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UNSCO > UNSCO 2016 > Flashcards

UNSCO 2016 Flashcards

1
Q

One mole of which hydrocarbon requires 8 mol O2 to achieve complete combustion to give carbon dioxide and water?

C3H8
C4H10
C5H10
C5H12

A

C5H12

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2
Q

What is the concentration of calcium ions in 350. mL of an aqueous solution containing 7.50 g CaCl2?

  1. 0676 M
  2. 193 M
  3. 284 M
  4. 535 M
A

0.193 M

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3
Q

0.422 g of an element Z reacts with oxygen to form 0.797 g of the oxide Z2O3. What is the element Z?

Al
Sc
Cr
Ga

A

Al

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4
Q

At constant temperature and pressure, 5.0 L of SO2 is combined with 3.0 L of O2 according to the equation:

2 SO2(g) + O2(g)  2 SO3(g) After SO3 formation is complete, what is the volume of the mixture?

  1. 5 L
  2. 0 L
  3. 5 L
  4. 0 L
A

5.5 L

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5
Q

A student wishes to determine the molar mass of a pure solid organic compound. Which measurement would be most useful?

Melting point of the solid

Melting point depression of a mixture of the solid with 1,4-dichlorobenzene

Heat of combustion

Solubility in water

A

Melting point depression of a mixture of the solid with 1,4-dichlorobenzene

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6
Q

A student has 10 mL of a solution that might contain any or all of the following cations at 0.01 M concentrations:

Mn2+, Ba2+, Ag+, and Cu2+.

Addition of 10 mL of 1 M HCl causes a precipitate to form. After the precipitate is filtered off, 1 M H2SO4 is added to the filtrate and another precipitate forms. What is the second precipitate?

MnSO4
BaSO4
Ag2SO4
A mixture of BaSO4 and Ag2SO4

A

BaSO4

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7
Q

When 6 M sodium hydroxide is added to an unknown white solid, the solid dissolves. What is a possible identity for this solid?

Mg(OH)2
Al2(SO4)3
BaCO3
AgBr

A

Al2(SO4)3

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8
Q

A student standardizes a solution of aqueous NaOH against a measured mass of solid potassium hydrogen phthalate.

She then uses this NaOH solution to titrate a measured mass of an unknown monocarboxylic acid to its phenolphthalein endpoint to determine its molar mass.
Which errors will lead to a value of the molar mass that is too high?

I. The potassium hydrogen phthalate is partially hydrated.
II. The NaOH solution is allowed to stand after being standardized and absorbs some carbon dioxide from the air.

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

A

Neither I nor II

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9
Q

Which is the safest method for performing a flame test?

Dissolve the metal salt in methanol, then squirt the solution into a lit Bunsen burner from at least 1 meter away.

Dissolve the metal salt in methanol, then pour the methanol into a crystallizing dish, igniting it with the flame from a Bunsen burner.

Soak a wooden splint in an aqueous solution of the metal salt, then burn the splint in the flame from a Bunsen burner.

Soak a wooden splint in an aqueous solution of the metal salt, then heat the splint on top of a ceramic hotplate.

A

Soak a wooden splint in an aqueous solution of the metal salt, then burn the splint in the flame from a Bunsen burner

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10
Q

Which compound has the highest normal boiling point?

CH3CH2COOH
CH3CH2CH2OH
CH3COOCH3
HCOOCH2CH3

A

CH3CH2COOH

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11
Q

Nitrogen, N2, has the following properties: normal melting point: 63.2 K normal boiling point: 77.4 K triple point: 0.127 atm, 63.1 K critical point: 33.5 atm, 126.0 K Which statement about N2 is correct?

Liquid N2 is denser than solid N2.

At sufficiently high pressure, N2 can be liquefied at 150 K.

Liquid N2 and gaseous N2 can coexist at 63.1 K and 1 atm.

If N2 is heated from 60 K to 70 K at 0.100 atm, it sublimes.

A

If N2 is heated from 60 K to 70 K at 0.100 atm, it sublimes.

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12
Q

The vapor pressure of iodomethane, CH3I (M = 141.9), is 110. mm Hg at 266 K. A 0.824 g sample of iodomethane is placed in a closed, evacuated 370. mL container at 266 K. At equilibrium, what will be the pressure in the container?

  1. 4 mm Hg
  2. mm Hg
  3. mm Hg
  4. mm Hg
A

96.4 mm Hg

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13
Q

Which statement about the properties of barium chloride and mercury(II) chloride is correct?

BaCl2 has a higher melting point than HgCl2.

BaCl2 has a higher solubility in nonpolar solvents than HgCl2.

BaCl2 has a higher vapor pressure than HgCl2.

Molten BaCl2 has a lower electrical conductivity than molten HgCl2.

A

BaCl2 has a higher melting point than HgCl2.

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14
Q

Which of the following properties is not typical of metallic solids?

High vapor pressure
High coordination number of atoms in the lattice
High electrical conductivity
High thermal conductivity

A

High vapor pressure

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15
Q

A hot metal coin is dropped into cold water in a wellinsulated container. Which statements are true as the system approaches equilibrium?

I. |qmetal| = |qwater|
II. |∆Smetal| = |∆Swater

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

A

I only

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16
Q

Cyclopropane isomerizes to propene in an irreversible, first-order reaction.
At 700 K, a sample of 22.0 mm Hg of cyclopropane is introduced into a reaction vessel.
After 1.0 min, the partial pressure of the product, propene, was found to be 17.5 mm Hg.
What is the rate constant for the isomerization at this temperature?

  1. 8 × 10–3 s–1
  2. 6 × 10–2 s–1
  3. 23 s–1
  4. 6 s–1
A

2.6 × 10–2 s–1

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17
Q

Which statements about the collision theory of reactions are correct? I. Molecules must have the correct spatial orientations for collisions to lead to reactions. II. Only collisions with an energy greater than a certain threshold lead to reactions. (A) I only (B) II only (C) Both I and II (D) Neither I nor II

A

Both I and II

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18
Q

Nitric oxide is formed at high temperature in the presence of oxygen and nitrogen. A proposed mechanism for its formation is shown:

O2(g) 2 O(g) fast, unfavorable
N2(g) + O(g)  NO(g) + N(g) slow
N(g) + O(g)  NO(g) very fast

What rate law is predicted by this mechanism?

Rate = k[O2]
Rate = k[N2][O2] 
Rate = k[N2][O2]1/2
Rate = k[N2][O2]2
A

Rate = k[N2][O2]1/2

19
Q

At 400.0 K, the rate constant of a reaction is 3.2 × 10–2 s–1. The activation energy of the reaction is 41.0 kJ mol–1. What is the rate constant at 410.0 K?

  1. 4 × 10–2 s–1
  2. 2 × 10–2 s–1
  3. 3 × 10–2 s–1 (
  4. 9 × 10–1 s–1
A

4.3 × 10–2 s–1

20
Q

In a reaction between two substances A and B, the rate is found to be proportional to the concentration of A at all concentrations studied. At low concentrations of B, the rate of the reaction is found to be proportional to [B], but to level off at high concentrations of B. What is a reasonable explanation for the observed dependence of rate on [B]?

B binds to A prior to the rate-determining step.
The reaction has an order of –1 in B.
The reaction involves a 1:2 stoichiometry of A:B.
The reaction is catalyzed by one of its products.

A

B binds to A prior to the rate-determining step.

21
Q

The reaction below is exothermic. PCl3(g) + Cl2(g) PCl5(g) Which change will increase the number of moles of PCl5(g) present at equilibrium?

The volume of the reaction vessel is tripled.
The reaction vessel is cooled.
Some of the Cl2(g) is removed.
Krypton gas is added to the reaction vessel

A

The reaction vessel is cooled.

22
Q

Which of the following has the greatest molar solubility in water?

ZnC2O4 (Ksp = 2.7  10–8)
BaCrO4 (Ksp = 2.3  10–10)
CaF2 (Ksp = 3.9  10–11)
AgBr (Ksp = 5.0  10–13)

A

CaF2 (Ksp = 3.9  10–11)

23
Q

A 0.100 M solution of a weak monoprotic acid HX is 3.5% ionized. What is the pH of a 0.500 M solution of HX?

  1. 30
  2. 76
  3. 10
  4. 46
A

2.10

24
Q

Hydrocyanic acid, HCN, is a weak acid with Ka = 4.9  10–10. Nickel(II) ion complexes strongly with cyanide ion to form Ni(CN)42–, Kf = 1.0  1022. What is the pH of 1.00 L of a 0.100 M solution of HCN to which 0.025 mol NiCl2 has been added?

  1. 00
  2. 05
  3. 15
  4. 92
A

4.05

25
Q

. What is the oxidation state of nitrogen in magnesium nitride?

–3
–2
+3
+5

A

–3

26
Q

For the galvanic cell Zn(s) ǀ Zn2+(aq) ǀǀ Cu2+(aq) ǀ Cu(s) the standard cell potential is 1.10 V. What is the potential at 25 °C if the concentrations of Zn2+ and Cu2+ are 2.5 M and 0.10 M respectively?

  1. 14 V
  2. 10 V
  3. 06 V
  4. 02 V
A

1.06 V

27
Q

Which of the following metals is most likely to be produced through electrolysis?

Aluminum
Gold
Iron
Mercury

A

Aluminum

28
Q

If water is electrolyzed for 2.0 hr with a current of 10.0 A, what volume of dry oxygen gas is collected at STP?

4.2 L
4.6 L
8.4 L
17 L

A

4.2 L

29
Q

In a hydrogen atom, which transition requires the greatest input of energy?

n = 7  n = 3
n = 2  n = 1 
n = 3  n = 7 
n = 1  n = 2
A

n = 1  n = 2

30
Q

How many unpaired electrons does a ground-state gasphase Mn2+ ion have?

1
3
5
7

A

5

31
Q

Which elements are most similar in atomic size?

H (Z = 1) and Li (Z = 3)
C (Z = 6) and Si (Z = 14)
Mn (Z = 25) and Tc (Z = 43)
Zr (Z = 40) and Hf (Z = 72)

A

Zr (Z = 40) and Hf (Z = 72)

32
Q

Which halogen has the greatest first ionization energy?

F
Cl
Br
I

A

F

33
Q 
The isotope 69Zn undergoes what mode of radioactive decay? 
Alpha emission 
Beta emission 
Gamma emission 
Positron emission
A

Beta emission

34
Q

What is the bond order of carbon monoxide, CO?

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

3.0

35
Q

Which statements about the Lewis structure of the fulminate ion, CNO–, are correct?

I. The nitrogen atom has a positive formal charge.
II. The nitrogen atom has a lone pair of electrons.

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

A

I only

36
Q

In which molecule are there two distinct sets of sulfurfluorine bond lengths?

SF2
SOF2
SF4
SF6

A

SF4

37
Q

Which species contains three sigma bonds and one pi bond?

PF3
NH4+
C2H2
CO32–

A

CO32–

38
Q

How many stereoisomers of octahedral CoCl2(NH3)2(CN)2– are possible?

3
4
5
6

A

6

39
Q

What is the best description of the geometry of the nitrogen atoms in dimethylnitrosamine, (CH3)2NNO?

N bonded to CH3 groups N bonded to O

Trigonal planar Linear
Trigonal planar Bent
Trigonal pyramidal Linear
Trigonal pyramidal Bent

A

Trigonal planar Bent

40
Q

A student wishes to prepare ethyl acetate from the reaction of ethanol and acetic acid. To be successful, this reaction requires

an acidic catalyst.
a basic catalyst
an oxidizing agent.
a reducing agent.

A

an acidic catalyst.

41
Q

Which alkyl halide reacts most rapidly with aqueous sodium hydroxide solution?

CH3Cl
CH3I
(CH3)3CCH2Cl
(CH3)3CCH2I

A

CH3I

42
Q

How many isomers are there with the formula C6H14?

3
4
5
6

A

5

43
Q

An enzyme catalyzes the hydrolysis of an ester with a certain activity, but this activity is lost in a 3 M urea solution. What is the most likely explanation for the loss of activity?

Urea binds to the active site of the enzyme competitively with the substrate.

Urea causes the cleavage of the peptide bonds in the enzyme.

Urea causes the enzyme to denature and lose its specific three-dimensional shape.

Urea reacts with disulfide bonds in the enzyme.

A

Urea causes the enzyme to denature and lose its specific three-dimensional shape

44
Q

END

A

END

UNSCO (9 decks)

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