates partially when dissolved in water.
NH4OH(aq) H2O NH4+
(aq) + OH-(aq)
Aceitic Acid,
HC2H3O2 (aq) H2O H+
(aq) + C2H3O2
-(aq)
{Strong&WeakElectrolytes}
1 1
1 .20 .80 .20
10
.25 .25 1.75
molecules ions
AqueousReactions
Strong Electrolytes & Ion Concentration
NaCl (s)
CaCl2 (s)
Na3PO4 (s)
Na+ + Cl-
Ca2+ + 2Cl-
3Na+ + PO4
3-
H2O
H2O
H2O
1
1
1
1 1
1 2
3 1
(=3)
(=2)
(=4)
1M Na3PO4 4M in IonsWhat Molarity of Ions?
AqueousReactions
The Solution Process: Ionic vs. Molecular
(2) Molecular (covalent) Compounds: mostly insoluble gases, except polar organic (C) liquids containing O & N (polar: acids, bases, alcohols, etc.)
Insoluble gases: NO2, CH4, CO2, O2, P2O5, N2, CO, etc.
Polar Covalent {carbon (C) chains containing H,O or N}: CH3OH, C6H12O6, C6H5OH, etc.
C6H12O6(s) C6H12O6 (aq)
H2O
{Ethanol+Water}
C3H5OH(l) C3H5OH (aq)
H2O
Dissolve without dissociating into ions
AqueousReactions
Molecular CompoundsMolecular compounds tend to be nonelectrolytes,
except for strong acids (and weak acids & bases).
Strong Electrolytes: HCl.
Weak Electrolytes: HF, Ammonia NH3, Acetic acid HC2H3O2
Non-Electrolyte: H2O, Ethanol C2H5OH
Solubility Rules:3. All salts containing the anions:
NO3-, ClO3
-, ClO4-, (C2H3O2
-) are
soluble.4. All Cl-, Br-, and I- are soluble
except for Hg22+, Ag+, and Pb2+
salts.5. All SO4
2- are soluble except for
Pb2+, Ba2+, and Sr2+.
Covalent Compounds: HCl, CO2, O2, P2O5, C6H14, C6H12O6, etc.
100% ions
Some ions
Dissolve, but no ions
AqueousReactions
Chemical Reactions Occurring in Aqueous
Environments
(1) Precipitation
(2) Gas-Forming
(3) Acid-Base Neutralization
(4) Oxidation-Reduction
(Redox)
Mostly Single & Double–Replacement Reactions
AqueousReactions
(1) Precipitation Reactions
A special category of Metathesis (Double Replacement, Exchange)
Reactions
AqueousReactions
Pb(NO3)2 + 2KI 2 KNO3 + PbI2(aq) (aq) (aq) (s)
Precipitate (ppt)
Precipitation Reactions
Predict the solubility of compounds in reaction:
{Movie}
Solubility Rules:3. All salts containing the anions: NO3
-, ClO3-, ClO4
-,
(C2H3O2-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+,
and Pb2+ salts.5. All SO4
2- are soluble except for Pb2+, Ba2+, and
Sr2+.
Aqueous solutions, reacting to produce a precipitate (an insoluble compound). Example: KI(aq) + Pb(NO3)2 (aq)
PbI2
KI
Pb(NO3)2
AqueousReactions
Precipitation Reactions are Double Displacement (Replacement)
• It appears the ions in the reactant compounds exchange ion
AgNO3 + KCl AgCl + KNO3(aq) (aq) (aq)(s)
{*AgNO3+NaCl&NaI}
Does a reaction occur? Does the activity series apply to double displacement reactions?
• Reaction occurs only if a precipitate is formed!
Solubility Rules:3. All salts containing the anions: NO3
-, ClO3-, ClO4
-,
(C2H3O2-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+,
and Pb2+ salts.5. All SO4
2- are soluble except for Pb2+, Ba2+, and Sr2+.
AqueousReactions
Ways of Expressing Precipitation Reactions
There are three different:
(1) Molecular Equations
(2) Ionic Equations
(3) Net Ionic Equations
AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq)
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)
AgCl (s) + K+ (aq) + NO3- (aq)
Ag+(aq) + Cl-(aq) AgCl (s)
AqueousReactions
Molecular EquationThe molecular equation lists the reactants and products in their molecular (formula unit) form.
AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq)
Ionic Equation• In the ionic equation all strong electrolytes (strong
acids, strong bases, and soluble ionic salts) are dissociated into their ions.
• This more accurately reflects the species that are found in the reaction mixture.
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)
AgCl (s) + K+ (aq) + NO3- (aq)
AqueousReactions
Net Ionic Equation• To form the net ionic equation, cross out anything
that does not change from the left side of the equation to the right.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)
AgCl (s) + K+(aq) + NO3-(aq)
• The only things left in the equation are those things that change (i.e., react) during the course of the reaction.
Ag+(aq) + Cl-(aq) AgCl (s)
• Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions.
AqueousReactions
Solution ChemistryThere are three different ways of expressing
precipitation reactions:
(1) Molecular Equations
(1) Ionic Equations
(2) Net Ionic Equations
AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq)
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)
AgCl (s) + K+ (aq) + NO3- (aq)
Ag+(aq) + Cl-(aq) AgCl (s)
AqueousReactions
Writing Net Ionic Equations
1. Write a balanced molecular equation.2. Dissociate all strong electrolytes (ionic
equation).3. Cancel-out ions that remains
unchanged from the left side to the right side of the equation (spectator ions).
4. Write the net ionic equation with the species that remain.
AqueousReactions
Writing Net Ionic Equations
2NH4+ + SO4
2- + Ba2+ + 2NO3- 2NH4
+ + 2NO3- + BaSO4
Ba2+ + SO42- BaSO4(aq) (aq) (s)
(aq) (aq) (aq) (aq) (aq) (aq) (s)
Solubility Rules:3. All salts containing the anions: NO3
-, ClO3-, ClO4
-, (C2H3O2-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+, and Pb2+ salts.
5. All SO42- are soluble except for Pb2+, Ba2+, and Sr2+.
AqueousReactions
Precipitation ReactionsSOLUBILITY RULES: for Ionic Compounds (Salts)1. All salts of alkali metals (IA) are soluble.2. All NH4
+ salts are soluble.
3. All salts containing the anions: NO3-, ClO3
-, ClO4-, (C2H3O2
-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+, and Pb2+ salts.
5. All SO42- are soluble except for Pb2+, Ba2+, and Sr2+.
SOLUBILITY RULES: for Ionic Compounds (Salts)1. All salts of alkali metals (IA) are soluble.2. All NH4
+ salts are soluble.
3. All salts containing the anions: NO3-, ClO3
-, ClO4-, (C2H3O2
-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+, and Pb2+ salts.
5. All SO42- are soluble except for Pb2+, Ba2+, and Sr2+.
AqueousReactions
SOLUBILITY RULES: for Ionic Compounds (Salts)1. All salts of alkali metals (IA) are soluble.2. All NH4
+ salts are soluble.
3. All salts containing the anions: NO3-, ClO3
-, ClO4-, (C2H3O2
-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+, and Pb2+ salts.
5. All SO42- are soluble except for Pb2+, Ba2+, and Sr2+.
SOLUBILITY RULES: for Ionic Compounds (Salts)1. All salts of alkali metals (IA) are soluble.2. All NH4
+ salts are soluble.
3. All salts containing the anions: NO3-, ClO3
-, ClO4-, (C2H3O2
-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+, and Pb2+ salts.
5. All SO42- are soluble except for Pb2+, Ba2+, and Sr2+.
AqueousReactions
(2) Gas-Forming Reactions
A special category of Metathesis (Double Replacement, Exchange)
Reactions
AqueousReactions
Gas-Forming Reactions
• The expected products decompose to give a gaseous products
• Carbonate + Acid produce H2CO3 CO2 + H2O
• Sulfites + Acids produce H2SO3 SO2+ H2O.
CaCO3 (s) + 2HCl (aq)
NaHCO3 (aq) + HBr (aq)
SrSO3 (s) + 2 HI (aq)
{CaCO3 + HCl*}
These metathesis reactions do not give the expected products.
CaCl2 (aq) + CO2 (g) + H2O (l)
NaBr (aq) + CO2 (g) + H2O (l)
SrI2 (aq) + SO2 (g) + H2O (l)
H2CO3
H2CO3
H2SO3
AqueousReactions
Aspirin: 2-(acetyloxy)benzoic acid or acetyl-salicylic acid CH3
{Alka Seltzer Movie}
Gas-Forming Reactions
Alka Seltzer: aspirin + baking soda
Aspirin
C6H4(OCOCH3)COOH
1) C6H4(OCOCH3)COOH + NaHCO3
C6H4(OCOCH3)COONa(aq) + {H2CO3 (aq) }
H2O
NaHCO3
2) { H2CO3(aq) } CO2 + H2O
C9H8O4
H
AqueousReactions
Gas-forming Reactions1.
2.
3.
4.
5.
AqueousReactions
2003 A
AqueousReactions
(3) Acid-Base Neutralization
ReactionsAnother special category of
Metathesis (Double Replacement, Exchange) Reactions
AqueousReactions
Acids
molecule ions
ions
100%
15%
molecule
• Arrhenius: Substances that release their H+ when dissolved in water.
• Examples:Strong:
HCl(g) H+(aq) + Cl-(aq)
Weak:
HC2H3O2 (aq). H+ + C2H3O2-
(aq)
AqueousReactions
AcidsThere are only seven strong acids:• Hydrochloric (HCl)• Hydrobromic (HBr)• Hydroiodic (HI)
• Nitric (HNO3)
• Sulfuric (H2SO4)
• Chloric (HClO3)
• Perchloric (HClO4)
Solubility Rules:3. All salts containing the anions: NO3
-, ClO3-, ClO4
-, (C2H3O2-) are soluble.
4. All Cl-, Br-, and I- are soluble except for Hg22+, Ag+, and Pb2+ salts.
5. All SO42- are soluble except for Pb2+, Ba2+, and Sr2+.
AqueousReactions
Bases
• Arrhenius: Substances that release their OH− when dissolved in water.
{IntroBases}
Ba(OH)2 (s) Ba2+(aq) + 2OH-
(aq)
Mg(OH)2 (s) Mg2+(aq) + 2OH-
(aq)
100%
5%
Strong:
Weak:
AqueousReactions
Bases
The strong bases are :• Alkali metals (IA)
Hydroxides• Barium Hydroxide• Strontium Hydroxide• (weaker: Ammonium,
Calcium Hydroxides)
SOLUBILITY RULES: for Ionic Compounds (Salts)7. All OH- are insoluble except for IA metals, NH4
+, Ba2+, and Sr2+.
AqueousReactions
Neutralization Reactions (Arrhenius).
Generally, when solutions of an acid and a base are combined, the products are a salt and water.
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq)
Na+ (aq) + Cl- (aq) + H2O (l)
H+ (aq) + OH- (aq) H2O (l)
AqueousReactions
Neutralization Reactions
Observe the reaction between a weak base, Milk of Magnesia, Mg(OH)2 (s) and a strong acid HCl (aq).
Mg(OH)2(s) + 2HCl (aq) MgCl2(aq) + 2H2O (l)
{Movie}
Mg(OH)2(s) + 2H+(aq) + 2Cl-
(aq) Mg2+(aq) + 2Cl-
(aq) + 2H2O (l)
How would you write the net ionic equation for such a reaction?
Mg(OH)2(s) + 2H+(aq) Mg2+
(aq) + 2H2O (l)
AqueousReactions
Acid-Base Neutralization Rxs
AqueousReactions
Solution Stoichiometry
Quantitative aspects of chemical reactions occurring in aqueous
environments.
AqueousReactions
Preparing Solutions: Molarity• Most useful way to measure the concentration of a
solution.
?g
moles of solute
volume of solution in litersMolarity (M) =
Example 1: How would you prepare a 1M solution of CuSO4
. 5H2O (FW= 249.7 g/mol) in a 250 mL volumetric flask ?
{Prep1MSoln}
mL 1000
L 1
Example 2: How would you prepare a 0.5M solution of CuSO4
. 5H2O (FW= 249.7 g/mol) in a 50 mL volumetric flask?
?g
mL 1000
L 1
mol 1
g 7.249 g 62.42 mL 250 L
mol 1
mL 50 L
mol 0.5
mol 1
g 7.249 g 6.242
AqueousReactions
Calculations using Molarity
moles of solute ( )
volume of solution in liters (L)Molarity (M) =
moles of solute ( ) = Molarity ( /L) x volume of solution (L)
mol () = = M x V(mol/L) x L
AqueousReactions
Problem: What is the molecular weigh (g-MM) of an acid of which it takes 18.25 g to make 250. mL of a 2.00M concentration?
Calculations using Molarity
L
L
MM-g
1 g#
Molarity (M)
g
18.25 g g 36.5
2.00
L 1
mL 250
1
L 1
mL 1000
AqueousReactions
Preparing Solutions: Dilution
M1 x V1 = M2 x V2
M1 x V1
M2 x V2
(mol/L)1 x L1 = (mol/L)2 x L2
mol1 = mol2
Solution 1Solution 1
ConcentratedConcentrated Solution 2 Solution 2 DilutedDiluted
Moles of chemical from Solution 1
Moles of chemical in Solution 2
AqueousReactions
Preparing Solutions by DilutionM1 x V1 = M2 x V2
How would you prepare 500 mL of a 1.0 M solution from a 2.0 M solution?
M
VM V
1
221 L 0.25
mol/L) (2.0
)L 500.0)(mol/L (1.0
M1 x V1
M2 x V2
mol/L1 x L1 = mol/L2 x L2
mol1 = mol2
AqueousReactions
Preparing Solutions by Dilution
{*SolnByDilution}
M1 x V1 = M2 x V2
How would you prepare 500 mL of a 1.6 x 10-4 M solution from a 4.0 x 10-2 M solution?
M
VM V
1
221 L 0.002
mol/L) 10 x (4.0
)L 500.0)(mol/L 10 x (1.6
2-
4
M1 x V1
M2 x V2
mol/L1 x L1 = mol/L2 x L2
mol1 = mol2
AqueousReactions
2003A #5
AqueousReactions
2005 B
AqueousReactions
AqueousReactions
AqueousReactions
2006 (A)
100 mL Vol Flask
Prepare:100 mL1.0M NaOH
From:3.0M NaOH
AqueousReactions
A volumetric analytical technique in which one can determine the concentration of a solute in a solution, by making it react with another solution of known concentration (standard).
Determining the Concentration of Solutions by Titration
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
Solution of known concentration (MB) (Standard)
Solution of unknown concentration (MA?)
Neutralization:
# moles(acid) = # moles(base)
React a known volume (VA) Measure reacting volume (VB)
(MxV)acid = (MxV)base
AqueousReactions
Titrations
moles base () = MBVB
moles acid () = MAVA
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
acid
MM-g
1 g#
Does the acid need to be in solution? Can you titrate a solid acid to determine number of moles of acid?
moles base () moles acid () =
AqueousReactions
Titration
Neutralization: #moles1(acid) = #moles2(base)
ACID (clear) ↔ BASE (red)
Phenolphthalein indicator
{A-B w/o Ind} {*A-B w Ind}
AqueousReactions
A pH meter or indicators are used to determine when the solution has reached the equivalence point, at which the stoichiometric amount of acid equals that of base.
Methyl orange in acid
Titration: measuring the equivalence point
Phenolphthalein in base
AqueousReactions
Titration: pH vs. Volume Graph
Excess acid
Excess base
Acid = Base
{Titration2}
AqueousReactions
Titration Calculations: Stoichiometry using Molarities
MAVA = MBVB
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
Neutralization: #moles(acid) = #moles(base)
Problem: When 20.0 mL of an HCl solution of unknown concentration was titrated with a STANDARD 0.1M NaOH solution, a volume of 10.3 mL of NaOH was required to neutralize the acid. What is the concentration of the HCl solution?
V
VM M
A
BBA
L) (0.020
(0.0103L) mol/L) (0.100 HCl M 0.052
AqueousReactions
Using Molarities inStoichiometric Calculations
(M x V)acid = (M x V)base
HN + MOH MN + HOH
(M x V)acid
(M x V)baseη base
η acidg acid
g base
MM-g
mole 1
MM-g
mole 1
AqueousReactions
mol of soluteL of solution
=Molarity (M)
MM-g
mole 1 Solute g # moles
2H3PO4 + 3 Ca(OH)2 6 HOH + Na3PO4
BxAxMA x VA MB x VB
B or Ax = coefficients from balanced equations Where
For titrations:
=
AqueousReactions
Solution Stoichiometry Problems: Molarity
A
BBA V 3
V2M M
2H3PO4 + 3 Ca(OH)2 6 HOH + Na3PO4
BxAx
MA x VA = MB x VB
2 3
Problem: A volume of 16.3 mL of a 0.30M Ca(OH)2 solution was used to titrate 25.00 mL H3PO4. What is the concentration of H3PO4 in the solution of unknown concentration?
mL 25.00 3
mL 3.160.30M 2 = 0.13 M H3PO4
baseacid ?
Base 3
2
Acid
ORbase
base
acid
acid
32
B or Ax = coefficients from balanced equations Where
AqueousReactions
Titrations of Polyprotic Acids
In these cases there is an equivalence point for each dissociation.
AqueousReactions
AqueousReactions
(4) Oxidation-Reduction (Redox)
Reactions
These Reactions fall in the categories of either Double or
Single Replacement Reactions
AqueousReactions
Oxidation-Reduction ReactionsOxidation occurs when an atom or ion loses electrons.
Reduction occurs when an atom or ion gains electrons.
Zn Zn Zn
Zn Zn Zn Zn
Zn2+ ZnZn2+Zn
O OO2- O2-
2 2
2 Zn (s) + O2 (g) 2 Zn (s) + O2 (g) 2 ZnO (s)
AqueousReactions
Oxidation-Reduction Reactions
One cannot occur without the other.
2 Zn (s) + O2 (g) 2 ZnO (s) {oxy-red1}
AqueousReactions
How can we determine when an oxidation-reduction reaction has
occurred?
To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number (charge) to each element in a neutral compound or charged entity.
Zn (s) + 2 HCl (aq)
Zn (s) + 2 CuNO3 (aq)
Cu (s) + 2 AgNO3 (aq)
ZnCl2 (aq) + H2 (g)
2 Cu (s) + Zn(NO3)2 (aq)
2 Ag (s) + Cu(NO3)2 (aq)
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) + H2S (g)
AqueousReactions
Rules for Determination of Oxidation Numbers
1. Elements in their natural elemental form have an oxidation number of 0.
2 Fe (s) + O2 (g) 2 FeO (s)
Feo O2o
{Fe+O2}
• The oxidation number of a monatomic ion is the same as its charge.
AqueousReactions
Oxidation Numbers
• Nonmetals in copounds tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
2 Fe (s) + O2 (g) 2 FeO (s)
O2-Feo O2o
Peroxide ion O22-
HCl NaH
2. Oxygen has an oxidation number of −2, except in the peroxide ion in which it has an oxidation number of −1.
3. Hydrogen is −1 when bonded to a metal, +1 when bonded to a nonmetal.
AqueousReactions
Oxidation Numbers• Nonmetals tend to have negative oxidation
numbers, although some are positive in certain compounds or ions.4. Fluorine always has an oxidation number of −1.
5. The other halogens have an oxidation number of −1 when they are negative (they can have positive oxidation numbers, however, most notably in the polyatomic oxyanions).
BrO- ClO3-
Br + (-2) = -1Br = +1
Cl + 3(-2) = -1
Cl = +5
hypobromite chlorate
AqueousReactions
Oxidation Numbers
6. The sum of the oxidation numbers in a neutral compound is 0.
7. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.
2 Fe (s) + O2 (g) 2 FeO (s)
[Fex + O2- ] = 0Feo O2o
PO43- SO4
2-
P + 4(-2) = -3
S + 4(-2) = -2
P = +5
S = +6
AqueousReactions
Combustion Reaction:
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Oxidation Reduction Reactions
2 Mg (s) + O2 (g) 2 MgO (s)
2 Fe (s) + O2 (g) 2 FeO (s) 2 Fe (s) + 3 Cl2 (g) 2 FeCl3(g)
2 NO (g) + O2 (g) 2 NO2 (g)
Combination (Synthesis) Reactions
Displacement Reactions: Zn (s) + 2 HCl (aq)
Zn (s) + 2 Cu(NO3) (aq)
Cu (s) + 2 AgNO3 (aq)
Cu (s) + 2 HNO3 (aq)
Zn (s) + 2 HNO3 (aq)
ZnCl2 (aq) + H2 (g)
2 Cu (s) + Zn(NO3)2 (aq)
2 Ag (s) + Cu(NO3)2 (aq)
Cu2+ (aq) + NO2 (g) + H2O
Zn2+ (aq) + NO2 (aq) + H2O
{Cu+AgNO3}
{OxyRed}
{Mg+O2}
{*Cu+HNO3}
{*Zn+HNO3}
{Fe+O2}
{*Fe+Cl2}
{NO+O2}
Cu in Brass Lab
(0) C + 2(-2) = 0 (+1) + (-2) = 0C + 4(+1) = 0
AqueousReactions
• In displacement reactions, ions oxidize an element.• The ions, then, are reduced.
Zn (s) + SnCl2 (aq) Sn (s) + ZnCl2 (aq){*Zn+SnCl2}
Oxidation Reduction Reactions
AqueousReactions
In this reaction, silver ions oxidize copper metal. Cu(s) + 2 Ag+
(aq) + 2 NO3-(aq) Cu2+
(aq) + 2 NO3-(aq) + 2 Ag (s)
{*Cu+AgNO3}
Oxidation Reduction Reactions
AqueousReactions
The reverse reaction, however, does not occur.
Cu2+ (aq) + 2 Ag (s) Cu (s) + 2 Ag+ (aq) x
x
Oxidation Reduction Reactions
AqueousReactions
Activity Series
AqueousReactions
Most active Non-Metal
Most active Metal
Table Continues
AqueousReactions
Most active Non-Metal
Most active Metal
Continuation
AqueousReactions
Redox Reactions
Cl2 + 2 KBr 2 KCl + Br2
1.
2.
AqueousReactions
2006 (B)
AqueousReactions
AqueousReactions
AqueousReactions
Difficult Questions
AqueousReactions
Expressing Concentrations of
Solutions: Molarity (& Normality*)
* For MDC students only!
AqueousReactions
moles of soluteLiters of solution
=Molarity (M)
BxAx
B or Ax = coefficients for the acid (A) and the base (B) from the balanced neutralization equations
Where
MA x VA = MB x VB
Ax
(mol/L)A x LA (mol/LB) x LB
Bx
Ax Bx
mol molA B=
=
xA HN + xB MOH MN + HOH
AqueousReactions
BxAxMA x VA MB x VB
Ax
(mol/L)A x LA (mol/LB) x LB
Bx
Ax Bx
mol molA B=
=
=
BxAxmolesA MB x VB=
AqueousReactions
For titrations:
MM-g
solute g #
MM-g
mole 1 solute g # moles
AAA
MB x VBAx Bx =
Since
xA HN + xB MOH MN + HOH
AqueousReactions
mol of soluteL of solution
M =
Molarity (M) vs. Normality (N)
n
MM-g EW-g
n
equiv of soluteL of solution
N =
MM-g
mole 1 Solute g # moles
EW-g
mole 1 Solute g # sequivalent
A/B = # H+ or #OH-
nRedox = #e- involved in balanced
redox equation.
Where:M = N
When n = 1
That is when using HCl, KHP NaOH
But not when using H2SO4, Ca(OH)2
Lesson for MDC students only:
AqueousReactions
Acid g-MM (g/)
+ H20 to
HCl 36 g + 1L =
H2SO4 98 g + 1L =
H3PO4 98 g + 1L =
Molarity (M) vs. Normality (N)
Molarity (/L) Normality (eq/L)
1M
1M
1M
1N
2N
3N
=
=
=
g-EW
36/1
=36
98/2
=49
98/3
=32.7
Eq(g/gEW)
36/36
98/49
98/33
AqueousReactions
2M H3PO4 3M Ca(OH)2 Using Molarity
1N H3PO4 1N Ca(OH)2 Using Normality
n
2H3PO4 + 3 Ca(OH)2 6 HOH + Na3PO4
N = M or M = N
NA x VA = NB x VB
n
Using Normality for titrations: