Monday, 29 February 2016

TEXTBOOK ANSWERS AND SOLUTIONS OF CBSE CLASS VIII SCIENCE Chapter 4 MATERIALS:METALS AND NON METALS




Exercises

1) Which of the following can be beaten into thin sheets?
(a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen

ANSWER :-( a) Zinc

2) Which of the following statements is correct?
(a) All metals are ductile.
(b) All non-metals are ductile.
(c) Generally, metals are ductile.
(d) Some non-metals are ductile.

ANSWER:-c) Generally, metals are ductile

3) Fill in the blanks:
(a) Phosphorus is a very __reactive__ non-metal.
(b) Metals are __good__ conductors of heat and__electricity__.
(c) Iron is __more__ reactive than copper.
(d) Metals react with acids to produce __hydrogen__ gas.

4) Mark ‘T’ if the statement is true and ‘F’ if it is false.
(a) Generally, non-metals react with acids. ( )
(b) Sodium is a very reactive metal. ( )
(c) Copper displaces zinc from zinc sulphate solution. ( )
(d) Coal can be drawn into wires. ( )

ANSWER:-
a)F
b)T
c)F
d)F

5) Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.

Properties.                                       Metals Non-metal

1. Appearance
2. Hardness
3. Malleability
4. Ductility
5. Heat
Conduction
6. Conduction of Electricity

ANSWER:-
Metals-Lustrous, hard, Can be beaten into thin sheets; Can be beaten into wires, Good conductors of heat, Good conductors of electricity.

Non-Metals-dull, soft, Cannot be beaten into thin sheets, Cannot be beaten into wires, Poor conductors of heat, Poor conductors of electricity.

6) Give reasons for the following.
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods for heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene

ANSWER :-(a) Aluminium foils are used to wrap food items because aluminium metal is malleable. Therefore, it can be beaten into thin foils.

(b) Metals are good conductors of heat and electricity. Therefore, immersion rods for heating liquids are made of metallic substances.

(c) A metal can displace a less reactive metal from its salt in an aqueous solution. But zinc is more reactive than copper. Therefore, copper cannot displace zinc from its salt solution.

d) Sodium and potassium are stored in kerosene because they are highly reactive elements. They can easily catch fire even when in contact with air.

7) Can you store lemon pickle in an aluminium utensil? Explain.

ANSWER:-Lemon pickle cannot be stored in aluminium utensils because lemon pickle contains acids, which can react with aluminium (metal) liberating hydrogen gas. This can lead to the spoiling of the pickle.

8) Match the substances given in Column A with their uses given in Column B.
A                                                                 B
(i) Gold                                      (a) Thermometers
(ii) Iron                                     (b) Electric wire
(iii) Aluminium.                        (c) Wrapping food
(iv) Carbon                                (d) Jewellery
(v) Copper                                 (e) Machinery
(vi) Mercury                               (f) Fuel

ANSWER:-
A.                                                      B
(i) Gold                                     d) Jewellery
(ii) Iron                                     e) Machinery
(iii) Aluminium.                         c) Wrapping food
(iv) Carbon                               f) Fuel
(v) Copper                                b) Electric wire
(vi) Mercury                             a) Thermometers

9) What happens when?
(a) Dilute sulphuric acid is poured on a copper plate?
(b) Iron nails are placed in copper sulphate solution?
Write word equations of the reactions involved.




ANSWER:-a) When dilute sulphuric acid is poured on a copper plate, the copper metal reacts with sulphuric acid to liberate hydrogen gas.

(b) Iron being more reactive displaces copper from copper sulphate solution. In this reaction, the blue colour of copper sulphate fades and there is deposition of copper on the iron nail.

10) Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(a) How will she find the nature of the gas?
(b) Write down word equations of all the reactions taking place in this process.

ANSWER :-( a) Add a few drops of water in the test tube containing gas. Now, cover the test tube and shake it well. After shaking, test the solution with blue litmus and red litmus. It will turn blue litmus red. Thus, the gas is acidic in nature.

(b) Charcoal reacts with oxygen to form carbon dioxide gas. Carbon dioxide reacts with water to form carbonic acid, which turns blue litmus paper red.


Written By Badal Paul
The author is a passionate blogger, writer and educationalist. This blog is created to ease troubles of the Cbse students. The author holds multiple blogs and the writer of the Novel KALCHAKRA, OOM AND THE CHOSEN FIVE.