Electrochemistry Electrolysis Electrolytic Cells An electrolytic cell is an electrochemical cell that undergoes a redox reaction when electrical energy is applied. It is most often used to decompose chemical compounds, in a process called electrolysis. An electrolytic cell is an electrochemical cell that undergoes a redox reaction when electrical energy is applied. It is most often used to decompose chemical compounds, in a process called electrolysis.

Electrochemistry Electrolysis Electrolytic Cells One of the simplest electrolytic cell consists of two copper strips dipping in an aqueous solution of copper sulphate.

Electrochemistry Electrolysis If a DC voltage is applied to the two electrodes, then Cu 2+ ions discharge at the cathode, thus copper metal is deposited on the cathode. Cu 2+ (aq) + 2e - → Cu(s) At the anode, copper is converted into Cu 2+ ions. Cu(s) → Cu 2+ (s) + 2e - Thus, copper is dissolved (oxidised) at anode and deposited (reduced) at cathode. Thus, copper is dissolved (oxidised) at anode and deposited (reduced) at cathode.

Electrochemistry Electrolysis Electrolysis is the basis for an industrial process in which impure copper is converted into copper of high purity. The impure copper is made an anode that dissolves on passing current and pure copper is deposited at the cathode.

Electrochemistry Electrolysis Many metals like Na, Mg, Al, etc. are produced on large scale by electrolytic reduction of their respective cations where no suitable chemical reducing agents are available for this purpose.

Electrochemistry Electrolysis Quantitative Aspects of Electrolysis Michael Faraday first described the quantitative aspects of electrolysis. He put forward two laws of electrolysis. He put forward two laws of electrolysis. Michael Faraday

Electrochemistry Electrolysis Faraday’s First Law of Electrolysis The mass of substance (m) deposited at any electrode during electrolysis by a current is directly proportional to the quantity of charge (q) passed through the electrolyte. The mass of substance (m) deposited at any electrode during electrolysis by a current is directly proportional to the quantity of charge (q) passed through the electrolyte. m  q or m = Zq where Z is a constant called Electrochemical Equivalent. since q = It  m = ZIt

Electrochemistry Electrolysis Faraday’s Second Law of Electrolysis The amounts of different substances liberated by the same quantity of electricity passing through the electrolytic solution are proportional to their chemical equivalents. The amounts of different substances liberated by the same quantity of electricity passing through the electrolytic solution are proportional to their chemical equivalents.

Electrochemistry Electrolysis Faraday’s Second Law of Electrolysis If m 1, m 2 are masses of substance liberated or deposited on various electrode and E 1, E 2 are Chemical equivalents of the substances liberated or deposited, then,

Electrochemistry Electrolysis Faraday’s Second Law of Electrolysis Faraday’s second law of electrolysis also states that the electrochemical equivalent of a substance is directly proportional to its chemical equivalent. If Z 1, Z 2 are Electrochemical equivalents of the two substances and E 1, E 2 are their respective Chemical equivalents, then,

Electrochemistry Electrolysis Faraday’s Constant From Faraday’s second law of electrolysis, Z  E or E  Z or E = FZ  The amount of charge that must be passed through an electrolyte to liberate 1 gram equivalent of the substance at an electrode is called Faraday’s constant which has a value Coulomb.

Electrochemistry Electrolysis Problem Solution

Electrochemistry Electrolysis Solution Thus, the mass of copper metal deposited = X Kg or g. Thus, the mass of copper metal deposited = X Kg or g.

Electrochemistry Electrolysis Product s of Electrolysis Products of electrolysis depend on the nature of material being electrolysed and the type of electrodes being used. Products of electrolysis depend on the nature of material being electrolysed and the type of electrodes being used. If the electrode is inert (e.g., platinum or gold), it does not participate in the chemical reaction and acts only as source or sink for electrons. If the electrode is reactive, it participates in the electrode reaction.