ICSE Class 7 Chemistry Chapter 7 Chemistry in Our Life

Chemistry In Our Life

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In This Chapter You Will Learn

Metals and non-metals and their uses

Fertilizers and some other useful compounds

Solutions

Noble metals

Alloys

Man-made materials

Introduction

The knowledge of chemistry plays a vital role in the development of human society and civilization. Directly or indirectly, all human activities depend on the knowledge of chemistry. Nature is a vast reservoir of different kinds of substances. They need to be minutely observed and exploited for their proper use. Of these natural substances, metals and non-metals are the most important. Interaction between these two has given rise to a number of new substances, like alloys, cement, plaster of paris, fuels, plastics, fertilizers, medicines, soaps and detergents and many more. All these make our life comfortable and help in improving our national economy. In this unit you will learn about the properties and the uses of metals and non-metals and their various compounds.

Occurrence of metals and non-metals

Most of the metals are reactive, so they do not occur in free state they are found in combined states as minerals in the Earth's crust, which is the major source of metals. The minerals from which metals can be extracted profitably are called ores.

Sea water is also a source of a large number of metals such as sodium, potassium, magnesium, calcium, etc., in the form of their salts.

Gold, silver and Platinum being unreactive are found in free state in earth's crust and in river beds.

Non-metals occur in

Earth's crust in combined state as oxides, carbonates, sulphates, nitrates, phosphates etc.

Atmosphere, both in free state as O2, N2, and in combined state as CO2, H2O.

Noble gases occur only in free state.

You have already studied the properties of metals and non-metals in chapter 1. Here is a comparative study of properties of metals and non-metals in the following table.

Useful Elements

Table 7.1 - A comparative study of the general properties of metals and non-metals

Uses of Common Metals

Activity 1

Take samples of iron, copper, aluminium and magnesium. Note the appearance of each sample.

Clean the surface of each sample by rubbing them with sand paper and note their appearance again.

Property: Metals, in their pure state, have a shining surface. This property is called metallic lustre.

Activity 2

Take small pieces of iron, copper, aluminium, and magnesium. Try to cut these metals with a sharp knife and note your observations.

Hold a piece of sodium metal with a pair of tongs. Caution - Always handle sodium metal with care. Dry it by pressing between the folds of a filter paper.

Put it on a watch-glass and try to cut it with a knife.

What do you observe?

You will find that metals are generally hard.

Activity 3

Take pieces of iron, zinc, lead and copper.

Place any one metal on a block of iron and strike it four or five times with a hammer. What do you observe?

Repeat with other metals.

Record the change in the shape of these metals.

You will find that some metals can be beaten into their sheets. This property is called malleability. Did you know that gold and silver are the most malleable metals.

1. Gold (Au)

Gold is a shiny yellow metal. It is considered as a very precious substance for its beauty, scarcity and chemical stability. Due to its chemical stability, it does not react easily with other substances. Therefore, gold is a durable substance. Gold is highly malleable and resistant to corrosion, and it is also a very good conductor of electricity. Therefore, it is used:

(i) in the manufacture of electronic devices, like computers, telephones, home appliances, etc.

(ii) for making ornaments and coins.

(iii) in dentistry, to fill in teeth cavities (in the form of an alloy, a mixture of gold and silver).

Pure gold is a very soft metal. In fact, it is the most malleable metal known to man. It is variously mixed with copper, nickel, silver, etc., to make it harder and cheaper. 100% pure gold is 24 carat. Generally, in India, 22 carat gold is used for making ornaments. It means that 22 parts of pure gold is alloyed with 2 parts of either copper or silver.

2. Silver (Ag)

Silver is an off white, lustrous metal. It is one of the the most ductile metal and also the best known conductor of electricity. Its chemical reactivity is more than gold. It is used:

(i) for making jewellery.

(ii) for filling in teeth cavities (in the form of a gold-mixed alloy).

(iii) as a purifier of water.

(iv) as an electrode metal, and in electroplating.

(v) in photography in the form of silver bromide and silver nitrate.

Silver is not used for making electric wires, because it is a costly metal.

3. Platinum (Pt)

Platinum is lustrous and a very precious metal. Like gold, platinum too does not react easily with other substances. Platinum is also an excellent catalyst. It is used:

(i) for making electrodes and electrolytic cells.

(ii) for making expensive ornaments and watches.

(iii) in 'flame test' and 'borax bead test' conducted for qualitative analysis.

(iv) As a catalyst it is used in hydrogenation of unsaturated oil to prepare vanaspati ghee, in the manufacture of acids, etc.

4. Iron (Fe)

Iron is the most useful metal of all. It is known to man since ancient times. It is a reactive metal and is found in combined state. Iron is used:

(i) to make pipes, tanks, cylinders, agricultural tools, nails, wire meshes, railings, furniture, etc.

(ii) to make bridges, ships, machine parts, buildings, utensils, etc. in the form of steel, an alloy containing carbons.

(iii) in the construction of power transmission towers.

5. Copper (Cu)

Copper is a reddish brown metal. It is highly ductile and a very good conductor of heat and electricity. It finds applications in:

(i) making electric wires and cables, utensils, and even semi-precious ornaments.

(ii) making coins and statues in the form of its alloys called bronze and brass.

(iii) electronic devices.

Activity 4

Consider some metals such as iron, copper, aluminium, lead, etc.

Which of the above metals are also available in the form of wires?

The ability of metals to be drawn into thin wires is called ductility. Gold is the most ductile metal. You will be surprised to know that a wire of about 2 km length can be drawn from one gram of gold.

Activity 5

To find out metals are good conductors of heat.

Procedure: On a cold day, touch a metal rod and a wooden rod. Metal rod appears to be much more colder than the wooden rod though both are at the same temperature. This is due to the reason that metals are good conductors of heat and conduct heat from our body quickly, while wood being bad conductor of heat, does not conduct heat so quickly.

6. Aluminium (Al)

Aluminium is the most abundant metal found in the earth's crust, and the second most useful metal after iron. It is silvery white in colour. It is malleable and ductile, and it is a very good conductor of heat and electricity. Therefore, it is used:

(i) as a substitute for copper to make electric wires, because it is cheaper.

(ii) to make utensils, cans for drinks, furniture, window frames, etc.

(iii) for packaging foodstuffs and wrappers of medicines in the form of aluminium foil.

(iv) as a paint to prevent rust in the form of a powder foil.

Aluminium is light and strong. It is mixed with other metals to make it stronger, and then it is used to make the bodies of aircraft and automobiles, machine parts and tools.

Teacher's Note

Understanding the properties of metals like conductivity and malleability helps us choose the right material for everyday items like cooking vessels and electrical wiring.

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