Download Ch. 17-21: Electrochemistry and Radiochemistry AP

Ch. 17-21: Electrochemistry and Radiochemistry
AP Review Questions
Radioactivity: Zone of Stability
All nuclides with 84 or more protons are unstable (radioactive).
Light elements like the neutron to proton ratio to be equal to one.
Heavier elements like the neutron to proton ratio to be greater than one.
Even numbers of protons and neutrons are more stable than odd numbers of protons and neutrons.
The “magic” (stable) numbers for protons and neutrons are 2, 8, 20, 28, 50, 82, 126.
The “magic” (stable) numbers for electrons are 2, 10, 18, 36, 54, 86 (noble gas configurations.)
1) Which of the following radioactive isotopes is
most likely to decay by emitting a beta
particle?
a) 235U b) 40Cl c) 35Ar d) 246Cf e) 21Na
3) Radioactive decay often results in the emission
of alpha particles, beta particles, positrons or
neutrons. If in the radioactive decay of 210Bi a
single particle is observed to be emitted, which
of the following is it most unlikely to be?
a) 209Bi b) 208Au c) 210Pb d) 206Tl e) 210 Po
4) Which of the following choices represents
239Pu producing a positron?
a) 239Pu → 235Pu + 4He
94
94
2
2) The nuclide 12N is unstable. What type of
radioactive decay would be expected?
a) β- b) β+ c) Φ d) α e) 01n
b)
239
Pu → 0e + 239Np
94
+1 93
c)
239
Pu + 0e → 239Np
94
-1
93
d)
239
e)
239
Pu + 0e → 239Np
94
+1 93
Pu + 4He → 235U
94
2
92
5) The nuclide produced after thorium-232
undergoes alpha emission is
224
a) Fr b) 228Ra c) 228Fr d) 228Th e) 224Ra
6) …. + n → 7Li + 4He
For the reaction shown above, what is the missing
reactant?
a) 9Be b) 9B c) 10Be d) 10B e) 11B
10) A radioactive isotope has a half-life, t1/2, of 4.5
hr. What expression should be used to
calculate the rate constant for this process?
a) k = ln t1/2 b) k = (1 / t1/2) ln2 c) k = 0.5
d) k = ln (t1/2 / 2)
e) k = rate / t1/2
7) A 222Rn nuclide decays through the emission of
two beta particles and two alpha particles. The
resulting nuclide is
a) 214Po b) 210Po c) 214Bi d) 210Bi e) 214 Bb
11) Calculate the rate constant for the radioactive
disintegration of an isotope that has a half-life
of 6930 years.
a) 1.00 X 10-5 yr -1
b) 1.00 X 10-4 yr -1
-3
–1
c) 1.00 X 10 yr
d) 1.00 X 103 yr –1
4
–1
e) 1.00 X 10 yr
8) What happens to the nucleus of a radioactive
nuclide when it emits an alpha particle?
a) Atomic number decreases by one and
the mass number increases by one.
b) Atomic number increases by 2 and the
mass number increases by 2.
c) Atomic number increases by 2 and the
mass number stays constant.
d) Atomic number decreases by 2 and the
mass number stays constant.
e) Atomic number decreases by 2 and the
mass number decreases by 4.
9) What happens to the nucleus of a radioactive
nuclide when it emits a beta particle?
a) The atomic number increases by one
and the mass number decreases by
one.
b) The atomic number increases by one
and the mass number increases by one.
c) The atomic number increases by one
and the mass number stays constant.
d) The atomic number decreases by one
and the mass number stays constant.
e) The atomic number decreases by one
and the mass number increases by one.
12) The half-life of a radioactive nuclide is two
years. What fraction of the nuclide remains
after 6 years?
a) 1/6 b) 1/8 c) 1/4 d) 1/2 e) 1/16
13)
235
U has a half-life of 7.04 X108 years and can
be used to determine the length of time since
rocks have solidified. Which of the following
rocks can be dated most precisely?
a) lava from Mount St. Helens, less than
20 years old
b) lava from the Mount Etna eruption of
700 B.C.
c) lava from lunar craters, 1.5 billion
years ago
d) lava from Mount Vesuvius,
5 million years old
e) lava from Mount Kenya,
20 million years old
15) The half-life of strontium-90 is twenty-nine
years. A sample was found to have 2.25 mg of
strontium-90. What mass of strontium-90
must have been present in the sample 116
years ago?
a) 225 mg b) 36 mg
c) 22.5 mg d) 1440 mg
e) cannot be calculated from given information
14) A radioactive isotope has a half-life of 6.93
years and decays by beta emission. Determine
the approximate fraction of the sample that is
left undecayed at the end of 11.5 years.
a) 1% b) 5% c) 30% d) 75% e) 99%
16) If 87.5 percent of a sample of pure 131I decays
in 24 days, what is the half-life of 131I?
a) 6 days b) 8 days c) 12 days
d) 14 days e) 21 days
17) A 100 gram sample of pure 37Ar decays be
electron capture with a half-life of 35 days.
How long will it take for 90 grams of 37Cl to
accumulate?
a) 31 days b) 39 days c) 78 days
d) 116 days e) 315 days
20) At the anode in a galvanic cell (voltaic cell),
a) reduction takes place
b) electrons are accepted
c) electrons are produced
d) oxidation takes place
e) both (c) and (d)
Questions 21-23
a) anode b) cathode c) salt bridge
d) electrode e) saturated calomel electrode
21) Its symbol is a double line, // or ||, in a cell
diagram.
22) Oxidation occurs here in a galvanic cell.
23) It is a common reference electrode.
18) 2 Fe0 + 3 Cu2+ → 2 Fe3+ + 3 Cu0
This reaction was an alchemist’s trick to convince
greedy nobility that base metal (Fe) could be
converted to gold (Cu freshly deposited does
resemble gold.) If the reaction is spontaneous, the
standard cell voltage (potential), Eo/cell, and the
standard free energy, ∆Go,
a) will both be positive
b) will both be negative
c) will have Eocell positive and ∆Go negative
d) will have Eocell negative and ∆Go positive
e) will both be zero
19) Which of the following cannot be used alone to
predict if a reaction is spontaneous or not?
a) ∆Go b) Kc c) Eocell d) ∆Ho e) ∆So and ∆Ho
Questions 24-28
a) Atomic mass unit, amu, or Dalton
b) Frequency, ν
c) Standard reduction potential, Eo
d) Change in the Gibbs Free Energy, ∆Go
e) Principal quantum number, n
24) Measured in volts
25) Is always negative for a spontaneous process
26) Can only have values equal to positive whole
numbers
27) Defined in terms of the carbon-12 isotope
28) Measures the number of cycles per second for light
waves
31) How many coulombs of charge are needed to
reduce 1 mole of Ag1+ ion to silver metal? 1 mole Ag =
108 g Ag
a) 1 b) 6.02 X1023 c) 108 d) 108 / 6.02 X1023
e) 96500
32) An electrolysis cell operates for 45 minutes at a
current of 0.15 amperes. How many coulombs are
passed through the cell?
a) (45)(0.15)
b) (45)(60)(0.15)
c) (45)(3600)(0.15) d) (45)(60) / (0.15)
e) (3600)(0.15) / (45)
29) Copper is electroplated from CuSO4 solution. A
constant current of 10.00 amps is applied by an
external power supply for exactly 75.0 minutes. How
many grams of copper can be plated out during this
time interval? The atomic mass of copper is 63.55.
a) 3.67 X10-3 g b) 0.247 g c) 7.4 g
d) 14.8 g e) 29.6 g
30) A large, old car bumper is going to be chrome
plated. This can be accomplished using an electrolytic
cell where the bumper will act as a cathode in an acidic
dichromate, Cr2O72-, solution. If the current is 20.0
amperes, how long will it take to deposit 100 grams of
Cr(s) onto the bumper? The atomic mass of Cr is 52.00;
1 faraday = 96,500 coulombs.
a) 15.5 h b) 1.29 days c) 309 min
d) 76.3 s e) 5.3 days
33) Molten NaCl is electrolyzed with a constant
current of 1.00 ampere. What is the shortest amount of
time, in seconds, that it would take to produce 1.00
mole of solid sodium? (1 faraday = 96,500 coulombs)
a) 19,300 seconds b) 32,200 seconds
c) 48,300 seconds d) 64,300 seconds
e) 96,500 seconds
34) When 1 Faraday of electrons is used in electrolysis
to reduce copper (II) ion, the number of grams of
elemental copper produced is approximately
a) 1 b) 29 c) 63 d) 31 e) 96485
35) Which of the following is produced by the
electrolysis of bauxite and cryolite?
a) chlorine gas b) copper
c) bromine
d) aluminum
e) sodium hydroxide
36) The reaction Cu + 2 Ag+ → 2 Ag + Cu2+ is
spontaneous. This means that
a) ∆Go for the reaction must be positive
b) Eo for copper must be positive
c) Eo for silver must be positive
d) ∆So for the reaction must be positive
e) Keq must be greater than 1.00
38) AlF63- + 3 e- → Al + 6 FWhich of the following occurs in the reaction?
a) AlF63- is reduced at the cathode.
b) Al is oxidized at the anode.
c) Aluminum is converted from the –3 oxidation
state to the 0 oxidation state.
d) F- acts as a reducing agent.
e) F- is reduced at the cathode.
39) Which of the following is produced commercially
by electrolysis?
a) NaOH b) aluminum c) hydrogen
d) chlorine e) all of these
37) Based on the following half reactions,
Cl2(g) + 2 e- → 2Cl-(aq)
Eo = +1.36 V
I2(s) + 2 e → 2I (aq)
Eo = +0.535 V
2+
Eo = -0.126 V
Pb (aq) + 2 e → 2 Pb(s)
2+
V (aq) + 2 e → 2 V(s)
Eo = -1.18 V
The following is a true statement:
a) The strongest oxidizing agent in the list is V2+.
b) Iodine will oxidize chloride.
c) Vanadium will oxidize lead.
d) Chlorine is the strongest oxidizing agent in the
list.
e) No galvanic cell can be constructed using these
half reactions.
40) For the following reaction
Zn(s) + 2 Ag+(aq) → Zn2+(aq) + 2 Ag(s)
the standard voltage Eocell has been calculated to be
1.56 volts. To decrease the voltage from the cell to
1.00 volts, one could
a) increase the size of the zinc electrode
b) reduce the coefficients of the reactions so
that it reads ½ Zn(s) + Ag+(aq) → ½ Zn2+(aq) +
Ag(s)
c) decrease the concentration of the silver ion in
solution
d) increase the concentration of the silver ion in
solution
e) decrease the concentration of the zinc ion in
solution
41) Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq)
A galvanic cell that uses the reaction shown above has
a standard state electromotive force of 1.1 volts.
Which of the following changes to the cell will
increase the voltage?
I.
An increase in the mass of Zn(s) in the cell.
II.
An increase in the concentration of Cu2+(aq)
in the cell.
III.
An increase in the concentration of Zn2+(aq)
in the cell.
a) I only b) II only c) III only
d) I and III only e) I and III only
42) In a voltaic cell, one half cell contains a cobalt
electrode immersed in a 1.0 M Co2+ solution. In the
other half cell, a lead electrode is immersed in a 1.0 M
Pb2+ solution. The value for Eo is 0.15 V in this cell.
In a similar voltaic cell, a cobalt electrode is immersed
in a 0.0010 M Co2+ solution and a lead electrode is
immersed in a 0.10 M Pb2+ solution. Which statement
below accurately describes the second voltaic cell?
Co2+ + 2 e- → Co Eo = -0.28 V
Pb2+ + 2 e- → Pb Eo = -0.13 V
a) The cell will have a lower E.
b) The cell will have a higher E.
c) The cell will have an identical E, since E is
unaffected by concentration.
d) Cobalt will become the cathode.
e) The cathode will dissolve.
43) Ni(s) | Ni2+(aq) || Ag+(aq) | Ag(s)
Ni2+ + 2 e- → Ni(s) Eored = -0.25 volt
Ag+ + e- → Ag(s)
Eored = 0.80 volt
Which of the following statements is true of the above
reaction?
a) The reaction is spontaneous, Eo = 1.05 volts.
b) The reaction is nonspontaneous, Eo = -1.05
volts.
c) The reaction is spontaneous, Eo = -1.05 volts.
d) The reaction is spontaneous, Eo = 0.55 volts.
e) The reaction is nonspontaneous, Eo = -0.55
volts.
44) Based on the following half reactions,
I2(s) + 2 e- → 2I-(aq)
Eo = +0.535 V
2+
Pb (aq) + 2 e → 2 Pb(s)
Eo = -0.126 V
2+
V (aq) + 2 e → 2 V(s)
Eo = -1.18 V
Cu2+(aq) + 2 e- → Cu(s)
Eo = +0.340 V
what is the standard voltage expected for the reaction
2 I-(aq) + Cu2+(aq) → I2(s) + Cu(s)?
a) +0.875 V b) –0.875 V c) –0.195 V
d) +0.195 V e) Standard voltage can not be
determined from these values.
45) Which of the following reactions is possible at the
anode of a galvanic cell?
a) Zn → Zn2+ + 2 eb) Zn2+ + 2 e- → Zn
c) Ag+ + e- → Ag
d) Mg + Ag+ → Mg2+ + Ag
e) Pb2+ + 2 e- → Pb
46) Co2+ + 2 e- → Co
Eo = -0.28 V
Cr3+ + e- → Cr2+
Eo = -0.41 V
According to the information shown above, which of
the following statements is true regarding the reaction
below?
2 Co + Cr3+ → 2 Co2+ + Cr2+
a) Cr3+ acts as the reducing agent.
b) The reaction would take place in a galvanic
cell.
c) Keq for the reaction is less than 1.
d) Cobalt metal is reduced in the reaction.
e) Chromium metal will plate out in the reaction.
47) Mn(s) + Cu2+(aq) → Mn2+(aq) + Cu(s)
A voltaic cell based on the reaction above was
constructed from manganese and zinc half-cells. The
standard cell potential for this reaction was 1.52 volts,
but the observed voltage at 25 oC was 1.66 volts.
Which of the following could explain this observation?
a) The Mn2+ solution was more concentrated than
the Cu2+ solution.
b) The Cu2+ solution was more concentrated than
the Mn2+ solution.
c) The manganese electrode was larger than the
copper electrode.
d) The copper electrode was larger than the
manganese electrode.
e) The atomic weight of copper is greater tan the
atomic weight on manganese.
48) Ag+(aq) + e- → Ag(s) Eo = +0.80 V
M(s) + 3 Ag+(aq) → 3 Ag(s) + M3+(aq) Eo = +2.46 V
According to the information above, what is the
standard reduction potential for the half-reaction M3+(aq)
+ 3 e- → M(s)?
a) –1.66 V b) –0.06 V c) 0.06 V
d) 1.66 V e) 3.26 V
Written Questions:
1) In an electrolytic cell, a current of 0.250 ampere is passed through a solution of a chloride of iron,
producing Fe(s) and Cl2(g).
a) Write the equation for the half-reaction that occurs at the anode.
b) When the cell operates for 2.00 hours, 0.521 gram of iron is deposited at one electrode.
Determine the formula of the chloride of iron in the original solution.
c) Write the balanced equation for the overall reaction that occurs in the cell.
d) How many liters of Cl2(g), measured at 25 oC and 750 mm Hg, are produced when the cell
operates as described in part (b)?
e) Calculate the current that would produce chlorine gas from the solution at a rate of 3.00
grams per hour.
2) A strip of Ni metal is placed in a 1-molar solution of Ni(NO3)2 and a strip of Ag metal is placed in a
1-molar solution of AgNO3. An electrochemical cell is created when the two solutions are
connected by a salt bridge and the two metal strips are connected by wires to a voltmeter.
a) Write the balanced chemical equation for the overall reaction that occurs in the cell and
calculate the cell potential, Eo.
b) Calculate how many grams of metal will be deposited on the cathode if the cell is allowed
to run at a constant current of 1.5 amperes for 8.00 minutes.
c) Calculate the value of the standard free energy change, ∆Go, for the cell reaction.
d) Calculate the cell potential, E, at 25 oC for the cell shown above if the initial concentration
of Ni(NO3)2 is 0.100-molar and the initial concentration of AgNO3 is 1.20-molar.
3) Answer the following questions regarding the electrochemical cell shown below.
a) Write the balanced net-ionic equation for the spontaneous reaction that occurs as the cell
operates, and determine the cell voltage.
b) In which direction do anions flow in the salt bridge as the cell operates? Justify your
answer.
c) If 10.0 ml of 3.0-molar AgNO3 solution is added to the half-cell on the right, what will
happen to (calculate) the cell voltage? Explain.
d) If 1.0 gram of solid NaCl is added to each half-cell, what will happen to the cell voltage?
Explain.
e) If 20.0 ml of distilled water is added to both half-cells, the cell voltage decreases. Explain.
4) A galvanic cell is set up assuming that an iron electrode dipping into a Fe2+(aq) solution is the anode
and that a platinum electrode dipping into a solution containing Co2+(aq) and Co3+(aq) ions is the
cathode.
a) Write the two balanced half-reactions and the complete balanced chemical reaction that is
being studied using these assumptions.
b) Under standard conditions show whether or not this reaction is spontaneous.
c) What is the standard free energy change, ∆Go, for this reaction at 20 oC?
d) If the iron (II) concentration is 0.200 M, what is the [Co3+] / [Co2+] ratio when the cell
voltage is 2.00 V in this galvanic cell?
5) Sr(s) + Mg2+ ↔ Sr2+ + Mg(s)
Consider the reaction represented above that occurs at 25 oC. All reactants and products are in their
standard states. The value of the equilibrium constant, Keq, for the reaction is
4.2 X1017 at 25oC.
a) Predict the sign of the standard cell potential, Eo, for a cell based on the reaction. Explain your
prediction.
b) Identify the oxidizing agent for the spontaneous reaction.
c) If the reaction were carried out at 60 oC instead of 25 oC, how would the cell potential change?
Justify your answer.
d) How would the cell potential change, if the reaction were carried out at 25 oC with a 1.0-molar
solution of Mg(NO3)2 and a 0.10-molar solution of Sr(NO3)2? Explain.
e) When the cell reaction in (d) reaches equilibrium, what is the cell potential?
6) Neon-23 is an unstable nuclide with a half-life of 38 seconds.
a) What form of decay would neon-23 be expected to undergo? Write the balanced nuclear
reaction for that process.
b) Explain why the nucleus of a neon-23 atom weighs less than the sum of its constituent
protons and neutrons.
c) Describe the change that a sample of neon-23 undergoes in 38 seconds.
d) Describe alpha, beta (β-), and gamma radiation in terms of mass and charge.
7) Answer each of the following questions regarding radioactivity.
a) Write the nuclear equation for decay of 239Pu by alpha emission.
b) Account for the fact that the total mass of the products of the reaction in part (a) is slightly
less than that of the original 239Pu.
c) Describe how α, β, and γ rays each behave when they pass through an electric field. Use
the diagram below to illustrate your answer.
d) Why is it not possible to eliminate the hazard of nuclear waste by the process of
incineration?