Chemistry 2
Practice Exam 3

1.  Which species is the reducing agent for the forward direction in the reaction below? (The reaction is unbalanced.)

H+(aq) + ClO3–(aq) + I–(aq) " H2O(l) + Cl–(aq) + I2(aq)

a)  I–
b)  I2
c)  H+
d)  Cl–
e)  ClO3–

 

2.  Which chemical species has the highest oxidation state of Cr ?

a)   CrO2
b)   Cr2O3
c)   Cr2O5
d)  Cr2O72–
e)  Cr(OH)3

 

3.  Which of the following are oxidation–reduction reactions ?

I.   CH3OH(aq) + MnO4–(aq) + OH–(aq " HCO2H(aq) + MnO2(s)
II.   H3O+(aq) + NH3(aq) " NH4+(aq) + H2O(l)
III.  H2(g) + Cl2(g) " 2 HCl(g)

a)  I & II
b)  I & III
c)  II & III
d)  II only
e)  I & II & III

 

4.  Which metal is the strongest reducing agent?

a)  Ag
b)  Cu
c)  Fe
d)  Mg
e)  Ni

 

5.  Arrange the following species in order of decreasing strength as oxidizing agents: Ni2+, Fe2+, and MnO4–

a)  Ni2+ > Fe2+ > MnO4–
b)  Fe2+ > Ni2+ > MnO4–
c)  Fe2+ > MnO4– > Ni2+
d)  MnO4– > Ni2+ > Fe2+
e)  MnO4– > Fe2+ > Ni2+

 

6.  Which of the following reactions will occur as written ?

I.  H2(g) + Fe2+(aq) " Fe(s) + 2H+(aq)
II.  2 Ag+(aq) + Cu(s) " 2 Ag(s) + Cu2+(aq)
III.  2 Sn4+(aq) + 2 H2O(l) " 2 Sn2+(aq) + O2(g) + 4 H+(aq)

a)  I & II
b)  I & III
c)  II & III
d)  II only
e)  I & II & III

 

7.  When a clean iron nail is placed in a CuSO4 solution , the nail immediately gains a brown–black coating. Which statement describes this reaction?

a)  The E°rxn is –0.10 V.
b)  This is an electrolytic cell.
c)  Iron in the oxidizing agent.
d)  The iron nail is being reduced.
e)  Copper metal is produced by reduction.

 

8.  Using the following redox equations, which statement is TRUE ?

I.  2 Fe2+(aq) + I2(aq) " 2 Fe3+(aq) + 2 I– E°rxn = – 0.235 V
II.  2 Fe2+(aq) + Br2(aq) " 2 Fe3+(aq) + 2 Br– E°rxn = + 0.317 V

a)  I2 is a stronger oxidizing agent than Br2.
b)  Fe2+ is a stronger reducing agent than I–.
c)  Fe2+ is oxidized spontaneously in Reaction I.
d)  Fe2+ is oxidized spontaneously in Reaction II.
e)  Fe2+ is oxidized spontaneously in Reactions I & II.

 

9.  What is E°rxn for the reaction below ?

2 Mn2+(aq) + 5 Br2(l) + 8 H2O(l) " 2 MnO4–(aq) + 10 Br–(aq) + 16 H+(aq)

a)  – 2.33 V
b)  – 0.44 V
c)  + 0.44 V
d)  + 2.33 V
e)  + 2.58 V

 
  1.   Which statement best describes the voltaic cell below ?

A picture of: An Fe(s) electrode immersed in a solution of Fe2+ connected by a wire to a Cu(s) electrode which is immersed in a solution of Cu2+. The two cells are spaned by a KNO3 salt bridge. The Fe/Fe2+ side is labeled as the anode and the Cu/Cu2+ side is labeled as the cathode.

a) Iron is the cathode.
b) Fe2+ is reduced as the reaction proceeds.
c) Electrons will flow from the Cu to the Fe electrode.
d) The potential for the overall chemical reaction is negative.
e) The Cu electrode becomes heavier as the reaction proceeds.

 

11.  What is the correct balanced oxidation–reduction equation for the dissolution of Cu(s) in dilute nitric acid ?

Cu(s) + HNO3(aq) " Cu2+(aq) + NO(g)

a)  Cu(s) + HNO3(aq) + 3 H+(aq) " Cu2+(aq) + NO(g) + 2 H2O(l)
b)  Cu(s) + 2 HNO3(aq) + 6 H+(aq) " Cu2+(aq) + 2 NO(g) + 4 H2O(l)
c)  3 Cu(s) + HNO3(aq) + 3 H+(aq) " 3 Cu2+(aq) + NO(g) + 2 H2O(l)
d)  3 Cu(s) + 2 HNO3(aq) + 6 H+(aq) " 3 Cu2+(aq) + 2 NO(g) + 4 H2O(l)
e)  2 Cu(s) + 3 HNO3(aq) + 9 H+(aq) " 2 Cu2+(aq) + 3 NO(g) + 6 H2O(l)

12.  What is the correct balanced oxidation–reduction equation in BASIC solution ?

Se2–(aq) + SO32–(aq) " Se(s) + S2O32–(aq)

a)  Se2–(aq) + 2 SO32–(aq) " Se(s) + S2O32–(aq) + 3 OH–(aq)
b)  Se2–(aq) + 2 SO32–(aq) + 3 H2O(l) " Se(s) + S2O32–(aq) + 6 OH–(aq)
c)  2 Se2–(aq) + 2 SO32–(aq) + 3 H2O(l) " 2 Se(s) + S2O32–(aq) + 6 OH–(aq)
d)  2 Se2–(aq) + 2 SO32–(aq) + 6 H+(aq) " 2 Se(s) + S2O32–(aq) + 3 H2O(l)
e)  2 Se2–(aq) + 4 SO32–(aq) + 6 H+(aq) " 2 Se(s) + 2 S2O32–(aq) + 6 OH–(aq)

13.  How many grams of gold can be electroplated onto a piece of jewelry by passing a 1.50 A current for 1.50 hours through a Au(NO3)3 solution?

a)  0.00153 g
b)  0.181 g
c)  0.276 g
d)  5.51 g
e)  16.5 g

 

14.  What is the oxidation of Ce if electrolysis of an aqueous solution of this salt for 16.5 hours with a 1.00 A current deposits 21.6 g of Ce metal?

a)  +2
b)  +3
c)  +4
d)  +5
e)  +6

 

15.  Which statement best describes what happens when molten NaBr undergoes electrolysis ?

a)  Na metal forms at the cathode.
b)  Br– ions flow toward the cathode.
c)  Na+ ions are oxidized at the cathode.
d)  Br2 is formed at the cathode by reduction.
e)  The reaction generates a current spontaneously.

 

16.  The reaction below is initially at standard conditions.  Which statement is TRUE concerning the spontaneous reaction as it proceeds ?

2 Ag+(aq) + Zn(s) " 2 Ag(s) + Zn2+(aq)      E°rxn = +1.56 V

a)  When the reaction reaches equilibrium, Erxn equals E°rxn.
b)  The concentration of Ag+ increases as the reaction progresses.
c)  The concentration of Zn2+ decreases as the reaction progresses.
d)  The driving force, Erxn, becomes larger as the reaction progresses.
e)  At equilibrium, there is no flow of electrons, so the "battery" is dead.

 

17.  Balance the following oxidation–reduction reaction in BASIC solution.  You must show your work to receive credit.

Co2+(aq) + OCl–(aq) " Co(OH)3(s) + Cl–(aq)

 

18.  BONUS: If a fuel cell is designed to produce 1.5 A of current and the H2(g) is contained in a 1.0 L tank at 200 atm pressure at 25°C, how many hours will the fuel cell operate until the H2 runs out?   (The supply of O2 is unlimited.)

O2(g) + 2 H2O(l) + 4 e– " 4 OH–(aq)
2 [H2(g) + 2 OH–(aq) " 2 H2O(l) + 2 e–]
O2(g) + 2 H2(g) " 2 H2O(l)

a)  0.229 hours
b)  71.5 hours
c)  292 hours
d)  584 hours
e)  3480 hours

 

IMPORTANT CONSTANTS :

Gas constant

R = 0.0821 L·atm/K·mol

Faraday's constant

F = 96,485 C / 1 mol of e–

 

1 C = 1 A · sec

 

STANDARD REDUCTION POTENTIALS

E°red (V)

Na+(aq) + e– " Na(s)

– 2.71 V

Mg2+(aq) + 2 e– " Mg(s)

– 2.37 V

Fe2+(aq) + 2 e– " Fe(s)

– 0.44 V

Ni2+(aq) + 2 e– " Ni(s)

– 0.25 V

2 H+(aq) + 2 e– " H2(g)

0.00 V

Sn4+(aq) + 2 e– " Sn2+(aq)

+ 0.13 V

Cu2+(aq) + 2 e– " Cu(s)

+ 0.34 V

Ag+(aq) + e– " Ag(s)

+ 0.85 V

NO3–(aq) + 4 H+(aq) + 3 e– " NO(g) + 2 H2O(l)

+ 0.96 V

Br2(l) + 2 e– " 2 Br–(aq)

+ 1.07 V

MnO4–(aq) + 8 H+(aq) + 5 e– " Mn2+(aq) + 4 H2O(l)

+ 1.51 V

O2(g) + 4 H+(aq) + 4 e– " 2 H2O(l)

+ 1.23 V