2011 Chem 13 News Exam

UNIVERSITY OF WATERLOO

DEPARTMENT OF CHEMISTRY

12 MAY 2011

TIME: 75 MINUTES

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Carefully detach the last page. It is the Data Sheet.

1. At 25°C and 100 kPa, most of the known elements are

  1. monatomic gases
  2. diatomic gases
  3. liquids
  4. metallic solids
  5. non-metallic or semi-metallic solids

2. Which of the following series lists the compounds in order of increasing boiling point? (from lowest to highest)

  1. H2Te < H2Se < H2S < H2O
  2. H2S < H2Se < H2Te < H2O
  3. H2S < H2O < H2Se < H2Te
  4. H2O < H2S < H2Se < H2Te
  5. H2O < H2Te < H2Se < H2S

3. In which of the following compounds does oxygen have the highest oxidation state?

  1. CSO2
  2. H2O
  3. O2
  4. H2O2
  5. OF2

4. Which of the following processes is the most endothermic?

  1. H2O(l) → H2O(g)
  2. F(g) + e- → F-(g)
  3. NaCl(s) &xrightarrow{H_2O} NaCl(aq)
  4. Na(g) → Na+(g) + e-
  5. K+(g) + Cl-(g) → KCl(s)

5. Which of the following atoms has electrons in its outermost shell arranged in the configuration 4s24p3? Assume each atom is in its lowest energy state.

  1. Rb
  2. Kr
  3. As
  4. Cr
  5. Sb

6. The following reaction reaches equilibrium in a closed reaction vessel at 200 °C.

CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g), ΔH° = -206 KJ

Which of the following actions causes the reaction to proceed from left to right in order to restore equilibrium?

  1. increasing the volume of the container, holding temperature constant
  2. adding some CH4 gas to the system, with volume and temperature held constant
  3. adding some H2 gas to the system, with volume and temperature held constant
  4. increasing the temperature, holding the pressure constant
  5. removing some CO gas from the system, with volume and temperature held constant

7. At a certain temperature, the following equilibrium constants have been measured.

A2(s) + 2 B(g) ⇌ 2 C(g)   K1 = 36
D(s) + 2 E(g) ⇌ C(g)   K2 = 20

What is the equilibrium constant at the same temperature for the reaction below?

½ A2(s) + B(g) ⇌ D(s) + 2 E(g)

  1. 720
  2. 1.8
  3. 0.56
  4. 0.30
  5. 0.090

8. In a particular solution, [Br-] = 0.020 mol L-1 and [CrO42-] = 0.0030 mol L-1. Finely divided solid silver nitrate, AgNO3, is slowly added to the solution. What is [Br-] when Ag2CrO4(s) just begins to precipitate?

  Ksp
Ag2CrO4 1.9×10-12
AgBr 5.2×10-13
  1. 2.1×10-8 mol L-1
  2.  6.0×10-8 mol L-1
  3. 2.7×10-7 mol L-1
  4. 5.2×10-13 mol L-1
  5. 6.4×10-4 mol L-1

9. What is the formula of the stable compound formed by magnesium and nitrogen?

  1. MgN
  2. Mg2N
  3. Mg3N2
  4. Mg2N3
  5. MgN2

10. Which of the following ions has the smallest tendency to be protonated when dissolved in liquid acetic acid, CH3COOH(l)?

  1. hydroxide, OH-
  2. fluoride, F-
  3. chloride, Cl-
  4. bromide, Br-
  5. iodide, I-

11. X-ray radiation is more energetic than microwave radiation because

  1. photons of X-ray radiation travel faster than those of microwave radiation
  2. photons of X-ray radiation are heavier than those of microwave radiation
  3. X-ray radiation has a higher frequency than does microwave radiation
  4. X-ray radiation has a longer wavelength than does microwave radiation
  5. photons of X-ray radiation travel slower than those of microwave radiation

12. Which of the following contains only single bonds?

  1. NO+
  2. CO
  3. CN-
  4. N22-
  5. O22-

13. What is the empirical formula of a compound that is 66.64% carbon, 7.45% hydrogen and 25.91% nitrogen by mass?

  1. C3H4N
  2. C3H4N2
  3. C3H3N
  4. C4H4N
  5. C4H3N2

14. Let DC=C represent the C=C bond dissociation energy in ethene, H2C=CH2 and DC-C the C-C bond dissociation energy in ethane, H3C-CH3. How do these bond dissociation energies compare?

  1. DC=C equals DC-C
  2. DC=C is exactly equal to 2×DC-C
  3. DC=C is exactly equal to ½×DC-C
  4. DC=C is greater than DC-C but less than 2×DC-C
  5. DC=C is greater than 2×DC-C

15. Which of the following bonds is most polar?

  1. B-O
  2. B-F
  3. C-O
  4. C=O
  5. C-F

16. Consider the following energy level diagram for the reaction R → P.

Graph of Potential energy (y) vs. reaction progress (x). The potential energy increases with each PE valley (labeled R, X, Y, P) as the reaction progresses.

Which of the following statements is false?

  1. The conversion of R to P occurs via a two-step process.
  2. X and Y represent reaction intermediates.
  3. The conversion of R to P is endothermic.
  4. At equilibrium, the rate of conversion of R to P is equal to the rate of conversion of P to R.
  5. The rate-limiting step is the conversion of X to Y.

17. A solution in which the bromide concentration is 2.0×10-3 mol L-1 is in equilibrium with solid AgBr and solid AgI. What is the concentration of iodide ion?

  Ksp
AgBr 5.2×10-13
AgI 1.5×10-16
  1. 2.6×10-8 mol L-1
  2. 5.8×10-9 mol L-1
  3. 1.5×10-16 mol L-1
  4. 7.5×10-12 mol L-1
  5. 2.9×10-4 mol L-1

18. Consider the hydrogen halides HF, HCl, HBr and HI. Which of the statements about them is true?

  1. They are all strong acids.
  2. They are all weak acids.
  3. The boiling point increases with molar mass.
  4. The bond dissociation energy increases with molar mass.
  5. none of above

19. For the reaction below, Kc = 1.0×10-20.

2 A(g) + B(g) ↔ C(g)

In an experiment, 1.0 mol each of A, B and C are placed in an empty 1.0 L container and then the container is quickly sealed. When equilibrium is established, which of the following will be true?

  1. [A]<[B]<[C]
  2. [A]>[B]>[C]
  3. [A]=[B]=[C]
  4. [A]=[B]<[C]
  5. [A]>[B]=[C]

20. What percentage of CH3COOH molecules are ionized in 1.8×10-5 mol L-1 CH3COOH(aq)?

Ka(CH3COOH) = 1.8×10-5

  1. 1.8%
  2. 4.2%
  3. 42%
  4. 62%
  5. almost 100%

21. A technician recorded the following curve during a titration.

Titration curve: pH vs. volume of reagent added from burette (in mL). The curve starts at a high pH value (around 10) at 0 mL, indicating an initial basic solution. The pH gradually decreases as the reagent is added, then drops sharply around 30 mL (the equivalence point), before leveling off at a low pH value (around 2).

The curve represents the titration of a

  1. weak acid by adding strong base
  2. strong acid by adding weak base
  3. strong base by adding weak acid
  4. strong base by adding strong acid
  5. a weak base by adding strong acid

Use the table of standard reduction potentials given below to answer questions 22 through 25.

Half-Reaction E°
Ag+(aq) + e- ⇌ Ag(s) +0.80 V
O2(g) + 2H2O(l) + 4e- ⇌  4 OH-(aq) +0.40 V
2 H+(aq) + 2e- ⇌ H2(g) 0.0 V
Sn2+(aq) + 2e- ⇌ Sn(s) -0.14 V
Ni2+(aq) + 2e- ⇌ Ni(s) -0.25 V
Fe2+(aq) + 2e- ⇌ Fe(s) -0.41 V
Zn2+(aq) + 2e- ⇌ Zn(s) -0.76 V
2 H2O(l) + 2e- ⇌ H2(g) + 2 OH-(aq) -0.83 V
Al3+(aq) + 3e- ⇌ Al(s) -1.66 V

22. Which of the following is the strongest oxidizing agent under standard conditions?

  1. Ag+(aq)
  2. Ag(s)
  3. H+(aq)
  4. Al(s)
  5. Al3+(aq)

23. When Ag+(aq) reacts completely with exactly one mole of H2(g) under standard conditions, how many moles of solid Ag are produced?

  1. 1 mol
  2. 2 mol
  3. 0.5 mol
  4. 4 mol
  5. 0.25 mol

24. What is E° for the reaction 2 H2(g) + O2(g) ⇌ 2 H2O(l)?

  1. 1.23 V
  2. 0.43 V
  3. 4.06 V
  4. 0.43 V
  5. 2.06 V

25. Which of the following reagents would spontaneously reduce Ni2+(aq) to Ni(s) under standard conditions?

  1. Ag+(aq)
  2. Ag(s)
  3. Zn(s)
  4. Sn(s)
  5. Al3+(aq)

26. Consider the ions K+, Ca2+, Cl- and S2-. In which series are the species listed in order of decreasing radius? (from largest to smallest)

  1. S2->Cl->K+>Ca2+
  2. K+>Ca2+>S2->Cl-
  3. S2->Ca2+>Cl->K+
  4. Ca2+>K+>Cl->S2-
  5. Ca2+>K+>S2->Cl-

27. A solution is prepared by completely dissolving a solid mixture of NaOH and Mg(OH)2 in water. For the resulting solution, which of the following conditions must be satisfied?

  1. [Na+] = [Mg2+] = [OH-]
  2. [Na+] = [Mg2+] = 3 [OH-]
  3. [Na+] + [Mg2+] = 3 [OH-]
  4. [Na+] + 2 [Mg2+] = [OH-]
  5. [Na+] + [Mg2+] = [OH-]

28. What is the minimum volume of water needed to dissolve completely 1.0 g SrF2?

Ksp(SrF2) = 2.8 x 109

Sr, 87.62 g mol-1

F, 19.00 g mol-1

  1. 9.0 L
  2. 150 L
  3. 10.5 L
  4. 5.6 L
  5. 2.8 L

29. What is the molecular geometry of SF4?

  1. T-shaped
  2. tetrahedral
  3. see-saw
  4. square planar
  5. square pyramidal

30. In the incomplete equation below, NH3 acts as a Bronsted-Lowry acid and "X" represents a Bronsted-Lowry base. What is the conjugate base of NH3?

NH3 + X → ?

  1. X
  2. XH+
  3. NH4+
  4. NH2-
  5. OH-

31. What is the general trend observed for the first ionization energies of the elements in groups 13 through 17?

  1. Ionization energies tend to increase from left to right in a period, and are approximately constant in a group.
  2. Ionization energies tend to increase from left to right in a period, and decrease from top to bottom in a group.
  3. Ionization energies tend to decrease from left to right in a period, and increase from top to bottom in a group.
  4. Ionization energies tend to decrease from left to right in a period, and decrease from top to bottom in a group.
  5. Ionization energies are approximately constant in a period, and decrease from top to bottom in a group.

32. What is the hybridization of the sulfur atom in the SO32- ion?

  1. sp
  2. sp2
  3. sp3
  4. sp3d
  5. sp3d2

33. The phase diagram for an unidentified substance is shown below.

The image itself is a typical pressure-temperature phase diagram, which illustrates the conditions under which different phases of matter can exist. The diagram features a vertical axis for Pressure and a horizontal axis for Temperature, with labeled regions for the solid, liquid, and gas states.

Which of the following statements is true?

  1. Liquid can be converted to solid by increasing the pressure at constant temperature.
  2. The melting temperature of the solid increases as pressure increases.
  3. Solid cannot be converted into gas without first being converted to liquid.
  4. There is only one combination of temperature and pressure for which solid, liquid and gas can coexist.
  5. More than one of the statements above are true.

34. When the following equation is balanced using the smallest whole number coefficients, what is the coefficient of O2?

NH3 + O2 → NO + H2O

  1. 2
  2. 3
  3. 4
  4. 5
  5. 6

35. What is [CH3COOH] at equilibrium if 0.10 moles of CH3COOH and 0.15 moles of NaOH are dissolved in enough water to make 1.0 L of solution at 25 °C? For Ka = 1.8×10−5 at 25 °C

  1. 0 mol L−1
  2. 1.8×10−5 mol L−1
  3. 5.6×10−10 mol L−1
  4. 1.1×10−9 mol L−1
  5. 1.3×10−3 mol L−1

36. The following diagram is sometimes used to illustrate the structure of benzene, C6H6.

two resonance structures of the benzene molecule, \(\text{C}_{6}\text{H}_{6}\), connected by a double-headed resonance arrow.

Which of the statements concerning the structure of benzene is false?

  1. The double bonds oscillate rapidly back and forth between adjacent pairs of carbon atoms.
  2. The H-C-C angles are 120°
  3. The carbon atoms form a flat hexagonal ring.
  4. The oxidation state of carbon is −1.
  5. The carbon-carbon bonds are all the same length.

37. A particular substance, X, decomposes such that its concentration decreases by a factor of two every 35 s. If the initial concentration of X was 1.0 mol L−1, what is [X] after exactly 140 s?

  1. 0.33 mol L−1
  2. 0.13 mol L−1
  3. 0.25 mol L−1
  4. 0.063 mol L−1
  5. 0.67 mol L−1

38. The bond dissociation energies for F2 and Cl2 are approximately 158 and 242 kJ mol−1 respectively. Given that the enthalpy change for the reaction below is ΔH = −54 kJ mol−1, what is the bond dissociation energy for the F-Cl bond?

½F2(g) + ½Cl2(g) → FCl(g)

  1. 200 kJ mol−1
  2. 254 kJ mol−1
  3. 146 kJ mol−1
  4. 454 kJ mol−1
  5. 346 kJ mol−1

39. Which of the following has the greatest number of unpaired electrons in its ground electronic state?

  1. Al
  2. Cl
  3. Ti2+
  4. Zn2+
  5. S2−

40. Let HA represent a weak monoprotic acid with Ka = 1.0×10−5. In an experiment, a 50.0 mL sample of 0.10 mol L−1 HA(aq) is titrated with 0.10 mol L−1 NaOH(aq). At which point during the titration are the equilibrium concentrations of H+ and OH− equal?

  1. after the addition of exactly 25.0 mL of NaOH(aq)
  2. after the addition of slightly less than 50.0 mL of NaOH(aq)
  3. after the addition of exactly 50.0 mL of NaOH(aq)
  4. after the addition of more than 50.0 mL of NaOH(aq)
  5. The equilibrium concentrations of H+ and OH− are never equal.

CHEM 13 NEWS EXAM 2011 DATA SHEET

DETACH CAREFULLY

Periodic table for reference during the exam. Click one of the interactive periodic tables in the text to use as a reference.

Additional interactive periodic tables

Constants

NA = 6.022 x 1023 mol-1
R = 0.08206 atm L K-1 mol-1 = 8.3145 kPa L K-1 mol-1 = 8.3145 J K-1 mol-1

Kw = 1.0 \times 10^{-14} (at 298 K)
F = 96 485 C mol-1

Conversion factors

1 atm = 101.325 kPa = 760 torr = 760 mm Hg
0oC = 273.15 K

Equations

PV = nRT
k t1/2 = 0.693
pH = pKa + log ([base]/[acid])

The quadratic formula: x equals the fraction with numerator negative b plus or minus the square root of b squared minus 4ac, and denominator 2a

CHEM 13 NEWS EXAM © 2011 UNIVERSITY OF WATERLOO

Chem 13 News Exam 2011 Answer key
  1. D. metallic solids
  2. B. H2S < H2Se < H2Te < H2O
  3. E. OF2
  4. D. Na(g) → Na+(g) + e-
  5. C. As
  6. C. adding some H2 gas to the system, with volume and temperature held constant
  7. D. 0.30
  8. A. 2.1×10−8 mol L−1
  9. C. Mg3N2
  10. E. iodide, I−
  11. C.  X-ray radiation has a higher frequency than does microwave radiation
  12. E. O22-
  13. A. C3H4N
  14. D. DC=C is greater than DC−C but less than 2 × DC−C
  15. B. B-F
  16. A. The conversion of R to P occurs via a two-step process.
  17. B. 5.8×10−9 mol L−1
  18. E. none of above
  19. B. [A] > [B] > [C]
  20. D. 62%
  21. E. a weak base by adding strong acid
  22. A. Ag+(aq)
  23. B. 2 mol
  24. A. 1.23 V
  25. C. Zn(s)
  26. A. S2− > Cl− > K+ > Ca2+
  27. D. [Na+ ] + 2 [Mg2+] = [OH−]
  28. A. 9.0 L
  29. C. see-saw
  30. D. NH2−
  31. B. Ionization energies tend to increase from left to right in a period, and decrease from top to bottom in a group.
  32. C. sp3
  33. D. There is only one combination of temperature and pressure for which solid, liquid and gas can coexist.
  34. D. 5
  35. D. 1.1×10−9 mol L−1
  36. A. The double bonds oscillate rapidly back and forth between adjacent pairs of carbon atoms.
  37. D. 0.063 mol L−1
  38. B. 254 kJ mol−1
  39. C. Ti2+
  40. B. after the addition of slightly less than 50.0 mL of NaOH(aq)