Chapter Four : Electrolysis Flashcards
Electrolysis
Is a chemical reaction caused by the passage of a current through an electrolyte
Features of an electrolytic cell
An electrolyte solution that contains free-moving ions
Two electrodes at which electrolysis reactions occur
An external source of electrons, such as a battery
Electrode charges
Cathode is neg
Anode is pos
Where is ions in solution attracted to
Cations are attracted to cathode
Anions are attracted to anode
Electrolysis of molten ionic compounds
Have inert electrodes
The cations attract to the cathode
The anions attract to the anode
Electrolysis of water
When a current is applied to pure water, no electrolysis occurs
If an electrolyte is added in low concentration then electrolysis occurs
Produces hydrogen and oxygen
Electrolysis of aqueous solutions of ionic compounds
There are 2 oxidising and 2 reducing agents
Water may react at the cathode or the anode
The highest E value for the oxidisng agent and lowest E value for reducing agent
Voltage = E oxidising agent - E reducing agent
Factors affecting the electrolysis of aq solutions
The concentration of the electrolytes
Nature of the electrolyte
Nature of the electrodes
Effect of concentration
When solutions are >6M the reducing agents can change positions on the electrochemical series
Nature of electrolyte
Depending on the reactants in the solution, different products can form at the anode or cathode
Nature of electrodes
When metals are used at the anode they may be oxidised in preference to the electrolytic solution
Electroplating
The item being plated is always at the cathode and the metal plating the onto the article is at the anode
The solution contains the salt of the metal being plated
Faraday’s formula 1
Q=It
Q= electrical charge in coloumbs
I= current in amperes
t= time in seconds
Faraday’s constant
96500 C per mol
Faraday’s formula 2
n(electrons) = Q/F
