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UNSCO > UNSCO 2015 > Flashcards

UNSCO 2015 Flashcards

1
Q

Calcium carbonate, CaCO3, decomposes upon heating to calcium oxide and carbon dioxide. What mass of solid calcium carbonate is required to produce 2.40 liters of carbon dioxide measured at STP?

  1. 7 g
  2. 4 g
  3. 0 g
  4. g
A

10.7 g

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2
Q

Aspirin, C9H8O4, is prepared by the acetylation of salicylic acid, C7H6O3, according to the following equation:

C7H6O3 + (CH3CO)2O → C9H8O4 + CH3COOH If the yield of this reaction is 83%, what mass of salicylic acid would be required to prepare 1.0 kg of aspirin?

  1. 77 kg
  2. 92 kg
  3. 2 kg
  4. 3 kg
A

0.92 kg

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3
Q

A solution is prepared by mixing 25.0 mL of 6.0 M HCl with 45.0 mL of 3.0 M HNO3. What is [H+] in the resulting solution?

  1. 9 M
  2. 1 M
  3. 1 M
  4. 5 M
A

4.1 M

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4
Q

A 5.73 g sample of a liquid hydrocarbon burned in excess oxygen produces 17.48 g CO2. What is the formula of the hydrocarbon?

C5H12
C6H6
C6H10
C6H12

A

C5H12

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5
Q

A solution of 3.00 g of which substance, dissolved in 100 g H2O, has the highest boiling point?

HOCH2CH(OH)CH2OH (M = 92.1)
RbF (M = 104.5)
AlCl3 (M = 133.3)
TlNO3 (M = 390.4)

A

AlCl3 (M = 133.3)

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6
Q

Each of the following substances dissolves exothermically in water EXCEPT

NaOH(s).
NH4NO3(s).
CuSO4(s).
H2SO4(l).

A

NH4NO3(s).

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7
Q

Which solid is most soluble in water at 25 ºC?

AgNO3
CaCO3
PbO
ZnS

A

AgNO3

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8
Q

A student standardizes a solution of Na2S2O3 by titrating it against a solution containing a known mass of NaIO3 that has been dissolved in an excess of a freshly prepared solution of KI in dilute HCl. Which of the following errors will lead to a value of the molarity of the thiosulfate solution that is higher than the true value?
.
The student overshoots the endpoint of the titration.

The NaIO3 is contaminated with NaCl.

The KI/HCl solution is allowed to stand overnight before it is used in the titration.

The sample of sodium thiosulfate pentahydrate used to make the Na2S2O3 solution had partially dehydrated on standing

A

The NaIO3 is contaminated with NaCl.

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9
Q

Mixing equal volumes of 0.1 M Ca(NO3)2 and AgF solutions results in

no precipitate and a colorless solution.
no precipitate and a colored solution.
a white precipitate and a colorless solution.
a colored precipitate and a colorless solution.

A

a white precipitate and a colorless solution.

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10
Q

Elemental silicon is oxidized by O2 to give a compound which dissolves in molten Na2CO3.
When this solution is treated with aqueous hydrochloric acid, a precipitate forms.
What is the precipitate?

SiH4
SiCO3
SiO2
SiCl4

A

SiO2

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11
Q

A metal dissolves in 3.0 M NaOH solution with evolution of gas to form a clear, colorless solution. Upon neutralization, the solution forms a gelatinous precipitate. What is the metal?

Al
Ag
Cu
Mg

A

Al

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12
Q

Which of the following substances experience London dispersion forces?

I. CH3CH3 II. CH3OH

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

A

Both I and II

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13
Q 
Which of these pure substances has the highest normal boiling point? 
(A) CH4  
(B) NH3 
(C) SiH4 
(D) PH3
A

NH3

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14
Q

Which of these pure substances has the highest normal boiling point?

CH4
NH3
SiH4
PH3

A

NH3

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15
Q

A mixture of 0.50 mol of H2 gas and 1.3 mol of Ar gas is in a sealed container with a volume of 4.82 L. If the temperature of the mixture is 50.0 °C, what is the partial pressure of H2 in the sample?

  1. 5 atm
  2. 8 atm
  3. 2 atm
  4. 9 atm
A

2.8 atm

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16
Q

For which pair of allotropes is one a molecular solid and the other a network covalent solid?

Dioxygen and ozone
White phosphorus and red phosphorus
Rhombic sulfur and monoclinic sulfur
Gray tin and white tin

A

White phosphorus and red phosphorus

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17
Q

centered cubic (bcc) crystal structure is correct?

It is not observed as the structure of any metallic elements.

It is also called the cubic closest-packed (ccp) structure.

The unit cell contains two atoms.

Each atom has 6 nearest neighbors

A

The unit cell contains two atoms.

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18
Q

A system consists of a gas contained in a thin balloon. If the balloon deflates as the temperature of the gas changes from 90 ºC to 25 ºC, then

Heat is transferred out of the system and work is done on the system.

Heat is transferred out of the system and work is done by the system.

Heat is transferred into the system and work is done on the system.

Heat is transferred into the system and work is done by the system.

A

Heat is transferred out of the system and work is done on the system.

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19
Q

The ∆Hfº of MgO is –602 kJ•mol1. When 20.15 g MgO is decomposed at constant pressure according to the equation below, how much heat will be transferred?

2 MgO(s) → 2 Mg(s) + O2(g)

  1. 20 × 103 kJ of heat is released
  2. 02 × 102 kJ of heat is absorbed
  3. 02 × 102 kJ of heat is released
  4. 01 × 102 kJ of heat is absorbed
A

3.01 × 102 kJ of heat is absorbed

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20
Q

What mass of ice at 0.0 ºC must be added to 100. g H2O at 25.0 ºC to cool it to 0.0 ºC? The heat of fusion of ice is 334 J•g1.

  1. 25 g
  2. 49 g
  3. 3 g
  4. g
A

31.3 g

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21
Q

Which halogen has the highest standard entropy, Sº?

F2(g)
Cl2(g)
Br2(l)
I2(s)

A

Cl2(g)

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22
Q

Which halogen has the highest standard entropy, Sº?

F2(g)
Cl2(g)
Br2(l) (
I2(s)

A

Cl2(g)

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23
Q

Which halogen has the highest standard entropy, Sº?

F2(g)
Cl2(g)
Br2(l)
I2(s)

A

Cl2(g)

24
Q

A chemical reaction has Keq = 1 × 105 at 25 ºC, and the value of Keq increases with increasing temperature. From these statements, what may one conclude?

∆Hº > 0 and ∆Sº > 0

∆Hº < 0 and ∆Sº < 0

∆Hº < 0 and ∆Sº > 0

∆Hº > 0 and no conclusion may be drawn about the sign of ∆Sº

A

∆Hº > 0 and no conclusion may be drawn about the sign of ∆Sº

25
Q

For the reaction 2 H2(g) + 2 NO(g) → N2(g) + 2 H2O(g) the rate law is rate = k[H2][NO]2. At a given temperature, what is the effect on the reaction rate if the concentration of H2 is doubled and the concentration of NO is halved?

The reaction rate is halved.
The reaction rate is unchanged.
The reaction rate is doubled.
The reaction rate increases eightfold.

A

The reaction rate is halved.

26
Q

A substance X decomposes in a second-order reaction. A solution that is initially 1.00 M in X requires 0.50 h for its concentration to decrease to 0.50 M. How much time will it take for a solution of X to decrease in concentration from 1.00 M to 0.25 M?

  1. 50 h
  2. 0 h
  3. 5 h
  4. 0 h
A

1.5 h

27
Q

The reaction H2O2(aq) + 3 I(aq) + 2 H+(aq) → I3(aq) + 2 H2O(l) has a rate law of rate = k[H2O2][I]. What is the order of the reaction with respect to H+, and what is the overall order of the reaction?

0th order in H+, 2nd order overall
1st order in H+, 2nd order overall
1st order in H+, 3rd order overall
2nd order in H+, 6th order overall

A

0th order in H+, 2nd order overall

28
Q

Which of the following are reasons why reaction rates increase as temperature increases?

I. Collisions are more frequent between molecules at higher temperatures.
II. A greater fraction of collisions have sufficient energy to exceed Ea at higher temperatures
III. Reactant concentrations are higher at higher temperatures.

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

A

I and II

29
Q

What is the effect of adding a catalyst on the rate of a reversible reaction in the forward and the reverse direction?

It has no effect on the rate in either direction.

Both rates increase by the same factor.

The rate in the forward direction increases by a greater factor than the rate in the reverse direction.

The rate in the reverse direction increases by a greater factor than the rate in the forward direction

A

Both rates increase by the same factor.

30
Q

Consider the proposed mechanism for the destruction of ozone in the stratosphere:
O3 + Cl• → ClO• + O2 ClO• + O3 → Cl• + 2 O2

Which of the statements about this mechanism is correct?

Cl• is a catalyst.
O2 is an intermediate.
Equal amounts of Cl• and ClO• are present.
The number of moles of O2 produced equals the number of moles of O3 consumed.

A

Cl• is a catalyst.

31
Q

For the reaction 2 SO2(g) + O2(g) 2 SO3(g) which statements are correct?
I. Kc = [SO2][O2]/[SO3]
II. Addition of O2(g) to the system at constant temperature and volume would decrease the value of Kc.

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

A

Neither I nor II

32
Q

Which solution has the greatest percent ionization?

  1. 10 M NH3 (Kb = 1.8 × 105)
  2. 25 M HNO2 (Ka = 4.5 × 104)
  3. 00 M HCOOH (Ka = 1.7 × 104)
  4. 00 M CH3NH2 (Kb = 4.4 × 104)
A

2.00 M CH3NH2 (Kb = 4.4 × 104)

33
Q

What is the pH of a 0.200 M solution of C6H5COONa? (The Ka of C6H5COOH is 6.4 × 105.)

  1. 25
  2. 40
  3. 60
  4. 75
A

8.75

34
Q

Silver chloride, AgCl (Ksp = 1.8 × 1010), can be dissolved in solutions containing ammonia due to the formation of the soluble complex ion Ag(NH3)2+ (Kf = 1.0 × 108). What is the minimum amount of NH3 that would need to be added to dissolve 0.010 mol AgCl in 1.00 L of solution?

  1. 010 mol
  2. 020 mol
  3. 095 mol
  4. 13 mol
A

0.095 mol

35
Q

What is the oxidation number of Re in Mg(ReO4)2?

+4
+5
+6
+7

A

+7

36
Q

It takes 126.5 minutes using a current of 5.15 A to deposit all of the nickel from 225 mL of a solution containing Ni2+. What was the original concentration of Ni2+ in the solution?

  1. 60 M
  2. 80 M
  3. 900 M
  4. 50 × 102 M
A

0.900 M

37
Q

What is the coefficient of I2 (s) when the reaction below is balanced with smallest whole number coefficients?

__ Cr2O72–(aq) + __ I–(aq) + __ H+(aq) → __ I2(s) + __ Cr3+(aq) + __ H2O(l)

2
3
4
6

A

3

38
Q

Lithium ion batteries are now commonly used in rechargeable consumer electronic devices. The main reason lithium is used in these devices is because

lithium has a lower electronegativity than nickel in common nickel-cadmium batteries.

lithium batteries are not as toxic as common alkaline batteries.

lithium batteries have a reduced risk of leakage of chemicals.

lithium batteries achieve a greater amount of energy stored per unit mass than other common batteries.

A

lithium batteries achieve a greater amount of energy stored per unit mass than other common batteries.

39
Q

The standard reduction potential of Cd2+(aq) is –0.402 V. A voltaic cell described by Cd(s) + 2 H+(aq) → Cd2+(aq) + H2(aq) has [Cd2+] = 0.900 M and a hydrogen pressure of 0.975 atm.

Its cell potential at 25 ºC is measured as
E = +0.192 V. What is the pH in the H+ | H2 half-cell?

  1. 28
  2. 58
  3. 54
  4. 15
A

3.58

40
Q

Which of the following sets of quantum numbers n, l, ml, ms correspond to a valence electron in a neutral atom of arsenic (As)?

3, 0, 0, +1/2
3, 2, 1, –1/2
4, 0, 0, +1/2
4, 2, 1, –1/2

A

4, 0, 0, +1/2

41
Q

Which gas-phase atom has the largest radius?

Na
K
Mg
Ca

A

K

42
Q

Which element’s electronegativity is closest to that of S?

O
P
Cl
Se

A

Se

43
Q

Atomic nitrogen has a higher ionization energy than atomic oxygen. This is best explained by

the lower electron-electron repulsion in nitrogen.

the greater effective nuclear charge of nitrogen.

the fact that the electron ionized in N is from the 2s subshell, while that ionized from O is from the 2p subshell.

the fact that N has an odd number of electrons while O has an even number.

A

the lower electron-electron repulsion in nitrogen.

44
Q

The energy required to break one mole of hydrogenhydrogen bonds in H2 is 436 kJ. What is the longest wavelength of light with sufficient energy to break a single hydrogen-hydrogen bond?

122 nm
132 nm
274 nm
656 nm

A

274 nm

45
Q

In the Lewis structure for the selenite ion, SeO32–, how many lone pairs are around the central atom?

0
1
2
3

A

1

46
Q

Removing an electron from molecular oxygen, O2, to form the dioxygenyl cation, O2+, causes what changes in the bond length and in the number of unpaired electrons?

Bond length Number of unpaired electrons

Increase Increase
Increase Decrease
Decrease Increase
Decrease Decrease

A

Decrease Decrease

47
Q

Which of the following molecules has a dipole moment of zero?

HCN
CH2Cl2
SO2
CO2

A

CO2

48
Q

Formamide has the structure HC(O)NH2. Which atoms in formamide have a trigonal planar geometry?

(A) C only
(B) N only
C) Both C and N
D) None of them

A

Both C and N

49
Q

What is the coordination geometry of nickel in Ni(CO)4?

Tetrahedral
Square planar
See-saw
T-shaped

A

Tetrahedral

50
Q

Which of the following are ionic compounds?

I. NH2NO2
II. NH4NO3

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

A

II only

51
Q

What is the formula for ethyl propanoate?

CH3CH2CO2CH2CH3
CH3CH2CH2CO2CH2CH3
CH3CH2CO2CH2CH2CH3
CH3CH2COCH2CH2OCH3

A

CH3CH2CO2CH2CH3

52
Q

Which substance can exist in enantiomeric forms?

3-methylpentane
2-methylpentane
3-methyl-1-butanol
2-methyl-1-butanol

A

2-methyl-1-butanol

53
Q

Which of the following is a difference between benzene and cyclooctatetraene?

Benzene reacts rapidly with bromine and cyclooctatetraene does not.

Benzene contains sp2-hybridized carbon atoms and cyclooctatetraene does not.

Benzene has the formula CnHn and cyclooctatetraene does not.

Benzene is planar and cyclooctatetraene is not.

A

Benzene is planar and cyclooctatetraene is not.

54
Q

Which base is found in RNA, but not DNA?

Adenine
Guanine
Thymine
Uracil

A

Uracil

55
Q

A triglyceride is formed from

one molecule of glycerin and two molecules of fatty acid.

one molecule of glycerin and three molecules of fatty acid.

three molecules of glycerin and one molecule of fatty acid.

two molecules of glycerin and one molecule of fatty acid.

A

one molecule of glycerin and three molecules of fatty acid.

56
Q

Which of these amino acids has the most hydrophobic side chain at neutral pH?

Cysteine, HSCH2CH(NH2)COOH
Glutamine, H2NC(O)CH2CH2CH(NH2)COOH
Leucine, (CH3)2CHCH2CH(NH2)COOH
Lysine, H2NCH2CH2CH2CH2CH(NH2)COOH

A

Leucine, (CH3)2CHCH2CH(NH2)COOH

57
Q

END

A

END

UNSCO (9 decks)

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