Refining of Metals - UNSOLVED PRACTICE SET

Q7. What is refining of metals? Why is it necessary? Name two methods of refining.

Q8. Describe the process of electrolytic refining of copper with a labelled diagram. What happens at the anode and cathode?

Q9. Your uncle works in a copper refinery. He tells you that the impure copper blocks are hung in a tank, and after some time, pure copper sheets are removed. Explain the electrolytic refining process he is describing.

Q10. What is anode mud? Why is it valuable? What metals are typically found in anode mud during copper refining?

Q11. Differentiate between distillation and liquation as methods of refining metals. Give one example for each.

Q12. Why is electrolytic refining preferred over other methods for producing high-purity metals? What is the typical purity achieved?

Q13. Define refining of metals and explain why it is necessary. Describe the process of electrolytic refining with a labelled diagram. Explain what happens at the anode, cathode, and in the electrolyte during the refining of copper. What is anode mud, and why is it economically valuable?

Q14. A student visits a copper refinery and observes the electrolytic refining process:

(a) Draw a labelled diagram of the electrolytic cell used for refining copper.

(b) Identify the anode, cathode, and electrolyte.

(c) Write the reactions occurring at the anode and cathode.

(d) Explain why the cathode gains mass while the anode loses mass.

(e) What happens to impurities like gold, silver, and iron during this process?

(f) Why is the electrolyte acidified with sulphuric acid?

Q15. "Refining is the final step that transforms crude metal into a material suitable for high-tech applications." Discuss this statement by explaining: (i) why 99.9% pure copper is needed for electrical wiring, (ii) how the purity of gold is measured in carats, (iii) the role of refining in the semiconductor industry, and (iv) why impure metals are unsuitable for medical implants.

Q16. A copper refinery processes impure copper containing 98% copper and 2% impurities (including silver and gold):

(a) If 1000 kg of impure copper is refined, calculate the mass of pure copper obtained (assuming 100% efficiency).

(b) If the impurities contain 0.5% silver and 0.1% gold, calculate the mass of silver and gold in the anode mud.

(c) If silver is worth ₹60,000 per kg and gold is worth ₹5,000,000 per kg, calculate the total value of precious metals recovered from 1000 kg of impure copper.

(d) The electrolytic refining process operates at 95% efficiency. Calculate the actual mass of pure copper obtained from 1000 kg of impure copper.

(e) If the refinery processes 50 tonnes of impure copper daily, calculate the annual production of pure copper (assuming 300 working days).

Q17. An electrolytic refining cell operates with the following parameters:

Current (I) = 100 A

Time (t) = 8 hours

Electrolyte: CuSO₄ solution acidified with H₂SO₄

Impure copper anode, pure copper cathode

(a) Calculate the total charge passed through the cell. (Q = I × t)

(b) If 1 mole of electrons (96,500 C) deposits 0.5 mole of copper (Cu²⁺ + 2e⁻ → Cu), calculate the mass of copper deposited on the cathode. (Atomic mass of Cu = 63.5)

(c) If the anode loses 1.2 kg during this period, calculate the mass of impurities released as anode mud.

(d) If the electricity cost is ₹8 per kWh, and the cell operates at 2 V, calculate the cost of electricity for 8 hours. (Energy = V × I × t)

(e) Why is the voltage kept low (2-3 V) in electrolytic refining rather than using high voltage?

Q18. India is a major importer of gold, which is refined to high purity for jewellery and investment.

(a) Gold from mines is typically 90-95% pure. If 1 kg of impure gold contains 92% gold, 5% silver, and 3% copper, calculate the mass of each metal.

(b) Gold is refined to 24 carat (99.9% pure) using electrolysis. If the Wohlwill process is used, describe the electrolytic cell setup.

(c) If 10 kg of 92% pure gold is refined to 99.9% purity, calculate the mass of 24-carat gold obtained.

(d) 22-carat gold contains 91.6% gold. If a jeweller makes a 50 g necklace from 22-carat gold, calculate the mass of pure gold in it.

(e) Why do Indian jewellers prefer 22-carat gold over 24-carat gold for making jewellery?

(f) If gold is worth ₹5,500 per gram (22-carat), calculate the value of the 50 g necklace.