Metals and non-metals Chapter 3 of D.A.V Science book

 A. Fill in the blanks.

1. The property due to which a metal can be hammered into thin sheets, is known as malleability.

2. Bronze is an alloy of copper and tin.

3. Gold is mixed with copper and/or silver to make it hard.

4. Iodine is the only non-metal to have a natural lustre.

5. Phosphorous is a non-metal which catches fire in the air.

6. The only metal, which exists in the liquid state at room temperature, is mercury.

B. Match the following.

1. Hardest substance- Diamond

2. Aluminium ore- Bauxite

3. A non-metal, normally, existing in the liquid state- Bromine

4. A good electrical conductor- Graphite

5. A metalloid- Arsenic

C. Tick the correct options.

1. The two most abundant metals, found in the earth's crust, are-----

Ans- aluminium and iron

2. The metals, used in making the alloy 'german silver', are----

Ans- Copper+zinc+nickel

3. When a metal reacts with oxygen, the resulting oxide of the metal -----

Ans- is a basic oxide

4. Out of the metals, gold, silver, copper and aluminium, the one, that is most ductile, is -----

Ans- gold

5. Two of the metals, that cannot be stored either in the air or underwater, are----

Ans- potassium and sodium

D. Answer the following questions in brief.

1. Name (i) one metal and (ii) one non-metal which normally exists in the liquid state.

Ans- (i) Mercury

       (ii) Bromine

2. State the fraction of gold present in an 18-carat gold piece.

Ans- 18/24=3/4parts

3. State the property of copper wires that make them useful for electrical fittings.

Ans- Copper wires are a good conductor of electricity. That's why they are useful for electrical fittings.

4. Define an alloy.

Ans- An ally is a homogenous mixture of two or more metals, and metal or a non-metal.

5. List any two uses of non-metals.

Ans- Following are two uses of non-metals---

      (i) Iodine is used as an antiseptic.

      (ii) Phosphorous is used in the matchbox industry and in fertilizers.

E. Answer the following questions.

1. Write the balanced chemical equations for the following reactions:

 Sodium reacts with oxygen

(b) Aluminium reacts with dilute hydrochloric acid 

Ans- (a) 4Na+O2----> 2Na2O2  

       (b) 2Al+6Hcl ----> 2AlCl3  +H2

2. Why are gold and platinum suitable for making jewellery?

Ans- Gold and platinum are the least reactive metals and they have their own lustre. That's why they are suitable for making jewellery.

3. Sodium and potassium are stored under kerosene. Give reason.

Ans- Sodium and potassium are stored under kerosene because when they come in contact with moisture present in the air they catch fire. So, in kerosene air is avoided.

4. Why is bronze preferred over copper metal for making statues?

Ans- Bronze is an alloy. Therefore, it is more stronger and harder than copper. It is corrosion resistant also.