electrolytic cells

What do electrolytic cells do?

They use an external source of electrical energy to bring about redox reactions that would otherwise be non-spontaneous.

What is an electrolyte?

Liquid, usually molten, ionic compound or a solution of an ionic compound.

What happens to ions in this process?

They are discharged.

Why are electrodes described as inert?

Since they do not take part in the redox reactions

Cathode

negative electrode

Anode

positive electrode

What happens at the cathode?

Reduction of cations

What happens at the anode?

Oxidation of anions

What does selective discharge depend on?

the relative E values for the ions, the relative concentrations of ions in the electrolyte, the nature of the electrode

water oxidation reaction

anode, 2H20 --> 4H+ + O2 +4e-

water reduction reaction

cathode, 2H2O + 2e- --> H2 + 2OH-

electrolysis of copper (II) sulfate with copper electrodes - observations

- no pH change
- disintegration of Cu anode
- no change in the intensity of the blue colour of the Cu2+ solution
- pinky brown colour deposited at the cathode

electrolysis of copper ions with graphite electrodes - observations

- pinky brown colour deposited at the cathode
- colourless gas O2 discharged at the anode
- decrease in pH due to the release of H+ ions
- loss of intensity of the blue colour of Cu2+ solution because of the discharge of Cu2+

if we look at the cell potentials for oxidation we have to do what?

turn them into -Ecell, so that positive values become negative and vice versa

factors affecting the amount of product of electrolysis

charge, time, current

charge

the lower, the more product

What is the process of electroplating?

The process of using electrolysis to deposit a layer of a metal on top of another metal or other conductive object.

features of an electrolytic cell used for electroplating

- an electrolyte containing the metal ions which are to be deposited;
- the cathode made of the object to be plated;
- sometimes the anode is made of the same metal which is to be coated because it may be oxidized to replenish the supply of ions in the electrolyte.