ELECTROCHEMISTRY

Question 1

Difference between galvanic and electrolytic cell

Answer 1

Galvanic cell
- chemical to electrical energy
- spontaneous redox rxn
- anode (-ve), cathode (+ve)

Electrolytic cell
- electrical to chemical energy
- non-spontaneous redox rxn
- anode (+ve), cathode (-ve)

Question 2

purpose of salt bridge in galvanic cell

Answer 2

1. complete electrical circuit through the flow of electrons within the salt bridge
2. prevent direct mixing of the 2 solutions
3. maintain electrical neutrality in each half-cell

Question 3

factors affecting electrode potential

Answer 3

1. nature of metal and ions (in redox series)
2. concentration of ions
3. temperature (cause metal to dissolve)
4. pressure (if have gas)

Question 4

formula for E⦵cell

Answer 4

E⦵(reduction) - E⦵(oxidation)

aka E⦵(cathode) - E⦵(anode)

Question 5

how to tell if redox reaction is feasible

Answer 5

If ∆E⦵ > 0V: energetically feasible, spontaneous rxn

If ∆E⦵ < 0V: not energetically feasible, non-spontaneous rxn

Question 6

Formula linking Gibbs free energy and electrode potential

Answer 6

∆G⦵ = -nFE⦵

Question 7

Limitations of standard electrode potentials

Answer 7

Indicates energetic feasibility, but NOT kinetic stability

Question 8

Features of improved batteries

Answer 8

Smaller size, Smaller mass, Higher voltage, Lower cost, Longer shelf-life

Question 9

Advantages and disadvantages of zinc-carbon dry cell

Answer 9

Advantages: cheap, portable source of energy

Disadvantages: cannot recharge, low shelf-life cos Zn disintegrates

Question 10

Advantages and disadvantages of nickel-cadmium rechargeable cell

Answer 10

Advantages: rechargeable, portable source of energy

Disadvantages: high cost of nickel and cadmium, prone to damage by overcharging

Question 11

Advantages and disadvantages of fuel cells

Answer 11

Advantages: pollution free (produce water only), high power to mass ratio

Disadvantages: High cost of platinum and nickel metals, require high temp for rxn to occur

Question 12

Definition of standard electrode potential, E⦵

Answer 12

Standard electrode potential of an electrode is the relative potential of this electrode

under standard conditions,

compared with the standard hydrogen electrode,

whose potential is assigned as 0V

Question 13

Definition of standard hydrogen electrode

Answer 13

Standard hydrogen electrode consists of H2(g) at 1 bar bubbling over platinum electrode coated with finely divided platinum, which is dipped into 1moldm^-3 H+ (aq)

Question 14

Definition of standard cell potential, E⦵cell

Answer 14

Standard cell potential is the emf of a galvanic cell which consists of two half-cells connected under standard conditions.

The E⦵cell value is the difference between the two standard electrode potentials.

Question 15

Factors affecting selective discharge of ions

Answer 15

1. State of electrolyte (molten / aqueous)
2. Species of ions (position in redox series)
3. Concentration of ions
4. Nature of electrode

Question 16

What is faraday’s law of electrolysis about

Answer 16

mass of substance liberated / dissolved from an electrode is PROPORTIONAL to the quantity of electricity

Question 17

Formulas for quantitative electrolysis

Answer 17

Q = I x t = n x F

F = L x e

Question 18

Industrial applications of electrolysis

Answer 18

Anodising of aluminium (anode)
Purification of copper (anode)
Electroplating (cathode)