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UNSCO > UNSCO 2012 > Flashcards

UNSCO 2012 Flashcards

1
Q

Fe2O3 reacts with excess CO at a high temperature according to the equation below. Fe2O3 + 3CO  2Fe + 3CO2 If 6.50 g of Fe2O3 yields 3.85 g of Fe what is the percentage yield of the reaction?

  1. 2%
  2. 9%
  3. 3%
  4. 7%
A

84.7%

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2
Q

What is the final [Na+] in a solution prepared by mixing 70.0 mL of 3.00 M Na2SO4 with 30.0 mL of 1.00 M NaCl?

  1. 00 M
  2. 40 M
  3. 00 M
  4. 50 M
A

4.50 M

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3
Q

The mass percentage of O in a potassium salt, K2S2Ox, is 36.0%. What is the formula of the polyatomic ion?

S2O32–
S2O52–
S2O72–
S2O82–

A

S2O52–

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4
Q

Cu reacts with HNO3 according to the equation Cu + HNO3  Cu(NO3)2 + NO + NO2 + H2O If NO and NO2 are formed in a 2:3 ratio, what is the coefficient for Cu when the equation is balanced with the simplest whole numbers?

2
3
6
9

A

9

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5
Q

The active ingredient in commercial bleach is sodium hypochlorite, NaOCl, which can be determined by iodometric analysis as indicated in these equations. OCl– + 2H+ + 2I–  I2 + Cl– + H2O I2 + 2S2O32–  S4O62– + 2I– If 1.356 g of a bleach sample requires19.50 mL of 0.100 M Na2S2O3 solution, what is the percentage by mass of NaOCl in the bleach?

  1. 68%
  2. 70%
  3. 35%
  4. 7%
A

5.35%

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6
Q

A 12.0 M acid solution that contains 75.0% acid by mass has a density of 1.57 g/mL. What is the identity of the acid?

HCl (M = 36.5)
CH3CO2H (M = 60.0)
HBr (M=80.9)
H3PO4 (M = 98.0)

A

H3PO4 (M = 98.0)

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7
Q

Which solid is much more soluble in 1 M HCl than in H2O?

CaHPO4
CaCl2
BaBr2
BaSO4

A

CaHPO4

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8
Q

Which experimental procedure is best suited to determine the H2O2 concentration in an aqueous solution?

precipitation with standard MgCl2 solution
reaction with excess Zn to form H2
titration with standard H2SO4
titration with standard KMnO4

A

titration with standard KMnO4

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9
Q

When equal volumes of 0.2 M solutions of the following compounds are mixed, which combination forms a red precipitate?

AgNO3 + Na2S
AgNO3 + K2CrO4
(NiCl2 + NaOH
CuSO4 + NH3

A

AgNO3 + K2CrO4

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10
Q

Which combination represents an n-type semiconductor?

Si doped with Ge
Si doped with As
Si doped with Ga
As doped with Ga

A

Si doped with As

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11
Q

In an experiment to determine the empirical formula of magnesium oxide, a student weighs an empty crucible then adds a strip of magnesium metal and reweighs the crucible. The crucible and magnesium are heated with a burner flame, which ignites the magnesium and forms a gray-white solid. After cooling, the crucible and solid are reweighed and the data are analyzed to give an empirical formula of Mg5O4. Which could account for the observed Mg5O4 result rather than the expected MgO?

Some of the magnesium reacts with atmospheric nitrogen to produce magnesium nitride.

A mixture of magnesium oxide and magnesium peroxide forms during combustion.

The piece of magnesium ribbon is shorter than recommended in the procedure.

The crucible and magnesium are heated longer than recommended in the procedure.

A

Some of the magnesium reacts with atmospheric nitrogen to produce magnesium nitride.

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12
Q

An acidic solution of methyl red has an absorbance of 0.451 at 530 nm in a 5.00 mm cell. Calculate the molarity of methyl red in this solution. [molar absorptivity = 1.06 X 105 L•mol–1•cm–1 at 530 nm]

  1. 13 X 10–6 M
  2. 26 X 10–6 M
  3. 51 X 10–6 M
  4. 05 X10–5 M
A

`8.51 X 10–6 M

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13
Q

A sample of H2 collected over H2O at 23 °C and a pressure of 732 mm Hg has a volume of 245 mL. What volume would the dry H2 occupy at 0 °C and 1 atm pressure? [vp H2O at 23 °C = 21 mm Hg]

211 mL
218 mL
224 mL
249 mL

A

211 mL

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14
Q

Two samples of gas, one of argon and one of helium, have the same pressure, temperature and volume. Which statement is true assuming both gases behave ideally?

The helium sample contains more atoms than the argon sample and the helium atoms have a higher average speed.

The two samples have the same number of atoms but the helium atoms have a higher average speed.

The two samples have the same number of atoms and both types of atoms have the same average speed

The two samples have the same number of atoms but the argon atoms have a higher average speed.

A

The two samples have the same number of atoms but the helium atoms have a higher average speed.

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15
Q

For a sample of liquid in a closed container, which aspect(s) of vaporization depend on the surface area of the liquid?
I rate of vaporization
II vapor pressure

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

A

I only

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16
Q

Which statement about the triple point of a substance is correct?

The triple point for a substance varies with the pressure.

The three phases (solid, liquid, gas) have the same density.

The three phases (solid, liquid, gas) are in equilibrium.

indistinguishable in appearance.

A

The three phases (solid, liquid, gas) are in equilibrium. (

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17
Q

Diethyl ether has a normal boiling point of 34.6 °C and a boiling point of –1.5 °C at 100 mm Hg. What is the value of ∆H°vaporization in kJ/mol?

  1. 4
  2. 1
  3. 2
  4. 7
A

39.1

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18
Q

An ice cube at an unknown temperature is added to 25.0 g of liquid H2O at 40.0 °C. The final temperature of the 29.3 g equilibrated mixture is 21.5 °C. What was the original temperature of the ice cube? [Cp (J/g•°C) water = 4.184, ice = 2.06, ∆H°fusion = 333 J/g]

–6.5 °C
–13.1 °C
–35.3 °C (
–56.8 °C

A

–13.1 °C

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19
Q

For the reaction, 2H(g)  H2(g), what are the signs of ∆H° and ∆S°?

∆H° < 0, ∆S° < 0
∆H° < 0, ∆S° > 0
∆H° > 0, ∆S˚ > 0
∆H° > 0, ∆S˚ < 0

A

∆H° < 0, ∆S° < 0

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20
Q

Which substance has the greatest molar entropy at 298 K?

NO2(g)
N2O4(l)
N2O4(g)
N2O5(s)

A

N2O4(g)

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21
Q

For the process, CH3OH(l)  CH3OH(g) ∆G° = 4.30 kJ/mol at 25 °C. What is the vapor pressure of CH3OH(l) at 25 °C in mm Hg?

0.176 mm Hg
14.0 mm Hg
134 mm Hg
759 mm Hg

A

134 mm Hg

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22
Q

Which elementary reaction characteristic(s) change(s) significantly for a 10 °C temperature increase for a reaction carried out near room temperature?

I fraction of molecules with required Ea
II fraction of molecules with correct orientation

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

A

I only

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23
Q

The hypothetical reaction 2A + B  C + D is catalyzed by E as indicated in the possible mechanism below.

(Step 1) A + E AE (fast)
(Step 2) AE + A  A2 + E (slow)
(Step 3) A2 + B  C + D (fast)

Which rate law best agrees with this mechanism?

Rate = k[A][B] 
Rate = k[A][E] 
Rate = k[A]2[E] 
Rate = k[A]2[B]
A

Rate = k[A]2[E]

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24
Q

Diethyl ether has a normal boiling point of 34.6 °C and a boiling point of –1.5 °C at 100 mm Hg. What is the value of ∆H°vaporization in kJ/mol?

  1. 4
  2. 1
  3. 2
  4. 7
A

39.1

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25
Q

An ice cube at an unknown temperature is added to 25.0 g of liquid H2O at 40.0 °C. The final temperature of the 29.3 g equilibrated mixture is 21.5 °C. What was the original temperature of the ice cube? [Cp (J/g•°C) water = 4.184, ice = 2.06, ∆H°fusion = 333 J/g]

–6.5 °C
–13.1 °C
–35.3 °C
(–56.8 °C

A

–13.1 °C

26
Q

For the reaction, 2H(g)  H2(g), what are the signs of ∆H° and ∆S°?

∆H° < 0, ∆S° < 0
∆H° < 0, ∆S° > 0
∆H° > 0, ∆S˚ > 0
∆H° > 0, ∆S˚ < 0

A

∆H° < 0, ∆S° < 0

27
Q

Which substance has the greatest molar entropy at 298 K?

NO2(g)
N2O4(l)
N2O4(g)
N2O5(s)

A

N2O4(g)

28
Q

For the process, CH3OH(l)  CH3OH(g) ∆G° = 4.30 kJ/mol at 25 °C. What is the vapor pressure of CH3OH(l) at 25 °C in mm Hg?

0.176 mm Hg
14.0 mm Hg
134 mm Hg
759 mm Hg

A

134 mm Hg

29
Q

Which elementary reaction characteristic(s) change(s) significantly for a 10 °C temperature increase for a reaction carried out near room temperature?
I fraction of molecules with required Ea
II fraction of molecules with correct orientation

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

A

I only

30
Q

What is the first-order rate constant for a reaction that is 36.5% complete in 0.0200 seconds?

  1. 4 s–1
  2. 7 s–1
  3. 7 s–1
  4. 86 s–1
A

22.7 s–1

31
Q

The hypothetical reaction 2A + B  C + D is catalyzed by E as indicated in the possible mechanism below.

(Step 1) A + E AE (fast)
(Step 2) AE + A  A2 + E (slow)
(Step 3) A2 + B  C + D (fast)

Which rate law best agrees with this mechanism?

Rate = k[A][B] 
Rate = k[A][E] 
Rate = k[A]2[E] 
Rate = k[A]2[B]
A

Rate = k[A]2[E]

32
Q

Automobile catalytic converters are designed to

oxidize both CO and NOx.
reduce both CO and NOx.
oxidize CO and reduce NOx.
reduce CO and oxidize NOx.

A

oxidize CO and reduce NOx.

33
Q

A 1 M aqueous solution of which molecule has the lowest pH?

HOCl
H2SO3
H3PO4
H2SO4

A

H2SO4

34
Q

If the initial pH values are the same for titrations of separate 25 mL samples of weak and strong monoprotic acids, which other value(s) is(are) also the same?

I the pH at the equivalence point
II the volume of base needed to reach the eq. point

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

A

Neither I nor II

35
Q

The addition of 0.01 mol of which of the following to 100 mL of H2O will give the most alkaline aqueous solution?

NH3
HONH2
CH3NH2
H2NNH2

A

CH3NH2

36
Q

What is the pH of a 1.00 L sample of a buffer solution containing 0.10 mol of benzoic acid and 0.10 mol of sodium benzoate to which 0.010 mol of NaOH has been added? [Ka benzoic acid = 6.5  10–5]

  1. 27
  2. 23
  3. 15
  4. 10
A

4.27

37
Q

Consider these reactions and their corresponding Ks. ½N2 + O2  NO2

K1 2NO2  2NO + O2
K2 NOBr  NO + ½Br2
K3 Express the K value for the reaction below in terms of K1, K2, and K3. ½N2 + ½O2 +½Br2  NOBr

K = ?

K1 + K2/2 – K3
K1 + (K2)1/2 – K3
K1K2/2K3
K1(K2)1//2/K3

A

K1(K2)1//2/K3

38
Q

What is the average oxidation state of copper in the superconductor YBa2Cu3O7?

+2
+2.33
+2.67
+3

A

+2.33

39
Q

Sn4+(aq) + 2e–  Sn2+(aq)

E° = 0.15 V Cr3+(aq) + e–  Cr2+(aq)
E° = -0.41 V
According to the standard reduction potentials above, what is the value of E˚ for the reaction below? 2Cr3+(aq) + Sn2+(aq)  2Cr2+(aq) + Sn4+(aq)

–0.97 V
–0.56 V
+0.56 V
+0.97 V

A

–0.56 V

40
Q

Ag+(aq) + e–  Ag(s) E° = 0.80 V Mg2+(aq) + 2e–  Mg(s) E° = –2.73 V Use the equations above to calculate the value of ∆G° (in kJ/mol) for the reaction: Mg(s) + 2Ag+(aq)  Mg2+(aq) + 2Ag(s)

681
341
–341
–681

A

–681

41
Q

What is the [Fe2+] in a cell at 25 ˚C for which E = –0.458 V vs a standard hydrogen electrode?

Fe2+(aq) + 2e–  Fe(s) E° = –0.440 V

  1. 246 M
  2. 496 M
  3. 01 M
  4. 06 M
A

0.246 M

42
Q

Rechargeable batteries include which of those below?

I dry cell
II lead-acid storage battery
III nickel-cadmium battery

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

A

II and III only

43
Q

How many liters of chlorine gas, Cl2, measured at 0 °C and 1 atm (STP) are released by the passage of 6.25 amperes for 1.85 hours through molten magnesium chloride?

  1. 0805 L
  2. 161 L
  3. 83 L
  4. 67 L
A

4.83 L

44
Q

Albert Einstein’s explanation of the photoelectric effect confirmed which of the following concepts?

Electrons can absorb energy and change levels in atoms.

Light energy can be converted into the mass of electrons.

Light has both particle and wave properties.

A

Light has both particle and wave properties.

45
Q

Which gas phase ion in its ground state has the greatest number of unpaired electrons?

Cr3+
Mn3+
Fe3+
Co3+

A

Fe3+

46
Q

For the element with the electron configuration 1s2 2s2 2p6 3s2, one of the 3s electrons will be shielded from the nuclear charge most effectively by a

1s electron
2s electron
2p electron
3s electron

A

1s electron

47
Q

In which list are atoms of the elements Be, B, Mg and Al arranged from smallest to largest atomic radius?

Be < B < Mg < Al
Mg < Be < Al < B
B < Be < Al < Mg
Al < Mg < B < Be

A

B < Be < Al < Mg

48
Q

Which ionic compound has the smallest lattice energy?

LiI
NaF
MgCl2
MgO

A

LiI

49
Q

What is the geometry of BrF3?

seesaw
T-shaped
trigonal planar (
trigonal pyramidal

A

T-shaped

50
Q

Three monosulfur fluorides are known: SF2, SF4 and SF6. Of these, polar species include

SF2 only.
SF4 only.
SF2 and SF4 only.
SF2, SF4 and SF6

A

SF2 and SF4 only

51
Q

Which reaction forms a product with a trigonal planar geometry?

N2 + 3H2 
2CO + O2 
PCl3 + Cl2 
2SO2 + O2 

A

2SO2 + O2 

52
Q

What is the best description of the hybridization of each of the carbon atoms (from left to right) in the compound NCCH2CO2H?

sp, sp3, sp2
sp, sp2, sp3
sp2, sp3, sp2
sp2, sp3, sp3

A

sp, sp3, sp2

53
Q

How many isomers exist for the square planar species Pt(H2O)(NH3)ClBr?

1
2
3
4

A

3

54
Q

Which polymer is manufactured by condensation?

Polyethylene terephthalate
Polypropylene
Polystyrene
Polyvinylchloride

A

Polyethylene terephthalate

55
Q

How many non-cyclic compounds have the formula C4H8?

1
2
3
4

A

4

56
Q

Which is a Grignard reagent?

Ag(NH3)2+
C2H5MgBr
FeBr3 + Br2
LiAlH4

A

C2H5MgBr

57
Q

A racemic mixture consists of equal quantities of

cis-trans isomers.
diastereomers.
enantiomers.
structural isomers

A

enantiomers.

58
Q

How many carbon-carbon double bonds are present in linolenic acid, –C17H29COOH?

1
2
3
4

A

3

59
Q

Recently scientists reported a bacterium that they believe incorporates arsenic into its DNA by substituting it for another element. Which element in DNA is arsenic most likely to replace?

carbon
nitrogen
oxygen
phosphorus

A

phosphorus

60
Q

END

A

END

UNSCO (9 decks)

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