Chemistry 1AA3 Test 2
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1. A reaction has an activation energy of25 kJ mol−1 . The reaction rate doubles when the temperature is increased from 300 K to a new temperature. What is the new temperature?
A) 387 K
B) 349 K
C) 373 K
D) 322 K
2. A student made a mistake while preparing the acetic acid/acetate buffer for the final casein titration in Laboratory 7. They intended to prepare 100. mL ofpH 4.85 buffer, but combined 15.0 mL of0.100 M CH3COOH with 85.0 mL of0.100 M CH3COONa by mistake, resulting in a pH 5.50 solution. They used a 3.0 M HCl solution to correct the buffer's pH. What volume of a 3.0 M HCl solution must be added to correct the buffer pH to 4.85?
Ka(CH3COOH) = 1.8 × 10–5
A) 1.2 mL
B) 0.85 mL
C) 1.0 mL
D) 0.97 mL
3. Hydrochloric acid in the stomach gives gastric juice a pH of 1.5. If someone ingests an antacid that neutralizes 99.9% of the HCl, what would the pH be?
4. A 10. mL aliquot of a 0.050 M solution of an unknown monoprotic weak acid is titrated with 0.10 M NaOH. At the equivalence point, pH = 9.25. What is the pKa value ofthe unknown acid?
5. The following data were obtained for the disappearance ofA at 25°C:
time (s) [A] (M)
What is the reaction order?
A) cannot be determined
6. The reaction A → G follows second-order kinetics. The following values of [A] were measured during the reaction.
time (s) [A] (M)
What is the rate constant, k?
A) 0.019 M−1 s−1
B) 0.40 M−1 s−1
C) 0.017 M−1 s−1
D) 0.21 M−1 s−1
7. Determine the enzyme concentration for a reaction in which:
v0 = 4 × 10−5 M/s,
kcat = 200 s−1,
KM = 2 μM,
[S] = 1 μM
A) 3 × 10-7 M
B) 6 × 10-8 M
C) 3 mM
D) 0.6 µM
8. Which statement about catalysis is false?
A) In the reaction A → G, a catalyst will increase the concentration of G at equilibrium.
B) A catalyzed reaction can involve more elementary steps than an uncatalyzed reaction.
C) The hydrogenation of ethene(g) in the presence ofPt(s) is an example of heterogeneous catalysis.
D) A catalyst can change the rate-limiting step of a reaction.
9. Cooking an egg causes a protein in the egg white, albumin, to change conformation and solidify. On the Hamilton Escarpment (324 m elevation), water boils at 99.0 °C and it takes 3 min for an egg white to solidify. In Mexico City (2,250 m elevation) water boils at 92.5 °C and it takes 6 min for an egg white to solidify. What is the activation energy for solidifying albumin?
A) 8.12 kJ mol−1
B) 81.2 kJ mol−1
C) 12.1 kJ mol−1
D) 121 kJ mol−1
10. Which of the following statements regarding the first-order reaction A → G is false?
A) Doubling [A]0 will double [G].
B) v0 = k[A]
C) average rate = [G]/t
D) A graph of [G] vs. time is a horizontal line.
11. What is the rate constant, k, for the reaction 2 A + B → G, shown below?
A) 0.013 M−1 s−1
B) 0.15 M−1 s−1
C) 0.058 M−1 s−1
D) 0.026 M−1 s−1
12. Which statement regarding Michaelis-Menten kinetics involving a substrate, S, is false?
A) Doubling [E]0 when [S] = KM will double v0 .
B) The value ofKM depends on both the enzyme and substrate concentrations.
C) When [S] ≪ KM, doubling [S] will approximately double v0/[E]0 .
D) The order of an enzymatic reaction with respect to [S] decreases as [S] increases.
13. During Chem 1AA3 Experiment #3, the rate law for the bromination ofacetone was experimentally determined.
(CH3)2CO(aq) + Br2 (aq)
BrCH2COCH3(aq) + HBr(aq)
Considering plots ofBr2 absorbance vs. time for various trials, which of the following statements is false?
A) The slope of each plot is proportional to the rate ofreaction.
B) The plots measure average, not instantaneous, rates.
C) The slope ofBr2 absorbance vs time for every trial will be negative.
D) The wavelength ofthe incident light can be any value in the visible spectrum.
14. For the reaction A → C, which of the following statements is false, given the mechanism below?
A) Ifk2 >> k1 and k – 1 0, then v0 = k1[A].
B) Ifthe magnitudes of k1, k – 1 and k2 are unknown, then a reasonable starting assumption for the rate law is v0 = k2[I].
C) Ifk1 >> k2 and k – 1 >> k2, then k2 is rate-limiting.
D) Ifk2 is rate-limiting then v0 = k1k2[A].
15. The decomposition of dinitrogen pentoxide follows first-order kinetics: N2O5(g) → 2 NO2(g) + ½ O2(g)
The half-life for the reaction is 34.5 s. Ifthe initial pressure ofN2O5 is 0.157 bar, what will the total pressure be in the flask after 100 s? (Assume an irreversible reaction.)
A) 0.361 bar
B) 0.429 bar
C) 0.157 bar
D) 0.021 bar
16. Which statement about the reaction profile below is false?
A) k2 > k−1
B) The rate-limiting step is A + B → I.
C) k2 > k1
D) The reaction could be zero order with respect to [B].
17. A reaction occurs in two steps with Ea1 = 30 kJ mol– 1 and Ea2 = 25 kJ mol– 1 . The first step is reversible with Ea– 1 = 20 kJ mol– 1 . The enthalpy change for the overall reaction is –25 kJ mol– 1 . What is the activation energy (kJ mol–1) for the reverse of step 2?
18. The plot shown below shows the sucrose inversion reaction with excess water. What is [sucrose] at t = 35. min?
A) 0.0085 M
B) 0.0031 M
C) 0.0016 M
D) 0.0072 M
19. Which of the vapour pressure curves correspond to water (H2O), diethyl ether (CH3CH2OCH2CH3) and ethanol (CH3CH2OH)?
0 40 80
Water Diethyl ether Ethanol
c b a
a b c
b(c) a b
20. This is the phase diagram for iodine.
Which statement about this phase diagram is false?
A) Reducing the pressure from 2 bar to 0 bar at a temperature of 100 °C will cause iodine to sublime.
B) Above (TC,PC), liquid and gas phases are in equilibrium with each other.
C) The triple point temperature is the same as the standard melting point temperature.
D) The standard boiling point is 184.4 °C.
21. In pure samples of the following compounds, which ones will exhibit hydrogen bonding?
A) ii, v
B) i, iii
C) ii, iv
D) i, v
22. Which of the following statements and reasonings are both true?
There is no difference in the boiling points of xenon and neon.
Both are noble gases.
The melting point of (H3C)3N is higher than NH3
London forces are less important than dipole - dipole interactions
The viscosity ofH3COCH2CH2OCH3 is higher than that ofHOCH2CH2OH.
H3COCH2CH2OCH3 has a higher molecular weight and stronger van der Waals forces
A) All contain a false statement.
C) I, III
23. What is the expected order of boiling points (from high to low) for these compounds, with the molecular formula C6H10O2?
A) I > II > III
B) III > II > I
C) I > III > II
D) III > I > II
24. Which molecule is drawn correctly, using the proper conventions for line-angle drawings?
25. This is Efavirenz, an HIV drug. Which statement is false?
A) There are 14 carbon atoms.
B) Each heteroatom has a formal charge of zero.
C) There are 9 hydrogen atoms.
D) There are 16 lone pairs of electrons in the molecule.