chapter 3 section 6

Question 1

How are standard reduction potentials measured?

Answer 1

Using voltages generated in reaction half-cells

Question 2

What is a half-cell?

Answer 2

A solution with 1 M of the oxidized and reduced forms of a substance plus an electrode.

Question 3

What is a redox couple?

Answer 3

The oxidized and reduced forms of a substance in a half-cell.

Question 4

What does the voltmeter measure?

Answer 4

The electromotive force (emf) between the sample and reference half-cells.

Question 5

When is a sample half-cell reduction potential positive?

Answer 5

positive when the sample gains electrons spontaneously.

Question 6

When is a sample half-cell reduction potential negative?

Answer 6

When electrons flow away from the sample cell (oxidation occurs there).

Question 7

How is the standard reduction potential determined for a half-cell?

Answer 7

By measuring electron flow relative to a reference half-cell; direction of electron flow indicates sign of ℰ₀′.

Question 8

What do ℰ₀′ values indicate?

Answer 8

They predict the direction of redox reactions.

Question 9

How are redox reactions tabulated?

Answer 9

As reductions, regardless of what actually occurs in the half-cell.

Question 10

What does a large positive ℰ₀′ mean?

Answer 10

The oxidized form strongly accepts electrons; it’s a strong oxidizing agent (e.g., O₂).

Question 11

What does a large negative ℰ₀′ mean?

Answer 11

The reduced form strongly donates electrons; it’s a strong reducing agent (e.g., NADPH).

Question 12

Does the standard reduction potential (ℰ₀′) always reflect cellular conditions?

Answer 12

No, it assumes 1 M concentrations, which are rarely present in cells.

Question 13

What affects reduction potentials besides concentration?

Answer 13

The molecular environment, especially for flavins

Question 14

Why do flavoproteins have different reduction potentials than free flavins?

Answer 14

Protein binding alters the local environment, changing the redox properties.

Question 15

How can standard reduction potentials (ℰ₀′) be used in redox reactions?

Answer 15

They help predict electron flow and calculate energy changes (ΔG°′).

Question 16

In a spontaneous redox reaction, which half-reaction donates electrons?

Answer 16

The half-reaction with the more negative ℰ₀′.

Question 17

Which half-reaction accepts electrons?

Answer 17

The half-reaction with the more positive ℰ₀′.

Question 18

How is Δℰ₀′ calculated?

Answer 18

Δℰ₀′ = ℰ₀′(acceptor) − ℰ₀′(donor)