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UNSCO > UNSCO 2010 > Flashcards

UNSCO 2010 Flashcards

1
Q

A student prepares a 100 mL aqueous solution containing a small amount of (NH4)2SO4 and a second 100 mL solution containing a small amount of NaI, then mixes the two solutions. Which statement describes what happens?

Both compounds dissolve and remain in solution when the two solutions are mixed.

Both compounds dissolve initially but NH4I precipitates when the solutions are mixed.

Both compounds dissolve initially but Na2SO4 precipitates when the solutions are mixed.

The NaI dissolves but the (NH4)2SO4 does not. There is no change upon mixing.

A

Both compounds dissolve and remain in solution when the two solutions are mixed.

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2
Q

A colored gas is observed with which combination?

calcium hydride and water
lead metal and nitric acid
sodium carbonate and sulfuric acid
zinc sulfide and hydrochloric acid

A

lead metal and nitric acid

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3
Q

Mixing which pair of 0.10 M solutions produces two precipitates that cannot be separated from one another by filtration?

aluminum chloride and copper(II) nitrate
strontium bromide and lead(II) acetate
magnesium perchlorate and lithium carbonate
barium hydroxide and copper(II) sulfate

A

barium hydroxide and copper(II) sulfate

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4
Q

Which gas turns limewater, a saturated solution of Ca(OH)2, cloudy?

H2
O2
CO2
CH4

A

CO2

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5
Q

For aqueous solutions of which of the following substances could the concentration be determined by visible spectrophotometry?

I Cr(NO3)3 II KMnO4 III Zn(NO3)2

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

A

I and II only

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6
Q

What is the molarity of Na+ ions in a solution made by dissolving 4.20 g of NaHCO3 (M = 84.0) and 12.6 g of Na2CO3 (M = 126) in water and diluting to 1.00 L?

  1. 050 M
  2. 100 M
  3. 150 M
  4. 250 M
A

0.250 M

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7
Q

Which solute has the greatest solubility (in mol/L) in water at 25 ˚C and 1 atm?

CH4
NH3
AgCl
CaSO4

A

NH3

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8
Q

Which 2.00 M solution can be used to separate Al3+ from Fe3+ in an aqueous solution?

HCl
H2SO4
NaCl
NaOH

A

NaOH

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9
Q

The percent composition of the high explosive HNS is

C 37.35%
H 1.34%
N 18.67%
O 42.65%

The molar mass of HNS is 450.22. What is the molecular formula of HNS?

C13H4N7O12
C14H6N6O12
C15H10N6O11
C16H12N5O11

A

C14H6N6O12

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10
Q

A student prepares four 0.10 M solutions, each containing one of the solutes below. Which solution has the lowest freezing point?

CaCl2
KOH
NaC2H3O2
NH4NO3

A

CaCl2

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11
Q

What is the molarity of a hydrochloric acid solution if 20.00 mL of it neutralizes 18.46 mL of a 0.0420 M Ba(OH)2 solution?

  1. 0194 M
  2. 0388 M
  3. 0455 M
  4. 0775 M
A

0.0775 M

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12
Q

Ar and He are both gases at room temperature. How do the average molecular velocities (V) of their atoms compare at this temperature?

VHe = 10VAr 
VAr = 10VHe 
VHe = 3VAr    
VAr = 3VHe
A

VHe = 3VAr

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13
Q

Lithium reacts with water to produce hydrogen gas and lithium hydroxide. What volume of hydrogen collected over water at 22˚C and 750 mm Hg pressure is produced by the reaction of 0.208 g of Li? [VPH2O = 19.8 mm Hg]

367 mL
378 mL
735 mL
755 mL

A

378 mL

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14
Q

Correct statements about samples of ice and liquid water at 0 ˚C include which of the following? I Molecules in ice and liquid water have the same kinetic energy. II Liquid water has a greater entropy than ice. III Liquid water has a greater potential energy than ice.

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

A

I, II, and III

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15
Q

A sample of a volatile liquid is introduced to an evacuated container with a movable piston. Which change occurs as the piston is raised? (Assume some liquid remains.) I The fraction of the molecules in the gas phase increases II The pressure in the container decreases

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

A

I only

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16
Q

The kinetic energy of the molecules in a sample of H2O in its stable state at –10 ˚C and 1 atm is doubled. What are the initial and final phases?

solid → liquid
liquid → gas
solid → gas
solid → solid

A

solid → gas

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17
Q

Barium metal crystallizes in a body-centered cubic lattice with barium atoms only at the lattice points. If the density of barium metal is 3.50 g/cm3, what is the length of the unit cell?

  1. 19 × 10–8 cm
  2. 02 × 10–8 cm
  3. 07 × 10–8 cm
  4. 39 × 10–8 cm
A

5.07 × 10–8 cm

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18
Q

Calculate E when one mole of liquid is vaporized at its boiling point (80 ˚C) and 1 atm pressure. [Hvap = 30.7 kJ/mol]

  1. 6 kJ
  2. 4 kJ
  3. 0 kJ
  4. 8 kJ
A

27.8 kJ

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19
Q

Use the following data to calculate the molar enthalpy of combustion of ethane,
C2H6. 2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(l) H = –2511 kJ/mol C2H2(g) + 2H2(g) → C2H6(g) H = –311 kJ/mol 2H2(g) + O2(g) → 2H2O(g) H = –484 kJ/mol

–1428 kJ/mol
–2684 kJ/mol
–2856 kJ/mol
–3306 kJ/mol

A

–1428 kJ/mo

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20
Q

A 10.00 g piece of metal is heated to 80.00 ˚C and placed in 100.0 g of water at 23.00 ˚C. When the system has reached equilibrium the temperature of the water and metal are 23.50 ˚C. What is the identity of the metal? [Specific heat capacity of H2O = 4.184 J/g ˚C]

Ag (Cp 0.236 J/g ˚C)
Cu (Cp 0.385 J/g ˚C)
Fe (Cp 0.449 J/g ˚C)
Al (Cp 0.901 J/g ˚C)

A

Cu (Cp 0.385 J/g ˚C)

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21
Q

The gaseous compound NOBr decomposes according to the equation NOBr(g) NO(g) + 1/2 Br2(g) At 350 K the equilibrium constant, Kp, is 0.15. What is the value of G˚?

–5.5 × 103 J/mol
–2.4 × 103 J/mol
2.4 × 103 J/mol
5.5 × 103 J/mol

A

5.5 × 103 J/mol

Page

22
Q 
The rate of decomposition of a certain compound in solution is first order. If the concentration of the compound is doubled, what happens to the reaction's half-life? 
It doubles 
It decreases to ½ of the original value 
It decreases to ¼ of the original value 
It remains the same 26
A

It remains the same

23
Q

Consider the reaction: 2 ICl(g) + H2(g) → 2 HCl(g) + I2(g) At a certain temperature the rate constant is found to be 1.63 x 10–6 L/mol.s. What is the overall order of the reaction?

zero
first
second
third

A

second

24
Q

A compound decomposes with a first-order rate constant of 0.00854 s–1. Calculate the concentration after 5.0 minutes for an initial concentration of 1.2 M.

  1. 010 M
  2. 093 M
  3. 92 M
  4. 1 M
A

0.093 M

25
Q

Ozone in the earth’s atmosphere decomposes according to the equation: 2 O3(g) → 3 O2(g) This reaction is thought to occur via the two-step mechanism: Step 1 O3(g) O2(g) + O(g) Fast, reversible Step 2 O3(g) + O(g) → 2 O2(g) Slow What rate law is consistent with this mechanism?

–[O3]/t = k[O3] 
–[O3]/t = k[O3]2 
–[O3]/t = k[O3]2/[O2]   
–[O3]/t = k[O3]2/[O2]3
A

–[O3]/t = k[O3]2/[O2]

26
Q

Consider the system at equilibrium: NH4HS(s) NH3(g) + H2S(g) H > 0 Factors which favor the formation of more H2S(g) include which of the following?

I adding a small amount of NH4HS(s) at constant volume
II increasing the pressure at constant temperature
III increasing the temperature at constant pressure

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

A

III only

27
Q

A 2.0 L container is charged with a mixture of 6.0 moles of CO(g) and 6.0 moles of H2O(g) and the following reaction takes place:
CO(g) + H2O(g) CO2(g) + H2(g) When equilibrium is reached the [CO2] = 2.4 M. What is the value of Kc for the reaction?

16

  1. 0
  2. 25
  3. 063
A

16

28
Q

Which range includes the value of the equilibrium constant, Keq, for a system with G˚ &laquo_space;0?

–1 < Keq < 0
0 < Keq < 1
Keq < –1
1 < Keq

A

1 < Keq

29
Q

What volumes of 0.200 M HNO2 and 0.200 M NaNO2 are required to make 500. mL of a buffer solution with pH = 3.00? [Ka for HNO2 = 4.00 x 10–4]

  1. mL of each
    143 mL of HNO2 and 357 mL of NaNO2
  2. mL of HNO2 and 300. mL of NaNO2
    357 mL of HNO2 and 143 mL of NaNO2
A

357 mL of HNO2 and 143 mL of NaNO2

30
Q

A sample of sparingly soluble PbI2(s) containing radioactive I-133 is added to 0.10 M KI(aq) and stirred overnight. Observations about this system include which of the following?

I The radioactivity of the liquid phase increases significantly.
II The concentration of the I– ion in solution increases significantly.

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

A

I only

31
Q

An unknown metal, M, and its salt, M(NO3)2, are combined with a half-cell in which the following reaction occurs:

Ag+(aq) + e– → Ag(s) [E˚red = 0.80 V] If E˚cell = 1.36 V,

what is E˚ red for M2+(aq) + 2e– → M(s)?

0.56 V
0.24V
–0.24V
–0.56V

A

–0.56V

32
Q

Zn(s) / Zn2+(aq) // H+(aq) / H2(g) E˚ = 0.76 V What must be the pH in the hydrogen compartment of the cell designated above if the cell voltage is 0.70 V? (Assume that both the [Zn2+] and the H2(g) pressure are at standard values and T = 25 ˚C.)

  1. 51
  2. 01
  3. 50
  4. 21
A

1.01

33
Q

The equilibrium constant, K, is 2.0 × 1019 for the cell Ni(s) / Ni2+(aq) // Hg22+(aq) / Hg (l)
The value of E˚ at 25 ˚C for this cell is closest to

–1.14V
–0.57V
0.57V
1.14V

A

0.57V

34
Q

In a battery with a zinc anode, what is the minimum mass of zinc required if a current of 250 mA is drawn for 12.0 minutes?

  1. 0610 g
  2. 122 g
  3. 244 g
  4. 02 g
A

0.0610 g

35
Q

Which set of quantum numbers (n, l, ml, ms) is possible for the outermost electron in a strontium atom in its ground state?

5, 0, 0, –1/2
5, 0, 1, 1/2
5, 1, 0, 1/2
5, 1, 1, –1/2

A

5, 0, 0, –1/2

36
Q

How many orbitals are in an f sublevel (l = 3)?

3
5
7
14

A

7

37
Q

What is the energy of photons with a wavelength of 434 nm?

  1. 76 × 105 kJ/mol
  2. 76 × 102 kJ/mol
  3. 76 × 10–1 kJ/mol
  4. 76 × 10–4 kJ/mol
A

2.76 × 102 kJ/mol

38
Q

In which choice are the species listed in order of increasing radius?

Na+, Mg2+, Al3+
Cl–, S2–, P3–
Ar, K+, Cl–
Cl–, Ar, K+

A

Cl–, S2–, P3–

39
Q

Which element forms a compound with the formula H3XO4?

As
Cl
N
S

A

As

40
Q

Which molecule contains the smallest F-S-F angle?

SF2
SOF2
SO2F2
SF6

A

SF6

41
Q

Which species has the longest N–O bond?

NO
NO+
NO2
NO2+

A

NO2

42
Q

How many pi bonds and how many lone pairs are in the Lewis structure of hydrazine, N2H4?

2 pi bonds, 0 lone pairs
1 pi bond, 0 lone pairs
1 pi bond, 1 lone pair
0 pi bonds, 2 lone pairs

A

0 pi bonds, 2 lone pairs

43
Q

How many isomers of octahedral Co(NH3)3Cl3 are there?

2
3
4
5

A

2

44
Q

The bond angle in H2O is approximately 105˚ while the bond angle in H2S is approximately 90˚. Which explanation best accounts for this difference?

H–S bonds are longer than H–O bonds
.
H–S bonds are less polar than H–O bonds.

S has d orbitals available for bonding, O does not.

O uses sp3 hybrid orbitals for bonding, S uses its 3p orbitals

A

O uses sp3 hybrid orbitals for bonding, S uses its 3p orbitals.

45
Q

Which compound exists in optically active forms?

CH3CFCClCH3
CH2FCH2CH2Cl
CH2FCHClCH3
CHF2CH2CH2Cl

A

CH2FCHClCH3

46
Q

What product results when 2-butene reacts with chlorine?

2-chlorobutane
1,2-dichlorobutane
2,2-dichlorobutane
2,3-dichlorobutane

A

2,3-dichlorobutane

47
Q

Which chloroalkane undergoes substitution with OH– exclusively by an SN1 mechanism?

CH3)2CHCH2Cl
(CH3)3CCl
CH3CH2CHClCH3
CH3CH2CH2CH2Cl

A

(CH3)3CCl

48
Q

Which is a monosaccharide?

fructose
lactose
maltose
sucrose

A

fructose

49
Q

All of the following statements concerning benzene, C6H6, are correct EXCEPT

Each carbon atom forms three sigma bonds.
Each carbon is sp2 hybridized.
Pi electrons are delocalized over all 6 carbon atoms.
Benzene forms cis and trans isomers when it reacts.

A

Benzene forms cis and trans isomers when it reacts

50
Q

Which functional group is not commonly found in nucleic acids?

alcohol
amine
carboxylic acid
dialkyl phosphate

A

arboxylic acid

51
Q

END

A

END

UNSCO (9 decks)

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