Reactivity series and displacement reaction
Galvanic cell
Electrolytic cells
Electrolysis of molten sodium chloride
Electrolysis of sodium chloride solution.
Electroplating
Reactivity series and displacement reaction
Reactivity of metals are not similar. The series in which metals have been arranged in the decreasing order of their reactivity is called reactivity series.
When a more reactive metal comes in contact with metallic salt solution of a less reactive metal, the more reactive one replaces the less reactive one from its salt solution. This is called displacement reaction.
Galvanic cell
Galvanic cell is an arrangement in which chemical energy is converted to electrical energy by means of a redox reaction.
Electrode that is more reactive undergoes oxidation and it is called anode, it attains negative charge Electrode that is less reactive undergoes reduction and it is called cathode, it gains positive charge.
Salt bridge – U. tube filled with a paste of gel and salt like KCI.KNO3 etc. This maintains electrical neutrality of the cell.
Electrolytic cells
The process of chemical change taking place in an electrolyte by passing electricity is known as electrolysis.
Substances which conduct electricity in molten state or in aqueous solution and undergoes chemical charge are called electrolytes. Acids, alkalies and Salts are electrolytes in their molten state or in aqueous solution.
Electrode in which oxidation takes place is anode, this is the positive electrode here.
Electrode in which reduction takes place is cathode, this is the negative electrode here.
During electrolysis,
positive ions (cations) are attracted to cathode.
Negative ions (anions) are attracted to anode.
Electrolysis of molten sodium chloride
In solid state sodium chloride can’t conduct electricity as there is no freedom of movement for ions. But molten sodium chloride conducts electricity. When NaCI meNaCI Na‘ + Cr
Electrolysis of sodium chloride solution
Ions like Na+, Cl -,H3O+, OH- , and H2O are present in Sodium chloride solution. When Sodium chloride solution is electrolysed, hydrogen is produced at cathode and Chlorine at anode.
At Cathode: 2H2O + 2e“ 4 H2 + 2OH ’
At Anode: 2CP Cl2 + 2e“
Practical utility of electrolysis:
Production of metals like potassium, calcium, sodium etc.
Production of non metals like hydrogen, chlorine etc.
Production of compounds like sodium hydroxide, potassium hydroxide etc.
. Refining of metals like copper, gold etc.
Electroplating:
The process of obtaining a coating of one metal over another metal.The metal to be coated is connected to the negative terminal of battery and metal to be plated is connected to the positive terminal of battery. A salt solution of the metal to be plated is the elctrolyte.
If we want to plate copper on iron bangle, copper strip is to be connected to positive terminal, iron bangle to the negative terminal of battery. Copper sulphate solution is the electrolyte here.
To plate silver, we have to use silver nitrate solution/ sodium cyanide solution + silver cyanide solution as electrolyte.
If gold is to be plated we have to use sodium cyanide + gold cyanide solution.
Examples of electroplating:
. Gold plated jewellery
. Chromium plated handle bars
. Silver plated utensils
