chem 26 - breakthelight · chem 26.1 midterms review prepared by: cmfr. expt 1: statistical...
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Chem 26.1
Midterms Review
Prepared by: CMFR
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Expt 1: Statistical Concepts
• Significant Figures
• Accuracy vs. Precision
• Mean, Median
• Average deviation, variance, standard deviation, relative standard deviation, coefficient of variation, pooled standard deviation, range and relative range
• Absolute and relative error
• Confidence Limits
• Q-Test
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Expt 1: Statistical Concepts
• Use of analytical balance
• Weighing techniques
• Types of errors:
– Systematic (determinate)
– Random (indeterminate)
– Gross
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Expt 2: Solution Preparation
• Ways of expressing concentration
• Aliquot factor vs. Dilution factor
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Expt 3: Kinetics of Thiosulfate and HCl
• Method of Initial Rates
– Ratio and proportion
• Effect of temperature on reaction rate: Arrhenius equation k=Ae-Ea/RT
• Rate law for reaction of thiosulfate with HCl: rate = k[S2O3
2-]
• Reaction mechanisms: only the rate-determining steps appear in the rate law
– Thus the correct mechanism is multi-step process b or 4 (see your lab manual)
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Expt 4: Common Ion Effect and Buffers
• Le Chatelier’s Principle!
• Common ion effect – consequence of Le Chatelier’s principle
– Salt is less soluble in solution containing an ion which is the same as one of the constituent ions of that salt
• Buffer solution
– Resists large changes in pH
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Expt 4: Common Ion Effect and Buffers
Different approaches to calculating pH:
• ICE table
• Henderson Hasselbalch equation
Color changes brought about by the indicator also signify changes in pH.
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Expt 5: Shifting Equilibrium• Q = Keq equilibrium
• Q > Keq (right to left/backward)
• Q < Keq (left to right, more products)
• Properties of Keq when adding/subtracting equations– Adding equations: Keq’s are multiplied
– Subtracting: Keq’s are divided
– Multiplying by a coefficient: raise Keq to the nth power where n = coefficient multiplied to equation
• Different types of Keq’s– Ka, Kb, Ksp, Kf, etc…
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Expt 5: Shifting Equilibrium
Cu2+ + OH- <-> Cu(OH)2(s) Keq = Ksp [Cu(OH)2]
Cu(OH)2(s) <-> Cu2+ + 2OH- Ksp [Cu(OH)2]
H2C2O4 <-> H+ + HC2O4- Ka1 (H2C2O4)
HC2O4- <-> H+ + C2O42- Ka2 (H2C2O4)
2(OH- + H+) <-> H2O** 1/Kw
Cu2+ + C2O42- <-> CuC2O4 1/Ksp(C2O4)
Overall eqn: Cu(OH)2 + H2C2O4 <-> CuC2O4 + H2O
Keq =
[(Ksp [Cu(OH)2])(Ka1)(Ka2)]/[Kw2Ksp(CuC2O4)]
• Reactions in Test tubes 1-6
1. + water
2. + H2C2O4
** considered because there is base initially present in the soln.
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Expt 5: Shifting Equilibrium
3. + ZnCu(OH)2(s) <-> Cu2+ + 2OH- Ksp [Cu(OH)2]
Cu2+ + Zn(s) <-> Cu(s) + Zn2+ Kredox
Zn2+ + 2OH- <-> Zn(OH)2 1/Ksp[Zn(OH)2]
Overall eqn: Cu(OH)2 + Zn(s) <-> Cu(s) + Zn(OH)2
Keq = [(Ksp [Cu(OH)2])(Kredox)/[Ksp(Zn(OH)2)]
4.+ HNO3Cu(OH)2(s) <-> Cu2+ + 2OH- Ksp [Cu(OH)2]
2(OH- + H+) <-> H2O** 1/Kw
Overall eqn: Cu(OH)2 + 2H+ <-> Cu2+ + 2H2O
Keq = [(Ksp [Cu(OH)2])/Kw2
** considered because there is base initially present in the soln.
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Expt 5: Shifting Equilibrium
5. + excess NH3Cu(OH)2(s) <-> Cu2+ + 2OH- Ksp [Cu(OH)2]
Cu2+ + 4NH3<-> [Cu(NH3)4]2+ Kf[Cu(NH3)4]2+
Overall eqn: Cu(OH)2 + 4NH3 <-> 2OH- + [Cu(NH3)4]2+
Keq = (Ksp [Cu(OH)2])(Kf[Cu(NH3)4]2+)
6. + Na3PO4Cu(OH)2(s) <-> Cu2+ + 2OH- Ksp [Cu(OH)2]
2(PO43- + H2O <-> HPO4
2- + OH-) Kw2[Ka3 (HPO42- )]2
Overall eqn: Cu2+ + 2PO4
3- <-> Cu(OH)2(s) + 2HPO42-
Keq = Kw2/[Ka3 (HPO4
2- )]2(Ksp[Cu(OH)2])
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Expt 5: Shifting Equilibrium
Ksp = (s)(2s)2 for Cu(OH)2
Cu2+ + 2OH- <-> Cu(OH)2
- Common ion effect vs. diverse ion effect
- Effect of solvent
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Expt 6: Ksp of Ca(OH)2
Ca2+ + 2OH- <-> Ca(OH)2
• [Ca2+] = [OH-]/2
• Ksp’ = [Ca2+][OH-]2
• Ksp = γ(Ca2+)[γ(OH-)]2 [Ca2+][OH-]2
= γ(Ca2+)[γ(OH-)]2Ksp’
• Debye-Hückel equation
• Ionic strength
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Expt 7: Soda Ash
V1 (Vphth) V2 (Vm.o.)
NaOH
>0
Na2CO3 = <NaHCO3 0
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God bless on your exam!!!