Electrochemistry

Question 1

What is Electrochemistry?

Answer 1

A branch of chemistry which deals with the study of production of electricity happening from chemical reactions.

Question 2

What are Redox Reactions?

Answer 2

A chemical reaction in which electrons are used by one substance and gained by another is Redox Reactions.

Question 3

What are Galvanic Cells?

Answer 3

Electrochemical cells which convert the chemical energy of spontaneous redox reactions into electrical energy are called galvanic or voltaic cells.

Question 4

Explain how oxidation and reduction generates electricity?

Answer 4

Oxidation occurs at anode whereas reduction occurs at cathode, they both result in the development of potential difference between the two half cells and hence, generate electricity.

Question 5

How does a Daniell cell work?

Answer 5

It consists of two dissimilar electrodes i.e. zinc and copper. The zinc rod is dipped in zinc sulfate solution and the rod in a copper sulfate solution. The zinc electrode is the oxidation half-cell and the copper electrode is the reduction half-cell.

Zn(s) + Cu²⁺ (aq) — Zn²⁺ (aq) + Cu(s)
It has an electric potential of 1.1V.

Question 6

What happens when the external potential of a Daniell cell is lower than 1.1V?

Answer 6

When this happens the electrons flow from Zn to Cu rod and current from Cu to Zn rod. Zinc then dissolves at anode and copper deposits at the cathode.

Question 7

What happens when the external potential of a Daniell cell is equal to 1.1V?

Answer 7

Chemical reactions in the cell stop and there is no flow of electrons or current.

Question 8

What happens when the external potential of a Daniell cell is more than 1.1V?

Answer 8

The reactions get reversed which also reverses the polarity of the electrodes. This cell is called an electrolytic cell.

Question 9

What is a Salt-Bridge?

Answer 9

It is a U-shaped tube containing electrolytes (KCl, KNO³, NH⁴Cl) mixed with some kind of gel. It maintains electrical neutrality of solutions in each of the respective half-cells.

Question 10

What is Electrode Potential?

Answer 10

Potential difference between electrode and electrolyte in an electrochemical cell.

Question 11

What is Oxidation Potential?

Answer 11

The oxidation potential is when the metal electrode loses electrons and becomes oxidized.

Question 12

What is Reduction Potential?

Answer 12

Metal ions usually leave the electrolyte and deposit at the electrode causing the metal to undergo reduction.

Question 13

Explain the Cell potential.

Answer 13

The potential difference between two half-cells.
E° (cell) = E° (cathode) - E° (anode)

Question 14

What does Cell potential depend upon?

Answer 14

1) Nature of metal and its ions
2) Concentrations of electrolytes
3) Temperature

Question 15

What is Standard Hydrogen Electrode?

Answer 15

An arbitrary value that is given to a half cell to assign values to other half cells. Its value is zero.
Pt(s) | H2(g) | H⁺(g)

Question 16

Explain applications of Electrochemical Series.

Answer 16

Shows stability in reduced form.
Negative, Reducing agent.
Positive, Oxidizing agent.
Tells feasibility of reaction, if negative will not proceed.
Nature of electrode, higher E° value is cathode lower is anode.

Question 17

What is Nerst Equation?

Answer 17

Under standard conditions,
E (Mn⁺/M) = E° (Mn⁺/M) - RT/nF ln[1]/[Mn⁺]

For EMF of a cell,
E (cell) = E° (cell) - 0.0592log[Zn⁺²]/[Cu⁺²]

Question 17

What is the Equilibrium Constant from the Nerst equation?

Answer 17

In general at equilibrium,
E° (cell) = 2.303 RT/nF log Kc

Question 18

What is Gibbs energy for an Electrochemical cell?

Answer 18

It is given by,
ΔrG° = - 2.303 RT log Kc

Question 19

What is Resistance and Resistivity?

Answer 19

Resistance is the hindrance in the flow of current provided by the conductor while resistivity is defined as resistance provided by a conductor of 1m length and cross-sectional area of 1m².

Question 20

What is Conductance and Conductivity?

Answer 20

The ease with which current flows in a conductor.
G = kA/l
The inverse of resistivity is called conductivity.
k= G x l/A (cell constant)

Question 21

What are the factors affecting the conductivity of electrolytic solutions?

Answer 21

1) Nature of the electrolyte
2) Size of ions and their solvation
3) Nature of solvent and its viscosity
4) Concentration of the electrolyte in the solution
5) Temperature

Question 22

What is a cell constant?

Answer 22

The quantity l/A is called a cell constant.
G* = R x k

Question 23

What is Molar Conductivity?

Answer 23

Conductance of solution containing one mole of electrolyte kept between two electrodes having a cross-sectional area and unit length between them.

Λm = k×1000/M

Question 24

What is molar conductivity for strong electrolytes?

Answer 24

Strong electrolytes completely disassociate at all concentrations so it increases slowly with dilution.
Λm = Λm – A√c

Question 25

What is limiting molar conductivity?

Answer 25

It is when the concentration approaches zero, the molar conductivity reaches a limiting value.

Question 26

What is molar conductivity for weak electrolytes?

Answer 26

It is used by measuring Kohlrausch’s law as it increases steeply first and suddenly afterward becomes parallel with the graph.

Question 26

What is Kohlrauch’s law?

Answer 26

It states that the limiting molar conductivity of an electrolyte is the sum of the individual contributions of the cation and anion of the electrolyte.
Λ°m = v+λ°+ + v-λ°-

Question 27

What is an electrolytic cell?

Answer 27

Cells in which electricity is used to bring about a reaction. In this copper gets oxidized at the anode and deposited at the cathode causing reduction.
At anode,
Cu (s) → Cu2+ (s) + 2e-
At cathode,
Cu2+ (aq) + 2e- → Cu (s)

Question 27

What is Faraday’s first law?

Answer 27

Chemical deposition at any electrode is directly proportional to the quantity of electricity passed through the electrolyte.
w = Zit

Question 28

What is Faraday’s second law?

Answer 28

When the same quantity of electricity is passed through different electrolytes connected in a series, the weights of different substances liberated at the electrodes are directly proportional to their equivalent weight.
w1/E1 = w2/E2

Question 29

What is Faraday’s Constant?

Answer 29

The amount of electricity required for oxidation and reduction depends on the stoichiometry of the electrode reaction.
Its value is 96500 mol⁻¹

Question 30

What do the products of Electrolysis depend upon?

Answer 30

1) Nature of material being electrolyzed.
2) Types of electrodes being used.
3) Nature of species present in electrolytic cells.
4) Kinetic barrier or overvoltage.