Chapter 23 - Redox and electrode potentials

Question 1

What is reduction?

Answer 1

A gain of electrons or a decrease in oxidation number

Question 2

What is oxidation?

Answer 2

A loss of electrons or an increase in oxidation number

Question 3

What does the oxidising agent do?

Answer 3

Takes electrons from the species being oxidised

Question 4

What does the reducing agent do?

Answer 4

Adds electrons to the species being reduced

Question 5

What happens when potassium manganate is titrated?

Answer 5

MnO4- ions are reduced

Question 6

Describe the process of a potassium manganate titration

Answer 6

Potassium manganate is added to a burette
Sulfuric acid is added to a conical flask
The end-point of the titration is judged when there is a permanent pink colour change

Question 7

What happens during an iodine/thiosulfate titration?

Answer 7

Thiosulfate ions are oxidised and iodine is reduced

Question 8

Describe the process of an iodine/thiosulfate titration

Answer 8

Sodium thiosulfate is added to the burette
Add an excess of potassium iodide to a solution of the oxidising agent in a conical flask
The end-point is when a dark, straw colour is reached

Question 9

What happens when copper reacts with iodide ions?

Answer 9

A solution of I2 and CuI is formed

Question 10

How many moles of Cu2+ does one mole of S2O32- produce?

Answer 10

1

Question 11

What is a voltaic cell?

Answer 11

One which converted chemical energy into electrical energy

Question 12

What is a half cell?

Answer 12

It contains the species present in one half-equation

Question 13

\What does a half cell consist of?

Answer 13

Typically a metal electrode in a solution of its aqueous metal ions

Question 14

What is an ion-ion half cell?

Answer 14

Contains ions of the same element in different oxidation states using an inert metal electrode

Question 15

Which is the negative electrode?

Answer 15

The one where the more reactive metal loses electrons

Question 16

Which is the positive electrode?

Answer 16

The one where the less reactive metal gains electrons

Question 17

What is the definition for standard electrode potential?

Answer 17

The e.m.f of a half-cell connected to a standard hydrogen half-cell under standard conditions

Question 18

What is the standard electrode potential of a hydrogen half cell?

Answer 18

0v

Question 19

How do you measure the standard electrode potential?

Answer 19

Two electrodes are connected by a wire to allow the transfer of electrons
The two solutions are connected by a salt bridge which allows ions to flow

Question 20

What does a very negative standard electrode potential indicate?

Answer 20

The greater the tendency to lose electrons and undergo oxidation
The metal is more reactive

Question 21

What does a very positive standard electrode potential indicate?

Answer 21

The greater the tendency to gain electrons and undergo reduction
The metal is less negative

Question 22

How do you calculate the standard electrode potential of a cell?

Answer 22

The potential of the positive electrode - the potential of the negative electrode

Question 23

When ordering various electrode potentials from most negative to most positive, where will you find the strongest reducing agent?

Answer 23

The top left

Question 24

When ordering various electrode potentials from most negative to most positive, where will you find the strongest oxidising agent?

Answer 24

The bottom right

Question 25

When will the oxidising system on the left of an equation react?

Answer 25

When there are redox systems with a more negative electrode potential

Question 26

What are the limitations when considering electrode potentials?

Answer 26

The reaction might be feasible, but have a high activation energy with a very slow rate
The conditions might not be standard
Don’t apply to equilibria or solutions that aren’t aqueous

Question 27

What are primary cells?

Answer 27

Non-rechargeable

Can only be used once

Question 28

How is energy produced in primary cells?

Answer 28

Oxidation and reduction at the electrodes

Question 29

What are secondary cells?

Answer 29

Rechargeable cells - the reaction can be reversed

Question 30

How do fuel cells produce energy?

Answer 30

The fuel and oxygen flow into a cell and the products flow out. This type of cell can operate continuously