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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