ELECTROLYSIS Products of Electrolysis

ELECTROLYSIS The Process of Chemical decomposition of the electrolyte by the passage of electricity through its molten or dissolved state

ELECTROLYTIC CELL Device consists of i) Electrolytic tank It is made of glass, wood or bakelite. ii) Electrolyte it is in dissolved state or molten state. iii) Source of Electricity cell or battery iv) Electrodes 2 RODS a) Cathode electrode connected to negative terminal of battery b) Anode electrode connected to positive terminal of battery

ELECTROLYTIC CELL CATIONS Positively charged ions move towards CATHODE (-) , gain electrons and get reduced Anions Negatively charged ions move towards ANODE(+) , lose electrons and get oxidised

Class XI-XII - Electrolysis of Aq. CuSO4 Using Inert Electrode - Dr Class XI-XII - Electrolysis of Aq. CuSO4 Using Inert Electrode - Dr. Amal K Kumar.mp4

PRODUCTS OF ELECTROLYSIS PRODUCTS OF ELECTROLYSIS depend on i) Nature of Materials ii)Type of electrode a)INERT ELECTRODE They act as source or sink for electrons. They do not participate in electrode reactions. eg)Pt,Au b) ACTIVE ELECTRODE They participate in the electrode reactions. eg) Cu,Ag

OVER VOLTAGE Thermodynamically faesible reactions do not seem to occur because at lower voltage they are slow. This creates electrical resistance at the electrodes. A higher potential called OVER POTENTIAL is required to make the reaction occur

ELECTROLYSIS OF AQUEOUS SODIUM CHLORIDE SOLUTION

At the Cathode At the cathode(-): Na+(aq) + e- → Na(s) reduction Eo =-2.71 v H2O+ 2e-  ½ H2 + OH- reduction Eo = -0.41 v (l) (g) ( aq) The reaction with higher reduction potential will take place. So H2 gas will be formed instead of Na

ANODE H2O  ½ O2 + 2H+ + 2e- Eo =-1.23 v Cl -  ½ Cl2 + e- - Eo =-1.36 v The one with lower reduction potential should take place. But because of over voltage the reduction potential of chloride ion is less and so it takes place. So Cl2 gas is liberated at anode. Na+ and OH- remain in solution.

ELECTROLYSIS Electrolysis of aqueous ionic compounds (using inert electrodes)

INERT ELECTRODES In the electrolysis of molten electrolytes, there are only two kinds of ions. In aqueous solutions, there are four kinds of ions; two come from the electrolyte and two from the water. Of the four ions in an aqueous solution, only two are discharged.

ELECTROLYSIS OF SULPHURIC ACID At the cathode: Hydrogen ions are discharged to produce hydrogen gas. 2H+(aq) + 2e- → H2(g) At the anode: Hydroxide ions are discharged, producing oxygen gas. 4OH-(aq) → O2(g) + 2H2O(l) + 4e- Overall change: 2H2O(l) → 2H2(g) + O2(g) Changes in solution: Only water decomposes.

ACTIVE ELECTRODES Electrolysis of aq. CuSO4 using copper electrodes copper being the same element as the ions present in solution, it is a reactive electrode The anode will take part in the reaction the copper electrode dissolves into solution to replenish the Cu2+ ions discharged at the cathode

Electrolysis of aq. CuSO4 using copper electrodes At the anode Cu  Cu2+ + 2e- copper anode dissolves At the cathode Cu2+ + 2e-  Cu copper metal deposited

Electrolysis of Copper(II) Sulphate Solution using Copper Electrodes At the cathode: Copper metal is deposited on the cathode. At the anode: The copper in the anode is oxidised to form copper(II) ions. Observation: The copper cathode gains copper and becomes larger. The copper anode is oxidised and becomes smaller. The amount of copper(II) sulphate and the colour of the solution do not change.