Exams Question Papers General Knowledge Election Directory
Question 2:
What are the two properties of carbon which lead to the huge number of carbon
compounds we see around us?
Answer:
The two features of carbon that give rise to a large number of compounds are as
follows:
(i) Catenation − It is the ability to form bonds with other atoms of carbon.
(ii) Tetravalency − With the valency of four, carbon is capable of bonding with four
other atoms.
Question 1:
How many structural isomers can you draw for pentane?
Answer:
Three structural isomers are possible for pentane.
(i) CH3 – CH2 – CH2 – CH2 – CH3
Question 2:
What would be the electron dot structure of a molecule of sulphur which is made up
of eight atoms of sulphur? (Hint − the eight atoms of sulphur are joined together in
the form of a ring.)
Answer:
Electron dot structure of a sulphur mole
Question 1:
What would be the electron dot structure of carbon dioxide which has the formula
CO2?
Answer:
Electron dot structure of CO2 is
Question 2:
Why do ionic compounds have high melting points?
Answer
Ionic compounds have strong electrostatic forces of attraction between the ions.
Therefore, it requires a lot of energy to overcome these forces. That is why ionic
compounds have high melting points.
Question 1:
Why is sodium kept immersed in kerosene oil?
Answer
Sodium and potassium are very reactive metals and combine explosively with air as
well as water. Hence, they catch fire if kept in open. Therefore, to prevent accidental
fires and accidents, sodium is stored immersed in kerosene oil.
Question 16:
Give reasons why copper is used to make hot water tanks and not steel (an alloy of
iron).
Answer
Copper does not react with cold water, hot water, or steam. However, iron reacts with
steam. If the hot water tanks are made of steel (an alloy of iron), then iron would
react vigorously with the steam formed from hot water.
3Fe + 4H2O → Fe3O4 + 4H2
Iron Steam Iron(II, III) oxide Hydrogen
That is why copper is used to make hot water tanks, and not steel.
Question 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 had used?
Answer
He must have dipped the gold metal in the solution of aqua regia − a 3:1 mixture of
conc. HCl and conc. HNO3. Aqua regia is a fuming, highly corrosive liquid. It dissolves
gold in it. After dipping the gold ornaments in aqua regia, the outer layer of gold gets
dissolved and the inner shiny layer appears. That is why the weight of gold ornament
reduced.
Question 14:
Differentiate between metal and non-metal on the basis of their chemical properties.
Answer
Question 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
Copper reacts with moist carbon dioxide in air to form copper carbonate and as a
result, copper vessel loses its shiny brown surface forming a green layer of copper
carbonate.The citric acid present in the lemon or tamarind neutralises the basis
copper carbonate and dissolves the layer. That is why, tarnished copper vessels
are cleaned with lemon or tamarind juice to give the surface of the copper vessel
its characteristic lustre.
Question 12:
Give reasons
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and 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 used to make jewellery because they are very
lustrous. Also, they are very less reactive and do not corrode easily.
(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously
with air as well as water. Therefore, they are kept immersed in kerosene oil in
order to prevent their contact with air and moisture.
(c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is
because aluminium reacts with oxygen present in air to form a thin layer of
aluminium oxide. This oxide layer is very stable and prevents further reaction of
aluminium with oxygen. Also, it is light in weight and a good conductor of heat.
Hence, it is used to make cooking utensils.
(d) Carbonate and sulphide ores are usually converted into oxides during the process
of extraction because metals can be easily extracted from their oxides rather than
from their carbonates and sulphides.
Question 11:
What type of oxides is formed when non-metals combine with oxygen?
Answer
Non-metals combine with oxygen to form acidic oxides.
For example:
S(s) + O2(g) → SO2(g)
(Acidic in nature)
Question 10:
State two ways to prevent the rusting of iron.
Answer
Two ways to prevent the rusting of iron are:
(i) Oiling, greasing, or painting: By applying oil, grease, or paint, the surface
becomes water proof and the moisture and oxygen present in the air cannot
come into direct contact with iron. Hence, rusting is prevented.
(ii) Galvanisation: An iron article is coated with a layer of zinc metal, which prevents
the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.
Question 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 figure below.
(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) There will be no action on dry litmus paper.
(ii) Since the gas is sulphur dioxide (SO2), it turns moist blue litmus paper to red
because sulphur dioxide reacts with moisture to form sulphurous acid.
S(s) + O2(g) → SO2(g)
Sulphur dioxide
SO2(g) + H2O(l) → H2SO3(aq)
Sulphurous acid
Question 8:
In the electrolytic refining of a metal M, what would you take as the anode, the
cathode and the electrolyte?
Answer
In the electrolytic refining of a metal M:
Anode → Impure metal M
Cathode → Thin strip of pure metal M
Electrolyte → Solution of salt of the metal M
Question 7:
Name two metals which will displace hydrogen from dilute acids, and two metals which
will not.
Answer
Metals that are more reactive than hydrogen displace it from dilute acids. For example:
sodium and potassium. Metals that are less reactive than hydrogen do not displace it.
For example: copper and silver.
Question 6:
What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer
Those oxides that behave as both acidic and basic oxides are called amphoteric
oxides.
Examples: aluminium oxide (Al2O3), zinc oxide (ZnO)
Question 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
nonmetals.
Answer
(a)With the hammer, we can beat the sample and if it can be beaten into thin sheets
(that is, it is malleable), then it is a metal otherwise a non-metal. Similarly, we
can use the battery, bulb, wires, and a switch to set up a circuit with the sample.
If the sample conducts electricity, then it is a metal otherwise a non-metal.
(b) The above tests are useful in distinguishing between metals and non-metals as
these are based on the physical properties. No chemical reactions are involved in
these tests.
Question 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 more reactive than tin.
(d) zinc is less reactive than tin.
Answer
(c) Food cans are coated with tin and not with zinc because zinc is more reactive than tin.
Question 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) The element is likely to be calcium.