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Carbon and its Compounds
Why Carbon forms Covalent Bonds
We know that a majority of substances used by us daily, from paper and plastics to coal and
petrol, are all made up of carbon
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are all made up of carbon
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In air, it
is present as carbon dioxide and comprises around 0
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Let us study about carbon and its bonding in its compound in more detail
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Since the atomic
number of carbon is six, its electronic configuration is 2, 4
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Hence, it has four
electrons in its valence shell
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Therefore, it is a tetravalent element
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e
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This, however,
requires a lot of energy and would make the system unstable
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The bonds that are formed by sharing electrons are known as covalent
bonds
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Carbon has four valence electrons and needs four more electrons to complete its octet
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For example, the molecule, methane can be formed with hydrogen (H) atoms that have only
one electron in its K shell
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Now, let us study the properties of carbon compounds
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Formation of ions does not
take place in this process
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Hence, covalent compounds are non- conductors of electricity
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This becomes evident from the following data
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Because of their low melting and boiling points, these compounds mostly exist as liquids or
gases at room temperature
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In addition,
all living structures are carbon based
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02% carbon in the form
of minerals and the atmosphere has 0
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In spite of the small amount of
carbon available in nature, the importance of carbon is immense
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It contains 2 and 4 electrons in
the K and L shell respectively
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Occurrence: Carbon occurs in free as well as in combined state
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Diamond and graphite are pure
forms of carbon while coal is an impure form of carbon in which the percentage of carbon
varies from 24% to 90%
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minerals in the form of carbonates

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calcium carbonate (CaCO3) in lime, marble, and chalk

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magnesium carbonate (MgCO3) in magnesite

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calcium and magnesium carbonate (MgCO3
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Natural gas, marsh gas, petroleum gas, and coal gas contain carbon in the form of its
compounds
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Reasons for allotropy are different arrangement of atoms in each allotrope, different
methods by which each allotrope is prepared, and different amount of energy associated in
the formation of each allotrope
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Carbon is considered to have two main kinds of allotropes i
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, crystalline and amorphous
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Diamond
2
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Buckminsterfullerene
Among these, diamond and graphite have been known for a very long time and are quite
common
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Thus, not
much is known about it
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The diamond crystal is a compact structure in which atoms of a single
unit lie in different planes
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Physical properties: The physical properties of diamond are:
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It is the hardest naturally occurring substance
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It is chemically inert under ordinary conditions as there are no free electrons available
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Its refractive index is 2
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Its specific gravity is 3
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It is the densest form of carbon, its density being 3
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It is transparent to X-rays, ultraviolet rays, and visible light rays
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It does not
leave behind any ash and therefore, it is the purest form of carbon
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Uses: The various uses of diamonds are:
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They are generally used for making ornaments
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They are used for making dies for drawing wires
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They are used in making laser beam in electronics
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Can you tell why?
All 4 valence electrons in diamond are involved in bonding
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Graphite
Crystal structure: In graphite, atoms of a single crystal are arranged in a hexagonal ring in
a single plane
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Thus, one plane can easily slide over another plane by applying pressure
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Physical properties: The physical properties of graphite are:
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It is dark grey solid, having lustre
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It is opaque to light
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2
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Chemical properties: The chemical properties of graphite are:

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Action of air or oxygen: Graphite does not burn in air
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Action of sodium carbonate: Like diamond, graphite also form sodium oxide and carbon
monoxide when heated with solid sodium carbonate
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It is used in making electrodes
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It is used as a moderator in a nuclear reactor
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Buckminsterfullerene is a cluster of sixty carbon atoms arranged in the form of a football
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Since it contains sixty carbon atoms, its chemical formula is C60
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Some amorphous forms of carbon:
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Charcoal: It is produced from the bones of animals, combustion of wood etc
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Coal: It is formed by decomposition of dead remains of plants when they got buried in the
land owing to the high temperature and pressure conditions present there
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Lignite with 25-35% of carbon content
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Bituminous coal with 60-80% carbon
Peat with less than 60% carbon content
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It is an almost pure form of carbon obtained
from coal
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Bonding In Carbon Compounds
Do you know that the number of carbon compounds outnumber the compounds of all
the other elements taken together? The number of carbon compounds is so vast that
there is one branch of chemistry dedicated only to the study of carbon and its compounds
...

Do you know why carbon is a part of so many compounds? Which properties of
carbon help it to be a part of so many compounds?
Here, we will try to find the answers to these questions
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Catenation is the ability of an element to combine with itself through
covalent bonds
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Carbon forms very strong bonds with itself
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Thus, these chains and rings are not only long,
but also very stable
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This can give rise to branches, chains, and rings as shown in
the figure below
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Now, carbon has a valency of four
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These properties depend on carbon as well as on elements other than carbon
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Silicon can join with other atoms of silicon, but the maximum length of the chains that can
be obtained in the case of silicon is limited to seven or eight atoms
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Saturated and Unsaturated Compounds
Saturated compounds:


The compounds of carbon having only single bonds between the carbon atoms are called
saturated compounds
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Similarly, butane (C4H10) can exist in two different structures, I and II
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Unsaturated compounds:


The compounds of carbon having double and triple bonds between the carbon atoms are
called unsaturated compounds
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Similarly, ethyne is an unsaturated compound containing one triple bond between the
carbon atoms
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For example, benzene is a six-member ring that contains three double bonds
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Organic compounds and Homologous Compounds
The number of carbon compounds is so vast that there is one branch of chemistry
dedicated only to the study of carbon and its compounds
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The compounds of carbon having only single bonds between the carbon atoms are
called saturated compounds and those that contain a double or a triple bond
between any two carbon atoms are known as unsaturated compounds
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There are two main groups of hydrocarbons:
Aliphatic hydrocarbons:

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They are derived from fossil fuels
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They are grouped as:
Alkanes: The general formula of alkanes is CnH(2n+2), n = number of carbon atoms
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For example, methane (CH4), ethane (C2H6) etc
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For example, ethene (C2H4), propene (C3H6) etc
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For example, ethyne (C2H2), propyne (C3H4) etc
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Their general formula is similar to that of alkenes (CnH2n)
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First recognised aromatic hydrocarbon is Benzene (C6H6)

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Benzene is a good organic solvent, which is used in the preparation of dyes, medicines,
perfumes etc
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You must have noticed that these structures have carbon atoms linked to each other in a
repeated manner
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Do you observe anything in the structure of butane? The carbon atoms can be linked in
two different ways (I and II)
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Both
have the same chemical formula, but they differ in their structures
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Carbon atoms in a molecule cannot only be linked in a chain or branch form, but these can
also be arranged in a ring
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Benzene is a six-member ring that contains three double bonds
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On the other hand, cyclohexane has only single bonds
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Structure of benzene

Structure of cyclohexane

However, the organic compounds which contain at least one benzene ring are known
as aromatic compounds
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Carbon not only bonds to carbon and hydrogen, but it can also bond to other atoms like
halogens (Br, Cl, I, F), nitrogen, oxygen etc
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In such cases, the replacing atom is
called a heteroatom
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Heteroatom Functional group

Formula of functional group

Cl/Br

Halo- (Chloro /
bromo)

—Cl, —Br (substitutes for
hydrogen atom)

Oxygen

Alcohol
Aldehyde
Ketone
Carboxylic acid

Thus, we see that carbon atoms can be linked to each other, or to hydrogen atoms, or to
functional groups
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However, it was noticed that the properties of CH3OH, C2H5OH, and C3H7OH are very
similar
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Organic compounds that have similar general formula belong to a series
called homologous series
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Therefore, the organic
compounds containing same functional group are tested using same identification tests
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Alkanes, alkenes, and alkynes form such series in which members differ in mass by 14
atomic mass units
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Each
member differs from the previous one by a CH2 group (or 14 atomic mass units)
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Name

Molecular Formula

Methane

CH4

Ethane

CH3CH3

Propane

CH3CH2CH3

Butane

CH3CH2CH2CH3

Thus, it is seen that any two consecutive members differ by a common difference
of CH2 group
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Similarly, in alcohol homologous series, we have methanol (CH3OH), ethanol (C2H5OH),
isopropanol (C3H7OH), and butanol (C4H9OH)
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This phenomenon is shown by organic compounds with same molecular formula but
different structural formula
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They have different
properties from one another
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Types of isomerism:
a) Chain/ skeletal/ nuclear isomerism:

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In this type, there is a difference in the structure of the carbon chain that forms the nucleus
of the molecule
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For example:

c) Functional group isomerism:
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It arises by virtue of the presence of different functional groups
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For example:

IUPAC Nomenclature of Carbon Compounds
Earlier, various organic compounds were known by their common names
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Hence, the International Union of Pure and
Applied Chemistry (IUPAC) devised rules to name organic compounds
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However, before the IUPAC system of nomenclature,
organic compounds were assigned trivial or common names based on their origin or
certain properties
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Also, the acid found in red ant is named formic acid since the Latin word for ant is ‘formica’
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The longest continuous chain of carbon atoms should be identified first
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The base name of an organic compound depends upon the number of carbon atoms present
in the chain
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The list of base names for one to ten carbon atoms is
given in the following table
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The presence of a functional group is indicated by adding either a suffix or prefix
to the base or root name
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e
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Therefore, CH4 becomes methane and CH3CH3 become ethane
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If a compound contains one or more triple bonds, then it is called alkyne and the suffix ‘yne’ is used
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The following table shows the list of functional groups along
with the suffixes/prefixes used to indicate their presence
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Halo-

Chloroethane

Iodoethane
Alcohol

R–OH

-ol
Ethanol

Aldehyde

-al
Ethanal

Ketone

-one
Propanone

Carboxylic acid

-oic acid
Ethanoic acid

If the last letter of a hydrocarbon is ‘e’ as in alkanes, then ‘e’ is deleted when the suffix for
the functional group is added
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Thus, we obtain pentanone from pentane and not
pentaneone
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Let us name a few compounds using IUPAC nomenclature
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Alcohol
If one hydrogen atom of an alkane is displaced by hydroxyl group(-OH), then alcohol
compound is obtained
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Hence, it is represented as
R-OH where R stands for alkyl group
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The carbon atom of carbonyl
group is attached with one alkyl group and one hydrogen atom in case of aldehyde
whereas, in case of a ketone carbon atom of carbonyl compound is attached with carbon
atoms of two alkyl groups
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Some of

them are ethanoic acid and propanoic acid
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The general formula of carboxylic acid is


...
See the example given below
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Step − I: Select the longest carbon chain
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Step − II: Assign the lowest number to the side chain
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Step-III: Arrangement of prefixes
In case more than one group is attached to the chain, these should be arranged
alphabetically
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Step-IV: Lowest number for functional group
In case some functional group is present in the chain, the lowest number is given to it
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Conversely, using the IUPAC of an organic compound, it's structure can be determined
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It forms the carbon skeleton in the structure
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Step − III: As per the suffix in the name, ascertain the type of bond present in the
compound
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Step − IV: Place the substituents at the carbon atoms mentioned in the IUPAC name
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Step − VI: Complete the valencies of the remaining carbon atoms by attaching hydrogen
atoms
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e
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Organic compounds such as coal and petroleum are of utmost
importance in the modern world
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Hence, it is important for us to know how these
compounds react with other substances
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Therefore,
hydrocarbons, when burnt, react with oxygen present in the air to give carbon dioxide and
water vapours
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Such reactions
are called combustion reactions
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Observe the nature of the flame produced by them when burnt
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Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the
release of heat and light
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For example, hydrocarbon such as methane gives out a large
amount of heat energy when burnt
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DO YOU KNOW?
The fuel that we use for cooking at home is Liquefied Petroleum Gas or LPG
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Do you know that burning of a carbon compound can help us in finding whether it is a
saturated or an unsaturated compound?
Alcohols also burn to give the same products as hydrocarbons
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Do you know?
Coal and petroleum were formed inside the Earth by the decomposition of organic matter
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Petroleum was formed by the decomposition of small
plants and animals, which lived in the seas and oceans that got buried inside the seabed
millions of years ago
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Can you explain why?
This is because if the holes meant for the inlet of air are blocked or closed, then a yellow
coloured sooty flame is produced
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Do you know that carbon compounds are oxidized on burning? Pure carbon is oxidized
to give carbon dioxide when burnt in air
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They are oxidized as they combine with oxygen (present in the air) on burning
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Substances that have the ability to oxidize other substances are known as oxidizing agents
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Compounds of carbon can also be oxidized partially with the help of oxidizing agents
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In these reactions, alkaline potassium permanganate and acidified potassium dichromate
act as oxidizing agents and convert alcohol to acids i
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, add oxygen to the starting material
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Warm it gently in a water bath
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It will be observed that the pink colour of potassium permanganate solution disappears
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The chemical equation representing the oxidation of ethanol to ethanoic acid in the
presence of potassium permanganate is as follows:

Addition and Substitution Reactions Of Carbon And Its Compounds
The compounds of carbon having double or triple bonds between the carbon atoms are
known as unsaturated compounds, and the carbon compounds having single bonds
between the carbon atoms are called saturated compounds
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A single product is obtained
in this reaction
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Atoms of different
elements like hydrogen, chlorine, bromine etc
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Do You Know:
A catalyst is a substance that does not take part in a reaction, but increases the rate at
which it proceeds
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Hydrogen can be added to unsaturated hydrocarbons in the presence of nickel to yield
saturated hydrocarbons
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This reaction is known as Hydrogenation reaction
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Vegetable oil contains unsaturated fatty acids, and is liquid at room temperature
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Do You Know:
Vegetable oil contains unsaturated fatty acids that are essential for our well-being, whereas
saturated fatty acids like those present in ghee are not healthy
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Important Note:
Saturated hydrocarbons do not undergo addition reactions
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Hence, we can differentiate saturated
compounds from unsaturated compounds on the basis of addition reactions
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However, in the presence of sunlight, the reaction between chlorine and alkanes takes
place readily
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Substitution reactions:
A substitution reaction is the one in which an atom or a group of atoms replaces another
atom present in a molecule undergoing the reaction
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Similar reactions in which bromine or iodine atoms replace hydrogen atoms are
called bromination and iodination reactions respectively
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Therefore, it is important for us to know about some compounds of carbon that we use in
our daily life
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e
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These two chemicals are very
important commercially
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Ethanoic acid is commonly used in homes as
vinegar
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It is an active ingredient of all alcoholic beverages,
namely beer, wine, whisky, rum etc
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It is a
neutral compound and has no effect on litmus paper
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Intake of even a small quantity of pure ethanol can be lethal
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Do You Know:
Ethanol is usually obtained from sugarcane
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When molasses (a concentrated and dark liquid formed by boiling sugarcane juice) is
fermented, ethanol is obtained
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There are
three major steps in production of ethanol by fermentation of molasses
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Yeast is added to this solution and the temperature is maintained between 308 K to 313 K
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Physical properties:
1
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2
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3
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Therefore, it is used in a lot of medicines, syrups,
and tonics
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Reaction with sodium: Ethanol reacts with sodium to produce hydrogen gas
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2
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This reaction is known as dehydration reaction
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In this reaction, concentrated
sulphuric acid acts as a dehydrating agent and removes water molecules from ethanol
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Combustion reaction: Combustion of alcohol results in the formation of carbon dioxide
and water along with a large amount of heat and light energy
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It burns to give only carbon dioxide and water
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It does not give out
poisonous gases such as sulphur dioxide and nitrogen dioxide
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Hence, coal and the fuels obtained from
petroleum are not clean fuels
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, to it
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Harmful effects of drinking alcohol:
1) It slows down the activity of the nervous system as well as brain
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3) It leads to blurred vision, dizziness and vomiting
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5) It can increase your risk of developing liver disease
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6) It can contribute to the condition that cause diabetes
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8) Drinking of adulterated alcohol containing pyridine, causes severe poisoning leading to
even death
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The
carboxyl group is named so because it consists of a carbonyl group attached to a hydroxyl
group
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Classification of Carboxylic Acids
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On the basis of number of −COOH groups
One −COOH group: Monocarboxylic acid, for example, HCOOH, CH3COOH, etc
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Now, let us discuss an industrially important carboxylic acid
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Its dilute solution in water is
known as vinegar, which is used for preserving food
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It is a weak acid in
nature and turns blue litmus paper red
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The melting point of ethanoic acid is 290 K
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Thus, it
freezes during winters
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Therefore, it is also known as
glacial acetic acid
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It is miscible with water, alcohol and ether in all proportions
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Chemical properties

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Acidic nature: Acetic acid is a weak acid
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It turns blue litmus red
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Reaction with alcohol or esterification reaction: The reaction of a carboxylic acid with
an alcohol to form an ester is known as esterification reaction
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As esters are volatile and pleasant to smell,
they are generally used for making perfumes
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When ethanoic acid reacts with ethanol in the presence of an acid, ethyl ethanoate is
formed
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Reaction with a base:
We know that an acid and a base react to form salt and water
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Sodium
ethanoate is commonly known as sodium acetate
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Carbon dioxide is also formed in the reaction
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It is commonly known as sodium acetate
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e
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Reaction with phosphorous pentoxide
Acetic acid forms another acid derivative when heated with phosphorous pentoxide
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Tests for Acetic acid
Reagent
Na2CO3 or NaHCO3
C2H5OH + Conc
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The gas is
CO2
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What are
soaps and detergents? Soaps are sodium or potassium salts of higher fatty acids such as
oleic acid (C17H33COOH), stearic acid (C17H35COOH), palimitic acid (C15H31COOH), etc
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Preparation of Soaps and Detergents:
Soaps are prepared by gentle heating of oil or fat with sodium hydroxide solution till it
boils
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The solution is cooled and soap is obtained at the top of the solution
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Oil + NaOH → Soap + Glycerol
This process is known as saponification
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Do you know that soaps and detergents help in dissolving dirt (oil and grease) in
water? A soap solution or detergent makes dirt soluble in water, thereby cleaning a dirty
cloth
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Soap
has one polar end (the end with sodium or potassium ion) and one non-polar end (the end
with fatty acid chain) as shown in the figure
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e
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The non-polar end is hydrophobic, but lypophilic
in nature i
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, it is attracted towards hydrocarbons, but not towards water
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This is known as micelle formation and the cluster that is formed is called a
micelle
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DO YOU KNOW?
Soap does not work properly when water is hard
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When soap is added to hard water, it reacts with
these salts to form an insoluble substance called scum
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In addition, soaps do not give lather with hard water
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This problem is overcome by using detergents
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Detergents can work well in acidic medium, whereas soaps do not work in an acidic
medium
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This
is one of the major drawbacks of using detergents

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