Class 10 Science Lesson 17

Exercise

1. Choose the best option for the following questions.

a) Which is the main ore of iron?

i) Bauxite
ii) Argentite
iii) Hematite
iv) Pyrite

Answer: iii) Hematite

b) Which metal is found in pure state in nature?

i) Aluminium
ii) Iron
iii) Copper
iv) Gold

Answer: iv) Gold

c) Which is the primary step of purifying metal?

i) Smelting
ii) Roasting
iii) Concentration
iv) Grinding

Answer: iii) Concentration

d) Which of the following ore is oxidised by roasting method?

i) Hematite
ii) Siderite
iii) Bauxite
iv) Cuprite 

Answer: iv) Cuprite

e) In which process is smelting included?

i) Grinding
ii) Refining
iii) Oxidation
iv) Reduction 

Answer: iv) Reduction

2. Give Reasons

a) All ores are minerals but all minerals are not ores.

Ans: Minerals are naturally occurring substances that contain metals or other valuable elements. However, only those minerals from which metals can be extracted economically are called ores. Hence, all ores are minerals, but not all minerals are ores because some are not commercially viable for metal extraction.

b) Ores are oxidised after concentration.

Ans: After the concentration process removes unwanted impurities (gangue), ores are oxidised through roasting or calcination. This is done to convert the metal compounds (like sulphides or carbonates) into oxides, which are easier to reduce to pure metals in the next steps of metallurgy.

3. Differences:

a) Mineral and Ore

b) Roasting and Calcination

(c) Oxidation and Reduction

4. Answer the following questions:

a. What are the sources of metals?

Answer: Metals are mainly obtained from minerals found in the Earth’s crust. These minerals are natural compounds or elements that contain metal in a combined form. Ores, which are specific types of minerals, are the main sources of commercially important metals as they contain a sufficient quantity of the metal to be extracted profitably.

b. Make a list of ores of iron, copper, aluminium, and silver.

Answer:

c. How is metallurgy a stepwise process? Explain.

Answer: Metallurgy is a step-by-step process used to extract and purify metals from their ores:

1. Concentration of Ore: The ore is first cleaned to remove impurities (gangue) using methods like gravity separation, froth flotation, or magnetic separation.
2. Conversion to Oxide: The concentrated ore is then heated (roasted or calcinated) to convert it into its oxide form.
3. Reduction: The oxide is reduced using a suitable reducing agent (like carbon) to extract the metal.
4. Refining: The impure metal is then purified using methods such as electro-refining or distillation.

Each step ensures that impurities are removed, and the metal is extracted in a usable and pure form.

d. How are pure metals obtained from electro-refining? Explain it with an activity.

Answer: Electro-refining is a process used to obtain pure metals by passing an electric current through a solution of the metal (electrolyte).

Activity: Electro-refining of copper

• Apparatus: Electrolytic cell, copper sulphate (CuSO₄) solution, impure copper rod (anode), and pure copper strip (cathode).
• Procedure:
  • Connect the impure copper rod to the positive terminal (anode).
  • Connect the pure copper strip to the negative terminal (cathode).
  • Fill the electrolytic cell with copper sulphate solution.
  • Pass electric current through the solution.
• Observation:
  • At the anode: Impure copper dissolves into Cu²⁺ ions.
  • At the cathode: Cu²⁺ ions gain electrons and deposit as pure copper.
  • Impurities like silver, gold settle at the bottom as anode mud.

• Conclusion: This method helps obtain highly pure copper and other metals by using electrochemical principles.