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Very Short Question and Answers - Extraction of Metals

Q 1.
What is meant by the term 'ore' in the context of extraction of metals?

Ans:

An ore is a naturally occurring rock containing enough metal or metal compound to make extraction of the metal economically worthwhile.

Q 2.
Name the three main steps involved in the extraction of metals from their ores.

Ans:

The three main steps are: (1) Concentration of ores, (2) Extraction of crude metal, and (3) Refining of the crude metal.

Q 3.
Why are highly reactive metals like sodium and potassium always found as compounds in nature?

Ans:

Highly reactive metals are very reactive and combine with other elements like oxygen and chlorine, so they are never found in free form in nature.

Q 4.
Which process is used to extract highly reactive metals from their ores? Give an example.

Ans:

Electrolysis is used to extract highly reactive metals. For example, sodium is extracted from molten sodium chloride using electrolysis.

Q 5.
During electrolysis of molten sodium chloride, what is deposited at the cathode and what is released at the anode?

Ans:

Sodium metal (Na) is deposited at the cathode and chlorine gas (Cl₂) is released at the anode.

Q 6.
Describe the function of cryolite in the extraction of aluminium from bauxite.

Ans:

Cryolite is added to alumina (Al₂O₃) to lower its melting point during electrolysis, making the process more energy-efficient.

Q 7.
What is the difference between roasting and calcination in the extraction process?

Ans:

Roasting involves heating an ore in the presence of air (for sulphide ores), while calcination involves heating in absence of air (for carbonate ores).

Q 8.
Give the chemical equation for the roasting of zinc sulphide (ZnS).

Ans:

2ZnS + 3O₂ → 2ZnO + 2SO₂

Q 9.
Which reducing agent is commonly used to extract metals like iron and zinc from their oxides?

Ans:

Carbon (as coke or charcoal) is commonly used to reduce metal oxides such as Fe₂O₃ and ZnO.

Q 10.
Write the equation for the reduction of iron(III) oxide with carbon in a blast furnace.

Ans:

Fe₂O₃ + 3C → 2Fe + 3CO

Q 11.
How is mercury extracted from its ore mercuric oxide (HgO)?

Ans:

Mercuric oxide is heated strongly, causing it to decompose into mercury and oxygen: 2HgO → 2Hg + O₂.

Q 12.
Name two metals that are usually found in the native (free) state in the Earth's crust.

Ans:

Gold (Au) and platinum (Pt) are commonly found in the native (free) state.

Q 13.
Why is electrolysis not used for the extraction of metals low in the reactivity series?

Ans:

Because these metals are either found native or can be easily obtained by simple heating; electrolysis is not required.

Q 14.
What is gangue? How is it removed?

Ans:

Gangue is the unwanted materials (like sand, clay, etc.) present in the ore. It is removed during the concentration of ore by methods such as froth flotation or gravity separation.

Q 15.
Give one example of a metal extracted by reduction with carbon monoxide.

Ans:

Iron is often extracted from its oxide using carbon monoxide as a reducing agent in the blast furnace.

Q 16.
Which metal is extracted by electrolytic reduction of molten alumina?

Ans:

Aluminium (Al) is extracted by electrolytic reduction of molten alumina (Al₂O₃).

Q 17.
What happens during the refining of metals?

Ans:

Refining of metals involves removing impurities from the extracted crude metal to obtain pure metal, often by methods like electrolytic refining.

Q 18.
Explain why reduction by carbon cannot be used to extract aluminium from its ore.

Ans:

Aluminium has a very high affinity for oxygen and forms very stable oxides; carbon is not reactive enough to reduce aluminium oxide. Therefore, electrolysis is used.

Q 19.
Write the reaction for thermal decomposition of silver oxide.

Ans:

2Ag₂O → 4Ag + O₂ (on heating)

Q 20.
Arrange the following metals in order of increasing ease of extraction from their ores: iron, gold, aluminium.

Ans:

Aluminium (most difficult), iron (moderate), gold (easiest).

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