Comprehensive WBBSE Class 10 Physical Science Notes Chapter 8.3 Electricity and Chemical Reactions can help students make connections between concepts.
Electricity and Chemical Reactions Class 10 WBBSE Notes
Electrochemistry: The branch of chemistry which deals with the relationship between chemical energy and electrical energy and how one can be converted into another.
Conductors: A substance which allows the electric current to flow through it is known as a conductor, e.g. Cu, Ag, Au etc.
Non-conductors: A substance which does not allow the electric current to flow through it is known as non-conductors.
Type of conductors :
(i) (a) Metallic conductors e.g. Cu, Ag, Au etc.
(b) Non-metallic conductors e.g. graphite (carbon)
(ii) Electrolytes
(a) Metallic conductors: These are the substances (metals) which allow the current to pass through them but do not undergo any change in themselves.
(b) Electrolytes: Compounds which in the fused state or in aqueous solution can conduct electricity and are decomposed chemically yielding new substances are known as electrolytes.
Non-electrolytes: Compounds which in the fused state or in aqueous solution do not conduct electricity are known as non-electrolytes, e.g. pure water, alcohol, acetone, sugar, urea etc.
Electrolytes: It is the process of chemical decomposition of an electrolyte in solution or in the fused state by the passage of electric current.
Electrodes: Two conducting metal plates or graphite strips or rods, placed in a voltameter to pass electric current through the electrolyte during electrolysis are called electrodes.
Anode: The electrode through which current enters into the voltameter is connected to the positive terminal of a battery is called anode.
Cathode: The electrode, which is connected to the negative terminal of the battery is called the cathode.
Voltameter: The complete set up or vessel consisting of two metal plates and electrolytes in which electolysis takes place is called Voltameter.
Ions: For the passage of electricity, electrolytes are decomposed reversibly into charged particles. These charged particles are called ions.
Cation: The positively charged particles are migrated towards cathode and is called cation
e.g. H+, Na+, NH4+ etc.
Anion: The negatively charged particles migrated towards anode is called anion,
e.g. Cl–, SO42-, NO3– etc.
Difference between Metallic conduction and Electrolytic conduction
| Metallic conduction | Electrolytic conduction |
| 1. Flow of electricity is due to the movement of electrons only and there is no movement of matter.
2. Flow of electricity takes place without the decomposition of the substance. 3. The electrical conduction decreases with increase of temperature. |
1. Flow of electricity is due to the movement of ions and hence there is transfer of matter.
2. Row of electricity is accompanied by the decomposition of the substance (electrolyte). 3. The electrical conduction increases with increase of temperature. |
Strong electrolytes : Those electrolytes which are ionised almost completely in the fused state or in aquous solution, are known as strong electrolytes, e.g. NaOH, NaCl, HCl, H2SO4
• Weak electrolytes : Those electrolytes which are ionised a little are called weak electrolytes
e.g. HCN, NH4OH, CH2COOH etc.
Difference between Atom and Ion :
| Atom | Ion |
| 1. Atom is a neutral, smallest and active particle of element. Number of electrons and protons are same in atom. | 1. Number of protons are not equal with number of electrons in ion. |
| 2. Atoms do not exist in free state. | 2. Ions exist in free state. |
| 3. Chemically atoms are more reactive. | 3. Ions are not reactive. |
Electrolysis of some electrolytes:
Electrolysis of water:
Voltameter : Two platinum plates are introduced through a rubber cock attached in the bottom of glass vessel.
Electrodes : Two platinum plates.
Electrolyte : Water acidified with a few drop of dilute H2SO4.
Procedure : Two hard glass tube are filled with water. They are inverted over the two electrodes. When electric current is passed through the electrodes from a battery into the acidified water, electrolysis takes place. Gases (hydrogen and oxygen) are collected in the tube by the downward displacement of water.
It shows from experiment that gas collected in anode is oxygen and that collected in cathode is hydrogen.
Electrolytic reaction:
(iii) Reaction in cathode : H++e → H; H + H → H2↑
(iv) Reaction in anode : OH– – e → OH ; 4OH → 2H2O + O2↑
Conclusion: In the electrolysis of water, it is found that at the same temperature and pressure one volume of oxygen (O2) and two volumes of hydrogen (H2) are evolved.
2. [Electrolysis of sulphuric acid
(a) Electrolysis of dilute sulphuric acid :
Electrodes: Two platinum plates
• Electrolytic reaction :
(b) Electrolysis of conc. H2SO4 (60%):
Conclusion : In the electrolysis of conc. H2SO4 (60%) it is found that at low temperature hydrogen gas is evolved at cathode and H2O2 is produced at anode.
3. Electrolysis NaCl
(a) Electrolysis of fused NaCl :
Electrodes :
Cathode — Platinum
Anode — Graphite
Electrolytic reaction :
(i) Decomposition of NaCl : NaCl \(\rightleftharpoons\) Na+ + Cl–
(ii) Reaction in Cathode : Na+ + e \(\rightleftharpoons\) Na
(iii) Reaction in anode : Cl– – e → Cl; Cl + Cl → Cl2↑
Conclusion: In the electrolysis of fused NaCl It is found that sodium is produced at cathode and chlorine is evolved at anode.
(b) Electrolysis of dilute aqueous solution of NaCl :
Electrodes :
Cathode — Platinum
Anode — Platinum
Electrolytic Reaction:
(i) Dissolution of NaCl : NaCl \(\rightleftharpoons\) Na+ + Cla–
(ii) Dissolution of water : H2O \(\rightleftharpoons\) H+ + OH–
(iii) Reaction in cathode : H+ + e → H; H + H → H2↑
(iv) Reaction in anode : OH– – e → OH; 4OH → 2H2O + O↑
Conclusion : In the electrolysis of dilute aqueous solution of NaCl it is found that hydrogen is evolved at cathode and oxygen is produced at anode.
Electrolysis of cone aqueous solution of NaCl:
Electrodes :
Cathode — Graphite
Anode — Graphite
Electrolytic reaction :
(i) Dissolution of NaCl : NaCl \(\rightleftharpoons\) Na+ + Cl–
(ii) Dissolution of water : H2O \(\rightleftharpoons\) H+ + OH–
(iii) Reaction in Cathode : H+ + e → H; H + H → H2↑
(iv) Reaction in Anode : Cl– – e → Cl ; Cl + Cl → Cl2↑
(v) Part of Cl2 produced at anode reacts with NaOH;
2NaOH + Cl2 = NaCl + NaOCl + H2O (which is produced in solution)
4. Electrolysis of aqueous solution of copper sulphate :
(a) Using platinum electrodes :
Electrodes :
Cathode — Platinum
Anode — Platinum
Voltameter : An iron pot is used for electrolysis.
Electrolyte : Aqueous solution of copper sulphate
Electrolytic reaction:
(i) Dissolution of CuSO4 : CuSO4 \(\rightleftharpoons\)Cu2++ SO42
(ii) Dissolution of water : \(\rightleftharpoons\) H+ + OH– – Cu2+ + 2e
(iii) Reaction in cathode : Cu2+ + SO42
(iv) Reaction in anode : OH– – e → OH; 4OH → 2H2O + O2↑
Conclusion : In the electrolysis of aqueous solution of copper sulphate using platinum electrodes, it is found that copper is deposited at cathode and oxygen is evolved at anode and the final solution becomes acidic due to the formation of sulphuric acid (H2SO4).
(b) Using copper electrodes :
Electrodes :
Cathode – Copper
Anode – Copper
Voltameter : An iron pot is used for electrolysis.
Electrolyte : Aqueous solution of copper sulphate
Electrolytic reaction:
(i) Dissolution of CuSO4 : CuSO4 \(\rightleftharpoons\) Cu2+ + SO42-
(ii) n resolution of water : H2O \(\rightleftharpoons\) H+ + OH–
(iii) Reaction in cathode : Cu2+ + 2e → Cu–
(iv) Reaction in anode : Cu – 2e → Cu2+
Conclusion : As a result of the electrolytic reaction describe above, anode is gradually dissoluted and due to deposition of copper in cathode it becomes thicker.
5. Electrolysis of aqueous solution of AgNO3 :
(a) Using platinum electrodes:
Electrodes:
Cathode – Platinum
Anode – Platinum
Electrolyte : Aqueous solution of AgNO3
Electrolytic reaction:
(i) Dissolution of AgNO3 : AgNO3 \(\rightleftharpoons\) Ag+ + NOg–3
(ii) Dissolution of water : H2O \(\rightleftharpoons\) H+ + OH–
(iii) Reaction in cathode : Ag+ + e → Ag
(iv) Reaction in anode : OH– – e → OH; 4OH → 2H2O + O2↑
(b) Using silver electrodes :
Electrodes :
Cathode – Silver
Anode – Silver
Electrolyte : Aqueous solution of AgNO3
Electrolytic reaction:
(i) Dissolution of AgNO3 : AgNO3 \(\rightleftharpoons\) Ag+ + NO–3
(ii) Dissolution of water : H2O \(\rightleftharpoons\) H+ + OH–
(iii) Reaction in cathode : Ag+ + e → Ag
(iv) Reaction in anode : Ag – e → Ag+
Practical application of electrolysis :
(i) Extraction of metal : Highly electro positive such as Na, Ca, Mg, Al etc. : metals are extracted by electrolysis method. e.g. Extraction of Aluminium (Al)
Electrolyte : It contains of pure alumina (Al2O3)-20% ;
Fused cryolite (Na3A/F6)-60% ; CaF2-20%.
Electrolytic reaction:
(i) Decomposition of cryolite :
(Na3AlF6>) A1F3 ; 3NaF \(\rightleftharpoons\)A1F3+ 3NaF; A/F3\(\rightleftharpoons\) Al3+ + 3F–
(ii) Reaction in cathode : Al3+ + 3e → Al
(iii) Reaction in anode : 3F– – 3e → 3F
(iv) Final reaction ; AF2O3 + 6F → 2A1F3 + 3O ; 6O → 3O2↑
Non-metals like oxygen, hydrogen, chlorine and industrial preparations of caustic soda (NaOH) and heavy water (D2O) are done by electrolysis.
Electro-plating: Some metals are required to be electroplated because sometimes for the preservation of the less active metal or article and to prevent rusting or for attractive appearance.
Electroplating of Cu, Ag. Ni, Sn, Cr, Zn, Au :
(iv) Metals after extraction by chemical means are purified by electrolysis, e.g. Purification of copper :
Electrolyte : In aqueous solution of copper sulphate, small amount of 1% H2SO4 is added to increase the conductivity of the solution.
Electrodes . Cathode : Pure thin copper plate Anode : Thick impure copper plate
Procedure : Electric current is now passed in the solution from a battery, copper ion is formed from anode and is mixed into the solution where in cathode copper metal is deposited.
Electrolytic reaction:
- Reaction in cathode : Cu2+ + 2e → Cu
- Reaction in anode : Cu – 2e → Cu2+
Conclusion : After passing electricity for sometimes it is found that anode, an impure copper metal is totally dissolved and a very thin plate of cathode gradually becomes thicker.
Ability to discharge ions in increasing order :
