Sunday, June 19, 2022

Class 10 Science | Chapter-end Exercise & Answers | Chapter 3 | Metals and Non-metals

1.   Which of the following pairs will give displacement reactions?

a.     NaCl solution and copper metal.

b.     MgCl2 solution and aluminium metal.

c.     FeSO4 solution and silver metal.

d.     AgNO3 solution and copper metal.


Answer:
(d) AgNO3 solution and copper metal.


2.  Which of the following methods is suitable for preventing an iron frying pan from rusting?

(a) Applying grease

(b) Applying paint.

(c) Applying a coating of zinc

(d) All the above.


Answer:

(c) Applying a coating of zinc.


3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

(a) calcium                

(b) carbon

(c) silicon                   

(d) iron


Answer:
(a) Calcium.


4.   Food cans are coated with tin and not with zinc because

(a) zinc is costlier than tin

(b) zinc has a higher melting point than tin

(c) zinc is less reactive than tin

(d) zinc is more reactive than tin.


Answer:
(d) Zinc is more reactive than tin.


5.   You are given a hammer, a battery, a bulb, wires and a switch.

(a)   How could you use them to distinguish between samples of metals and non-metals?

(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.


Answer:

(a) Metals can be beaten into thin sheets (malleable) with a hammer. Non-metals cannot be beaten with a hammer to form thin sheets (non-malleable).

When metals are connected into circuit using a battery, bulb, wires and switch, current passes through the circuit and the bulb glows. Metals are good conductors of electricity. When non-metals are connected, the bulb does not glow.

(b) Malleability of metals can be used to make metal sheets for various purposes. Metals are good conductors of electricity. So they can be used to make electric cables.


6.   What are amphoteric oxides? Give two examples of amphoteric oxides.


Answer:
Amphoteric oxides are the metal oxides showing both basic and acidic behaviour. They can react with acids and bases to form salt and water. E.g. Aluminium oxide and zinc oxide.


7.  Name two metals which will displace hydrogen from dilute acids and two metals which will not.


Answer:
Metals above hydrogen in the activity series displace hydrogen from dilute acids. E.g. sodium & magnesium.

Metals below hydrogen in the activity series cannot displace hydrogen from dilute acids. E.g. copper, silver.


8.  In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?


Answer:
Cathode: Pure metal

Anode: Impure metal

Electrolyte: Metal salt solution


9.  Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in the figure.

a.  What will be the action of gas on

(i) dry litmus paper?

(ii) moist litmus paper?

b.  Write a balanced chemical equation for the reaction taking place.


Answer:

a. (i) Dry litmus paper: No action.

(ii) Moist litmus paper: Becomes red.

b.  S    +     O2         SO2

(Sulphur)           (Sulphur dioxide)

SO2 + H2O H2SO3 (Sulphurous acid)


10. State two ways to prevent the rusting of iron.


Answer:
Painting, Galvanizing


11.  What type of oxides are formed when non-metals combine with oxygen?


Answer:
Acidic oxides (e.g., SO2) and neutral oxides (e.g., H2O).


12.  Give reasons:

a.   Platinum, gold & silver are used to make jewellery.

b.   Sodium, potassium & lithium are stored under oil.

c.   Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.

d.   Carbonate and sulphide ores are usually converted into oxides during the process of extraction.


Answer:

a. Platinum, gold and silver are malleable and ductile. They are also highly resistant to corrosion.

b. They are highly reactive and catch fire when exposed to air.

c.  Aluminium forms a non-reactive layer of aluminium oxide on its surface. This prevents aluminium from further reaction with other substances. So aluminium is used to make cooking utensils.

d. It is easier to reduce a metal oxide into free metal. Therefore, the carbonate and sulphide ores are first converted to oxides.


13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Answer:

Sour substances like lemon & tamarind contain acids. They dissolve the coating of copper oxide or basic copper carbonate present on the surface of tarnished copper vessels.


14. Differentiate between metal and non-metal on the basis of their chemical properties.


Answer:

Metals

Non-metals

(i) They form basic oxides or amphoteric oxides.

They form acidic or neutral oxides.

(ii) They replace hydrogen from acids and form salts.

They do not replace hydrogen from acids.

(iii) With chlorine, metals form chlorides which are electrovalent.

With chlorine, non-metals form chlorides which are covalent.

(iv) With hydrogen few metals form hydrides which are electrovalent.

With hydrogen, non-metals form many stable hydrides which are covalent.


15. A man went door-to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he has used?


Answer:
The goldsmith dipped the gold bangles in aqua-regia. It dissolved a considerable amount of gold from gold bangles and reduced their weight.


16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).


Answer:

·  Copper is a better conductor of heat than steel.

·  Copper does not corrode easily. Steel corrodes easily.

·  Copper does not react with water at any temperature. Iron reacts with water on heating.


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