Chapter 12

Question 1

Oxygen’s oxidation state is usually -2, except in hydrogen peroxide, in which it will equal ______.

Answer 1

-1

Question 2

Hydrogen’s oxidation state is usually +1, except when bonded to a metal, in which it will equal _____

Answer 2

-1

Question 3

What are the oxidation states of Al, Zn, Cd, and Ag?

Answer 3

Al = +3

Zn = +2

Cd = +2

Ag = +1

Question 4

In a voltaic cell, what is the purpose of the salt bridge?

Answer 4

serves to counter balance charges and as a source of unreactive cations

Question 5

In a galvanic cell, electrons will flow from ____ to _____ because the anode will always have a ____ energy than the cathode.

Answer 5

high, low, higher

Question 6

When the ∆G < 0 (negative), the Ecell is _____

When ∆G > 0 (positive), the Ecell is ______

Answer 6

positive

negative

Question 7

Electrolytic Cells

Answer 7

the opposite of galvanic; require an external power source to push electrons uphill and thus will have a non spontaneous ∆G (positive) and thus a negative Ecell

Question 8

T/F? Anode is the site of oxidation and the cathode is the site of reduction, regardless of the type of cell.

Answer 8

TRUE

flow of electrons is the same, spontaneity changes

Question 9

Molten electrolysis lacks a ____ _____; thus it requires an ____ ____ ___ to push the electrons towards the cathode.

Answer 9

salt bride, external power source

Question 10

If a reduction potential is more negative, this indicates that it is a ______ _____. If a reduction potential is more positive, this indicates that it is a _____ _____.

Answer 10

more negative = strong oxidant

more positive = strong reductant

Question 11

Nernst Equation

Answer 11

Ecell = 0.592/n x log (Q)

Question 12

Which of the following reduction reactions involve the greatest number of electrons per mol of oxidant?

  A. CO2 → C2O42-
  B. Cr2O72- → Cr3+
  C. NO3– → NO
  D. N2 → N2H5+
  E. Al3+ → Al

Answer 12

B

assign oxidation numbers!

Question 13

In which of the following compounds does nitrogen have the most positive oxidation state?

  A. NH3
  B. N2O4
  C. NO3
  D. N2H5+
  E. N2

Answer 13

C

practice this one out/write it out

Question 14

Given the following standard reduction potentials, which of the following statements is correct?

Ni2+ + 2 e– → Ni, –0.25 V
Cu+ + e– → Cu, +0.521 V
Co3+ + 3 e– → Co, +1.83 V

A. When Co3+/Co and Ni2+/Ni are used in a voltaic cell, Ni2+/Ni is the cathode.

B. Co3+/Co can reduce Ni2+/Ni

C. Cu+/Cu is a stronger oxidizing agent than Co3+/Co.

D. Ni2+/Ni is a stronger reducing agent that Cu+/Cu.

E. Ni2+/Ni can oxidize Cu+/Cu.

Answer 14

D

The higher the potential, the greater the tendency for reduction to occur, and therefore, the stronger the oxidizing agent is (or weaker the reducing agent). Thus, C is incorrect since cobalt has a more positive reduction potential, is more likely to be reduced, and cobalt a stronger oxidizing agent than copper.

A substance with a more positive reduction potential can oxidize those that have a less positive reduction potential. With cobalt and nickel, cobalt is more likely to be reduced and therefore will oxidize nickel. Therefore, B is incorrect. With nickel and copper, nickel is more likely to be oxidized and therefore would reduce copper. Thus, E is incorrect.

D is correct since nickel has a less positive reduction potential, is more likely to be oxidized, and therefore is a stronger reducing agent, than copper.

Question 15

Given the following standard electron potentials, which metal cation can oxidize Ni but not Ag?

Au3+ + 3e– → Au, +1.50 V 
Ag+ + e– → Ag, +0.80 V 
Cu2+ + 2e– → Cu, +0.34 V 
Ni2+ + 2e– → Ni, –0.25 V 
Fe2+ + 2e– → Fe, –0.44 V

A Au3+
  B. Fe2+
  C. Cu2+
  D. Fe2+ and Cu2+
  E. Au3+ and Cu2+

Answer 15

C - Cu

Substances that have a more positive electrode potential can oxidize those that have a less positive electrode potential.

Au3+ can oxidize both Ni And Ag, Fe2+ can oxidize neither Ni nor Ag, and Cu2+ can oxidize Ni but not Ag.

Question 16

Describe the relationship between electrode potential and reducing agent.

Answer 16

the smaller the electrode potential, the stronger the reducing agent is

Question 17

A voltaic cell was constructed using the following half-reactions (written as reduction half-reactions). What is the overall reaction and the standard cell potential of this voltaic cell?

Cd2+ + 2 e– → Cd, –0.40 V
Pb2+ + 2 e– → Pb, –0.13 V

A. Cd2+ + Pb → Cd + Pb2+, Ecell = +0.27 V
B. Cd2+ + Pb → Cd + Pb2+, Ecell = –0.27 V
C. Pb2+ + Cd → Pb + Cd2+, Ecell = +0.27 V
D. Pb2+ + Cd → Pb + Cd2+, Ecell = –0.27 V
E. Pb2+ + Cd → Pb + Cd2+,Ecell = –0.54 V

Answer 17

C

In order for Ecell to be positive, the half-reaction with a more positive potential must be the cathode (the site of reduction).

Thus, Pb2+/Pb must be the cathode (reduction) and Cd2+/Cd must be the anode (oxidation). So we flip the Cd half-reaction (and flip the sign of the Cd half reaction so we have our oxidation potential) and add the two equations to get the overall reaction: