CHE111 Exams

In water, what is the actual value for the H-O-H bond angle?
a. 90°

b. 104.5°

c. <109.5°

d. 109.5°

e. <120°

f. 120°

g. 180°

b. 104.5°

In carbon dioxide, how many 2p orbitals remain unhybridized on the carbon atom?

a. All three 2p orbitals remain unhybridized

b. Two 2p orbitals remain unhybridized

c. One 2p orbital remains unhybridized

d. No 2p orbitals remain unhybridized

b. Two 2p orbitals remain unhybridized

In isocyanate, which of the following correctly represents the formal charge (F.C.) and

oxidation number (O.N.) of the carbon atom?

a. F.C. = 0, O.N. = +4

b. F.C. = –1, O.N. = +5

c. F.C. = +1, O.N. = +3

d. F.C. = 0, O.N. = –4

e. F.C. = _______, O.N. = _________

a. F.C. = 0, O.N. = +4

In benzoic acid, what is the hybridization of all carbon atoms?

a. All carbons remain unhybridized

b. sp

c. sp2

d. sp3

e. sp3d

f. sp3d2

c. sp2

In ammonia, which of the following correctly represents the electron group geometry (EGG)

and the ideal H–N–H bond angle (∡HNH) for this EGG?

a. EGG = tetrahedral, ∡HNH = 109.5°

b. EGG = trigonal pyramidal; ∡HNH < 109.5°

c. EGG = trigonal planar; ∡HNH = 120°

d. EGG = tetrahedral; ∡HNH < 109.5°

e. EGG = trigonal pyramidal; ∡HNH =104.5°

f. EGG = trigonal planar; ∡HNH < 120°

g. EGG: ___________ ∡HNH: __________

a. EGG = tetrahedral, ∡HNH = 109.5°

In ammonia, which orbitals are used to form the N–H bonds?

a. H(1s) – N(2s)

b. H(1s) – N(2p)

c. H(1s) – N(sp3)

d. H(sp3) – N(sp3)

e. H(___________) – N(___________)

c. H(1s) – N(sp3)

In sulfurous acid, how many total sigma and pi bonds are present?

a. 4 sigma bonds, 1 pi bond

b. 5 sigma bonds, 1 pi bond

c. 6 sigma bonds, 0 pi bonds

d. _______ sigma bond(s), _______ pi bond(s)

b. 5 sigma bonds, 1 pi bond

Which bond present in isocyanate is the strongest according to the bond dissociation

energies given in Table G of Section V? Note that in the options below, any multiple bond(s)

present in the actual best Lewis structure are not shown.

a. H–N

b. N–C

c. C–O

d. N–O

e. H–C

c. C–O

In sodium borohydride, which of the following correctly represents the electron group

geometry (EGG) and molecular structure (MS) around the boron atom?

a. EGG = trigonal planar, MS = trigonal planar

b. EGG = tetrahedral, MS = trigonal pyramidal

c. No EGG or MS; all atoms are actually ionic with a whole-number charge

d. EGG = tetrahedral, MS = tetrahedral

e. EGG = ____________________, MS = ____________________

d. EGG = tetrahedral, MS = tetrahedral

In the xenon pentafluoride monocation, what is the hybridization of the xenon atom?

a. sp

b. sp2

c. sp3

d. sp3d

e. sp3d2

f. Other: ________________________________________________________

e. sp3d2

In the resonance hybrid structure for the nitrate anion, what is the average N–O bond order?

a. 1

b. 1.33

c. 1.5

d. 1.66

e. 2

f. Other: ________________________________________________________

b. 1.33

What are the ideal value(s) for the Cl–Br–Cl bond angle(s) (∡ClBrCl) in the bromine

tetrachloride monocation?

a. ∡ClBrCl < 90°

b. ∡ClBrCl = 109.5°

c. ∡ClBrCl = 90° (axial to equatorial) & ∡ClBrCl = 120° (equatorial to equatorial)

d. ∡ClBrCl < 109.5°

e. ∡ClBrCl = 109.5°

f. Other: ________________________________________________________

c. ∡ClBrCl = 90° (axial to equatorial) & ∡ClBrCl = 120° (equatorial to equatorial)

In the bromine tetrachloride monocation, which of the following correctly describes the

number and orientation of lone pair(s) on the central atom?

a. 1 lone pair on central bromine, in an equatorial position

b. 2 lone pairs on the central chlorine, both in an equatorial position

c. 2 lone pairs on the central bromine, both in an axial position

d. The central chlorine does not have any lone pairs

e. The central bromine does not have any lone pairs

a. 1 lone pair on central bromine, in an equatorial position

Regarding the polarities of all the species in #1, which of the following statements is correct?

a. Carbon dioxide, the bromine tetrachloride monocation, and oxygen are all nonpolar.

b. Isocyanate contains a more polar bond than any in carbonic acid.

c. Ammonia is more polar than isocyanate.

d. Sulfurous acid, isocyanate, and the resonance hybrid for the nitrate are all polar.

c. Ammonia is more polar than isocyanate.

Using the bond dissociation energies provided in Table G of Section V at the end of the

exam, determine the combustion enthalpy for benzoic acid.

-2580 kJ/mol

To calibrate a bomb calorimeter, you combusted 2.25 g of solid benzoic acid and observed a

temperature change of +13.41°C. What is the heat capacity of the calorimeter?

3.54 kJ/C

Acetone: CH3C(O)CH3 Water: H2O n-Pentane: CH3(CH2)3CH3 Diethyl Ether: CH3CH2OCH2CH3 Ethanol: CH3CH2OH

Which of the molecules above is the most polar?

a. Acetone

b. Water

c. n-Pentane

d. Diethyl Ether

e. Ethanol

f. None of these molecules are polar

b. Water

Acetone: CH3C(O)CH3 Water: H2O n-Pentane: CH3(CH2)3CH3 Diethyl Ether: CH3CH2OCH2CH3 Ethanol: CH3CH2OH

Which of the following mixtures would you expect to be miscible?

a. Acetone & water

b. Diethyl ether & n-pentane

c. Ethanol & water

d. Acetone & ethanol

e. Acetone & Diethyl ether

c. Ethanol & water

Acetone: CH3C(O)CH3 Water: H2O n-Pentane: CH3(CH2)3CH3 Diethyl Ether: CH3CH2OCH2CH3 Ethanol: CH3CH2OH

Which of the molecules above would you expect to melt at the lowest temperature?

a. Acetone

b. Water

c. n-Pentane

d. Diethyl Ether

e. Ethanol

c. n-Pentane

Ethanol: CH3CH2OH Pentanol: CH3(CH2)3 Decanol: CH3(CH2)8CH2OH 1-Eicosanol: CH3(CH2)18CH2OH

Using water as a solvent, which of the solvent molecules above would you expect to make the

most endothermic solution?

a. Ethanol

b. Pentanol

c. Decanol

d. 1-Eicosanol

d. 1-Eicosanol

Ethanol: CH3CH2OH Pentanol: CH3(CH2)3 Decanol: CH3(CH2)8CH2OH 1-Eicosanol: CH3(CH2)18CH2OH

A pure sample of which of the above molecules would you expect to be the most viscous?

a. Ethanol

b. Pentanol

c. Decanol

d. 1-Eicosanol

d. 1-Eicosanol

Ethanol: CH3CH2OH Pentanol: CH3(CH2)3 Decanol: CH3(CH2)8CH2OH 1-Eicosanol: CH3(CH2)18CH2OH

Which of the following pairs of the molecules above would you expect to have the most

favorable adhesive interactions?

a. Ethanol & pentanol

b. Ethanol & decanol

c. Ethanol & 1-eicosanol

d. Pentanol & decanol

e. Pentanol & 1-eicosanol

f. Decanol & 1-eiconsanol

a. Ethanol & pentanol

Chloroform (CHCl3) has boiling point Tb = 61.26°C and kb = 3.63 kg°C/mol. What would you

expect the boiling point to be of a solution of 92.1 g of iodine (I2) dissolved into 800.0 g of

chloroform? Assume an ideal solution and that all solute(s) are nonvolatile.

a. 62.91°C

b. 61.26°C

c. 64.56°C

d. 59.61°C

a. 62.91°C

Assuming ideal solution behavior, what is the freezing point of a 1.85 molal solution of a

nonvolatile, nonelectrolyte solution in nitrobenzene (Tf = 5.67°C, kf = 8.1 kg°C/mol)?

a. 5.67°C

b. 20.66°C

c. –9.3°C

d. –14.99°C

c. –9.3°C

Glucose (C6H12O6; 180.1559 g/mol) is a nonelectrolyte sugar molecule found in the

bloodstream. Assuming ideal solution behavior, what is the osmotic pressure (atm) of a

sample of blood serum that is 54.0 mg/mL in glucose at body temperature (37.5°C)?

a. 774 atm

b. 7.64 atm

c. 0.922 atm

d. 1.39 x 10^5 atm

b. 7.64 atm

A solution was prepared by adding enough iron(III) chloride to 100.0 g of

acetone (C3H6O) such that it was 1.000 M in formula units of iron(III) chloride. Strangely,

however, a conductivity measurement confirmed that the solution was actually 2.942 M in

total ion concentration rather than what would have been expected. Given the tabulated

information below for pure acetone,

∆vapH (kJ/mol): 32.0

Normal Tb (°C): 56.5

kb (°C kg mol–1): 1.67

d (g/mL): 0.78

a. What is the boiling point of pure acetone at a barometric pressure of 83.4 kPa? You may

assume that the vaporization enthalpy is pressure-independent.

b. What is the actual value for the van't Hoff factor for iron(III) chloride in this solution?

c. What is the boiling point of the actual iron(III) chloride solution at a barometric

pressure of 83.4 kPa? You may assume that the solute is nonvolatile and that its volume

is negligible.

a. 51.1°C

b. 2.942

c.

A certain species of freshwater trout requires a dissolved oxygen concentration of

7.5 mg/L. If the solubility of oxygen gas is 1.2 mM in water at 30.0°C under 1.00 atm of pure

oxygen gas, could these fish thrive in a thermally polluted mountain stream where the water

temperature is 30.0°C and partial pressure of atmospheric oxygen is only 0.17 atm?

Given the tabulated data below, what volume of acetone is present in an 820. mL

sample of an acetone/water mixture containing 20.195 mol of water? You may assume the

solution behaves ideally.

Substance Molar Mass (g/mol) P°vap (torr) Density (g/mL)

Acetone (C3H6O) 58.0791 225.0 0.784

Water (H2O) 18.0153 18.0 0.997

Acetone/Water Mixture N/A 66.3 N/A

Copper roofs and statues oxidize over the course of years due to the reaction of metallic

copper by water, carbon dioxide, and oxygen in the air to produce a green patina of copper

carbonates on their surfaces. For this process, which of the following is not true?

a. The oxidation reaction has a low reaction rate

b. The oxidation reaction would occur faster in the summer than the winter

c. The oxidation reaction would occur more slowly at higher altitudes due to reduced

reactant concentrations

d. Adding a catalyst would increase the rate of the oxidation reaction

e. The reaction has a low activation energy

e. The reaction has a low activation energy

The reaction A + B → 2 C has the rate law v = k [A] [B]³. By what factor does the rate of

reaction increase when [A] remains constant but [B] is doubled?

a. 1

b. 2

c. 3

d. 8

The following reaction was found to be first order in each reactant and second order overall.

Which of the statements about this reaction is true?

2 NO (g) + O2 (g) → 2 NO2 (g)

a. A plot of [NO] vs t will produce a linear trend

b. A plot of ln[O2] vs t will produce a linear trend

c. A plot of 1/[NO2] vs t will produce a linear trend

d. The half-life of the reaction is constant with respect to changing [NO2]

b. A plot of ln[O2] vs t will produce a linear trend

According to the collision theory of reaction dynamics, which of the following best describes

the reason why an increase in temperature will increase the observed rate of reaction?

a. Increasing temperature will cause the particles to be closer to one another, and therefore

more likely to react

b. Increasing temperature will decrease the activation energy, therefore increasing the rate

constant and the observed reaction rate

c. Increasing temperature will make it more likely that molecules collide in the correct

orientation, and therefore increase the rate of reaction

d. Increasing temperature will not increase the likelihood that molecules collide in the

correct orientation, but the increase in temperature will make such collisions more

energetic, and therefore more likely to overcome the activation barrier to react

d. Increasing temperature will not increase the likelihood that molecules collide in the

correct orientation, but the increase in temperature will make such collisions more

energetic, and therefore more likely to overcome the activation barrier to react

Dinitrogen pentoxide decomposes with second-order kinetics according to

2 N2O5 (g) → 4 NO (g) + 3 O2 (g)

At 650. K, the rate constant was measured to be k = 1.66 M–1 s–1

, whereas at 700. K the rate

constant is k = 7.39 M–1 s–1

. What is the activation energy for this reaction?

a. +1.12 kJ mol–1

b. +113 kJ mol–1

c. –113 kJ mol–1

d. –11.6 kJ mol–1

e. –2.74 kJ mol

b. +113 kJ mol–1

Which of the following statements is true about the macroscopically reversible reaction

A (aq) ⇌ B (aq) K = 1.00

begun with initial concentrations [A]0 = 0.3 M and [B]0 = 0.25 M?

a. Q < K; the reaction will shift rightwards to reach equilibrium

b. Q > K; the reaction will shift leftwards to reach equilibrium

c. Q = K; the reaction is already at equilibrium, and no net shift will occur

d. Q < K; the reaction will shift leftwards to reach equilibrium

e. Q > K; the reaction will shift rightwards to reach equilibrium

a. Q < K; the reaction will shift rightwards to reach equilibrium

If KC = 6.5 x 104 for the macroscopic equilibrium below, what is the value for KP at 250.0 °C?

2 NO (g) + Cl2 (g) ⇌ 2 NOCl (g)

a. 2.79 x 106

b. 1510 atm

c. 1510

d. 3170

e. 6.5 x 104

c. 1510

The macroscopically reversible reaction below was allowed to come to equilibrium at 50.0°C.

Which of the following externally applied stresses would result in a net shift to the left as

the reaction re-establishes equilibrium?

N2O4 (g) ⇌ 2 NO2 (g) ∆rH = +57.20 kJ mol–1

a. The total volume of the reaction vessel was expanded by a factor of 2

b. Additional dinitrogen tetroxide gas was added to the reaction vessel

c. Nitrogen dioxide gas was selectively removed from the reaction vessel

d. The temperature of the reaction vessel was lowered by submerging it in an ice bath

e. None of the above stresses would shift the equilibrium leftwards

d. The temperature of the reaction vessel was lowered by submerging it in an ice bath

At equilibrium, which of the following is true?

a. Q = K

b. v+ = v–

c. The reaction proceeds in both forward and reverse directions at equal rates

d. The reaction has completely halted unless acted upon by an external stress

e. A, B, & C

f. B & D

g. None of A-D are true

e. A, B, & C

You have been tasked by Dr. Sirianni to evaluate a mechanism for the formation

of nitrosyl chloride, with the balanced overall reaction

2 NO (g) + Cl2 (g) → 2 NOCl (g)

First, you performed a series of experiments at 25°C and collected the following data:

Trial # [NO] (mol∙L–1) [Cl2] (mol∙L–1) Initial Rate (mol∙L-1∙s-1)

1 0.10 0.10 0.002998

2 0.10 0.15 0.004499

3 0.15 0.20 0.013494

a. Based on these data, what is the experimentally observed rate law (i.e., vobs)?

b. Based on these data, what is the value of the rate constant, kobs, in appropriate units?

c. The following two-step mechanism has been proposed for this reaction:

Step 1: NO (g) + Cl2 (g) ⇄ NOCl2 (g)

Step 2: NOCl2 (g) + NO (g) ⇄ 2 NOCl (g)

In order for this mechanism to be consistent with the empirical rate law you found above, which step must be rate-determining?

Fully justify your claim by deriving the rate law for your proposed rate-determining step (vRDS), and show that it reproduces the observed rate law (vobs) you determined in part (a) above. Alternatively, prove that the mechanism is invalid because no choice of the rate-determining step is consistent with your empirical rate law.

a. Vobs= k[NO]²[Cl₂]

b. kobs= 3.0 M^-2S^-1

c. Step 2

The Blue Ridge mountains of Virginia are famous for their fireflies, whose

"twinkle" comes from the first-order chemical reaction L → products + hv taking place in a special chemiluminescent organ in their thorax. During an ecological survey of the region, the following data on the fireflies' rate of twinkling were collected:

Season Average Temperature Average # Twinkles Per 5 Minutes

Spring 13°C 15 twinkles

Summer 23°C 30 twinkles

a. Assuming that the concentration of the reactant L is constant across all fireflies

regardless of the season, what is the ratio of the rate constants (kspring/ksummer) for this

process? (Hint: Divide the rate laws and cancel!)

b. Based on the ratio of rate constants and the average temperatures when the data above

were collected, what is the activation energy for this first-order chemical reaction?

a. ½

b. 48.85 kJ/mol

Which of the following about the conjugate acid & base pair (HA & A–) is not true?

a. Ka(HA) ✕ Kb(A–) = Kw

b. pKa + pKb = 14 at 15°C

c. If HA is a strong acid, A– will be unable to deprotonate water

d. If A– is a weak base, HA will be able to protonate water

e. All of the above statements are true

b. pKa + pKb = 14 at 15°C

At body temperature of 37°C, Kw = 2.5 x 10^-14. What is the pH of a sample of pure water at

this temperature?

a. 2.5 x 10^–14 M

b. 1.0 x 10^–14 M

c. 1.0 x 10^–7 M

d. 1.58 x 10^–7 M

d. 1.58 x 10^–7 M

The bite of a fire ant is painful because it injects formic acid (HCOOH) into the wound. What

is the pH of a 0.0534 M solution of formic acid?

a. 2.521

b. –2.496

c. 2.509

a. 2.521

What is the concentration of hydroxide in a 0.25 M solution of trimethylamine, (CH3)3N?

a. 0.013 M

b. 0.012 M

c. 2.0 x 10^–6 M

d. 5.0 x 10^–9 M

b. 0.012 M

A 1.00 L flask is filled with 1.00 mol of H2 (g) and 2.00 mol of I2(g), and allowed to react at 50.0°C according to the following reaction:

H2 (g) + I2 (g) ⇌ 2 HI (g) K_p = 50.5

After equilibrium has been established, what will be the total pressure in the flask?

79.6 atm

What is the pH of a 0.440 M solution of sodium azide (NaN3), given that the pH

of a 0.00516 M solution of hydrazoic acid (HN3) is 3.46?

9.12

Prof. Swartz adds 0.640 g of ammonium dihydrogen phosphate (NH4H2PO4) to a

15.0 mL sample of pure water at 25.0°C.

a. Given the values of the acid and base ionization constants in Tables V.B.1-3 at the end of

the exam, what is the dominating ion in the resulting solution?

b. What is/are the equilibrium reaction(s) associated with the dominating ion you

identified above?

c. Based on the equilibrium reaction(s) for the dominating ion you identified above, what is the final pH of the resulting solution?

a. 1.40×10^-12; H₂PO₄^- dominates as an acid

b. 1. H₂PO₄^-_(aq) + H₂O_(l) ←→ H₃O⁺_(aq) + HPO₄^2-_(aq) K_a= 6.3×10^-8

2. HPO₄^2-_(aq) + H₂O_(l) ←→ H₃O⁺_(aq) + PO₄^3-_(aq) K_a= 4.2×10^-13

c. 3.82

Acetate buffers are used in biochemical studies of enzymes to prevent changes in

pH that might affect the biochemical function of these macromolecules.

a. Determine the pH of an acetate buffer where [CH3COOH] = [CH3COO^-] = 0.10 M.

b. Calculate the final pH after 5.0 mL of 0.10 M NaOH is added to 100.0 mL of the above

acetate buffer.

a. 4.76

b. 4.80