Electrolytic Processes Interview Questions and Answers:
1. What is electrolysis ?
Ans. The breaking of a substance (known as electrolyte) into ions by flow of electric current through it is known as electrolysis.
2. What happens when an electric current is passed through solution of copper sulphate ?
Ans. When an electric current is passed through solution of copper sulphate, the electrolyte (CuSO4) is decomposed into cations (Cu++) and anions (SO4—) according to chemical reaction
CuSO4 → Cu++ + SO4__
The cations move, toward the cathode (or negative electrode) and each of the positively charged copper ions reaching the cathode takes two electrons from it and becomes a metallic atom of copper. The negatively charged sulphions (SO4—) move towards the anode (or positive electrode) and each of the negatively charged sulphions reaching the anode gives up two electrons to it and ceases to be anion. Thus, metallic copper is deposited on the cathode, while the sulphions are collected at the anode and combine with water forming H2SO4 and O2 according to chemical reaction
2SO4 + 2H2O → 2H2SO4 + O2
The oxygen gas so formed is liberated at the anode.
3. Write the applications of electrolysis.
Ans. Electrolytic processes are widely used for the extraction of pure metals from their ores (such as aluminium, zinc, copper, magnesium, sodium etc.), manufacturing of various chemicals (such as caustic soda, potassium permanganate, hydrogen, oxygen, chlorine etc.), electrodeposition of metals including electroplating, electrotyping, electroforming, building tip of worn-out parts in metallurgical, chemical and other industries.
4. What is meant by electrochemical equivalent of a substance ?
Ans. Electrochemical equivalent (ECE) of a substance is the amount of substance deposited on passing a steady electric current of I A for one second through its solution.
5. What is relation between chemical equivalent, atomic weight and valency of any substance ?
Ans. Chemical equivalent of any substance may be defined as the ratio of its atomic weight to its valency
i.e., Chemical equivalent = Atomic weight/Valency
6. Define current efficiency in electrolytic process.
Ans. The current efficiency is defined as the ratio of the actual quantity of substance liberated or deposited to the theoretical quantity, as calculated from Faraday’s laws.
i.e., Current efficiency = Actual quantity of substance liberated or deposited/Theoretical quantity of substance liberated or deposited
Its value usually lies between 90 and 98%.
7. What is electrodeposition ?
Ans. The process of depositing a coating of one metal over another metal or non-metal electrically is called the electrodeposition.
8. What for electrodeposition process is used ?
Ans. The electrodeposition process is used for protective, decorative and functional purposes and includes electroplating, electroforming, electrotyping, electrofacing, electrometallisation, electrodeposition of rubber, building up of worn-out parts for repairs etc.
9. Enumerate the factors on which the quality of electrodeposition depends.
Ans. The factors on which the quality of electrodeposition depends are (i) nature of electrolyte (ii) current density (iii) temperature (iv) conductivity and concentration of electrolyte (v) additional agents (vi) throwing power and (vii) polarisation.
10. What is meant by ‘throwing power’ and how it can be improved ?
Ans. Throwing power is the ability of electrolyte to produce uniform deposit on an article of irregular shape and is one of the important characteristics of plating or depositing bath. It can be improved in two ways – firstly, by increasing the distance between the anode and cathode, and secondly, by reducing the voltage drop at the cathode surface.
11. What is polarization and how can it be made negligible ?
Ans. Use of current density, in electrodeposition process, beyond a certain limit causes electrolysis of water and hydrogen liberation on the cathode. This hydrogen evolved on the cathode blankets the base metal which reduces the rate of metal deposition. This phenomenon is called polarization.
Polarization can be reduced by agitating the electrolyte and can be made negligible by reverse current process.
12. What do you understand by “reverse current process” in electroplating ?
Ans. In reverse current process in electroplating, at regular intervals plating current is reversed for a second or so.
13. What is electroplating ?
Ans. Electroplating is an art of depositing a superior or more noble metal on an inferior or a base metal by means of electrolysis of an aqueous solution of a suitable electrolyte.
14. What is use of electroplating ?
Ans. Electroplating is done occasionally for ornamentation and decoration purposes. Sometimes, it is done, with a view to repair worn-out parts of a machinery.
15. Why the article to be electroplated is thoroughly cleaned, polished and degreased before putting it for electroplating ?
Ans. In case the object to be electroplated is not cleaned, polished, and degreased, the deposit formed may not be well adherent to the base metal and is likely to peel off.
16. What is electroforming ?
Ans. Reproduction of objects by electrodeposition on some sort of a mould or form is known as electroforming. This is another application of electrodeposition.
17. What is meant by anodising ?
Ans. Anodizing is a process of anodic oxidation in which a thin uniform passive (tough, thin, uniform and impermeable) film is produced artificially by the passage of electric current.
18. What is Faraday constant ?
Ans. According to Faraday’s second law of electrolysis; the chemical equivalent weight is proportional to electrochemical equivalent
i.e. e α Z or e = FZ
where F is called the Faraday constant. The quantity of electricity which liberates one gm equivalent of an element is known as Faraday constant i.e. 1 F = 96,540 coulombs.
19. What type of power supply is required for electrolytic processes ?
Ans. Power supply required for electrolytic processes is dc and at very low voltage ; usually very small in magnitude (between 100 and 200 A at 10 or 12 V).
20. Why it is preferred to instal large chemical plants near hydroelectric or atomic power plants ?
Ans. Because of huge power requirement and 100 per cent load factor, large chemical plants are located near the hydroelectric or atomic power plants. The advantage of a high load factor is greater with such plants than with steam power plants.