CHAPTER 12
CARBON AND ITS COMPOUNDS
(A) CARBON
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CARBON - The Chemical Basis for Life
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Life itself is based upon this remarkable chemistry of carbon.
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What is Carbon?
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ACTIVITY 12 A.1
1: Heat a little sugar taken in a spatula. You will observe a black residue.
This shows the presence of carbon in sugar.
2: You might have observed chapati or roti getting charred when over
heated, What might be the reason for this?
3: When a small quantity of milk is continuously boiled, it will get charred.
But when water is boiled it will not get charred, rather it just evaporates, Why?
4: Does salt get charred when heated like sugar? Try this activity and
draw your own inference.
5: When you heat sand, it does not get charred. Why?
6: Also many substances like calcium carbonate (CaCO 3 ) which
contain carbon do not get charred when heating, why? Give reasons.
Allotropes of Carbon
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ŏ Recall the differences between diamond and graphite.
Why are the physical properties of diamond and graphite so different?
The reason is the difference in the arrangement of carbon atoms in
diamond and graphite.
Diamond and Graphite are the two allotropes of carbon which are
chemically identical and differ markedly in their physical properties.
158
Do you know
A new allotrope of carbon that
was discovered in 1985, contains
60 carbon atoms C60.This form has
been named Buckminsterfullerene
after the architect Buckminster
Fuller, who designed domed
structures that also resemble C60
molecule. (C60 molecules are often
called buckyballs)
Their discoverers – Robert Curl, Harold Kroto and Richard Smalley –
received the Nobel Prize in Chemistry in 1996.
Know this
The carbon can form alloys with iron, of which the most common is carbon
steel. Graphite is combined with clays to form the ‘lead’ used in pencils used
for writing and drawing. It is also used as a lubricant and a pigment, as a
moulding material in glass manufacture, in electrodes for dry batteries and
in electroplating and electroforming, in brushes for electric motors and as a
neutron moderator in nuclear reactors .
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Carbon forms an exceptionally large number of compounds because
of its unique characteristics like catenation, tetravalency and
isomerism .
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Catenation
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Do you know ?
Why aren’t there millions of compounds of B, Si, Ge, Sn, N, P, O,
S, Se and Te ?
Like carbon, the above elements also catenate and compound with B-B,
Si-Si, Ge-Ge, Sn-Sn, N-N, P-P, O-O, S-S, Se-Se and Te-Te bonds are known.
These compounds are unstable and very reactive and do not last long
whereas many compounds with C-C bonds exist for centuries under ordinary conditions. The unusual stability of compounds with chains of carbon
atoms is a result of the great strength of the C-C bond . The C-C bond is the
second strongest single bond between like atoms after the H-H bond.
Tetravalent Character
Observe : (YHQ WKRXJK the methane
molecule is three dimensional with H-C-H
bond angle 1090281 by convention the
methane molecule is represented in two
dimension with H-C-H bond angle 900
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The simplest hydrocarbons methane (CH4), ethane (CH3CH3), and propane
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Difference between organic and Inorganic Compounds
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What is Organic Chemistry ?
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Organic chemistry, is the study of carbon compounds.
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After studying this chapter you
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Hydrocarbons
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UHPRYHUVSODVWLFEDJVDQGWKHUPRFROHV
Do you know?
The orange colour of carrots, the yellow colour of butter and yolk of egg,
the red colour of tomatoes, the wax coating on apples which increases the
shelf life of apples and the cooking gas are all Hydrocarbons.
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Activity 12 B.1
Make a list hydrocarbon products used in your daily life.
So what are these Hydrocarbons?
Hydrocarbons are the simplest binary organic compounds
containing carbon and hydrogen only.
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171
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SRO\VW\UHQH+\GURFDUERQVDUHHFRQRPLFDOO\LPSRUWDQWEHFDXVHPDMRU
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Know this
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Activity 12 B.2
Take a candle and observe the smell by holding it near your nose.
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Lastly put out the candle and notice the smell.
You will wonder to know that the smell is found only when the
candle is put out not in the previous cases. It clearly indicates that
the wax of the candle which is hydrocarbon has no smell either in the
solid or in the liquid state but has characteristic odour only in vapour
state. Hydrocarbons usually do not have any characteristic
odour but some higher hydrocarbons in their vapour state have
characteristic smell.
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172
Sources of Hydrocarbons
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K\GURFDUERQV 7KHVH K\GURFDUERQV FRQVLVW RI VWUDLJKW RU EUDQFKHG
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173
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Saturated Hydrocarbon
CnH2n+2
Unsaturated Hydrocarbon
CnH2n
CnH2n-2
An alkene
An alkyne
An alkane
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C
C
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Name
Methane Ethane Propane Butane pentane
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1
2
3
4
5
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4
6
8
12
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Nomenclature of Alkanes
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176
Activity 12 B.3
ƒ Follow the examples given above and write the structural formulae
for the other six alkanes, containing carbon atoms 5 to 10. Use the
formula CnH2n+2.
ƒ Using paper balls, clay balls and toothpicks, construct the structures
of following hydrocarbons.
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ƒ Take two methane molecules already prepared. Construct ethane
molecule.
ƒ Tabulate the changes that you made.
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General Name
DQH
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Marsh gas
Methane LV WKH ÀUVW PHPEHU RI WKH
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Preparation of Methane /DERUDWRU\0HWKRG
DBy heating fused sodium acetate with soda lime:$PL[WXUH
RIVRGLXPDFHWDWHDQGVRGDOLPH1D2+&D2LVKHDWHGLQDKDUGJODVV
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Physical Properties
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Chemical Properties
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Combustibility
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179
Do you know
What is carbon monoxide?
Carbon monoxide is a very poisonous gas. It can not be seen or smelt.
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a room without anyone knowing. Every year, people die from carbon monoxide
poisoning.
Why is carbon monoxide poisonous?
Carbon monoxide acts as a poison by combining with haemoglobin in the
blood. Haemoglobin normally reacts with oxygen from the air and transports
the oxygen to the parts of the body which need it. Carbon monoxide is much
more reactive with haemoglobin than oxygen is. It combines to form carboxy
haemoglobin a stable compound with haemoglobin, preventing the transport
of oxygen around the body. The person dies of suffocation from inside.
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Activity 12 B. 4
Complete the table below
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1
2
3
4
5
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4
6
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4
7
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Unsaturated hydrocarbons
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FDUERQDWRPVVRPHZKHUHLQWKHFKDLQ
Alkenes : $ONHQHV DUH XQVDWXUDWHG K\GURFDUERQV WKDW FRQWDLQ
GRXEOHERQGEHWZHHQWZRFDUERQDWRPV$ONHQHVDUHDOVRFDOOHG2OHÀQV
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OHVVZKHQFRPSDUHGZLWKWKHFRUUHVSRQGLQJVDWXUDWHG
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Activity 12 B. 5
Take the ethane model you prepared. Re organize this molecule into ethene
and answer the following questions.
ƒ What is the chemical structure of this new compound?
ƒ Is this still an organic hydrocarbon?
ƒ What have you done to the ethane molecule?
ƒ If the chemical formula for the compound has changed, is it still
ethane?
182
Naming Alkenes
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Observe the following examples.
Name
No. C
atoms
(n)
No. H
atoms
(2 un)
Moleculer
Formula
HWKHQH
2
[ C2H4
Structural formula
H
H
C
C
H
SURSHQH
3
[ C3H6
H
C
H
H
EXWHQH
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4
5
[ H
C4H8
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Compare the structure of ethene with that of ethane.
H
H
H
C
C
H
H
H
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VLQFHHDFKPROHFXOHKDVQRFDUERQWRFDUERQGRXEOHERQGDQG
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Alkynes
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FDUERQDWRPVDUHFDOOHGalkynes.
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Naming Alkynes :7KH,83$&QRPHQFODWXUHIRUDON\QHVLVVLPLODU
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185
Compare Alkanes, Alkenes, Alkynes, and Cycloalkanes
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$ONHQHVDQGF\FORDONDQHVKDYHWKHVDPHJHQHUDOIRUPXODZK\"
Aromatic hydrocarbonsDOVRNQRZQDVDUHQHVDUHK\GURFDUERQV
WKDW KDYH DW OHDVW RQH DURPDWLF ULQJ EHQ]HQH ULQJ 7KH DURPDWLF
FRPSRXQGVFDQEHWKRXJKWRIDVGHULYDWLYHVRIDVHULHVRIK\GURFDUERQV
ZKRVHVLPSOHVWPHPEHULVEHQ]HQHC6H6
Structure of Benzene: 7KH EHQ]HQH ULQJ LV RQH RI WKH PRVW
LPSRUWDQW VWUXFWXUHV LQ RUJDQLF FKHPLVWU\ ,W LV D ULQJ RI VL[ FDUERQ
DWRPVZLWKDOWHUQDWHVLQJOHDQGGRXEOHERQGV,QUHDOLW\WKHVHERQGV
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SUDFWLFHWKHVWUXFWXUHRIEHQ]HQHLVUHSUHVHQWHGE\KH[DJRQZLWKD
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186
Other Aromatic Hydrocarbons
Examples:
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H
CH3
C
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C
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H
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25
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Note
The name AROMA is a misnomer in the case of Aromatic Hydrocarbons.
$URPDPHDQVDQDWWUDFWLYHÁDYRXUEXWVXUSULVLQJO\DURPDWLFK\GURFDUERQV
do not have any odour or some have nauseating odour.
Eg; Naphthalene - smell of moth ball. Benzene and Toluene - smell of
Kerosene and so on. Camphor - having good smell but does not contain
aromatic ring.
Uses of Aromatic Compounds
1. Benzene is used DVDVROYHQWIRURLOVIDWVUHVLQVUXEEHUVXOSKXULRGLQHHWF
LQWKHPDQXIDFWXUHRIG\HVGUXJVSHUIXPHVH[SORVLYHVHWF
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187
2. Toluene is used
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LQWKHPDQXIDFWXUHRI7ULQLWURWROXHQH717DQH[SORVLYH
3. Napthalene is used
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VLQJOHERQGGRXEOHERQGWULSOHERQGDUHIRUPHG
188
(C) FUNCTIONAL GROUPS
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IUPAC Nomenclature of class of Organic Compounds
Alcohols
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191
Activity 12 C.1
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of above mentioned class of compounds
Poly functional compounds
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192
Know this
Molecular formula of Sodium hydroxide is NaOH-(contains one
hydroxyl ion).
Molecular formula of Ammonium hydroxide is NH4OH --- one hydroxyl
ion.
Molecular formula of Calcium Hydroxide is Ca(OH)2 --- two hydroxyl
ions.
In all the above examples, hydroxyl ions (OH- ions) are common, number
may change but hydroxyl ions present in the above compounds give
the properties of a base to the compound in which they are present.
How many hydroxyl ions are there in Aluminium hydroxide? Al(OH)3.
You have come across alcohols like Methyl alcohol- molecular formula
CH3OH and Ethyl alcohol- molecular formula C2H5OH in your previous
classes.
Though these compounds contain hydroxyl group they are not called
hydroxides but called alcohols. Why?
CH3OH is not called methyl hydroxide but called methyl alcohol
On the other hand compounds containing hydroxide ions are not called
alcohols but called hydroxides.
NaOH is not called sodium alcohol but called Sodium hydroxide
So how are these hydroxyl ions and hydroxyl groups different from one
another?
In the case of organic compounds like alcohols hydroxyl group is just a
group of atoms -OH which is cavalently bonded to a carbon atom. The
-OH is a functional group occurs in several classes of organic compounds
including alcohols, phenols and carboxylic acids. You should not
confuse it with the hydroxide ion, -OH of inorganic hydroxides which
is a diatomic ion.
193
(D) HYDROGENATION OF OILS
Activity 12 D.1
Take 5 used medicine bottles and clean them thoroughly. Allow them to dry.
In each of the bottle take one spoon of molten Vanaspathi, coconut oil, palm oil,
JURXQGQXWRLODQGVXQÁRZHURLOVHSDUDWHO\DQGODEHOWKHP$GGIHZGURSVRI
water to each of the bottle. Keep the bottles exposed to air and sunlight for about
a week. Smell the bottles. In which of the bottle can you get the foul smell of
rancid Fat or Oil more?
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194
How are fats different from oils?
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SDVVLQJ K\GURJHQ JDV WKURXJK WKHP LV FDOOHG hydrogenation RI RLOV
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195
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acids present in the oils or fats by adding sodium or potassium
hydroxide.,WLVWKHUHDFWLRQWKDWWDNHVSODFHEHWZHHQRLODQGVRGLXP
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(Unsaturated fatty acids)
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hydroxide in ‘mg’ (milligrams) required to neutralize the fatty acid present
in one gram of oil or fat. In the manufacture of soaps it helps to prepare
soap which does not contain excess of potassium hydroxide.
Know this
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,WLVDOVRDVRXUFHRIOLJKWIRUWULEDOSHRSOH(VNLPRVXVHDQLPDOIDW
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196
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OLIHDQGPDNHWKHRLOVPRUHVWDEOH+\GURJHQDWHGRLOLVRLOLQZKLFKWKH
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3DUDIÀQZD[LVDK\GURFDUERQ%HHVZD[DQDWXUDOZD[LVPDQO\HVWHUVRI
fatty acids and various long chain alcohols . It is used in cosmetics, preparation
of dripless candles and skin ointments.
Everything that looks like oil is not really oil. Hydrocarbon oils are not oils
as they do not contain fatty acids. Glycerol which is used in medicines and
cosmetics is obtained by the hydrolysis of oils.
Awarness
Next time You enter the grocery shop observe the label ‘PUFA’ on cooking
oil packets.
PUFA : Poly unsaturated fatty acids
What are PUFA’s?
Poly unsaturated fatty acids contain unsaturated hydrocarbon chain.
Because of the presence of double bonds the PUFA reacts. This makes
them more reactive than saturated fatty acids and more susceptible to being
attacked and damaged by free radicals. Free radical damage can cause
accelerated aging, hormone imbalance, cancer, and immune disorders.
197
Exercise
Chapter 12 (B),(C) and (D)
I.
Classify
the
following
into
saturated
and
unsaturated
hydrocarbons.
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II. Give reasons for the following
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