Chem 26.1

Midterms Review

Prepared by: CMFR

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

Expt 1: Statistical Concepts

• Use of analytical balance

• Weighing techniques

• Types of errors:

– Systematic (determinate)

– Random (indeterminate)

– Gross

Expt 2: Solution Preparation

• Ways of expressing concentration

• Aliquot factor vs. Dilution factor

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)

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

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.

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…

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.

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.

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])

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

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

Expt 7: Soda Ash

V1 (Vphth) V2 (Vm.o.)

NaOH

>0

Na2CO3 = <NaHCO3 0

God bless on your exam!!!