CARBON AND CARBON COMPOUNDS
14. CARBON AND CARBON
COMPOUNDS
14 CARBON AND CARBON COMPOUNDS
points
to remember :
1.
Carbon is a non-metallic element. Carbon is the main
constituent of all plant
and animal products. In nature, it is
found in the free state
as diamond and graphite and also in
compounds. Carbon is
present in air as carbon dioxide, as also in
fuels like biogas,
petroleum and marsh gas.
2.
Anthracite, Bituminous coal, Lignite, Peat are the different
types of coal.
3.
Allotropes : Some elements are found in nature in more
than
one form. They have same
chemical properties but different
physical properties.
These forms are called allotropes of an
element. Carbon exhibits
allotropy in two forms – crystalline and
amorphous form. Diamond,
graphite and fullerene are
crystalline allotropes
while coke, coal are amorphous allotropes.
4.
Carbon dioxide : Carbon dioxide occurs in free state in
atmospheric air. It is
found in chalk, Shahabad stone and
limestone in compound
form. Carbon dioxide is prepared in the
laboratory from calcium
carbonate and hydrochloric acid.
Carbon dioxide is a
tasteless, odourless and colourless gas. It is
heavier than air and
sparingly soluble in water. Carbon dioxide
neither burns nor
supports burning. It is used in the
manufacture of aerated
cold beverages, dry ice, washing soda
and sodium bicarbonate
(baking powder). It is used as fire
extinguisher. Plants use
carbon dioxide to make their own food.
5.
Methane : Methane is the first in the series of hydrocarbon
compounds. The molecular
formula of methane is CH
_
. Methane
molecule has one carbon
atom and four hydrogen atoms. It is
formed in marshy lands,
therefore methane is called marsh gas.
In the laboratory,
methane is produced by heating a mixture of
hydrogen and carbon
monoxide to 300 °C in the presence of
catalyst nickel.
Methane is an odourless,
tasteless and colourless gas. It is
lighter than air and
insoluble in water. Methane is highly
inflammable and burns
with a blue flame. It is used as a fuel. It is
used in the production of
acetylene.
Questions
and Answers
Q.
1 Answer the following questions :
(1)
Where does carbon occur in nature ?
Ans.
Carbon is the main constituent of all plant and animal
products. Carbon is a
non-metallic element. In nature, it is found in
the free state as
graphite and diamond and also in compounds.
Carbon is present in air
as carbon dioxide, as also in fuels like
biogas, petroleum and
marsh gas.
(2)
How did coal form in nature ?
Ans.
Plants and animals constantly receive solar energy.
Millions of years ago the
remains of plants and animals got buried
under the earth. Due to
action of microorganisms, the gaseous
substances in these
remains were released into the atmosphere
and the left behind was
carbon compounds. After this, under
tremendous pressure, the
liquid substances in these compounds
drained away and the
remaining mineral solidified into compact
and hard rock and this
material is called coal.
(3)
State the types of coal with the percentage of carbon
in
it.
Ans.
The types of coal with the percentage of carbon are as
follows :
Types
of coal Percentage of carbon
(1) Anthracite 80
(2) Bituminous coal 60
(3) Lignite 22
(4) Peat 11
Answer
to the Question given on page 136 of the textbook
What
common feature is there in sugar, paper,
plastic,
wood, cereals, pulses and petrol ?
Ans.
They are all carbon compounds.
*
(4) What is meant by allotrope ?
Ans.
Some elements are found in nature in more than one
form. They have same
chemical properties but different physical
properties. These forms
are called allotropes of an element.
(5)
In how many forms does carbon exhibit allotropy ?
Explain
with suitable examples.
Ans.
Carbon exhibits allotropy in two forms : crystalline form
and amorphous form. (1)
In the crystalline form, the atoms of
the element have a
specific arrangements. Example : diamond,
graphite and fullerene.
(2) In the amorphous form, the
arrangement of atoms is
irregular. Example : coke, coal, etc.
(6)
Write the properties of diamond.
Ans.
(1) Pure diamond is brilliant and an extremely hard
substance. (2) It is a
bad conductor of electricity. (3) When
diamond is heated to a
high temperature, it gives out carbon
dioxide. (4) Acids and
alkalies do not have any effect on diamond.
Answers
to the Questions given on page 137 of the textbook
*
(1) What makes a diamond shine ?
Ans.
A diamond is cut such that, it has number of faces,
therefore, the light rays
entering the diamond undergo
multiple internal
reflections before coming out. Therefore,
it shines.
* (2) What is the main
difference between diamond and
glass
?
Ans.
Diamond is in crystalline form while glass is in
amorphous form. The
refractive index of diamond is much
higher than that of
ordinary glass. Diamond is very hard while
glass is brittle.
* (3) Where are the
diamond mines in India located ?
Ans.
The diamond mines in India are located at Panna in
Madhya Pradesh.
(7) Write the properties of graphite.
Ans.
(1) The graphite that occurs in nature is black, soft and
smooth. (2) It is a good
conductor of heat and electricity.
(8)
Give the uses of graphite.
Ans.
(1) Graphite is used in pencils for writing on paper.
(2) Graphite is used as
positive electrode in dry cells. (3) Graphite
is used as lubricant. (4)
For bright light, graphite is used in arc
lamps.
*
(9) Why is graphite used as lubricant ?
Ans.
A lubricant is used to reduce friction among the moving
parts of a machine. Due
to the specific arrangement of carbon atoms
in a crystal of graphite
it is soft and smooth. Hence, graphite is used
as a lubricant.
Answers
to the Questions given on page 139 of the textbook
*
(1) Which coal is used for purifying water?
Ans.
Porous charcoal is used for purifying water.
*
(2) Why is charcoal brittle ?
Ans.
When carbon-rich plant material is burnt in
insufficient supply of
oxygen, the hydrogen, nitrogen and
oxygen escapes. The end
product is black and porous. As a
result charcoal becomes
brittle.
*
(3) Why is charcoal used as a domestic fuel ?
Ans.
Charcoal burns with a smokeless flame. Hence, it is
used as a domestic fuel.
(10)
Write the different sources of carbon dioxide.
Ans.
(1) Carbon dioxide occurs in free state in atmospheric
air. (2) It is produced
in respiration of plants and animals. (3) It is
found in chalk, Shahabad
stone and limestone in compound form.
How
to prepare Carbondioxide in the laboratory?_
Ans.
(1) Some pieces
of calcium carbonate
(lime-stone) is taken in
a
flat bottom flask. Set up
the apparatus as shown
in the diagram. The flask
is fitted with a
two-holed
cork, bearing thistle
funnel. (2) Hydrochloric
acid is slowly added
through the thistle
funnel. Ensure that the
lower end of the thistle funnel is immersed
in the hydrochloric acid.
(3) A chemical reaction takes place
between calcium carbonate
and hydrochloric acid and the carbon
dioxide gas is gradually
evolved. The gas is then collected in gas jars
by the upward
displacement of air.
(
(13)
Give the physical properties of carbon dioxide.
Ans.
(1) Carbon dioxide is a tasteless, odourless and
colourless gas. (2) It is
heavier than air. (3) It is sparingly soluble
in water. (4) Carbon
dioxide neither burns nor supports burning.
Answer
to the Question given on page 140 of the textbook
*
What happens when lemon juice spills on the marble
kitchen
counter?
Ans.
(1) Marble is a form of calcium carbonate. (2) When
lemon juice (Citric acid
is present in lemon juice) spills on the
marble (calcium
carbonate), a chemical reaction takes place
between them and carbon
dioxide gas evolves.
(14)
Give the uses of carbon dioxide. OR
*
Give two uses of carbon dioxide.
Ans.
(1) Carbon dioxide is used in the manufacture of aerated
cold beverages. (2) It is
used to produce dry ice. (3) It is used to
make washing soda. (4) It
is used to produce sodium bicarbonate
(baking powder). (5) It
is used as a fire extinguisher. (6) Plants use
carbon dioxide to make
their own food.
Answers
to the Questions given on page 142 of the textbook
*
(1) Why do food preparations become light and crisp
when
baking soda is used ?
Ans.
When baking soda is used in the preparation of food,
carbon dioxide is
released on heating. It escapes in the form
of bubbles. Therefore,
the food preparations become porous,
light and crisp.
*
(2) What is caustic soda ? Where is it used ?
Ans.
Caustic soda is sodium hydroxide. It is used in the
production of soap and
paper.
(15)
Give two methods of preparation of methane.
Ans.
(1) Methane is produced anaerobically (in the absence of
air) from plant and
animal waste in a biogas plant.
(2) In the laboratory,
methane is produced by heating a
mixture of hydrogen and
carbon monoxide to 300°C in the presence
of catalyst nickel.
(16) Give the properties of methane.
Ans.
(1) Methane is an odourless, tasteless and colourless gas.
(2) Methane is lighter
than air and insoluble in water. (3) Methane
is highly inflammable and
burns with a blue flame.
*
(17) Give the uses of methane.
Ans.
(1) Methane is used as a fuel. (2) It is used to prepare
acetylene, another carbon
compound.
Answers
to the Questions given on page 144 of the textbook
*
(1) Is carbon dioxide always formed when a hydrocarbon
is
burnt?
Ans.
Yes, carbon dioxide is always formed when a
hydrocarbon is burnt.
*
(2) What is the difference between methane and the
gas
in the cylinder we use at home?
Ans.
The gas in the cylinder we use at home is butane
(also propane). It is
liquefied under pressure. Methane cannot
be liquefied even under
pressure.
Q.
2 Write notes on the following : (1) Diamond
(2)
Graphite (3) Fullerene (4) Fire extinguisher.
Ans.
(1) Diamond : (1) Millions of years ago, brilliant and
pure diamonds were formed
by the crystallisation of carbon under
tremendous pressure. (2)
In the diamond crystal, each carbon
atom is linked to four
other carbon atoms at specific distance.
(3) Brilliant, pure diamond is the hardest
known substance. (4) It is
a bad conductor of
electricity. (4) When it is
heated to a very high
temperature, it gives out
carbon dioxide. (5) It
does not react with acids
or alkalies. (6) When
pure carbon is subjected
to extreme high pressure
and very high
temperature, synthetic
diamonds are formed.
(7) Diamond is used, as
an ornament, to cut
glass and in drilling
machines.
Fig. 14.3 : Graphite
(2)
Graphite : (1) Graphite is a hexagonal
crystal. (2) Six carbon
atoms form a hexagon
and are at specific
distances from each other.
Thus, the regular
arrangement of atoms in
graphite is in layers.
(3) Within each layer,
every carbon atom has
three other carbon
atoms around it at equal
distances. (4) The
graphite is black, soft
and smooth and it is a good conductor of
heat and electricity. (5)
It is used in pencils. (6) It is used as positive
electrode in dry cells.
(7) It is used as a lubricant. (8) It is used in
arc lamps for bright
light.
Fig. 14.4 : Fullerene
(3)
Fullerene : (1) Fullerene is allotrope
of carbon in which sixty
carbon atoms are
linked to form a stable
structure. (2) C
__
atoms
are joined to each other
in pentagonal and
hexagonal arrangements.
As a result, the
structure of Fullerene is
exactly like a football.
(3) The properties of
Fullerene are still being
studied. Scientists
believe that Fullerene may prove of great use in
research related to
superconductivity.
(4)
Fire extinguisher : The fire extinguisher consists
of a
cylinder filled with a
solution of sodium bicarbonate. A capsule
containing dilute
sulphuric acid is placed inside the cylinder. When
the knob is pressed, the
sulphuric acid in the capsule spills on the
sodium bicarbonate, a
chemical reaction takes place and carbon
dioxide is produced.
Carbon dioxide is not combustible and does not
support combustion.
Hence, it is used as a fire extinguisher.
Q.
3 Explain the following reactions, giving
their
balanced
equations :
(1)
Carbon dioxide is passed through lime water.
Ans.
When carbon dioxide is passed through lime water, lime
water turns milky due to
the formation of white insoluble calcium
carbonate.
oxide
reacts with carbon dioxide.
Ans.
When calcium oxide reacts with water, calcium
carbonate is formed.
(3) Carbon dioxide is passed through water.
Ans.
When carbon dioxide is passed through water, it
dissolves sparingly
forming carbonic acid.
(4) Carbon dioxide is passed through a
solution of sodium
hydroxide.
Ans.
When carbon dioxide is passed through a solution of
sodium hydroxide, sodium
carbonate is formed.
(5) Carbon dioxide is passed through a
solution of sodium
carbonate.
Ans.
When carbon dioxide is passed through a solution of
sodium carbonate, sodium
bicarbonate is formed.
(6) A mixture of hydrogen and carbon monoxide
is heated
to
300°C.
Ans.
When a mixture of hydrogen and carbon monoxide is
heated to 300°C, methane
is formed.
(7) Methane is burnt in air.
Ans.
When methane is burnt in air, it burns with a blue flame
forming carbon dioxide.
in
air.
Ans.
When carbon is burnt in air, it combines with oxygen to
form carbon dioxide.
(9) Sodium bicarbonate is treated with
sulphuric acid.
Ans.
When sodium bicarbonate is treated with sulphuric acid,
sodium sulphate and
carbon dioxide gas is formed.
(10) Calcium carbonate is treated with
hydrochloric acid.
Ans.
When calcium carbonate is treated with hydrochloric
acid, calcium chloride,
water and carbon dioxide is formed.
Q.
4 Give scientific reasons :
*
(1) Diamond is used to cut metals.
Ans.
(1) Diamond is a crystalline allotrope of carbon. The
atoms in a crystalline
form have a specific arrangement. (2) Since
diamond is the hardest
substance it is used to cut metals.
*
(2) Carbon dioxide is used for putting out fires.
Ans.
(1) Carbon dioxide is not combustible and does not
support combustion. (2)
It is heavier than air. (3) When it is spread
on a burning object, it
covers the object and separates it from air.
Thus, the fire is
extinguished. Hence, carbon dioxide is used for
putting out fires.
(3)
Marble tiles are not used in kitchen.
Ans.
(1) Marble is a form of calcium carbonate. (2) Calcium
carbonate reacts with an
acid to form the corresponding calcium
salt and carbon dioxide
gas. (3) In the kitchen, we use acidic
substance like lemon,
tamarind, buttermilk, etc. These substances
may react with marble and
the surface become rough. Hence,
marble tiles are not used
in kitchen.
*
Q. 5 Distinguish between the following :
(1)
Crystalline form of carbon and Non-crystalline or
amorphous
form of carbon :
Ans.
Crystalline form of
carbon
Non-crystalline
or amorphous
form
of carbon
1. The atoms of carbon in
a
crystalline form have a
specific arrangement.
1. The atoms of carbon in
noncrystalline
form have
irregular arrangement.
2. Carbon in crystalline
form is
an extremely hard
material.
2. Carbon in
non-crystalline
form is brittle.
(2)
Diamond and Graphite :
Ans.
Diamond Graphite
1. Diamond is an
extremely
hard material.
1. Graphite is black,
soft and
smooth.
2. In the diamond
crystal, each
carbon atom is linked to
four
other carbon atoms at
specific distances.
2. In graphite, six
carbon atoms
form a hexagon and are at
specific distances from
each
other. Within each layer
every carbon atom has
three
other carbon atoms around
it
at equal distances.
3. Diamond is a bad conductor
of electricity.
3. Graphite is a good
conductor
of electricity.
4. It is used, as an
ornament,
to cut glass and in
drilling
machines.
4. It is used as
lubricant.
Q.
6 Answer the following questions in one sentence
each
:
(1)
State atomic number, atomic mass number and
valency
of carbon.
Ans.
Atomic number of carbon : 6
Atomic mass number of
carbon : 12
Valency of carbon : 4.
(2)
Name a coal that contains highest percentage of
carbon.
Ans.
The coal that contains highest percentage of carbon is
anthracite.
(3)
Name the naturally occurring allotropic elements.
Ans.
Carbon, sulphur, phosphorus are some of the naturally
occurring allotropes of
carbon.
*
(4) Which are the allotropes of carbon?
Ans.
The diamond, graphite, fullerene, coke, coal are the
allotropes of carbon.
(5)
Name the crystalline forms of carbon.
Ans.
The diamond, graphite and fullerene are crystalline
forms of carbon.
(6)
How were diamonds formed?
Ans.
Millions of years ago, diamonds were formed by the
crystallization of carbon
under tremendous pressure.
(7)
How are synthetic diamonds made?
Ans.
Synthetic diamonds are made by subjecting pure carbon
to extremely high
pressure and heating it to a very high
temperature.
(8)
State the shape of graphite crystal.
Ans.
A graphite crystal is hexagonal.
*
(9) How is charcoal made?
Ans.
Charcoal is made by burning substances of plant origin
such as wood in an
insufficient supply of oxygen.
(10)
Name the compounds of carbon.
Ans.
Chalk, Shahabad stone and limestone are some
compounds of carbon.
Give two uses of carbon.
Ans.
(1) Graphite is a crystalline form of carbon. It is used
(i) in pencils for
writing on paper (ii) as a lubricant. (2) Coke is an
amorphous form of carbon.
It is mainly used as fuel.
Name a
gas used in fire extinguisher.
Ans.
Carbon dioxide is used as fire extinguisher.
Which
gas is used to produce aerated cold beverages ?
Ans.
Carbon dioxide is used to produce aerated cold beverages.
How
is hydrocarbon formed?
Ans.
Hydrocarbon is formed from the combination of carbon
and hydrogen.
Name
the first compound of hydrocarbon.
Ans.
The first compound of hydrocarbon is methane.
How
many atoms of carbon and hydrogen are present
in
the molecule of methane?
Ans.
The molecule of methane has one carbon atom and four
hydrogen atoms.
Why
is methane called marsh gas ?
Ans.
Methane is formed by the decomposition of plants and
animal matter in marshy
lands. Hence, methane is called marsh
gas.
(Which
gas is formed in a biogas plant ?
Ans.
Methane gas is formed in a biogas plant.
Q.
7 Find the odd one out and give the reason :
(1) Anthracite, Charcoal,
Bituminous, Peat.
(2) Carbon, Silicon,
Sulphur, Phosphorus.
(3) Coke, Diamond,
Graphite, Fullerene.
Ans. (1) Charcoal. The
others are the types of coal.
(2) Silicon. The
others are naturally occurring allotropic elements.
(3) Coke. The
others are crystalline allotropes of carbon.
Q.
8 Write whether following statements are True
or
False.
If a statement is false, correct it and rewrite :
(1) All plant and animal
products contain carbon as their main
constituent.
(2) Sulphur is a
naturally occurring allotropic element.
(3) The graphite is a
non-crystalline form of carbon.
(4) Fullerenes were named
after the architect Richard
Buckminster Fuller.
(5) The graphite found in
nature is a bad conductor of heat and
electricity.
(6) Charcoal is porous,
therefore, it has low density.
(7) Plants make their own
food by using oxygen.
(8) Methane is a natural
fuel.
(9) Methane has two
carbon atoms and four hydrogen atoms.
(10) Carbon dioxide is
heavier than air.
Ans.
(1) True. (2) True. (3) False. The graphite
is a
crystalline form of
carbon. (4) True. (5) False. The graphite found
in nature is a good
conductor of heat and electricity. (6) True.
(7) False. Plants
make their own food by using carbon dioxide.
(8) True. (9) False.
Methane has one carbon atom and four
hydrogen atom. (10) True.
Q.
9 Fill in the blanks :
1.
(1) In graphite crystal, six carbon atoms form a ……… and are
at specific distances
from one another.
* (2) Fullerene is an ………
of carbon.
* (3) ……… turns lime
water milky.
* (4) The charcoal is an
……… form of carbon.
* (5) Diamond is ………
conductor of electricity.
* (6) Biogas plant
produces ……… gas.
Ans.
(1) hexagon (2) allotrope (3) Carbon dioxide (4) amorphous
(5) bad (6) methane.
--
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
--
2.
(1) Graphite is a ……… form of carbon.
(2) ……… is used to
extinguish fires.
* (3) ……… is a good
conductor of heat and electricity.
(4) ……… are made by
subjecting pure carbon to extremely
high pressure and heating
it to a very high temperature.
184 NAVNEET GENERAL SCIENCE DIGEST : STANDARD VIII
(5) Charcoal is ……… and
therefore it has low density.
(6) Methane burns with a
……… flame.
Ans.
(1) crystalline (2) Carbon dioxide (3) Graphite
(4) Synthetic diamonds
(5) porous (6) blue.
Q.
10 Choose the correct options and
complete the
following
statements :
(1) Carbon has atomic
number ………
(a)
4 (b) 6 (c) 8 (d) 12
(2) Bituminous coal has
……… per cent of carbon.
(a)
60 (b) 80 (c) 22 (d) 44
(3) ……… is one of the
naturally occurring allotropic element.
(a)
Magnesium (b) Calcium (c) Phosphorus (d) Silicon
(4) In the diamond
crystal, every carbon atom has………atoms
of carbon at specific
distances around it.
(a)
3 (b) 5 (c) 6 (d) 4
(5) ……… is a
non-crystalline form of carbon.
(a)
Graphite (b) Coke (c) Fullerene (d) Diamond
(6) ……… gas is obtained
from biogas plant.
(a)
Ethane (b) Methane (c) Carbon dioxide (d) Oxygen
(7) The molecular formula
of methane is ……… .
(a)
C
_
H
_
(b)
C
_
H
_
(c)
CH
_
(d)
C
H
_
(8) ……… is produced and
it gushes out of fire extinguisher.
(a)
Carbon dioxide (b) Methane (c) Oxygen (d) Ethane
Ans.
(1) 6 (2) 60 (3) Phosphorus (4) 4 (5) Coke (6) Methane
(7) CH
_
(8) Carbon dioxide.
Q.
11 Match the following :
*
[1] ‘A’ ‘B’
(1) Fullerene (a) Na
_
CO
(2) Graphite (b) Cutting
metals
(3) Diamond (c) Hexagonal
arrangements of atoms
(4) Washing soda (d) C
__
Ans.
(1) Fullerene –C
__
(2) Graphite – Hexagonal
arrangements
of atoms (3) Diamond–
Cutting metals (4) Washing
soda –Na
_
CO
.
[2] ‘A’ ‘B’
(1) Methane (a) Amorphous
form of carbon
(2) Anthracite (b) Carbon
dioxide
(3) Coke (c) Marsh gas
(4) Fire extinguisher (d)
80% carbon
Ans.
(1) Methane– Marsh gas (2) Anthracite –80% carbon
(3) Coke – Amorphous form
of carbon (4) Fire extinguisher –
Carbon dioxide.
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