Download Unit Review XI

Chemistry Review Unit XI (Electrochemistry)
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Oxidation Numbers, Identifying Oxidation/Reduction Reactions
Balancing Redox Equations
Half-reactions
Electrolytical Cells
Electrochemical Cells
Chemical Activities of Elements and Applications of Electrochemistry (Electroplating,
Batteries, Corrosion)
Oxidation Numbers, Identifying Oxidation/Reduction Reactions
__ 1) When a neutral atom undergoes reduction, its oxidation number
a) decreases
b) increases
c) stays the same
__ 2)
What is the oxidation number of nitrogen in N2O4?
a) -1
b) -2
c) +3
d) +4
__ 3)
Oxygen has an oxidation number of -1 in
a) H3O+
b) OHc) H2O
d) H2O2
__ 4)
How many moles of electrons would be required to completely reduce 0.50 mole of Cu2+
ions to Cu?
a) 1.0
b) 2.0
c) 0.25
d) 0.50
__ 5)
Which is the oxidizing agent in Cl2 (aq) + 2 KBr (aq) —> 2 KCl (aq) + Br2 (aq)?
a) Cl2
b) KCl
c) KBr
d) Br2
Balancing Redox Equations
__ 6) Given the reaction __ Hg2+ + __ Ag —> __ Hg + __ Ag+
When the reaction is completely balanced using the smallest whole-number coefficients,
the coefficient of Hg will be
a) 1
b) 2
c) 3
d) 4
__ 7)
Given the balanced equation 3 Cu + 8 HNO3 —> 3 Cu(NO3)2 + 2 NO + 4 H2O
What is the total number of electrons lost by the copper in this reaction?
a) 1
b) 6
c) 8
d) 4
__ 8)
Given the reaction __ PbS + __ H2O2 —> __ PbSO4 + __ H2O
What is the sum of the coefficients in the correctly balanced equation?
a) 5
b) 8
c) 10
d) 13
__ 9)
When the equation __ HNO3 + __ MnCl2 + __ HCl —> __ NO + __ MnCl4 + __ H2O
is correctly balanced, the coefficent of HNO3 will be
a) 5
b) 2
c) 3
d) 6
__ 10) What is the coefficient of H2O when __ NH3 + __ O2 —> __ NO + __ H2O is balanced?
a) 12
b) 6
c) 5
d) 4
Half-reactions
__ 11) In the reaction Mg + Cl2
a) Mg + 2 e—>
b) Cl2 + 2 e—>
c) Mg
—>
d) Cl2
—>
—> MgCl2, the correct half-reaction for the oxidation is
Mg2+
2 ClMg2+ + 2 e2 Cl- + 2 e-
__ 12) Which half-reaction occurs at the negative electrode in an electrolytic cell in which an
object is plated with silver?
a) Ag + e—>
Ag+
b) Ag
—>
Ag+ + ec) Ag+ + e—>
Ag
d) Ag+
—>
Ag + e__ 13) Which half-reaction occurs at the positive electrode in an electrolytic cell in which an
object is plated with silver?
a) Ag + e—>
Ag+
b) Ag
—>
Ag+ + ec) Ag+ + e—>
Ag
d) Ag+
—>
Ag + e__ 14) Oxygen and copper are produced during the electrolysis of a CuSO4 (aq) solution. Which
reaction occurs at the negative electrode?
a) The copper atom is oxidized.
b) The copper ion is reduced.
c) The oxygen atom is oxidized.
d) The oxygen ion is reduced.
__ 15) Electrolysis of a solution of Na2SO4 (aq) yields hydrogen and oxygen. What reaction takes
place at the negative electrode?
a) 2 Na+ + 2 e- —>
2 Na
b) 2 H+ + 2 e- —>
H2
c) SO42—>
SO2 + O2 + 2 e2d) SO4 + H2O —>
H2SO3 + O2 + 2 e-
Electrolytical Cells
__ 16) Electrolysis requires a(n)
a) external power source (DC)
b) external power source (AC)
c) spontaneous oxidation
d) spontaneous reduction
__ 17) Electrolytical cells convert
a) chemical energy to electrical energy
b) electrical energy to chemical energy
c) thermal energy into electrical energy
d) chemical energy into thermal energy
__ 18) The electrolysis of NaCl (aq) yields
a) hydrogen and chlorine
b) sodium and oxygen
c) hydrogen and oxygen
d) sodium and chlorine
__ 19) In order to coat a steel frame with chromium, the steel frame has to be wired as the
a) cathode
b) anode
c) first anode, then cathode
d) first cathode, then anode
__ 20) In an electrolytic cell, to which electrode will a negative ion migrate and undergo
oxidation?
a) the anode, which is positively charged
b) the anode, which is negatively charged
c) the cathode, which is positively charged
d) the cathode, which is negatively charged
Electrochemical Cells
__ 21) The purpose of a porous cup or a salt bridge in an electrochemical cell is to
a) allow for the flow of molecules between the solutions
b) allow for the flow of ions between the solutions
c) prevent the flow of molecules between the solutions
d) prevent the flow of ions between the solutions
__ 22) Given the chemical cell Zn/Zn2+ — Cu/Cu2+
As the reaction in this cell takes place, the mass of the copper electrode
a) decreases
b) increases
c) stays the same
__ 23) Which reaction will take place spontaneously?
a) Cu + 2 H+
—>
Cu2+ + H2
+
b) 2 Au + 6 H —>
2 Au3+ + 3 H2
c) Pb + 2 H+
—>
Pb2+ + H2
d) 2 Ag + 2 H+ —>
2 Ag+ + H2
__ 24) As the reaction in a chemical cell approaches equilibrium, the voltage of the cell
a) decreases
b) increases
c) stays the same
__ 25) Given the cell reaction 3 Zn (s) + 2 Au3+ (aq) —> 3 Zn2+ (aq) + 2 Au (s)
The negative electrode in this cell is
a) Zn (s)
b) Au3+ (aq)
c) Zn2+ (aq)
d) Au (s)
Chemical Activities of Elements and Applications of Electrochemistry (Electroplating,
Batteries, Corrosion)
__ 26) Which molecule-ion pair will spontaneously react at 25 oC?
a) Cl2 + Fb) I2 + Brc) F2 + Id) Br2 + Cl__ 27) Which metal will react spontaneously with Cu2+ (aq) at 25 oC?
a) Ag
b) Au
c) Mg
d) Hg
__ 28) Which oxidation is most likely to occur?
a) Cu —> Cu2+ + 2 eb) Mg —> Mg2+ + 2 ec) Ag —> Ag+ + ed) Au —> Au3+ + 3 e__ 29) What is the key metal in a car battery?
a) lead
b) nickel
c) manganese
d) iron
__ 30) Coating iron with chromium protects the iron from corrosion because
a) the chromium layer corrodes before the iron does
b) the chromium layer separates the iron from water and oxygen
c) chromium is a nonmetal and therefore resistant to corrosion
d) iron and chromium form an alloy with a high E0
Answers
1)
A
2)
D
3)
D
4)
A
5)
A
6)
A
7)
B
8)
C
9)
B
10)
B
11)
12)
13)
14)
15)
16)
17)
18)
19)
20)
C
C
B
B
B
A
B
A
A
A
21)
22)
23)
24)
25)
26)
27)
28)
29)
30)
B
B
C
A
A
C
C
B
A
B