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Chapter 16 & 17 Test

PLEASE FORGIVE ME!!!

1. (3 pts)   6 I- + 2 MnO4- + 4 H2O(l) -->  3 I2(s) + 2 MnO2(s) + 8 OH-

 Which of the following statements regarding the reaction represented by the equation above is correct?

 A) Iodide ion is oxidized by hydroxide ion.
 B) MnO4- is oxidized by iodide ion.
 C) The oxidation number of manganese changes from +7 to +2.
 D) The oxidation number of manganese remains the same.
 E) The oxidation number of iodine changes from -1 to 0.

2. (3 pts)   ...Cr2O72- + ...e- + ...H+ -->  ...Cr3+ + ...H2O(l)

 When the equation for the half reaction above is balanced with the lowest whole-number coefficients, the coefficient for H2O is

 A) 2 B) 4 C) 6 D) 7 E)14

3. (3 pts)  Which of the following reactions has the largest positive value of  S per mole of Cl2?

 A) H2(g) + Cl2(g) -->  2 HCl(g)             D) 2 NH4Cl(s)  --> N2(g) + 4 H2(g) + Cl2(g)
 B) Cl2(g) + O2(g) -->  Cl2O(g)          E) Cl2(g) -->  2 Cl(g)
 C) Mg(s) + Cl2(g)  --> MgCl2(s)
 
4. (3 pts)  Which of the following must be true for a reaction that proceeds spontaneously from initial standard state conditions?

 A)   G  > 0 and Keq > 1  D)   G  < 0 and Keq < 1
 B)   G  > 0 and Keq < 1  E)   G  = 0 and Keq = 1
 C)   G  < 0 and Keq > 1
 
5. (5 pts)    Fe2+ + 2 e- -->  Fe(s)  E  = -0.44 volt
   Ni2+ + 2 e- -->  Ni(s)  E  = -0.23 volt

 The standard reduction potentials for two half reactions are given above.  The Nernst equation for a galvanic cell at 25 C in which Fe(s) reduces Ni2+ is the following.

E = E(standard) - .059/n(log([Fe2+]/[Ni2+]))

 What is the equilibrium constant for the reaction below?

  Fe(s) Ni2+  -->   Fe2+ + Ni(s)

 A) 1.9 x 10-23  C) 3.6 x 103  E) 5.2 x 1022
 B) 7.6 x 10-8  D) 1.3 x 107

6. (3 pts)    H2O(s)  -->  H2O(l)

 When ice melts at its normal melting point, 273.16 K and 1 atmosphere, which of the following is true for the process shown above? (Note:  V stands for volume)

 A)  H < 0,  S > 0,  V > 0  D)   H > 0,  S > 0,  V > 0
 B)  H < 0,  S < 0,  V > 0   E)   H > 0,  S > 0,  V < 0
 C)  H > 0,  S < 0,  V < 0

7. (5 pts)  If a copper sample containing some zinc impurity is to be purified by electrolysis, the anode and the cathode must be which of the following?
 
 

  Andoe Cathode
A) Pure copper Pure Zn
B) Pure zinc Pure Cu
C) Pure copper Impure Cu sample
D) Impure Cu sample Pure Cu
E) Impure Cu sample Pure Zn

Free Response

8. A) (5 pts)   Zn2+ + 2 e- -->  Zn(s)  E  = -0.76 volts
   Cu2+ + 2 e-  -->  Cu(s)  E  = 0.34 volts

  Given the above half reactions and voltages, calculate the value of  G  for the standard cell reaction

   Zn + Cu2+(1M) -->  Zn2+(1M) + Cu

 B) (5 pts)  One half-cell of an electrochemical cell is made by placing a strip of pure zinc in 500 mL of 0.10-molar ZnCl2 solution.  The other half-cell is made by placing a strip of pure copper in 500 mL of 0.010-molar Cu(NO3)2 solution.  Calculate the initial voltage of this cell when the two half-cells are joined by a salt bridge and the two metal strips are joined by a wire.

 C) (5 pts)  Calculate the final concentration of copper ion, Cu2+, in the cell described in part B) if the cell were allowed to produce an average current of 1.0 ampere for 3 minutes 13 seconds.

 9. The electrolysis of an aqueous solution of potassium iodide, KI, results in the formation of hydrogen gas at the cathode and iodine at the anode.  A sample of 80.0 milliliters of a 0.150-molar solution of KI was electrolyzed for 3.00 minutes, using a constant current.  At the end of this time, the I2 produced was titrated against a 0.225-molar solution of sodium thiosulfate, which reacts with iodine according to the equation below.  The end point of the titration was reached when 27.3 mL of the Na2S2O3 solution had been added.

   I2 + 2 S2O32- -->  2 I- + S4O62-

 A) (4 pts)  How many moles of I2 was produced during the electrolysis?
 B) (5 pts)  The hydrogen gas produced at the cathode during the electrolysis was collected over water at 25 C at a total pressure of 752 mmHg.  Determine the volume of hydrogen collected.  (The vapor pressure of water at 25 C is 24 mmHg)
 C) (3 pts)  Write the equation for the half reaction that occurs at the anode during the electrolysis.
 D) (5 pts)  Calculate the current used during the electrolysis.

10.  Br2(l) -->  Br2(g)

 At 25 C the equilibrium constant, Kp, for the reaction above is 0.281 atmosphere.

 A) (5 pts)  What is  G 298 for this reaction?
 B) (6 pts)  It takes 193 joules to vaporize 1.00 gram of Br2(l) at 25 C and 1.00 atmosphere pressure.  What are the values of  H 298 and of  S 298 for this reaction?
 C) (5 pts)  Calculate the normal boiling point of bromine.  Assume that  H  and  S  remain constant as the temperature is changed.
 D) (3 pts)  What is the equilibrium vapor pressure of bromine at 25 C?

Freebie (5 pts)

 What are some of your favorite song lyrics (please quote some and give the name of the group).


Answers

  1. E
  2. D
  3. D
  4. C
  5. D
  6. E
  7. D
  8. a. 212 kJ, b. 1.07 V, c. .008 M
  9. a. 3.07 x 10-3, b. .0784 L, c. 2 I- --> I2 + 2e-, d. 3.29 Amp
  10. a. 3140 J, b. 3.08 x 104, c. 332 K, d. .281 atm