Ch. 12: Electrochemistry

Question 1

List the 3 types of electrochemical cells.

Answer 1

Galvanic, electrolytic, and concentration

Question 2

What type of reactions do galvanic, electrolytic, and concentration cells house?

Answer 2

Galvanic and concentration: spontaneous reactions

Electrolytic: non-spontaneous reactions

Question 3

What are electrodes?

Answer 3

Site where oxidation or reduction takes place

Question 4

What reaction occurs at the anode vs the cathode?

Answer 4

Oxidation occurs at anode. Reduction occurs at cathode.

AN OX
RED CAT

Question 5

What is emf? How does it relate to Gibb’s free energy?

Answer 5

Emf is the electron motive force, which corresponds to the voltage or electrical potential difference of the cell.

If emf is POSITIVE, then ΔG is NEGATIVE.

If emf is NEGATIVE, then ΔG is POSITIVE.

Question 6

Which way do electrons move in an electrochemical cell?

Answer 6

Anode to cathode

Question 7

Which way does current run?

Answer 7

Cathode to anode

CURRENT CATHODE

Question 8

What is the function of a salt bridge?

Answer 8

It permits the exchange of cations and anions that do not react with the electrodes or ions in solution. This is needed to dissipate newly generated charges. If too much positive charge builds up on the anode and too much negative charge on the cathode then current will eventually cease.

Question 9

What does the double vertical line || indicate in a cell diagram?

Answer 9

Presence of salt bridge

Question 10

What does a single vertical line indicate in a cell diagram?

Answer 10

Indicates a phase boundary

Zn (s) | Zn2+ (aq)

Question 11

What is listed on the left side of the cell diagram shorthand?

Answer 11

Anode

anode | anode solution (concen.) || cathode | cathode solution (concen.)

Question 12

What is the ΔG of an electrolytic cell?

Answer 12

POSITIVE because it is non-spontaneous

Question 13

How are non-spontaneous reactions in an electrolytic cell driven forward?

Answer 13

By an external voltage change (battery)

Question 14

What is Faraday’s Law?

Answer 14

The liberation of gas and deposition of elements on electrodes is directly proportional to the number of electrons being transferred during the oxidation-reduction reaction.

Question 15

What is Faraday’s constant?

Answer 15

1 F = 10^5 C/mol e-

charge per mol of electrons

Question 16

What is the electrodeposition equation?

Answer 16

mol M = It/nF

mol M is amount of metal ion deposited at electrode
I is current
t is time
n is number of electron equivalents for metal ion
F is Faraday’s constant

Question 17

How is emf calculated?

Answer 17

E°cell = E° (red,cathode) - E° (red,anode)

Question 18

Describe the design of a concentration cell.

Answer 18

The electrodes are chemically identical and connected by a conductive material.

Question 19

What is isolelectric focusing?

Answer 19

A technique used to separate amino acids or polypeptides based on their isoelectric points (pH at net neutral charge)

Question 20

What does a more positive E°red mean?

Answer 20

Greater relative tendency for reduction to occur

Question 21

How do you determine which electrode is the cathode vs anode based on reduction potential for a galvanic cell?

Answer 21

The electrode with the more positive E° is the cathode because this is where reduction occurs. The less positive E° is the anode.

Question 22

What is considered the negative electrode in a galvanic vs electrolytic cell? Why?

Answer 22

Galvanic: anode because it is the source of electrons

Electrolytic: cathode because it is attached to the positive pole of the external voltage source and attracts anions

Question 23

What is considered the positive electrode in a galvanic vs electrolytic cell?

Answer 23

Galvanic: cathode

Electrolytic: anode

Question 24

Are cations attracted to the cathode or anode?

Answer 24

Cathode because that is where reduction takes place

Question 25

Are anions attracted to the cathode or anode?

Answer 25

Anode because that is where oxidation takes place.

Question 26

How do you determine which electrode is the cathode vs anode based on reduction potential for an electrolytic cell?

Answer 26

The electrode with the more positive reduction is forced by the external voltage source to be oxidized and is, therefore, the anode.

The electrode with the less positive reduction potential is forced to be reduced and is, therefore, the cathode.

Question 27

What is the equation that relates ΔG and E°cell?

Answer 27

ΔG = - nFE°cell NOTICE THE NEGATIVE SIGN

n is # of moles of electrons
F is Faradays constant (10^5)

Question 28

What is the Nernst equation and when is it used?

Answer 28

Ecell = E°cell - (RT/nF) ln Q

This equation is used when conditions deviate from standard conditions (298 K, 1 M, 1 atm)

Question 29

What is the Nernst equation assuming 298K conditions?

Answer 29

Ecell = E°cell - (0.0592/n) log Q

Question 30

If Keq is greater than 1, what is E°cell and ΔG?

Answer 30

If Keq is greater than 1 then products are favored. E°cell will be positive and ΔG will be negative.

Question 31

If Keq is less than 1, what is E°cell and ΔG?

Answer 31

If Keq is less than 1 then reactants are favored. E°cell will be negative and ΔG will be positive.

Question 32

What equation relates ΔG and Q?

Answer 32

ΔG = ΔG° + RT ln Q