Final Exam Review Ch 17-19

CHE 160

FINAL EXAM REVIEW CH 17-19

When the equation for the following reaction in basic solution is balanced, what is the sum of the coefficients?

MnO2 + HO2– ® MnO4–

a) 11

b) 31

c) 14

d) 9

e) 18

What is the oxidation state of Hg in Hg2Cl2?

a) +2

b) –1

c) –2

d) +1

e) 0

Which energy conversion shown below takes place in a galvanic cell?

a) electrical to chemical

b) chemical to electrical

c) mechanical to chemical

d) chemical to mechanical

e) mechanical to electrical

Which of the following reactions is possible at the anode of a galvanic cell?

a) Zn ® Zn2+ + 2e–

b) Zn2+ + 2e– ® Zn

c) Zn2+ + Cu ® Zn + Cu2+

d) Zn + Cu2+ ® Zn2+ + Cu

e) two of these

Which of the following is true for the cell shown here?

Zn(s) ú Zn2+(aq) úú Cr3+(aq) ú Cr(s)

a) The electrons flow from the cathode to the anode.

b) The electrons flow from the zinc to the chromium.

c) The electrons flow from the chromium to the zinc.

d) The chromium is oxidized.

e) The zinc is reduced.

How many electrons are transferred in the following reaction?

SO32–(aq) + MnO4–(aq) ® SO42–(aq) + Mn2+(aq)

a) 6

b) 2

c) 10

d) 4

e) 3

A strip of copper is placed in a 1 M solution of copper nitrate and a strip of silver is placed in a 1 M solution of silver nitrate. The two metal strips are connected to a voltmeter by wires and a salt bridge connects the solutions. The following standard reduction potentials apply:

Ag+(aq) + e– ® Ag(s) E° = +0.80 V

Cu2+(aq) + 2e– ® Cu(s) E° = +0.34 V

When the voltmeter is removed and the two electrodes are connected by a wire, which of the following does not take place?

a) Electrons flow in the external circuit from the copper electrode to the silver electrode.

b) The silver electrode increases in mass as the cell operates.

c) There is a net general movement of silver ions through the salt bridge to the copper half-cell.

d) Negative ions pass through the salt bridge from the silver half-cell to the copper half-cell.

e) Some positive copper ions pass through the salt bridge from the copper half-cell to the silver half-cell.

Which of the following is the strongest oxidizing agent?

MnO4- + 4H+ + 3e- ® MnO2 + 2H2O E° = 1.68 V

I2 + 2e- ® 2I- E° = 0.54 V

Zn2+ + 2e- ® Zn E° = -0.76 V

a) MnO4-

b) I2

c) Zn2+

d) Zn

e) MnO2

9–11. Consider the galvanic cell shown below (the contents of each half-cell are written beneath each compartment):

Pt Cr

0.50 M Br2 0.20 M Cr3+

0.10 M Br–

The standard reduction potentials are as follows:

Cr3+ + 3e– ® Cr(s) E° = –0.73 V

Br2(aq) + 2e– ® 2Br– E° = +1.09 V

What is E° for this cell?

a) 1.82 V

b) 0.36 V

c) 4.75 V

d) 1.79 V

e) 4.40 V

What is the value of E for this cell at 25°C?

a) 2.21 V

b) 1.76 V

c) 2.12 V

d) 1.88 V

e) 0.59 V

Which of the following statements about this cell is false?

a) This is a galvanic cell.

b) Electrons flow from the Pt electrode to the Cr electrode.

c) Reduction occurs at the Pt electrode.

d) The cell is not at standard conditions.

e) To complete the circuit, cations migrate into the left half-cell and anions migrate into the right half-cell from the salt bridge.

The galvanic cell described by Zn(s) ú Zn2+(aq) úú Cu2+(aq) ú Cu(s) has a standard cell potential of 1.101 volts. Given that Zn(s) ® Zn2+(aq) + 2e– has an oxidation potential of 0.762 volts, determine the reduction potential for Cu2+.

a) –1.863 V

b) 1.863 V

c) –0.339 V

d) 0.339 V

e) none of these

The reduction potentials for Au3+ and Ni2+ are as follows:

Au3+ + 3e– ® Au E° = +1.50 V

Ni2+ + 2e– ® Ni E° = –0.23 V

Calculate DG° (at 25°C) for the reaction:

2Au3+ + 3Ni ® 3Ni2+ + 2Au

a) –5.00 ´ 102 kJ

b) +5.00 ´ 102 kJ

c) –2140 kJ

d) +1.00 ´ 103 kJ

e) –1.00 ´ 103 kJ

For a reaction in a voltaic cell both DH° and DS° are positive. Which of the following statements is true?

a) E°cell will increase with an increase in temperature.

b) E°cell will decrease with an increase in temperature.

c) E°cell will not change when the temperature increases.

d) DG° > 0 for all temperatures.

e) None of the above statements is true.

A fuel cell designed to react grain alcohol with oxygen has the following net reaction:

C2H5OH(l) + 3O2(g) ® 2CO2(g) + 3H2O(l)

The maximum work one mole of alcohol can yield by this process is 1320 kJ. What is the theoretical maximum voltage this cell can achieve?

a) 0.760 V

b) 1.14 V

c) 2.01 V

d) 2.28 V

e) 13.7 V

Ni Ag

1.0 x 10-3 M Ni2+ 1.0 M HCl

1.0 M HCl AgCl(s)

Calculate E at 25°C for the cell shown above, given the following data:

Ag+ + e– ® Ag(s) E° = 0.80 V

Ni2+ + 2e– ® Ni(s) E° = –0.23 V

Ksp for AgCl = 1.6 ´ 10–10

a) 0.83 V

b) 0.54 V

c) 1.01 V

d) 2.98 V

e) cannot be determined from the data given

Which of the following statements about batteries is false?

a) A battery is a group of galvanic cells connected in series.

b) Lead storage batteries contain lead at the anode and lead coated with lead dioxide at the cathode.

c) The alkaline dry cell battery can last longer than a nickel-cadmium battery.

d) A fuel cell is a galvanic cell for which the reactants are continuously supplied.

e) Dry cell batteries are used in tape players and portable radios.

A galvanic cell consists of a left compartment with a tin electrode in contact with 0.1 M Sn(NO3)2(aq) and a right compartment with a lead electrode in contact with 1 ´ 10–3 M Pb(NO3)2(aq). The relevant reduction potentials are:

Pb2+ + 2e– ® Pb E° = –0.13 V

Sn2+ + 2e– ® Sn E° = –0.14 V

When this cell is allowed to discharge spontaneously at 25°C, which of the following statements is true?

a) Electrons will flow from left to right through the wire.

b) Pb2+ ions will be reduced to Pb metal.

c) The concentration of Sn2+ ions in the left compartment will increase.

d) The tin electrode will be the cathode.

e) No noticeable change will occur, because the cell is at equilibrium.

The equilibrium constant at 25°C for the reaction

2Al + 3Cu2+ ® 2Al3+ + 3Cu

is approximately

a) 10203

b) 1034

c) 1068

d) 10–203

e) none of these

Suppose that in starting a car on a cold morning a current of 125 amperes is drawn for 15.0 seconds from a cell of the type described above. How many grams of Pb would be consumed? (The atomic weight of Pb is 207.19.)

a) 8.05

b) 2.01

c) 0.0180

d) 0.0360

e) 4.02

Using the following data

E°

PbO2 + 4H+ + SO42– + 2e– ® PbSO4(s) + 2H2O +1.69

PbO2 + 4H+ + 2e– ® Pb2+ + 2H2O +1.46

calculate the Ksp value at 25°C for PbSO4(s).

a) 2.57 ´ 10105

b) 3.89 ´ 10–105

c) 5.9 ´ 107

d) 1.7 ´ 10–8

e) None of these is within 5% of the correct answer.

If oxidation of H2O occurs at the anode, how many moles of oxygen gas will evolve for every 1.00 ´ 102 grams of Cr(s) deposited?

a) 2.88

b) 0.48

c) 11.5

d) 7.7

e) 1.44

If the current is 10.0 amperes, how long will it take to deposit 100 ´ 102 grams of Cr(s) onto the bumper?

a) 10.3 h

b) 1.29 days

c) 309 min

d) 76.3 s

e) 2 mo, 25 days, 14 h, and 6 s

Copper is electroplated from CuSO4 solution. A constant current of 4.00 amp is applied by an external power supply. How long will it take to deposit 1.00 ´ 102 g of Cu? The atomic mass of copper is 63.546.

a) 21.1 h

b) 10.0 min

c) 1.60 days

d) 11.2 s

e) 2.91 h

What quantity of charge is required to reduce 40.0 g of CrCl3 to chromium metal? (1 faraday = 96,485 coulombs)

a) 2.45 ´ 104 C

b) 7.31 ´ 104 C

c) 2.20 ´ 105 C

d) 9.65 ´ 104 C

e) none of these

A solution of MnO42– is electrolytically reduced to Mn3+. A current of 8.64 amp is passed through the solution for 15.0 minutes. What is the number of moles of Mn3+ produced in this process? (1 faraday = 96,486 coulombs)

a) 0.0806

b) 0.0403

c) 0.0201

d) 0.0269

e) 0.778

How many seconds would it take to deposit 21.40 g of Ag (atomic mass = 107.87) from a solution of AgNO3 using a current of 10.00 amp?

a) 9649 s

b) 4825 s

c) 3828 s

d) 1914 s

e) 604 s

In the following nuclear equation, identify the missing product:

Ca + a ® ______+ H

a) Ti

b) Sc

c) Ti

d) Ar

An unstable isotope of rhenium, 191Re, has a half-life of 9.8 minutes and is a beta producer. What is the other product of the reaction?

a) 191Os

b) 191W

c) 192Pt

d) 190W

e) 190Os

In the following fission reaction, identify the other product:

U + n ® I + 2n + ______

a) Y

b) Y

c) Mo

d) Mo

e) Zr

The rate constant for the beta decay of thorium-234 is 2.88 ´ 10–2/day. What is the half-life of this nuclide?

a) 53.1 days

b) 1.22 days

c) 0.693 days

d) 24.1 days

e) 101 days

Electron capture transforms Be into what nuclide?

a) Li

b) B

c) Li

d) B

e) C

]Consider a certain type of nucleus that has a half-life of 32 min. Calculate the percent of original sample of nuclides remaining after 3.0 hours have passed.

a) 98.0%

b) 67%

c) 3.2%

d) 2.0%

e) 1.4%

The number of half-lives needed for a radioactive element to decay to about 6% of its original activity is (choose nearest number):

a) 2

b) 3

c) 4

d) 5

e) 6

What is the age of the sample?

a) 2.93 ´ 107 years

b) 3.67 ´ 1010 years

c) 2.18 ´ 109 years

d) 8.96 ´ 1012 years

e) none of these

A radioactive sample has an initial activity of 2.00 ´ 106 cpm (counts per minute), and after 4.0 days, its activity is 9.0 ´ 105 cpm. What is its activity after 40 days?

a) 4.5 cpm

b) 6.8 ´ 102 cpm

c) 9.0 ´ 104 cpm

d) 5.5 ´ 103 cpm

e) none of these

If a tree dies and the trunk remains undisturbed for 13,750 years, what percentage of original 14C is still present? (half-life of 14C = 5730 years)

a) 5.20%

b) 19.0%

c) 2.20%

d) 45.0%

The ratio of the decay rates at t = 0 to t = 3.0 h is 4.0. The value of the rate constant for this process is:

a) 2.2 h–1

b) 4.6 ´ 10–1 h–1

c) 1.6 ´ h–1

d) 3.0 h–1

e) none of these

Which statement is true about the following reaction?

N + He ® O + H

13.992 4.0015 16.9986 1.0073

amu amu amu amu

a) Energy is absorbed in the reaction.

b) Energy is released in the reaction.

c) No energy change is associated with the reaction.

d) Not enough information is given to determine the energy change.

e) None of these.

Consider the following process:

N + He ® O + H

Masses (amu): 14.003074 4.002603 16.999133 1.007825

Which statement describes DE for the process?

a) 1.15 ´ 1011 J are released.

b) 1.15 ´ 1014 J are released.

c) 1.15 ´ 1018 J are absorbed.

d) 1.15 ´ 1011 J are absorbed.

e) none of these

The smallest amount of radioactive material that will support a self-sustained reaction is called the

a) molar mass.

b) moderator.

c) supercritical mass.

d) subcritical mass.

e) critical mass.

Determine the amount of energy needed to “decompose” one mole of iron-56 nuclei.

a) 3.47 ´ 1011 J

b) 8.47 ´ 1011 J

c) 8.90 ´ 1011 J

d) 1.13 ´ 1014 J

e) 7.75 ´ 1013 J

Which of the following is true for the fission of uranium-235?

a) The electron is captured by the nucleus, which becomes unstable.

b) The products include neutrons.

c) The nuclides produced are individually heavier than the uranium nuclide.

d) The nuclides produced are more stable than the uranium nuclide.

e) Two of these

Radioactivity is not useful for:

a) dating artifacts and rocks

b) producing electricity

c) tracing pathways in biological systems

d) making chemicals like sulfuric acid

e) Radioactivity is useful for all of the above.

Which statement about fusion is incorrect?

a) Fusion requires starting nuclides that are difficult to find on Earth, which is a problem for scientists.

b) Studying fusion is a worthwhile research endeavor because this process could be used as an alternative energy source.

c) Fusion requires a very high temperature in order to begin, which is a problem for scientists.

d) In fusion, two nuclei must be traveling fast enough to overcome the electrostatic repulsion and “fuse” the particles into a new nucleus.

e) Both a and c are incorrect.

Which of the following is a metalloid?

a) carbon

b) oxygen

c) hydrogen

d) copper