19.2.3 Standard Reduction Potentials

Question 1

Standard Reduction Potentials

Answer 1

• E cell values can be compared by replacing one half-cell of a galvanic cell.
• By convention, E cell values are compared by reference to the standard hydrogen electrode (SHE).
• The standard reduction potential (E ̊) of a half-cell is the relative potential of a substance to be reduced by hydrogen.

Question 2

note

Answer 2

• By replacing one of the two half-cells in a galvanic cell, the relative ability of a substance to be oxidized or reduced can be measured. For example, iron has a greater potential to be oxidized than lead or copper.
• The standard hydrogen electrode (SHE) is constructed from 1 atm hydrogen gas bubbling over a platinum electrode in 1 M H + . The reaction at this electrode is the simplest reduction reaction, with a single proton gaining a single electron.
• This electrode is used as the standard half-cell against which other half-cell potentials are compared.
• By convention, standard reduction potentials are given for half-reactions. Standard reduction potentials are the relative potential of a substance to be reduced by hydrogen.
• The standard oxidation potential is the potential of a substance to be oxidized by hydrogen. Standard oxidation potentials can be calculated by multiplying standard reduction potentials by –1.

Question 3

The more negative the electrode reduction potential, the _____ the reducing agent and the _____ the oxidizing agent in the redox pair.

Answer 3

stronger, weaker

Question 4

The standard reduction potential of the tin ion (Sn2+) is -0.14 V.

SN2+ (aq) + 2e- -> Sn(s)

What is the standard oxidation potential of the tin (Sn(s))?

Answer 4

+0.14 V

Question 5

Which of the following species is the strongest oxidizing agent?

Answer 5

Reduction half-reaction:
Au3+ + 3e−
Standard reduction potential:
+1.42 V

Question 6

As a demonstration, a chemistry teacher sandwiched a small piece of blotter paper soaked with a solution of NaCl between a copper penny and a silver dime. She then touched the leads of a voltmeter to each coin. What did the voltmeter indicate?

Answer 6

A reading of approximately one-half volt

Question 7

Which of the following is not a reason why platinum was chosen as part of the standard hydrogen electrode?

Answer 7

Platinum is a very strong reducing agent

Question 8

Standard Reduction potentials of half-cells are measured against what?

Answer 8

The hydrogen half cell

½ H2 (1.0 atm) | H + (1.0 M)

Question 9

What are “standard conditions”?

Answer 9

1.0 M solutions, 1.0 atm pressure, and 298 K

Question 10

In order for a spontaneous reaction to occur, what must be true of the standard reduction potentials?

Answer 10

They can be any two values that are not equal.

Question 11

What is the relationship between the potential difference between two half-cells and the spontaneity of the overall reaction?

Answer 11

The larger the potential difference, the more spontaneous the reaction.

Question 12

The electrode potential of the standard hydrogen electrode is 0.00 V. How is this potential determined?

Answer 12

Any value could be chosen; 0.00 V is assigned for convenience.