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63 Cards in this Set

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The loss of electrons


The gain of elecrons

Oxidation-Reduction Reaction

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


The study of the relationship between electricity and chemical reactions.

Oxidation Number (Oxidation State)

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.

In a redox reaction this must happen.

Both oxidation and reaction must occur.

Oxidizing Agent (Oxidant)

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

Reducing Agent (Reductant)

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

Identify Oxidizing and Reducing Agents:

Cd+NiO2+2H2O → Cd(OH)2+Ni(OH)2

Cd increases in oxidation state from 0 to +2

Ni decreases from +4 to +2

Identify the Oxidizing and Reducing Agents

2H2O+All+MnO4^- → Al(OH)4^-+MnO2

Al is the reducing agent

MnO4 is the oxidizing agent

Half Reaction

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

Zn^2+ + 2e^- Zn

Electrons are shown as products in what type of reactions?

An Oxidation Half-Reactions

Electrons are shown as reactants in what type of reaction?

A Reduction Half-Reaction

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


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.

Equal; gained

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

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)

How do you balance a half-reaction?

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.

Complete and balance this equation:

MnO4^- + C2O4²^- → Mn²^+ + CO2

(Acidic Solution)

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

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

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

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

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

Cr2O7²^- + Cl^-Cr³^+ + Cl2

(Acidic Solution)

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

Page 849 in the AP Chemistry 11e textbook

Complete and balance the equation by half-reaction method:

Cu + NO3^-Cu²^+ + NO2

(Acidic Solution)

Cu + 4H^+ + 2NO3^-Cu²^+ + 2NO2 + H2O

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

Mn²^+ + NaBiO3Bi³^+ + MnO4^-

(Acidic Solution)

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

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

OH^- and H2O

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

CN^- + MnO4^-CNO^- + MnO2

(Basic Solution)

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

Page 850 in the AP Chemistry 11e textbook.

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

NO2^- + Al → NH3 Al(OH)4^-

(Basic Solution)

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

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

Cr(OH)3 + ClO^-CrO4²^- + Cl2

(Basic Solution)

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

Voltaic (or Galvanic) Cell

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


Two solid metals that are connected by an external circuit.


The electrode at which reduction occurs


The electrode at which oxidation occurs.


The two compartments of a voltaic cell

Anode is the _________ half-reaction.


Cathode is the __________ half-reaction.


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

Loses mass

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

Gains mass

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

Anions; Cations

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

To balance the charge in the anode compartment.

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

Anode; Cathode

Is the Anode positive or negative?


Is the Cathode positive or negative?


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?


Zn → Zn²^+ + 2e^-


ClO3^- 6H^+ + 6e^- → Cl^- + 3H2O

There are two reactions in a voltaic cell:

Zn → Zn²^+ + 2e^-

ClO3^- 6H^+ + 6e^- → Cl^- + 3H2O

Which electrode is consumed in the cell reaction?

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

There are two reactions in a voltaic cell:

Zn → Zn²^+ + 2e^-

ClO3^- 6H^+ + 6e^- → Cl^- + 3H2O

Which electrode is positive?

The cathode (Cl) is positive.

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


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

Electromotive Force (EMF)

Electromotive Force (EMF)

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.

Electromotive force is also known as...

Cell Potential

What is Ecell?

The EMF of a cell.

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


What is cell?

The Standard EMF or Standard Cell Potential

What is Standard EMF?

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

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


What is red?

Standard Reduction Potentials

What is the formula to calculate E°cell?

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

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

cell > 0

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

The reactant side (The left side)

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

Does not

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

E°red (cathode) = 0.34V

Page 858 in the AP Chemistry 11e textbook.

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

E°red = 0.34V

Page 858 in the AP Chemistry textbook.

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

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

E°cell = 0.79V

Page 859 in the AP Chemistry 11e textbook.

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^-


Page 859 in the AP Chemistry 11e textbook.

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


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