Electrochemistry (Chapter 20)

Front 1

Oxidation

Back 1

The loss of electrons

Front 2

Reduction

Back 2

The gain of elecrons

Front 3

Oxidation-Reduction Reaction

Back 3

Reactions that occur when electrons are transfered from an atom that is oxidized to an atom that is reduced.

Front 4

Electrochemistry

Back 4

The study of the relationship between electricity and chemical reactions.

Front 5

Oxidation Number (Oxidation State)

Back 5

A positive or negative whole number assigned to an element in a molecule or ion on the basis of a set of formula rules; to some degree it reflects the positive or negative character of that atom.

Front 6

In a redox reaction this must happen.

Back 6

Both oxidation and reaction must occur.

Front 7

Oxidizing Agent (Oxidant)

Back 7

The substance that is reduced and thereby causes the oxidation of some other substance in an oxidation-reduction reaction.

Front 8

Reducing Agent (Reductant)

Back 8

The substance that is oxidized and thereby causes the reduction of some other substance in an oxidation-reduction reaction.

Front 9

Identify Oxidizing and Reducing Agents:

Cd+NiO2+2H2O → Cd(OH)2+Ni(OH)2

Back 9

Cd increases in oxidation state from 0 to +2

Ni decreases from +4 to +2

Front 10

Identify the Oxidizing and Reducing Agents

2H2O+All+MnO4^- → Al(OH)4^-+MnO2

Back 10

Al is the reducing agent

MnO4 is the oxidizing agent

Front 11

Half Reaction

Back 11

An equation for either an oxidation or reduction that explicitly shows the electrons involved l, for example,

Zn^2+ + 2e^- → Zn

Front 12

Electrons are shown as products in what type of reactions?

Back 12

An Oxidation Half-Reactions

Front 13

Electrons are shown as reactants in what type of reaction?

Back 13

A Reduction Half-Reaction

Front 14

Equations that show either oxidation or reduction alone are called ___________.

Back 14

Half-Reactions

Front 15

In the overall redox reaction, the number of electrons lost in the oxidation half-reaction must be _____________ to the number of electrons ___________ in reduction half-reaction.

Back 15

Equal; gained

Front 16

What are the five steps for balancing a redox redaction that occurs in acidic solution ?

Back 16

1. Divide the equation into two half reactions

2. Balance each half-reaction

3. Multiply the half reactions to make the electron equal

4. Add the two half-reactions together

5. Check to make sure that atoms are balanced (If they're not you did something wrong)

Front 17

How do you balance a half-reaction?

Back 17

First, balance the elements other than H and O.

Next, balance the O atoms by adding H2O as needed.

Then, balance the H atoms by adding H^+ as needed.

Finally, balance the charge by adding e^- as needed.

Front 18

Complete and balance this equation:

MnO4^- + C2O4²^- → Mn²^+ + CO2

(Acidic Solution)

Back 18

16H^+ + 2MnO4^- + 5C2O4²^- → 2Mn²^+ + 8H2O + 10CO2

Hint 18

Page 847-848 in the AP Chemistry 11e textbook.

Front 19

If the equation for a redox reaction is balanced, will free electrons appear in the equation as either reactants or products?

Back 19

No, because the electrons should have been completely canceled out in step 3 and 4 when balancing and adding the half-reactions.

Front 20

Complete and balance the equation by the method of half-reactions:

Cr2O7²^- + Cl^- → Cr³^+ + Cl2

(Acidic Solution)

Back 20

14H^+ + Cr2O7²^- + 6Cl^- → 2Cr³^+ + 7H2O + 3Cl2

Hint 20

Page 849 in the AP Chemistry 11e textbook

Front 21

Complete and balance the equation by half-reaction method:

Cu + NO3^- → Cu²^+ + NO2

(Acidic Solution)

Back 21

Cu + 4H^+ + 2NO3^- → Cu²^+ + 2NO2 + H2O

Front 22

Complete and balance this equation by the half-reaction method:

Mn²^+ + NaBiO3 → Bi³^+ + MnO4^-

(Acidic Solution)

Back 22

2Mn²^+ + 5NaBiO3 +14H^+ → 2MnO4^- + 5Bi³^+ + 5Na^+ + 7H2O

Front 23

If a redox reaction occurs in basic solution, the equation must be completed by using ________ and ________ rather than H^+ and H2O.

Back 23

OH^- and H2O

Front 24

Complete and balance this equation for a redox reaction by half-reaction method:

CN^- + MnO4^- → CNO^- + MnO2

(Basic Solution)

Back 24

3CN^- + H2O + 2MnO4 → 3CNO^- + 2MnO2 + OH^-

Hint 24

Page 850 in the AP Chemistry 11e textbook.

Front 25

Complete and balance this equation using the half-reaction method:

NO2^- + Al → NH3 Al(OH)4^-

(Basic Solution)

Back 25

NO2^- + 2Al + 5H2O + OH^- → NH3 + 2Al(OH)4^-

Front 26

Complete and balance this reaction by using the half-reaction method:

Cr(OH)3 + ClO^- → CrO4²^- + Cl2

(Basic Solution)

Back 26

2Cr(OH)3 +6ClO^- → 2CrO4²^- + 3Cl2 + 2OH^- + 2H2O

Front 27

Voltaic (or Galvanic) Cell

Back 27

A device in which the transfer of electrons takes place through an external pathway rather than directly between reactants.

Front 28

Electrodes

Back 28

Two solid metals that are connected by an external circuit.

Front 29

Anode

Back 29

The electrode at which reduction occurs

Front 30

Cathode

Back 30

The electrode at which oxidation occurs.

Front 31

Half-Cells

Back 31

The two compartments of a voltaic cell

Front 32

Anode is the _________ half-reaction.

Back 32

Oxidation

Front 33

Cathode is the __________ half-reaction.

Back 33

Reduction

Front 34

The oxidized electrode in a redox reaction gains or loses mass?

Back 34

Loses mass

Front 35

The reduced electrode in a redox reaction gains or loses mass?

Back 35

Gains mass

Front 36

______ always migrate to toward Anode and _______ always migrate to the Cathode.

Back 36

Anions; Cations

Front 37

Why do anions in a salt bridge migrate toward the anode?

Back 37

To balance the charge in the anode compartment.

Front 38

In a voltaic cell electrons flow from the _______ to the _______.

Back 38

Anode; Cathode

Front 39

Is the Anode positive or negative?

Back 39

Negative

Front 40

Is the Cathode positive or negative?

Back 40

Positive

Front 41

There are two reactions in a voltaic cell:

Zn → Zn²^+ + 2e^-

ClO3^- 6H^+ + 6e^- → Cl^- + 3H2O

Which reaction occur at the anode and which occurs at the cathode?

Back 41

Anode:

Zn → Zn²^+ + 2e^-

Cathode:

ClO3^- 6H^+ + 6e^- → Cl^- + 3H2O

Front 42

There are two reactions in a voltaic cell:

Zn → Zn²^+ + 2e^-

ClO3^- 6H^+ + 6e^- → Cl^- + 3H2O

Which electrode is consumed in the cell reaction?

Back 42

The anode (Zn) is consumed in the cell reaction.

Front 43

There are two reactions in a voltaic cell:

Zn → Zn²^+ + 2e^-

ClO3^- 6H^+ + 6e^- → Cl^- + 3H2O

Which electrode is positive?

Back 43

The cathode (Cl) is positive.

Front 44

The difference in potential energy per electrical charge between two electrodes is measured in units of ______?

Back 44

Volts

Front 45

Volts (V) is the measure of .....

Back 45

Electromotive Force (EMF)

Front 46

Electromotive Force (EMF)

Back 46

A measure of the driving force, or electrical pressure, for the completion of an electrochemical reaction. Electromotive force is measured in volts: V = J/C. Also called the cell potential.

Front 47

Electromotive force is also known as...

Back 47

Cell Potential

Front 48

What is Ecell?

Back 48

The EMF of a cell.

Front 49

For any cell reaction that proceeds spontaneously the cell potential is ___________?

Back 49

Positve

Front 50

What is E°cell?

Back 50

The Standard EMF or Standard Cell Potential

Front 51

What is Standard EMF?

Back 51

The EMF of a cell at standard conditions. (25°C, 1 atm, 1 M, etc.)

Front 52

If the standard cell potential is +0.85V at 25°C, is the redox reaction of the cell spontaneous?

Back 52

Yes

Front 53

What is E°red?

Back 53

Standard Reduction Potentials

Front 54

What is the formula to calculate E°cell?

Back 54

E°cell = E°red (Cathode) - E°red (Anode)

Front 55

For all spontaneous reactions at standard conditions, E°cell is greater than, equal to, or less than 0.

Back 55

E°cell > 0

Front 56

In reduction reaction the electrons appear on what side of the reaction.

Back 56

The reactant side (The left side)

Front 57

Changing the stoichiometric coefficient in a half-reaction ___________ affect the value of the standard reduction potential.

Back 57

Does not

Front 58

Zn + Cu²^+ → Zn²^+ + Cu; E°cell = 1.10V

Given that the standard reduction potential of Zn²^+ to Zn is -0.76V, calculate the E°red for the reduction of Cu²^+ to Cu:

Cu²^+ + 2e^- → Cu

Back 58

E°red (cathode) = 0.34V

Hint 58

Page 858 in the AP Chemistry 11e textbook.

Front 59

A voltaic cell is based on the half-reactions

In^+ → Ln³^+ + 2e^-

Br2 + 2e^- → 2Br^-

The standard emf for this cell is 1.46V.

Calculate the E°red using Appendix E

Back 59

E°red = 0.34V

Hint 59

Page 858 in the AP Chemistry textbook.

Front 60

Using the standard reduction table in Appendix E calculate the standard emf of this reaction:

Cr2O7²^- + 14H^+ + 6I^- → 2Cr³^+ 3I2 + 7H2O

Back 60

E°cell = 0.79V

Hint 60

Page 859 in the AP Chemistry 11e textbook.

Front 61

Using Appendix E in the AP Chemistry 11e textbook, calculate the standard emf for a cell that employs the following overall reaction:

2Al + 3I2 → 2Al³^+ + 6I^-

Back 61

2.20V

Hint 61

Page 859 in the AP Chemistry 11e textbook.

Front 62

The more ________ the value of the E°red, the greater the driving force for reduction under standard conditions.

Back 62

Positive

Front 63

The smaller the difference is between the standard reduction potentials of the cathode and anode, the ________ the driving force for the overall redox reaction.

Back 63

Smaller