Extraction and Purification of Metals: Electrolysis, Electroplating and Electrode Potential Explained

Understanding how metals are extracted and purified is an important part of chemistry, especially for students preparing for WAEC, NECO, and JAMB. In this lesson, the processes of electrolytic extraction, electroplating, electrolysis of brine, and electrode potential are explained in a clear and simple way.

Electrolytic Extraction and Purification of Copper

Electrolysis is commonly used in the purification of copper. In this process, the impure copper is made the anode, while a thin sheet of pure copper serves as the cathode. The electrolyte is usually copper(II) tetraoxosulphate (VI) solution.

When current is passed, copper atoms from the anode lose electrons and enter the solution as copper ions. These ions move to the cathode where they gain electrons and are deposited as pure copper. Insoluble impurities fall to the bottom of the cell.

Electroplating

Electroplating is the process of coating one metal with another using electricity. It is used to improve appearance and prevent corrosion.

The object to be plated is cleaned and made the cathode, while the coating metal is used as the anode. The electrolyte is a solution containing ions of the coating metal.

In silver plating, silver is the anode, the object is the cathode, and the electrolyte is a silver salt solution. During the process, silver is deposited on the object.

Electrolysis of Brine

Brine is a concentrated solution of sodium chloride. Its electrolysis produces hydrogen gas, chlorine gas, and sodium hydroxide solution.

The process is carried out using a Kellner–Solvay cell. Graphite rods serve as the anode, while mercury acts as the cathode. Chlorine gas is released at the anode, while sodium forms an amalgam with mercury at the cathode. This amalgam later reacts with water to produce sodium hydroxide and hydrogen gas.

Electrode Potential

Electrode potential is the potential difference between a metal and a solution of its ions. It shows how easily a metal can lose or gain electrons.

For example, zinc loses electrons easily and has a negative electrode potential, while copper gains electrons and has a positive electrode potential.

Also read – Kingdom Monera Explained: Characteristics, Structure and Examples for Biology Students

Standard Electrode Potential

Standard electrode potential is measured under standard conditions:

• Temperature: 298 K
• Concentration: 1 mol/dm³

The standard hydrogen electrode is used as a reference and is assigned a value of 0 V.

Examples:

• Zinc: −0.76 V
• Copper: +0.34 V

Objective Questions

1. In electrolytic purification of copper, the impure copper acts as the:A. CathodeB. Electrolyte

   C. Anode

   D. Conductor

2. The pure copper sheet is the:A. AnodeB. Cathode

   C. Electrolyte

   D. Bridge

3. The electrolyte used is:A. Sodium chlorideB. Copper(II) tetraoxosulphate (VI)

   C. Hydrochloric acid

   D. Water

4. At the anode, copper:A. Gains electronsB. Loses electrons

   C. Does not react

   D. Forms gas

5. Impurities:A. DissolveB. Evaporate

   C. Settle at the bottom

   D. Form ions

6. Electroplating is:A. Removing metalsB. Coating metals

   C. Melting metals

   D. Cooling metals

7. The object plated is the:A. AnodeB. Cathode

   C. Electrolyte

   D. Conductor

8. The anode is:A. GraphiteB. Pure coating metal

   C. Impure metal

   D. Mercury

9. Silver plating uses:A. NaOHB. AgNO₃

   C. CuSO₄

   D. HCl

10. Chromium plating needs copper and nickel because:A. CheaperB. Better adhesion

    C. Faster

    D. Lighter

11. Brine electrolysis produces:A. Oxygen onlyB. Hydrogen, chlorine, sodium hydroxide

    C. Sodium only

    D. Chlorine only

12. The anode is:A. CopperB. Graphite

    C. Zinc

    D. Iron

13. Mercury acts as:A. AnodeB. Cathode

    C. Electrolyte

    D. Insulator

14. Electrode potential measures:A. CurrentB. Resistance

    C. Tendency to form ions

    D. Heat

15. Positive electrode potential means:A. Electrons flow from metalB. Electrons flow to metal

    C. No flow

    D. Reverse current

16. Standard hydrogen electrode is:A. 1 VB. −1 V

    C. 0 V

    D. 0.5 V

17. Standard temperature is:A. 0 KB. 273 K

    C. 298 K

    D. 500 K

18. Zinc value is:A. +0.34B. −0.76

    C. 0

    D. +1

19. Reduction occurs at:A. AnodeB. Cathode

    C. Electrolyte

    D. Bridge

20. Salt bridge allows:A. Heat flowB. Ion movement

    C. Gas flow

    D. Light flow

Answers

1. C
2. B
3. B
4. B
5. C
6. B
7. B
8. B
9. B
10. B
11. B
12. B
13. B
14. C
15. B
16. C
17. C
18. B
19. B
20. B