Cabrillo College Chemistry 1B Name:______________________ Circle Lab Section (1pt bonus)

Final Exam Spring 2004 Score:_____________

(1) MW 11:10 am

1. (15 pts) The initial rate of the reaction

[Cr(NH3)6]3+(aq)

+

H2O(l)

Æ

(2) TTH 8:00am

(3) TTH 2:30pm

[Cr(NH3)5(H2O)]3+(aq) +

NH3(aq)

at 25oC was measured using different initial concentrations of [Cr(NH3)6]3+(aq) . Results are summarized in the table below. Experiment Initial Conc. Initial Rate Number [Cr(NH3)6]3+(aq), M mol/Lmin 1 0.100 9.50 x 10-7 2 0.0500 4.80 x 10-7 3+ (2pts)(a) Show how you would obtain the order of the reaction with respect to [Cr(NH3)6] (aq) ? What 3+ is the order of the reaction with respect to [Cr(NH3)6] (aq) ? Show work:

Answer:

order = ________

(2pts)(b) What is the calculated value of the average rate constant, k, at 25o? Show work:

Answer:

k = _______________

(2pts)(c) What is the calculated half-life of the reaction at 25oC? Show work:

Answer:

t1/2 = ______________

(4pts)(d) If the value of the rate constant, k, is 8.00 x 10-5min-1 at 40oC, what is the activation energy for this reaction? Show work:

Answer:

Ea = ______________

(1pts)(e) Why can’t the order of the reaction with respect to water be measured in aqueous solution? Brief Discussion:

(2pts)(f)Name: [Cr(NH3)6]3+

____________________________________________

[Cr(NH3)5(H2O)]3+____________________________________________ (2 pts)(g) The [Cr(NH3)6]3+ ion has a yellow color, but when one NH3 ligand is replaced by H2O to give [Cr(NH3)5(H2O)]3+, the color shifts to red. Is this shift in the expected direction? Explain.

2. (15pts) The Co(en)33+ ion has a maximum absorption at 470 nm, appears yellow, but when the ethylenediamine (en) ligands are replaced by F- ligands the complex ion color changes to blue with a maximum absorption at 615nm. a)(1pts) What is the oxidation number of cobalt in both these compounds? (Hint it is the same number) Oxidation Number = b)(1pts) What is the coordination number in both these compounds? Coordination Number = c)(4pts) What is the calculated value for the crystal field splitting energy (kJ/mol) when the maximum absorption is 470 nm? At 625nm? (Planck’s constant = 6.626 x 10-34 J sec, Avogadro’s number = 6.023 x 1023 /mol, speed of light = 3.00 x 108 m/sec, 1.0m =109nm, 1kJ =1000J) Show Work:

CFSE@ 470 nm=

CFSE@ 635nm=

d) (4pts) Sketch the geometry of both these compounds, if any isomers are possible, what type?

e)(5pts) If the electron pairing energy is 215 kJ/mol, utilize the crystal field theory and write d orbital energy level diagrams to show why the color and magnetic properties are different for these two compounds. Give a brief discussion (Hint: buz words to include are strong field, weak field, high spin, low spin, paramagnetic and diamagnetic)

3. (15pts) Find the concentrations of Cu2+(aq), NH3(aq), and Cu(NH3)42+(aq) at equilibrium when 0.10 mol Cu2+(aq) and 0.40 mol NH3(aq) are made up to 1.00 L of solution. The dissociation constant, Kd, for the complex Cu(NH3)42+(aq) is 2.1 x 10-13. (Hint: Assume that the initial reaction goes to completion then the complex ion dissociates.) a)(1pts) Write a complete balanced reaction for the dissociation of the complex ion.

b)(4pts) Write an ICE table. I C E

c)(6pts)Calculate the equilibrium concentrations. Show Work:

Answer:

Cu(NH3)42+]=_____________ [Cu2+]=____________[NH3]=_________________

d)(4pts) Calculate the change in standard free energy (∆Go) for the reaction.

Answer:

∆Go=_____________________

4. (15 pts). The combustion of 2.18 g of liquid acetic acid, C2H4O2, raised the temperature of a bomb calorimeter from 23.46 oC to 26.54 oC. The total heat capacity, Ccal, of the bomb calorimeter was 10.31 kJ/oC. (2pts) a. Write a balanced equation for the combustion of glucose with oxygen to form carbon dioxide and water.

___ C2H4O2(l) + ___ O2(g) Æ ___ CO2(g) + ___ H2O(l) (5pts.) b. Calculate the constant volume change in internal energy of combustion (∆E) per mole of acetic acid combusted.

Answer:

_______________

(2 pts.) c. Calculate the change in enthalpy of combustion (∆H) per mole of acetic acid.

Answer:

_______________

(6 pts.) d. Given the thermodynamic values from the table located in your textbook. ∆Hof for CO2(g) = - 394 kJ/mol and ∆Hof for H2O(l) = - 286 kJ/mole Calculate the standard enthalpy of formation (∆Hof ) per mole of acetic acid.

Answer:

_______________

5. (15pts) The black silver sulfide discoloration of silverware can be removed by heating the silver article in a sodium carbonate solution in an aluminum pan. The reaction is + 2 Al(s) ÍÎ

3 Ag2S(s) ∆Gfo (kJ/mol) a)

-40

0

6 Ag(s)

+

0

3 S2-(aq) 86

+

2Al3+(aq) -480

(3pts)Calculate the change in standard free energy (∆Go) for the reaction.

∆Go =________________

b) (3pts)Calculate the standard cell potential (Eo) for the reaction.

Eo =______________ c)

(3pts)Calculate the equilibrium constant (K) for the reaction.

K = _________________ d) (6pts)Calculate the value of the standard reduction potential for the following half-reaction: (given the reduction potential from the table for Al3+(aq) + 3e- Î Al(s) Eredo =-1.66V Ag2S(s)

+ 2e-

Î 2 Ag(s)

+

S2-(aq)

Eredo = __________

6. (15pts) Match the following types of organic compounds in Column A with the structural formulas given in Column B. Place the letter of the correct classification type from Column A in the parenthesis next to the correct structural formula in Column B. Place the correct formula in Column C Give the correct IUPAC name for as many of the structural formulas as you can in Column D (1 bonus point/each). Bonus: Identify the compounds that are isomers of each other and indicate the type of isomerism in Column E.

Column A

Col B

a. b. c. d. e. f. g. h. i. j. k. l. m. n. o.

1.(___)

Alkane alkene alkyne cycloalkane aromatic alkylhalide alcohol ether aldehyde ketone carboxylic acid ester amine amide amino acid

Col C

Col D

Col E

______________________________________________________________ 2.(___) ______________________________________________________________ 3.(___) ______________________________________________________________ 4.(___)

______________________________________________________________ 5. (___)

______________________________________________________________ 6. (___)

______________________________________________________________ 7. (___)

______________________________________________________________ 8. (___)

______________________________________________________________ 9. (___)

______________________________________________________________ 10. (___)

7. (15 pts) A forensic chemist is developing a new acid base titration analysis for veronal (diethylbarbaturic acid) a weak monoprotic acid with a Ka = 3.92 E-8. a) (1pt)Write a balanced chemical equation for the ionization of veronal (HVer) in water. b) (4pts)What is the initial pH of a 0.020 M solution of veronal. Show work: suggest you show an ICE table

Ans. pH = c)

(4pts) What is the pH of 25.00 mL of 0.020 M solution of veronal after the addition of 10.00 mL of 0.025M of NaOH. (Hint: This point is not at the equivalence point)

Ans. pH = d) (4pts) Calculate the pH at the equivalence point. Show work:

Ans. pH = e)

(2pts)Circle your choice of indicator to use in this titration. Why? Indicator pKHIn 1. Methyl orange 3.46 2. Methyl red 5.00 3. Bromthymol blue 7.30 4. Phenolpthalein 8.50 5. Thymolphthalein 9.80

8. (15 pts) Cadmium metal is deposited from the aqueous solution of cadmium sulfate, CdSO4(aq), when an electric current of 1.51 A(amperes) flows through the solution for 156 minutes. 1 faraday =96500 coulomb a)(2 pts) Write a balanced net ionic half reaction for the reduction of cadmium ion to cadmium metal.

b)(4 pts) How many grams of cadmium metal is deposited?

c)(2 pts) Water must be oxidized if cadmium ion is reduced, write a balanced half reaction for the oxidation of water. ( HINT: oxygen gas and H+ are produced)

d)(4pts) How many liters of oxygen gas are produced at STP (1mole = 22.4 L)?

1.

Bonus:(10pts) (a) (2pts)What trends, if any, exist for Zeff across a period and down a

group?

(b) (2pts)How does Zeff influence atomic size, IE1, and EN across a period of elements?

(c) (2pts)Summarize the acid-base behavior of main-group metal and nonmetal oxides in water. How does oxide acidity in water change down a group and across a period?

(d) (2pts)If the leftmost element in a period combined with each of the other elements in the period, how would the type of bonding change form left to right? Explain in terms of atomic properties.

(e) (2pts)Hydrogen (H2) may act as a reducing agent or an oxidizing agent, depending upon the substance reacting with it. Using in turn, sodium (Na) and chlorine as the other reactant, write balanced equations for the two reactions and characterize the role of hydrogen in each.