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UNSCO > UNCSO 2013 > Flashcards

UNCSO 2013 Flashcards

1
Q

A reaction mixture is prepared containing 0.60 mol of aluminum and 1.20 mol of manganese dioxide. The mixture is heated until one of the reactants has been completely consumed according to the equation:

2 Al + 3 MnO2 → 3 Mn + Al2O3 What quantity of which reactant remains uncombined?

  1. 20 mol Al
  2. 40 mol Al
  3. 30 mol MnO2
  4. 60 mol MnO2
A

0.30 mol MnO2

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2
Q

A solution with a mass of 1.263 g containing an unknown amount of potassium ions was treated with excess sodium tetraphenylborate to precipitate 1.003 g of KB(C6H5)4 (M = 358.33). What is the mass percentage of potassium in the original solution?

  1. 67%
  2. 16%
  3. 9%
  4. 8%
A

8.67%

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3
Q

A typical polyethylene grocery bag weighs 12.4 g. How many metric tons of CO2 would be released into the atmosphere if the 102 billion bags used in one year in the United States were burned? [1 metric ton = 1000 kg]

  1. 52 × 104
  2. 99 × 106
  3. 98 × 106
  4. 98 × 109
A

3.98 × 106

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4
Q

Which mixture of water and H2SO4 represents a solution with a concentration that is closest to 30% by mass H2SO4?

30 g H2SO4 + 100 g H2O
1 mol H2SO4 + 200 g H2O
30 mol H2SO4 + 0.70 kg H2O
0.30 mol H2SO4 + 0.70 mol H2O

A

1 mol H2SO4 + 200 g H2O

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5
Q

How would the freezing point depression of a 0.05 m CaCl2 solution compare with that of a NaCl solution? It would be

less than that for a 0.10 m NaCl solution.

between that for a 0.10 m NaCl solution and a 0.20 m NaCl solution.

between that for a 0.20 m NaCl solution and a 0.30 m NaCl solution.

greater than that for a 0.30 m NaCl solution.

A

less than that for a 0.10 m NaCl solution.

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6
Q

What is the mole fraction of CH3OH in an aqueous solution that is 12.0 m in CH3OH?

  1. 178
  2. 216
  3. 400
  4. 667
A

0.178

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7
Q

Three different oxides of nitrogen each contain 7.00 g of nitrogen and weigh 15.0 g, 23.0 g and 19.0 g, respectively. What are their empirical formulas?

NO, NO2, N2O3
NO, N2O3, N2O5
N2O, NO2, N2O5
NO2, N2O3, N2O

A

NO, NO2, N2O3

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8
Q

Which substance is used in self-contained breathing equipment because it absorbs exhaled CO2 and H2O and releases O2 gas?

KO2
Na2O2
NaOH
Li2O

A

KO2

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9
Q

The infrared frequency of the CX vibration for CH3X depends on which of the following?
I. mass of X
II. strength of the CX bond
III. type of CX vibration (stretch or bend)

I. only
II. only
II. and III. only
I., II. and III.

A

I., II. and III.

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10
Q

In an experiment to verify the value of absolute zero, a student is instructed to measure the volume of He in a 10- mL syringe at 10 °C intervals between 0 ° and 100 °C. She is told to plot the volume versus temperature and to extrapolate this graph to zero volume and read the resulting temperature. Which modification of the experimental procedure will give the best value for absolute zero?

Correcting each measured volume to one atmosphere pressure before plotting.

Doubling the number of temperature-volume values between 0 ° and 100 °C.

Using a thermometer that can measure temperature to + 0.10 °C between 0° and 100 °C.

Measuring the volume of He in the syringe at – 40 °C and – 80 °C.

A

Measuring the volume of He in the syringe at – 40 °C and – 80 °C.

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11
Q

The Henry’s law constant for oxygen gas in water at 25 °C kO2 is 1.3×10–3 M •atm–1. What is the partial pressure of O2 above a solution at 25 °C with an O2 concentration of 2.3×10–4 M at equilibrium?

  1. 7 atm
  2. 18 atm
  3. 3×10–3 atm
  4. 0×10–7 atm
A

0.18 atm

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12
Q

sample of gas measured at 20 °C and 4.0 atm is heated to 40 °C at constant volume. Which statement(s) is (are) true of the gas after heating relative to its initial state?
I. The average molecular kinetic energy is increased. II. The average molecular speed is unchanged.
III. The pressure of the gas is increased to 8.0 atm.
IV. The number of molecular collisions per second is unchanged.

I. only
I. and IV. only
II. and III. only
II. and IV. only

A

I. only

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13
Q

Under what conditions does the behavior of real gases deviate most from that predicted by the ideal gas law?

low P, low T
high P, low T
low P, high T
high P, high T

A

high P, low T

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14
Q

When 0.25 L of liquid nitrogen (d = 0.807 g/mL) is vaporized, what volume does the resulting gas occupy at 25 °C and 5.00 atm?

71 L
54 L
35 L
32 L

A

35 L

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15
Q

What is the principal difference between crystalline and amorphous solids? crystalline solids amorphous solids

ionic bonding covalent bonding
higher molar masses lower molar masses
stoichiometric solids non-stoichiometric solids
long-range order lack of long-range order

A

long-range order lack of long-range order

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16
Q

Which is (are) state properties?
I. enthalpy
II. heat
III. volume (

I. only
II. only
I. and III. only
II. and III. only

A

I. and III. only

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17
Q

HNO2(l) + NaCl(s) → HCl(g) + NaNO2(s) Calculate the ∆H˚ value for the reaction above from the information below.

Reaction

∆H˚ kJ•mol–1 NO(g) + NO2(g) + Na2O(s) → 2NaNO2(s) – 427.0 NO(g) + NO2(g) → N2O(g) + O2(g) – 43.0 2NaCl(s) + H2O(l) → 2HCl(g) + Na2O(s) 507.0 2HNO2(l) → N2O(g) + O2(g) + H2O(l) 34.0

157 kJ
78.5 kJ
–78.5 kJ
–157 kJ

A

78.5 kJ

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18
Q

For which reaction(s) is the ∆H value close to the ∆E value? I. CH4(g) + 2 O2(g) → CO(g) + 2 H2O(l) II. C2H4(g) + 3 O2(g) → 2 CO2(g) + 2 H2O(g)

I. only
II. only
Both I. and II.
Neither I. nor II

A

II. only

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19
Q 
What is the temperature at which the reaction below is at equilibrium?                  
2 NO(g)  + O2(g) →  2 NO2(g)       Δ ˚rxn = –113 kJ•mol–1         ΔS˚rxn = –145 J•mol–1•K–1

–195 °C
77.9 °C
506 °C
779 °C

A

506 °C

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20
Q

The Ksp for Al(OH)3 is 2.0 x 10–31. What is the value of ∆G˚ for the precipitation of Al(OH)3 at 25 °C?

Al3+(aq) + 3 OH–(aq) → Al(OH)3(s)

–175 kJ•mol–1
–14.7 kJ•mol–1
14.7 kJ•mol–1
175 kJ•mol–1

A

–175 kJ•mol–1

21
Q

Ammonia reacts with oxygen according to the equation: 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(l) In an experiment in which the rate of change of nitric oxide is found to be 1.10 M•min–1, what is the rate of change of oxygen gas?

–1.38 M•min–1
–0.880 M•min–1
–0.275 M•min–1
–0.220 M•min–1

A

–1.38 M•min–1

22
Q

A first-order reaction has a rate constant of k = 0.320 min–1. For an initial reactant concentration of 1.22 M, how long does it take for its concentration to fall to 0.150 M?

(A) 0.671 min
(B) 2.60 min
(C) 6.55 min
(D) 25.4 min

A

6.55 min

23
Q

Which graph is linear for a reaction that is second order in [A]? (

[A] vs time
ln[A] vs time
[A]2 vs time
1/[A] vs time

A

1/[A] vs time

24
Q

The reaction of nitrogen dioxide with carbon monoxide NO2(g) + CO(g) → CO2(g) + NO(g) has been studied and the following mechanism has been proposed:

NO2(g) + NO2(g) → NO3(g) + NO(g) slow
NO3(g) + CO(g) → NO2(g) + CO2(g) fast

What rate law corresponds to this mechanism?

Rate = k[NO2] 
Rate = k[NO2][CO]  
Rate = k[NO2]2 
Rate = k[NO2]2[CO]
A

Rate = k[NO2]2

25
Q

A reaction has a rate constant
k = 8.54 × 10-4 M–1•.s–1 at 45 °C and an activation energy,
Ea = 90.8 kJ.
What is the value of k at 25 °C?

  1. 46 × 10–5 M–1•.s–1
  2. 54 × 10–5 M–1•.s–1
  3. 52 × 10–4 M–1•.s–1
  4. 54 × 10–3 M–1•.s–1
A

8.54 × 10–5 M–1•.s–1

26
Q

For which reaction will Kp be larger than Kc at 25 °C?

CO2(g) + C(s) 2 CO(g)
2 NO2(g) N2O4(g)
H2(g) + F2(g) 2 HF(g)
O3(g) + NO(g) NO2(g) + O2(g)

A

CO2(g) + C(s) 2 CO(g)

27
Q 
2 SO3(g)  2 SO2(g) + O2(g) When SO3(g) is added to a sealed bulb at a pressure of 2.0 atm, it undergoes the reaction above.
 At equilibrium, 76% of the SO3(g) has reacted. What is the value of Kp at this temperature?

15

  1. 6
  2. 8
  3. 4
A

7.6

28
Q

The pH of pure water at 50 °C is 6.63.

What is the value of Kw at 50 °C?

  1. 8 × 10–15
  2. 0 × 10–14
  3. 5 × 10–14
  4. 2 × 10–13
A

5.5 × 10–14

29
Q

Alanine, H2NCH(CH3)CO2H, has Ka = 4.5 × 10–3 and Kb = 7.4 × 10–5.
Which species has the highest concentration at a pH of 7.00 in H2O?

H2NCH(CH3)CO2H
+H3NCH(CH3)CO2H
H2NCH(CH3)CO2–
+H3NCH(CH3)CO2–

A

+H3NCH(CH3)CO2–

30
Q

What is the pH of the solution formed by mixing 25.0 mL of a 0.15 M solution of NH3 with 25.0 mL of 0.12 M HCl? (Kb for NH3 = 1.8 × 10–5)

  1. 14
  2. 34
  3. 65
  4. 86
A

8.65

31
Q

What is the [OH–] in a suspension of the antacid Mg(OH)2? (Ksp = 2.06 × 10–13)

  1. 4 × 10–5 M
  2. 9 × 10–5 M
  3. 7 × 10–5 M
  4. 7 × 10–5 M
A

7.4 × 10–5 M

32
Q

When the equation below is balanced correctly using the simplest whole number coefficients, what is the coefficient for

CO2(g)? __ Cr2O72–(aq) + __ H2C2O4(aq) + __ H+(aq) → __Cr3+(aq) + __ CO2(g) + __ H2O(l)

4
6
8
12

A

6

33
Q

Au3+ + 3e– → Au(s) E° = 1.50 V Ag+ + e– → Ag(s) E° = 0.80 V Cu2+ + 2e– → Cu(s)

E° = 0.34 V According to the standard reduction potentials above, a substance that can oxidize only one of these metals must have an E° value

less than 0.34 V.
between 0.34 and 0.80 V.
between 0.80 and 1.50 V.
greater than 1.50 V.

A

between 0.34 and 0.80 V.

34
Q

An aqueous solution of CuSO4 is electrolyzed for 1.50 hours with a current of 2.50 amps. What mass of copper metal is formed?

  1. 88 g
  2. 44 g
  3. 296 g
  4. 0741 g
A

4.44 g

35
Q

Under what conditions is the Nernst equation used to calculate cell potential voltages in a voltaic cell?

non-standard concentrations only
non-spontaneous reactions only
reactions at equilibrium only
reactions of ions with the same charge only

A

non-standard concentrations only

36
Q

Which is an acceptable set of quantum numbers for an electron?

1, 1, 0, 1/2
2, 1, 0, 0
2, 1, –1, –1/2
3, 2, –3, 1/2

A

2, 1, –1, –1/2

37
Q

Which orbital has the most radial nodes?

4s
4p
4d
4f

A

4s

38
Q

Ionization energies vary from left to right across the periodic table. Factors that contribute to this variation include which of the following? I. changes in the nuclear charge II. differences in shielding by valence electrons III. differences in shielding by core electrons

I. only
III. only
I. and II. only
I., II. and III.

A

I. and II. only

39
Q

Which gaseous ion has exactly three unpaired electrons?

Fe3+
Ni2+
Ti4+
V2+

A

V2+

40
Q

Which element has the highest second ionization energy?

Na
Mg
S
F

A

Na

41
Q

The ions below are listed in order of increasing radii except

Al3+ < Mg2+ < Na+
K+ < Cl– < Se2–
Cl– < Br– < I–
O2– < F– < Na+

A

O2– < F– < Na+

42
Q

How many sigma bonds are present in P4?

3
4
5
6

A

6

43
Q

What is the formal charge on the oxygen atom in
:C:::O:?

+1
0
–1
–2

A

+1

44
Q

Based on molecular orbital theory, which species has the highest bond order?

O2+
O2
O2–
O22–

A

O2+

45
Q

Which compound contains four co-linear carbon atoms?

butane
cis-2-butene
trans-2 butene
2-butyne

A

2-butyne

46
Q

Which substance can exist in boat and chair configurations?

benzene
cyclohexane
cyclopentadiene
naphthalene

A

cyclohexane

47
Q

All of the following are monosaccharides except

fructose
glucose
ribose
sucrose

A

sucrose

48
Q

A sample of a white solid is known to be NaHCO3, AgNO3,Na2S, or CaBr2. Which 0.1 M aqueous solution can be used to confirm the identity of the solid?

NH3(Aq)
HCl (Aq)
NaOH (aq)
KCl (aq)

A

HCl (aq)

49
Q

END

A

END

UNSCO (9 decks)

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