Engineering Chemistry S Datta

ELECTROCHEMISTRY 223
SHORT QUESTIONS AND ANSWERS
Q. 1. What is electrochemistry?
Ans. Electrochemistry is the study of interrelations of electrical energy and chemical
energy and interconversions of the two energies. This statement applies for both generation of
e.m.f. of a cell as well as electrolysis.
Q. 2. What are electrochemical reactions?
Ans. Electrochemical reactions are the reactions which involve the flow of current.
Q. 3. Mention the types of electrochemical reactions.
Ans.
(i) Electrolysis: Electrolysis requires electrical energy from some external source to bring
about a chemical change i.e., in this type of reaction, electrical energy is consumed.
(ii) Electrochemical cell reactions: Electrochemical cell reactions are mainly redox
reactions, involved in the cell where electrical energy is produced due to a chemical change.
Q. 4. What is electrolysis?
Ans. Electrolysis is a process where electric current is used to decompose a molten ionic
compound or a solution of ions into elements.
Q. 5. Why are the molten compounds or solutions used as electrolytes?
Ans. Ions can only conduct electricity when they are free to move, which is only possible
in molten state or in solution.
Q. 6. Mention some important uses of electrolysis process.
Ans.
(i) Extraction of Na, Al etc.
(ii) Electrolysis of brine to produce NaOH and Cl 2
(iii) Electroplating
(iv) Copper refining.
Q. 7. What are the products of electrolysis of molten salts?
Ans. Metals are deposited at the cathode and the nonmetals are liberated at the anode.
Q. 8. What are the products of electrolysis of an aqueous solution of a salt?
Ans. During electrolysis of a solution of a salt in water, the deposition at the cathode
depends on the type of metal ion in the salt. If the metal is in lower position of electrochemical
series, it gets deposited at the cathode viz. Cu +2
Cu +2 (aq) + 2e Cu°(s)
But if the metal is in higher position in electrochemical series, the product at the cathode
is hydrogen, from hydrogen ions produced by the ionisation of water
2H + (aq) + 2e H 2
(g)
During the electrolysis of a salt solution, the liberation at the anode depends on the type
of electrode. If the anode is graphite or platinum, the products are halogens from metallic
halides (Cl – , Br – , I – )
2X – (aq) ⎯⎯→ X 2
(g) + 2e (X = Cl, Br, I)