CHEMISTRY 120 FINAL EXAM

Name:________________________ I.D. #___________________

D.Klapstein April 2012 ********************************************************************************************** This is a three (3) hour exam. Read over the entire exam before beginning. There should be 37 different questions in this exam. If your exam copy does not contain 37 different questions notify the instructor immediately. Answer Part I (questions 1 - 30) on the multiple choice answer card. Use a black pencil to indicate your answer; press firmly on the pencil to leave a dark mark indicating your answer. Be sure to put your NAME, I.D. number and COURSE on the multiple choice answer card. Answer Part II (questions 31 - 37) in the space provided. Be sure to put your NAME and I.D. number on the exam.. At the end of the exam, hand in both the multiple choice answer card and exam paper. It is your responsibility to insure that your answers are legible. READ ALL QUESTIONS CAREFULLY A Periodic Table is found at the end of the exam. Other useful data: 1 standard atmosphere = 760.0 mm Hg = 101.325 kPa.

Avogadro's Number = 6.022 × 1023

Universal gas constant R = 0.08206 L atm/(K mol) = 62.37 mm Hg L/(K mol)

Standard Molar Volume = 22.414 L Kw = 1.00 × 10-14

= 8.3144 L kPa/(K mol) = 8.3144 J /(K mol) Standard molar volume = 22.414 L

Speed of light c = 2.9979  108 m s-1

Planck's Constant h = 6.626  10-34 J s

charge on an electron = 1.602  10-19 C

1 Faraday = 96,485 Coulombs

Arrhenius equation: k = A exp(Ea/RT)

Integrated Rate Laws:

th

0 order: 1st order: 2nd order:

[A] = -kt + [A]0 ln[A] = -kt + ln[A]0 1/[A] = kt + 1/[A]0

For a quadratic equation of the form ax2 + bx + c = 0, x

 b  b 2  4ac 2a

Henderson-Hasselbalch: pH = pKa + log ([conj. base]/[acid]) G = H - TS

G = - RT ln K

1 ampere (A) = 1 Coulomb/s

1 J = 1 V  1C

E  E 

G = - nFE

RT 0.0592 ln Q  E   log Q at 25C  nF n

********************************************************************************************** Part I – Multiple Choice. Use a pencil to mark the answer card. Value: 1 mark each ********************************************************************************************** 1. A sample of nickel(II) phosphate heptahydrate [Ni3(PO4)27H2O] contains 0.125 mol of phosphorus. How many moles of water does it contain? a. 0.0357 mol

b. 0.438 mol

c. 0.875 mol

d. 1.75 mol

e. none of these

2. Consider the unbalanced chemical equation Al(OH)3 + H2CO3  Al2(CO3)3 + H2O When balanced with the smallest whole number coefficients, the coefficient of H2CO3 will be a. 1

b. 2

c. 3

d. 5

e. none of these

3. For the following question, assume that the reaction between phosphorus and chlorine gas to produce phosphorus pentachloride goes as far as possible to give the product P4 + 10 Cl2  4 PCl5 If 0.010 mol of P4 is combined with 2.00 L of chlorine gas at STP, how many moles of PCl 5 would theoretically be produced? a. 0.0357 mol

b. 0.0400 mol

c. 0.0757 mol

d. 0.0893 mol

e. none of these

4. An element M is a main-group metal that reacts with oxygen to give the compound M2O. If the metal forms a chloride that is 21.06% Cl by mass, the element must be a. Sr

b. Rb

c. Na

d. Cs

e. none of these

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5. Which of the following generalizations can be made about intermolecular forces? a. b. c. d. e.

Intermolecular forces are generally stronger than covalent bonds. Intermolecular forces are more directional than covalent bonds. Intermolecular forces operate at shorter ranges than covalent bonds. All of these are valid generalizations. None of these are valid generalizations.

6. Potassium chloride is very soluble in water due to the formation of a. ion-ion interactions with water. b. ion-dipole interactions with water. c. dipole-dipole interactions with water.

d. dispersion force interactions with water. e. none of these

7. Which of the following would be expected to have the highest normal boiling point? a. Br2

b. BrCl

c. HBr

d. LiBr

e. cannot be predicted

8. The use of molarity for the accurate expression of solution composition has the disadvantage of a slight dependency on temperature. This disadvantage is also seen when concentrations are expressed in a. molality.

b. mole fraction.

c. mass percent.

d. all of these.

e. none of these.

9. A student combines 320 mL of a 1.00 M HCl solution with 1.18 L of a 0.125 M HCl solution to give a total volume of 1.50 L. The molarity of the HCl in the final solution will be a. 0.750 M

b. 0.312 M

c. 0.213 M

d. 0.175 M

e. none of these

10. Raoult's Law describes a simple relationship between the vapor pressure of an ideal solution and the vapor pressure of pure solvent. Non-ideal solutions, however, show deviation from this ideal behavior. Solutions with vapor pressures lower than predicted (negative deviation) are the result of a. b. c. d. e.

weak attractive forces between solute and solvent. stronger attractive forces between solute and solvent than between molecules of solvent. weak repulsive forces between solute and solvent. strong repulsive forces between solute and solvent. none of these

11. A researcher adds 1.00 g of a protein to enough water to produce 150 mL of solution. At 37C the osmotic pressure is found to be 0.0028 atm. The molar mass of the protein must be approximately a. 60,600 g mol-1 b. 121,000 g mol-1 c. 165,000 g mol-1

d. 343,000 g mol-1

e. none of these

12. A property that all colloidal suspensions have in common is a. b. c. d. e.

particle sizes larger than single molecules. the ability to scatter light as it passes through them. instability to the addition of salts to the background medium. all of these are properties of colloidal suspensions. none of these are properties of colloidal suspensions.

13. An aqueous ammonia solution at 25C has an [OH-] = 6.30 x 10-4 M. The pH of the solution is therefore a. 3.20

b. 4.70

c. 6.30

d. 10.8

e. none of these

14. A process will be spontaneous under all conditions when a. both H and S are positive b. both H and S are negative

c. H is positive and S is negative d. H is negative and S is positive

15. In the following galvanic cell, the cathode is Ag Ag+ (0.010 M )  MnO4- , Mn2+ Pt a. Ag

b. Ag+

c. MnO4-

d. Mn2+

e. Pt

16. An electrochemical cell in which current is applied to force a nonspontaneous redox reaction to occur is called a. an electrolytic cell

b. a galvanic cell

c. a cathode

17. Reaction rates generally a. b. c. d.

are greatest at the beginning of a reaction and decrease with time are smallest at the beginning and increase with time are constant throughout a reaction increase and decrease alternately as the reaction proceeds

d. an anode

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18. In the rate law of an elementary reaction, the exponents are a. the same as the coefficients in the balanced reaction b. always one

c. all equal to each other d. none of these

19. Molecularity is a. b. c. d.

a statement about the reaction rate the number of molecules that come together in an elementary process a statement about the number of reactant versus product molecules all of these

20. When a catalyst is added to a reaction system, a. the equilibrium position of the reaction is shifted b. the H of the reaction is changed

c. the reaction rate is changed d. all of these

21. 56 28 X is an isotope of the element a. barium

b. zinc

c. silicon

d. nickel

e. aluminum

22. Which of the following statements is true about the reaction 2A  B + C which is first order in A and first order overall? a. b. c. d. e.

The rate of the reaction will decrease at higher concentrations of B and C. The time required for one half of A to react is directly proportional to the quantity of A. The rate of formation of C is twice the rate of reaction of A. The rate of formation of B is the same as the rate of reaction of A. None of these

23. Which statement is NOT correct? a. b. c. d. e.

Activation energy is always the same for forward and reverse reaction. If the forward reaction is endothermic, the reverse will be exothermic. In an endothermic reaction, activation energy is usually greater than the enthalpy. An activated complex has higher energy than any molecule contributing to it. The activated complex will be the highest on the energy profile.

24. How will addition of sodium acetate to an acetic acid solution affect the pH? a. lower the pH b. the pH will not change c. the solution becomes hotter

d. the pH cannot be measured e. raises the pH

25. Proton donor is an abbreviated definition of: a. Brønsted-Lowry base

b. Brønsted-Lowry acid

c. Lewis base

d. Lewis acid

e. none of these

26. If the element with the electron configuration shown below existed, it would belong to which group? [Rn]5f14 6d10 7s2 7p4 a. boron group

b. carbon group

c. nitrogen group

d. oxygen group

e. fluorine group

27. Which one of the following has the highest first ionization energy? a. C

b. B

c. O

d. N

e. Be

28. Generally, there is a decrease in atomic size as one moves a. down a group b. up a group c. from left to right across a period

d. from right to left across a period e. both b and c

29. Solutions are made that contain 0.1 moles of each of the following compounds below in 100 g of H2O. Choose the compound whose solution will have the lowest freezing point. a. MgCl2

b. KClO3

c. CO2

d. MgSO4

e. NaBr

30. A solid was found to be a good insulator, brittle, and to have a high melting point. The substance readily conducted electricity when molten. The substance was a _____ solid. a. molecular

b. covalent

c. ionic

d. metallic

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********************************************************************************************* PART II - ANSWER ALL THE FOLLOWING QUESTIONS IN THE SPACE PROVIDED Each question has a value of 10 marks ********************************************************************************************* 31. Maleic acid is prepared by the catalytic oxidation of benzene. It is a dicarboxylic acid, i.e. it has two carboxylic acid (COOH) groups, and contains only the elements C, H, and O. (a) Combustion of 0.125 g of the acid gives 0.190 g of CO2 and 0.0388 g of H2O. Determine the empirical formula. (b) A 0.261 g sample of the acid requires 34.60 mL of 0.130 M NaOH solution for complete titration (so that the H+ ions from both carboxylic acid groups are used). What is the molecular formula of the acid? (c) Draw the best Lewis structure for the acid and describe the orbital hybridizations used by the C atoms. 32. An electrochemical cell is based on the following half-reactions: -

Fe2+(aq) + 2e → Fe(s) 2 H+(aq) + 2e → H2(g)

E = -0.440 V E = 0.000 V -3

where the iron compartment contains an iron electrode and [Fe2+] = 1.00  10 M and the hydrogen compartment contains a platinum electrode, hydrogen gas with a pressure of 1.00 atm, and an aqueous solution of a weak acid HA, at an initial concentration of 1.00 M (a) Write a balanced equation for the product-favored reaction that occurs in this cell under standard conditions. (b) Determine the standard cell potential E. (c) If the observed cell potential is 0.333 V at 25C, calculate the Ka value for the weak acid HA. 33. The net reaction for the two-electron transfer process occurring in a lead-acid storage battery can be represented as: Pb(s) + PbO2(s) + 2 H2SO4(aq)  2 PbSO4(s) + 2 H2O(l) E = +2.041 V (a) A typical battery might be rated at “80 ampere-hours (A-h)”. This means that it has the capacity to deliver 80. A for 1.0 h (or 1.0 A for 80. h). How many grams of lead metal would be consumed in order to deliver 1.0 amperes for 80. h? (b) What is the equilibrium constant for the reaction under standard conditions? 34.

At 65C, the half-life for the first-order decomposition of N2O5(g) is 2.38 minutes. N2O5(g)

→ 2 NO2(g) + ½ O2(g)

If 1.00 g of N2O5 is introduced into an evacuated 15.0-L flask at 65C, (a) What is the initial partial pressure, in mmHg, of N2O5(g)? (b) What is the partial pressure, in mmHg, of N2O5(g) after 9.00 minutes? (c) What is the total gas pressure in the flask, in mmHg, after 9.00 minutes? 35. Carbon dioxide is being studied as a source of carbon atoms for synthesizing organic compounds. One possible reaction involves the conversion of CO2 to methanol, CH3OH. CO2(g) + 3 H2(g) → CH3OH(g) + H2O(g) Given Data: Hf (kJ/mol) S (J/(mol K))

CO2(g) -393.5 213.7

H2(g) 0.0 130.7

CH3OH(g) -200.7 239.8

H2O(g) -241.8 188.8

(a) Determine G and state whether this reaction proceeds to any significant extent at 25C. (b) Is the production of CH3OH(g) favoured by raising or lowering the temperature from 25C? Explain. (c) Determine Kp for this reaction at 500 K (d) If CO2(g) and H2(g), each initially with a partial pressure of 1.00 atm, react at 500 K, determine the equilibrium partial pressure of CH3OH(g).

Chemistry 120 Exam – April 2012

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36. (a) The following two compounds are oxoacids (the acidic H is bonded to an oxygen). Draw a reasonable Lewis structure and predict the geometry about the central atom. Use your structures to predict which one of the compounds will be a strong acid and which will be a weak acid. Explain your choices. HNO2

HNO3

(b) A component of ‘hard water’ is dissolved CaSO4. A particular water sample has 131 ppm of CaSO4 (i.e. 131 g 6 CaSO4 per 10 g water). If this water is boiled in a kettle, approximately what fraction of the water must be -6 evaporated before CaSO4(s) begins to precipitate? Ksp of CaSO4(s) is 9.1  10 . Assume the density of all solutions is 1.00 g/mL. 37. (a) Write complete structural formulas for each of the following compounds: (i) 5-chloro-3-ethyl-Z-2-pentene

(iv) 1,3-diethylbenzene

(ii) 5-methylheptanal

(v) 3-octanol

(iii) 2-butyne (b) Give the IUPAC (or systematic) names of the following compounds: O (i)

CH3CH2CH2CH2

(ii)

C OH

CH3 CH CH3 OH

O (iii)

(iv)

CH3 CH C

CH3

CH3

(v)

Bonus Questions (two marks)! The Sydney Tar Ponds have received much press coverage. One class of contaminants found there are PCBs (polychlorinated biphenyls). For one bonus mark provide the chemical structure of a PCB. The ‘host’ in the film series we viewed in the tutorial sessions was Roald Hoffmann. For one bonus mark, what is he best known for (other than this film series)?

The End!