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.