Unit 17 Metals and Non-metals

1. Summary: Metals and Non-metals

2.1 Choose the correct options for the following questions:

2.2 Give reason:

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

Reason: Minerals are naturally occurring inorganic substances found in the earth’s crust with a definite chemical composition. Ores are specific minerals from which a metal can be extracted profitably and conveniently. While many minerals contain metals, they may contain objectionable impurities or low percentages of metal, making extraction economically unviable. Therefore, only those profitable minerals are called ores.

(b) Ores are oxidised after concentration.

Reason: After concentration, ores (specifically sulphide and carbonate ores) are converted into metal oxides through processes like roasting or calcination. This is done because it is chemically easier and more efficient to reduce a metal oxide into free metal (using reducing agents like Carbon) than it is to reduce metal sulphides or carbonates directly.

2.3 Differentiate between:

(a) Mineral and Ore

S.N.	Mineral	Ore
1	Minerals are naturally occurring substances found in the earth’s crust containing metals or their compounds.	Ores are minerals from which metals can be extracted profitably and conveniently.
2	All minerals are not ores.	All ores are essentially minerals.
3	They may or may not contain a high percentage of metal.	They always contain a sufficient percentage of metal for extraction.
4	Examples: Clay ($Al_2O_3 \cdot 2SiO_2 \cdot 2H_2O$) is a mineral of Aluminium.	Example: Bauxite ($Al_2O_3 \cdot 2H_2O$) is an ore of Aluminium.
5	Extraction of metal from all minerals is not economically viable.	Extraction of metal from ores is always economically viable.

(b) Roasting and Calcination

S.N.	Roasting	Calcination
1	It is the process of heating ore in the presence (excess) of air/oxygen.	It is the process of heating ore in the absence or limited supply of air.
2	It is generally used for Sulphide ores.	It is generally used for Carbonate or hydrated oxide ores.
3	Volatile impurities like Sulphur, Arsenic are removed as oxides (e.g., $SO_2$).	Carbon dioxide ($CO_2$) or water vapour is driven out.
4	Example: Zinc Sulphide is roasted to Zinc Oxide. $2ZnS + 3O_2 \xrightarrow{\Delta} 2ZnO + 2SO_2$	Example: Zinc Carbonate is calcined to Zinc Oxide. $ZnCO_3 \xrightarrow{\Delta} ZnO + CO_2$
5	The temperature is kept below the melting point of the ore but is usually high enough to oxidize impurities.	The temperature is kept below the melting point but high enough to decompose the carbonate.

(c) Oxidation and Reduction

S.N.	Oxidation	Reduction
1	It is the process involving the gain of oxygen by a substance.	It is the process involving the loss of oxygen from a substance.
2	It involves the loss of hydrogen from a substance.	It involves the gain of hydrogen by a substance.
3	In terms of electronics, it is the loss of electrons.	In terms of electronics, it is the gain of electrons.
4	The valency (positive charge) of the element increases.	The valency (positive charge) of the element decreases.
5	The substance that undergoes oxidation acts as a reducing agent.	The substance that undergoes reduction acts as an oxidizing agent.

2.4 Answer the following questions:

(a) What are the sources of metals?

Answer: The primary sources of metals are:

• Earth’s Crust: Most metals are found in the earth’s crust in the form of minerals and ores (oxides, sulphides, carbonates, etc.).

• Seawater: Seawater contains soluble salts of various metals such as sodium chloride (common salt), magnesium chloride, etc.

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

Answer:

Metal	Ores	Chemical Formula
Iron	Hematite (Main Ore)	$Fe_2O_3$
	Magnetite	$Fe_3O_4$
	Siderite	$FeCO_3$
Copper	Chalcopyrite (Copper Pyrite)	$CuFeS_2$
	Cuprite (Ruby Copper)	$Cu_2O$
	Malachite	$CuCO_3 \cdot Cu(OH)_2$
Aluminium	Bauxite (Main Ore)	$Al_2O_3 \cdot 2H_2O$
	Cryolite	$Na_3AlF_6$
Silver	Argentite (Silver Glance)	$Ag_2S$
	Horn Silver	$AgCl$

(c) How is metallurgy a stepwise process? Explain.

Answer: Metallurgy is considered a stepwise process because the extraction of pure metal from its mined ore cannot be achieved in a single jump. It requires a sequence of distinct scientific steps, each serving a specific purpose:

Since each step prepares the material for the next, skipping a step would make extraction impossible or inefficient.

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

Answer: Electro-refining is a method used to obtain high-purity metals (like Copper, Silver, Gold) using the principle of electrolysis.

Activity to refine impure Copper:

Materials Required: An electrolytic tank, impure copper rod, pure copper strip, acidified copper sulphate solution ($CuSO_4$), battery, and wires.

Setup:

• Anode (Positive Electrode): Connect the thick rod of impure copper to the positive terminal of the battery.

• Cathode (Negative Electrode): Connect the thin strip of pure copper to the negative terminal.

• Electrolyte: Fill the tank with acidified Copper Sulphate solution.

Procedure: Pass electric current through the electrolyte.

Observation & Result:

• The impure copper from the Anode dissolves into the solution as Copper ions ($Cu^{++}$).

• The pure Copper ions from the solution get attracted to the Cathode and deposit on it.

Chemical Reactions:

Conclusion: Over time, the anode (impure) gets thinner, and the cathode (pure) gets thicker. The impurities settle at the bottom as “anode mud.” Thus, pure metal is obtained at the cathode.