Carbon and Its Compounds Important Study Key points
The atmosphere has only 0.03% of carbon dioxide.
The number of electrons lost or gained by an atom to complete its octet (or duplet) is
called its valency. It depends on the number of valence electrons.
The tendency to attain a completely filled outermost shell (i.e. noble gas configuration)
by gaining or losing electrons is called reactivity.
The shared pair of electrons belongs to the outer shells of both the atoms so as to attain
noble gas configuration.
The simplest molecule formed by sharing of electrons is hydrogen.
The bonds which are formed by sharing of electrons between two atoms are known as
covalent bonds.
The compounds which are formed by sharing of electrons pair between two atoms are
known as covalent compounds. E.g. CH4, H2, O2, etc.
The melting and boiling points of covalent compounds are low because their
intermolecular forces are weak and less amount of energy is required to overcome these
forces.
The covalent compounds are generally poor conductors of electricity because the
electrons are shared between atoms and no charged particles are formed in their
solution.
Carbon has three allotropes – graphite, diamond and Buckminster Fullerene.
When a hydrogen atom is removed from an alkane, the group obtained is called an alkyl
group.
Saturated carbon compounds are usually not very reactive because the carbon-carbon
single bonds are very strong.
Unsaturated carbon compounds are very reactive than saturated carbon compounds.
Uses of graphite
1. It is used in lead pencils as it is soft and leaves black mark on the paper.
2. It, being a good conductor of electricity, is used in making electrode in the cells
3. Powdered graphite is used as lubricant because it is very soft and can withstand at high
temperature.
Uses of diamond
1. It is used in pencils for cutting glass etc because it is the hardest substance known.
2. It is used for making dies for drawing thin wires.
3. It is used in surgical tools.
4. It is used for making jewellery because of high refractive index.
Heteroatom In hydrocarbons, the elements like halogen, oxygen, etc replacing hydrogen is
called heteroatom. They are also present in some groups.
Graphite Diamond
1. Graphite has two dimensional
structure
2. oft and greasy.
3. It is a good conductor of heat and
electricity.
4. It is grayish black substance.
1. Diamond is a three dimensional
structure.
2. It is the hardest substance known.
3. It is the bad conductor of electricity
but good conductor of heat.
4. It is transparent.
Catenation The property of self linking of carbon atoms through covalent bonds to form long
chains or rings is called catenation.
Other element which shows the catenation property is silicon.
The bonds formed between the carbon and other elements are very strong because
small size of
carbon enables the nucleus to hold on to shared-pair of electron strongly.
Versatile nature of carbon
1. Catenation – self linking of carbon atoms to form long chains or rings.
2. Tetravalency –sharing of 4 electrons with other atoms of carbon or any other
monovalent element.
Saturated Carbon Compounds Compounds of carbon which have only single bonds between the
carbon atoms are called saturated carbon compounds.
E.g. methane, ethane, etc.
Unsaturated carbon compounds Compounds of carbon which have double or triple bonds
between the carbon atoms are called unsaturated carbon compounds.
E.g. ethene, ethyne, etc.
Straight chain compounds Carbon compounds in which no carbon atom of the chain is linked to
more than two other carbon atoms are called straight chain compounds.
E.g. methane, ethane, propane, etc.
Branched chain compounds Carbon compounds, in which at least one carbon atom of the chain
is linked to three or four other carbon atoms are called branched chain compounds. E.g. 2-
methylpropane.
Cyclic compounds Carbon compounds in which carbon atoms are arranged in a ring are called
cyclic compounds. These are of two types –
1. Saturated cyclic compounds. E.g. cyclopropane, cyclobutane, cyclopentane, etc.
2. Unsaturated cyclic compounds. E.g. benzene.
Hydrocarbons. The carbon compounds which contain only hydrogen and carbon are
called
Hydrocarbons
Hydrocarbons which contain only single bonds between the carbon atoms are called
alkanes. Their general formula is CnH2n+2.
Hydrocarbons which contain one or more double bonds between the carbon atoms are
called alkenes. Their general formula is CnH2n.
Hydrocarbons which contain one or more triple bonds between the carbon atoms are
called alkynes. Their general formula is CnH2n-2.
Functional group An atom or group of atoms present in a molecule which determines its
functions or chemical properties is called a functional group. It is the most reactive site of a
carbon compound.
Homologous series The family of organic compounds having same functional group, similar
chemical properties and the successive members of which differ by CH2 group is called a
homologous series.
Characteristics of a homologous series
1. All the members can be represented by same general formula.
2. The molecular formulae of two successive members differ by CH2 group or by 14u.
3. All the members have same functional group.
4. All the members show similar chemical properties.
The melting and boiling points of the members of homologous series increase gradually
because their molecular masses increase.
Allotropy The phenomenon in which one element exists in two or more forms having same
chemical properties but different physical properties is called allotropy. The substances that
show allotropy are carbon, sulphur, etc.
Allotropes The different forms of an element having same chemical properties but different
physical properties are called allotropes.
Isomerism The phenomenon in which a compound can be represented by different structures
having different properties is called isomerism.
Isomers The compounds which can be represented by different structures having different
properties are called isomers.
IUPAC – International Union of Pure and Applied Chemistry.
Combustion The process of heating a substance strongly in the presence of excess of oxygen or
air is called combustion.
Carbon and carbon compounds release carbon dioxide, water and a large amount of heat
and light on burning.
C + O2 CO2 + Heat and Light
CH4 + O2 CO2 + H2O + Heat and Light
C2H5OH + O2 CO2 + H2O + Heat and Light
Saturated hydrocarbons generally give a clean blue flame because complete combustion
of these substances takes place.
Saturated hydrocarbons burn with a yellow flame with lots of black smoke due to the
incomplete combustion of carbon contents.
Condition in which saturated carbon compounds burn with sooty flame – If a saturated
carbon compound is burnt in limited (insufficient) supply of air, it burns with sooty flame
due to incomplete combustion.
The gas/kerosene stoves used at homes have inlets for air so that a sufficient oxygen
rich mixture is burnt to give a clean blue flame with a lot of heat.
Sometimes bottoms of cooking vessels get blackened due to incomplete combustion of
gas/kerosene. It means the holes are blocked. This problem can be removed by cleaning
the burner by opening holes.
The pollutants released in the environment by burning coal and petroleum are oxides of
sulphur and nitrogen e.g. SO2 , NO, NO2 , etc.
Combustion of hydrocarbons is regarded as oxidation reaction because during
combustion, carbon is oxidised to CO2 and hydrogen is oxidised to water by addition of
oxygen.
Only the gaseous substances produce flame on burning.
Wood and charcoal are solid but they produce flame when ignited because when they are
ignited the volatile substances present vaporize and burn with a flame in the beginning
only.
Fossil fuels The fuels formed by the dead animals and plants buried under the earth
millions of years ago due to intense heat and pressure are called fossil fuels. E.g. coal
and petroleum.
When an alcohol is heated in the presence of alkaline KMnO4 (or acidified K2 Cr2 O7 )
then corresponding carboxylic acid is formed.
Addition reaction The reaction which involves addition of two reactants to form a single
product is called an addition reaction. Only unsaturated hydrocarbons perform addition
reactions.
CH2 = CH2 + Cl2 CH2Cl – CH2Cl
Industrial application of addition reaction Addition reaction is commonly used in the
hydrogenation of vegetable oils using a nickel catalyst to form vegetable ghee.
Vegetable oil (liquid) + H2 Ni (473K) Vegetable ghee (solid)
Saturated fatty acids are harmful for health so oils containing unsaturated fatty acids should be
used for cooking because Saturated fats increase the level of bad cholesterol (low density
lipoprotein LDL) in blood which sticks to the walls of arteries and causes heart diseases.
Substitution reaction The reaction which involves direct replacement of an atom or group of
atoms in an original molecule is called substitution reaction. Only saturated hydrocarbons
perform substitution reactions.
CH4 + Cl2 CH3Cl + HCl
Functional group Symbol/formula Prefix/suffix Compound name
Halo -Cl, -Br, - I Halo (prefix) Haloalkane
Alcohol -OH -ol Alkanol
Aldehyde -CHO -al alkanal
Ketone - CO - -one Alkanone
Carboxylic -COOH -oic acid Alkanoic acid
Simplest compound Common name IUPAC name Formula
Alcohol Methyl alcohol Methanol CH3OH
Aldehyde Formaldehyde Methanal HCHO
Ketone Acetone Propanone CH3COCH3
Carboxylic acid Formic acid Methanoic acid HCOOH
alkane Methane Methane CH4
Alkene Ethylene Ethene C2H4
alkyne Acetylene Ethyne C2H2
ETHANOL (CH3CH2OH or C2H5OH)
Physical properties
1. It is liquid at room temperature.
2. It is colourless and has distinct smell and burning taste.
3. It is soluble in water in all proportions.
Chemical properties
1. It reacts with sodium to form sodium ethoxide and hydrogen gas.
2CH3CH2OH + 2Na 2CH3CH2ONa + H2
2. It reacts with hot concentrated H2SO4 to give ethene.
CH3CH2OH CH2=CH2 + H2O
USES
1. It is used in all alcoholic drinks like wine, beer, etc.
2. In the form of rectified spirit (95% alcohol + 5% water), it is used as an antiseptic for
wounds.
3. It is used in medicines like tincture iodine, cough syrups, tonics etc because it is a good
solvent.
4. In cold countries it is used as antifreeze in automobiles.
Harmful effects of ethanol
1. Consumption of its small quantity causes drunkenness.
2. It depresses the central nervous system which results in mental confusion and
drowsiness.
3. It damages liver and kidney.
4. It decreases the sense of judgment and sense of timing.
5. It increases crime in the society.
Denatured alcohol To prevent the misuse of ethanol produced for industrial use, it is made unfit
for drinking by adding poisonous substances like methanol, copper sulphate, etc. it is called
denatured alcohol.
ETHANOIC ACID (acetic acid or vinegar, CH3COOH)
Physical properties.
1. It is a colourless and pungent smelling liquid.
2. Its melting point is 290K so it often freezes during winter and looks like glacier.
Therefore, it is also known as glacial acetic acid.
3. It is soluble in water in all proportions.
5% to 8% solution of Ethanoic acid in water is called vinegar.
Chemical properties
1. Reaction with alcohol. Ethanoic acid reacts with ethanol in the presence of an acid to
give ester.
CH2COOH + C2H5OH Acid CH3COOC2H5 + H2O
2. Reaction with base. Ethanoic acid reacts with sodium hydroxide to give sodium
ethanoate (sodium acetate) and water.
CH3COOH + NaOH CH3OONa + H2O
3. Reaction with carbonates and bicarbonates. Ethanoic acid reacts with carbonates and
bicarbonates to salt carbon dioxide and water.
2CH3COOH + Na2CO3 2CH3COONa + CO2 + H2O
CH3COOH + NaHCO3 CH3COONa + CO2 + H2O
Esterification The reaction between a carboxylic acid and an alcohol to form an ester is called
Esterification reaction.
CH2COOH + C2H5OH Acid CH3COOC2H5 + H2O
The reaction between the ester and hot base to give original alcohol and carboxylic acid
back is called saponification reaction because this reaction is used in preparing soaps.
CH3COOC2H5 NaOH CH2COOH + C2H5OH
The product formed when a carboxylic acid reacts with an alcohol having the formula R-COO-R’
is called an ester. Esters are sweet smelling substances. They are widely spread in nature. The
smell of fruits and flowers is due to the presence of esters. Esters are used as flavorings agents
and in making perfumes.
Cleansing action of soap The molecules of soap are sodium or potassium salts of long chain of
carboxylic acids. The hydrocarbon tail being hydrophobic reacts with oil or grease while the ionic
end being hydrophilic reacts with water. As a result micelles are formed. They form an emulsion
in water.
When the surface of clothes is beaten or agitated, micelles are thrown away and the cloth is
cleaned.
Micelle The cluster of about 100 – 200 molecules with hydrophilic ends on the surface of cluster
and hydrophobic ends towards the centre, is called a micelle.
Soaps Detergents
Soaps are sodium salts of long chain carboxylic
acids.
Detergents are sodium salts of long chain
sulphonic acids.
Soaps do not form leather with hard water. Detergents form leather with hard water.
Soaps are biodegradable. They are non biodegradable.
Soaps do not have strong cleansing action. They have strong cleansing action.
These are prepared from animal fats.
They are prepared from hydrocarbons of
petroleum.
Advantage of soaps over detergents Soaps are biodegradable so they do not produce pollution.
While detergents being non biodegradable produce pollution.
Advantage of detergents over soaps Detergents can be used in hard water. Also, they have
strong cleansing action. While soaps have weak cleansing action and they cannot be used in
hard water.
Properties of Alkanes/ Alkenes/ Alkynes (10th Carbon and its compounds)
Properties of Alkanes/ Alkenes/ Alkynes
(a) Alkanes are gas (C1to C4) ; liquid (C5to C17) and rest are solid at room temperature.
(b) The melting and boiling point of Alkanes increases with increase in number of C – atom in
Alkanes.
Reason: Alkanes experience inter-molecular van der Waals forces. Stronger inter-molecular van
der Waals forces give rise to greater boiling points of alkanes.
A straight-chain alkane will have a boiling point higher than a branched-chain alkane due to the
greater surface area in contact.
Note: In Chemistry the Van der Waals forces include attractions and repulsions between atoms,
molecules, and surfaces, as well as other intermolecular forces.
(c) The density of the alkanes usually increases with increasing number of carbon atoms
Alkane Formula Density
Pentane C5H12 0.626 (liquid)
Hexane C6H14 0.659 (liquid)
Heptane C7H16 0.684 (liquid)
Octane C8H18 0.703 (liquid)
Nonane C9H20 0.718 (liquid)
(d) Solubility: Alkanes are generally insoluble in polar compound like water but dissolve in
organic solvents (Non polar compound) like benzene. The liquid alkanes are good solvents for
many other covalent compounds.
Reason: Alkanes do not conduct electricity, nor are they polarized by electricity. For this reason
they do not form hydrogen bonds and are insoluble in polar solvents such as water.
(e) Reactivity: Alkanes are stable and less reactive than alkenes
Reason: This is because saturated hydrocarbons contain only single bonds which are very stable
and difficult to break. On the other hand, unsaturated hydrocarbons contain pie bonds, which
can be easily broken as they are more strained.
(f) Combustion: Alkanes are generally good combustible material due presence of the good
percentage of Hydrogen.
Since Alkanes burn with non smoky and non sooty flame due to presence of the good
percentage of Hydrogen, It is used as a fuel like LPG and CNG
2CH4 + 2O2 ----------- CO2 + H2O + Heat and light
2C2H6 + 7O2 ----------- 4CO2 + 6H2O + Heat and light
C2H4 + 3O2 ----------- 2CO2 + 2H2O + Heat and light
2C2H2 + 5O2 ----------- 4CO2 + 2H2O + Heat and light
2CH3 CH2OH + 3O2 ----------- 2CO2 + 3H2O + Heat and light
However, if the supply of air or oxygen is not sufficient for complete combustion, carbon
monoxide is formed. Carbon monoxide (CO) is highly poisonous.
2CH4 + 3O2 ----------- 2CO + 4H2O
2CH4 + 3O2 ----------- 2CO + 4H2O
2C4H10 + 9O2 ----------- 8CO + 10H2O
Q. What is the difference between Oxidation and combustion?
Answer: Combustion is the complete oxidation of organic compound into carbon dioxide and
water molecules in presence of oxygen gas while oxidation is the addition of oxygen in a organic
compound or with an element the loss of electron from an atom or ion is also oxidation.
Hence, all Oxidation reactions are not combustion reaction but all combustion reactions are
Oxidation. Oxidation reaction does not involve heat where as combustion reactions do.
(g) Substitution reaction: Alkanes do not undergo addition reaction due to strong van der wall
force but take part in substitution reaction:
Alkanes undergo substitution reaction because hydrogen attached to carbon easily replaced by
atom more reactive than hydrogen like halo atom Cl , Br ,I etc.
Sunlight
CH4 + Cl2 ---------- CH3Cl + HCl
Sunlight
CH4Cl + Cl2 ----------- CH2Cl2 + HCl
Sunlight
CH2Cl2 + Cl2 ----------- CHCl3 + HCl
Sunlight
CHCl3 + Cl2 ----------- CH3Cl + HCl
If chlorine present in excess, then reaction does not stop in between but keep on reacting till it
form carbon tetra chloride.
(h) Addition reaction:
Unlike alkane, generally alkene Undergo addition reaction with hydrogen gas in the presence of
Palladium or nickel at (473 k) catalyst and gives saturated hydrocarbon.
Example: Ethene Undergo addition reaction with hydrogen gas in the presence of Palladium or
nickel at (473 k) catalyst and gives saturated hydrocarbon Ethane
Ni
CH2 = CH2 + H2 ---------- CH3 - CH3
473 k
Ethyne Undergo addition reaction with hydrogen gas in the presence of Palladium or nickel at
(473 k) catalyst and gives saturated hydrocarbon Ethane . This reaction is known as
Hydrogenation Reaction.
Pd
CH2 CH2 + 2H2 ----------- CH3 - CH3
This addition reaction of hydrogen is helpful in converting vegetable Oil into saturated fat like
vanaspati gee. This reaction is commonly called Hydrogenation of Oil. This test helps to
distinguish between saturated and saturated fats.
Note: Butter contain saturated compound where as cooking oil contain unsaturated compound.
If Alkaline KMno4 added to both, pink color of KMno4 disappear in cooking oil but remain in pink
in butter.
Bromine and chlorine react with alkene to form vicinal dihalides (iodine does not undergo
addition reaction under normal conditions).
CCl4
CH2 = CH2 + Cl2 ----------- CH2 - CH2
I I
Cl Cl
Ethene 1,2- Dichloroethane
CCl4
CH2 = CH2 + Br2 ----------- CH3 - CH - CH2
I I
Br Br
Ethene Bromine water 1,2-Dibromoethane
Bromine water test: Solution of Bromine in water is reddish brown in colour but 1, 2-
Dibromoethane formed from the addition reaction is colourless. This helps us to identify
unsaturated carbon compound. If an organic compound is unsaturated Solution of Bromine in
water became colourless.
Note: In Alkanes, the four valencies of carbon atom are saturated and they have stable
(sigma) bonds. Any nuleophile comes; one hydrogen atom is replaced to accommodate the
nucleophile.
e.g. CH4 + Cl2 CH3Cl + HCl
In case of Alkene or Alkyne, Carbon atom has double or triple bonds. In this, one is stable
(sigma) bond and the rests are unstable (or weak) bonds. When nucleophile approaches to
the carbon atom that has double or triple bonds, they easily break to accommodate it.
e.g., H2C=CH2 + Cl2 H2ClC-CH2Cl.
(i) Cracking (or pyrolysis):
When heated to a sufficiently high temperature in the absence of oxygen, alkanes decompose to
produce hydrocarbons of shorter chain length. This reaction is called thermal cracking or
pyrolysis.
For example, when octane is heated to 6500C in the absence of oxygen, it forms ethene and
exane.
6500C
C8H18 -------> C6H14 + C2H4
Octane Hexan
e
Ethene
In this process, vapour of higher alkanes is passed through a hot metal tube (5000C – 7000C).
Propane on cracking gives
C3H6 + H2
C3H8ca ----------
CH4 + C2H4
Cracking of hexane gives butane and ethane.
C6H14 ---------- C4H10 + C2H4
Cracking is used to convert some of the less volatile fraction of petroleum containing high
moleculer mass into compounds of lower molecular masses of higher volatility. Such
hydrocarbons with lower molecular masses are more suitable as fuels for automobiles.
C16 H34 → C8H18 + C8H16
n - Hexadecane n-octane octene (unsaturated)
Q. What's the difference between cracking and Pyrolysis?
Pyrolysis: The decomposition of a compound on heating in absence of air is known as pyrolysis.
Cracking: is the breakdown of large organic compounds by use of a catalyst and low
temperature to form fewer different compounds
Q. In cracking will the decomposed hydrocarbon always be a saturated and a unsaturated
hydrocarbons? Can they both be either unsaturated or saturated hydrocarbons?
Cracking is defined as the process of breaking or decomposition of large hydrocarbons into
smaller compounds. This process is widely used in the petroleum industry. Usually, we get a
mixture of alkane and alkenes by the process of cracking of hydrocarbons. This is because the
bonds in the hydrocarbons can be cleared in any way. As a result, we will not get alkane and
alkene exclusively but a mixture of both.
(j) Oxidation: The chemical reaction in which oxygen added to substance is called oxidation of
substance. The substance which donate oxygen to other substance during chemical reaction is
called oxidizing agent like K2Cr2O7, HNO3 and KMnO4 . Alkane on oxidation produces heat and
light known as combustion.
(a) Ethene on treating with alkaline KMnO4 oxidized to Ethylene Glycol
H H H H
I I Alk. KMnO4 I I
H - C = C - H + H2O + O ----------- H – C – C - H
I I
OH OH
Ethene Ethylene Glycol
(b) Ethyne on treating with alkaline KMnO4 oxidized to Oxalic Acid
Alk. KMnO4 COOH
H – C C – H + 4O ----------- I
COOH
Ethyne Oxalic Acid
(c) Ethanol on treating with alkaline KMnO4 or acidified K2Cr2O7 oxidized to Ethanoic Acid.
During oxidation of Ethanol alkaline KMnO4 losses its purple colour .
Alk. KMnO4 + Heat
CH3 CH2 OH + 4O ------------------------ CH3COOH
Ethanol Ethanoic Acid
Ethanol is highly inflammable and catches fire readily. This is why during oxidation it should
never be heat directly on a burner. it should be heated on a water bath.
1. Ethanol (C2H5OH)
Ethanol or ethyl alcohol or simply alcohol is one of the most important members of the family
of alcohols.
Physical properties
(i) Ethanol is a clear liquid with burning taste.
(ii) Its boiling point is 351K which is higher than corresponding alkane.
(iii) It is completely miscible with water in all proportions.
Chemical properties
(i) Dehydration
(a) Intra molecular dehydration :
Ethanol, when heated with excess conc. H2SO4 at 443 K undergoes intra molecular dehydration
(i.e. removal of water within a molecule of ethanol).
CH3CH2OH -------Conc.H2SO4/443K-----> CH2 = CH2 +H2O
(b) Inter molecular dehydration :
When excess of alcohol is heated with conc. H2SO4 at 413K two molecules condense by losing a
molecule of water to form ether (i.e. removal of water from two molecules of ethanol).
C2H5- OH + HO- C2H5 -------Conc.H2SO4/413K----> C2H5-O-C2H5 (Diethyl ether)+H2O
(ii) Reaction with sodium :
Ethanol reacts with sodium metal to form sodium ethoxide and hydrogen gas.
2C2H5OH + 2Na ------------> 2C2H5ONa (sodium ethoxide) + H2 ↑
(iii) Oxidation:
Ethanol is oxidized to Ethanoic acid with alkaline KMnO4 or acidified K2Cr2O7
CH3CH2OH ----Oxidation---> CH3COOH (Ethanoic acid) + H2O
During this reaction, orange colour of K2Cr2O7 changes to green. Therefore, this reaction can
be used for the identification of alcohols.
(iv) Esterificaiton :
Ethanol reacts with ethanoic acid in the presence of conc.H2SO4 (catalyst) to form ethyl
ethanoate and water. The compound formed by the reaction of an alcohol with carboxylic acid is
known as ester (fruity smelling compound) and the reaction is called esterification.
C2H5OH + CH3COOH ---conc.H2SO4-----> CH3COOC2H5 (Ethyl ethanoate) + H2O
(v) Dehydrogenation :
When the vapour of ethanol is passed over reduced copper catalyst at 573 K, it is
dehydrogenated to acetaldehyde.
CH3CH2OH -----------Cu/573K ------> CH3CHO (Acetadehyde) +H2
Ethanol is used
1. As an anti-freeze in automobile radiators.
2. As a preservative for biological specimen.
3. As an antiseptic to sterilize wounds in hospitals.
4. As a solvent for drugs, oils, fats, perfumes, dyes, etc.
5. In the preparation of methylated spirit (mixture of 95% of ethanol and 5% of
methanol),rectified spirit (mixture of 95.5% of ethanol and 4.5% of water), power alcohol
(mixture of petrol and ethanol) and denatured sprit (ethanol mixed with pyridine).
6. In cough and digestive syrups.
Evil effects of consuming alcohol
• If ethanol is consumed, it tends to slow down metabolism of our body and depresses the
central nervous system.
• It causes mental depression and emotional disorder.
• It affects our health by causing ulcer, high blood pressure, cancer,brain and liver damage.
• Nearly 40% accidents are due to drunken drive.
• Unlike ethanol, intake of methanol in very small quantities can cause death.
• Methanol is oxidized to methanal (formaldehyde) in the liver and methanol reacts rapidly with
the components of cells.
• Methanal causes the protoplasm to get coagulated, in the same way an egg is coagulated by
cooking. Methanol also affects the optic nerve, causing blindness.
2. Ethanoic acid (CH3COOH)
Ethanoic acid is most commonly known as acetic acid and belongs to a group of acids called
carboxylic acids. Acetic acid is present in many fruits and sour taste of fruits is because of this
acid.
1. Preparation of Ethanoic acid
Ethanol on oxidation in the presence of alkaline potassium permanganate or acidified potassium
dichromate gives Ethanoic acid.
CH3CH2OH (Ethanol) ------ Oxidation ------> CH3COOH (Ethanoic acid) + H2O
2. Physical properties
(i) Ethanoic acid is a colourless liquid and has a sour taste.
(ii) It is miscible with water in all proportions.
(iii) Boiling point (391 K) is higher than corresponding alcohols, aldehydes and ketones.
(iv) On cooling, pure ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it
is called glacial acetic acid.
3. Chemical properties
(i) Ethanoic acid is a weak acid but it turns blue litmus to red.
(ii) Reaction with metal
Ethanoic acid reacts with metals like Na, K, Zn, etc to form metal Ethanoate and hydrogen gas.
2CH3COOH + Zn --------------> (CH3COO)2 Zn + H2 ↑
2CH3COOH + 2Na ----------------> 2CH3COONa + H2 ↑
(iii) Reaction with carbonates and bicarbonates.
Ethanoic acid reacts with carbonates and bicarbonates and produces brisk effervescence due to
the evolution of carbon dioxide.
2CH3COOH + Na2CO3 ------------> 2CH3COONa + CO2 ↑ + H2O
CH3COOH + NaHCO3 -------------> CH3COONa + CO2 ↑ + H2O
(iv) Reaction with base
Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water
CH3COOH + NaOH ------------> CH3COONa + H2O
(v) Decarboxylation (Removal of CO2)
When sodium salt of Ethanoic acid is heated with soda lime (Solid mixure of 3 parts of NaOH
and 1 part of CaO) methane gas is formed
CH3COONa ------NaOH / CaO-------> CH4 ↑ + Na2CO3
Ethanoic acid is used
1. For making vinegar which is used as a preservative in food and fruit juices.
2. As a laboratory reagent.
3. For coagulating rubber from latex.
4. In the preparation of dyes, perfumes and medicine.
Important Questions
Question: Why does Ethanoic acid called glacial acetic acid? (Imp.)
Ans. On cooling, pure Ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it
is called glacial acetic acid.
Question: Why is the conversion of ethanol to ethanoic acid an oxidation reaction? (Imp.)
Ans. When ethanol is oxidized, hydrogen is removed from its molecule and oxygen is added so
as to form ethanoic acid. Thus, conversion of ethanol into acetic acid is an oxidation reaction.
Question: A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of
ethyne and air is not used? (Imp.)
Ans. Ethyne has only two hydrogen atoms and two carbon atoms in its molecule. It burns in air
with a sooty flame, because the oxygen from air is insufficient to burn the carbon completely.
Thus, pure oxygen is used which completely burns carbon and hydrogen and produces a very
hot flame.
Question: Why is the conversion of ethanol to Ethanoic acid considered an oxidation reaction?
Ans. Conversion of ethanol to Ethanoic acid is considered an oxidation reaction since it involves:
(i) addition of oxygen to the ethanol molecule
(ii) removal of hydrogen from the ethanol molecule
Q. An organic compound burns with a sooty flame. Is it saturated or unsaturated compound?
Justify
Answer: it is unsaturated compound. Unsaturated compound have low percentage of hydrogen
so incomplete combustion takes palace and produce sooty flame.
Q. (a) Differentiate between saturated and unsaturated hydrocarbons. Write any tow points of
difference.
(b) Why are carbon compounds (i) poor conductors of electricity (ii) have low melting and
boiling points?
(c) Name the simplest hydrocarbon and write its formula
Ans: (a) Compounds of carbon, which are linked by only single bonds between the carbon
atoms are called saturated compounds. Compounds of carbon having double or triple bonds
between their carbon atoms are called unsaturated compounds.
Saturated hydrocarbons will generally give a clean flame without soot while unsaturated carbon
compounds will give a yellow flame with lots of black smoke and soot on combustion.
(b)(i) carbon compounds are poor conductors of electricity because they do not have any free
electrons or an overall electric charge
(ii) Carbon compounds have low melting and boiling points this is because the weak
intermolecular forces break down easily.
(iii) The simplest hydrocarbon is methane CH4
Q. (a) Explain with the help of chemical equation the following properties of carbon compounds-
(i) Combustion (ii) Oxidation
(b) How do saturated and unsaturated hydrocarbons can be differentiated on the basis of their
combustion?
(c) What are oxidizing agents ?
Answer: (i) carbon compounds burns in oxygen to give carbon dioxide along with the release of
heat and light.
For example : C + O2 → CO2 + heat and light : CH4 + O2 → CO2 + H2O + heat and light
CH3CH2OH + O2 → CO2 + H2O + heat and light
(ii) Carbon compounds easily oxidised on combustion or in the presence of oxidising agents like
Alkaline potassium permanganate or acidified potassium dichromate. For example : alcohols are
converted to carboxylic acids .
CH3 – CH2OH Alkaline KMnO 4
𝐻𝑒𝑎𝑡
→ CH3COOH
(b) Saturated hydrocarbons will generally give a clean flame without soot while unsaturated
carbon compounds will give a yellow flame with lots of black smoke and soot on combustion.
(c) Any substances that add oxygen to others substance is called oxidising agents
The atmosphere has only 0.03% of carbon dioxide.
The number of electrons lost or gained by an atom to complete its octet (or duplet) is
called its valency. It depends on the number of valence electrons.
The tendency to attain a completely filled outermost shell (i.e. noble gas configuration)
by gaining or losing electrons is called reactivity.
The shared pair of electrons belongs to the outer shells of both the atoms so as to attain
noble gas configuration.
The simplest molecule formed by sharing of electrons is hydrogen.
The bonds which are formed by sharing of electrons between two atoms are known as
covalent bonds.
The compounds which are formed by sharing of electrons pair between two atoms are
known as covalent compounds. E.g. CH4, H2, O2, etc.
The melting and boiling points of covalent compounds are low because their
intermolecular forces are weak and less amount of energy is required to overcome these
forces.
The covalent compounds are generally poor conductors of electricity because the
electrons are shared between atoms and no charged particles are formed in their
solution.
Carbon has three allotropes – graphite, diamond and Buckminster Fullerene.
When a hydrogen atom is removed from an alkane, the group obtained is called an alkyl
group.
Saturated carbon compounds are usually not very reactive because the carbon-carbon
single bonds are very strong.
Unsaturated carbon compounds are very reactive than saturated carbon compounds.
Uses of graphite
1. It is used in lead pencils as it is soft and leaves black mark on the paper.
2. It, being a good conductor of electricity, is used in making electrode in the cells
3. Powdered graphite is used as lubricant because it is very soft and can withstand at high
temperature.
Uses of diamond
1. It is used in pencils for cutting glass etc because it is the hardest substance known.
2. It is used for making dies for drawing thin wires.
3. It is used in surgical tools.
4. It is used for making jewellery because of high refractive index.
Heteroatom In hydrocarbons, the elements like halogen, oxygen, etc replacing hydrogen is
called heteroatom. They are also present in some groups.
Graphite Diamond
1. Graphite has two dimensional
structure
2. oft and greasy.
3. It is a good conductor of heat and
electricity.
4. It is grayish black substance.
1. Diamond is a three dimensional
structure.
2. It is the hardest substance known.
3. It is the bad conductor of electricity
but good conductor of heat.
4. It is transparent.
Catenation The property of self linking of carbon atoms through covalent bonds to form long
chains or rings is called catenation.
Other element which shows the catenation property is silicon.
The bonds formed between the carbon and other elements are very strong because
small size of
carbon enables the nucleus to hold on to shared-pair of electron strongly.
Versatile nature of carbon
1. Catenation – self linking of carbon atoms to form long chains or rings.
2. Tetravalency –sharing of 4 electrons with other atoms of carbon or any other
monovalent element.
Saturated Carbon Compounds Compounds of carbon which have only single bonds between the
carbon atoms are called saturated carbon compounds.
E.g. methane, ethane, etc.
Unsaturated carbon compounds Compounds of carbon which have double or triple bonds
between the carbon atoms are called unsaturated carbon compounds.
E.g. ethene, ethyne, etc.
Straight chain compounds Carbon compounds in which no carbon atom of the chain is linked to
more than two other carbon atoms are called straight chain compounds.
E.g. methane, ethane, propane, etc.
Branched chain compounds Carbon compounds, in which at least one carbon atom of the chain
is linked to three or four other carbon atoms are called branched chain compounds. E.g. 2-
methylpropane.
Cyclic compounds Carbon compounds in which carbon atoms are arranged in a ring are called
cyclic compounds. These are of two types –
1. Saturated cyclic compounds. E.g. cyclopropane, cyclobutane, cyclopentane, etc.
2. Unsaturated cyclic compounds. E.g. benzene.
Hydrocarbons. The carbon compounds which contain only hydrogen and carbon are
called
Hydrocarbons
Hydrocarbons which contain only single bonds between the carbon atoms are called
alkanes. Their general formula is CnH2n+2.
Hydrocarbons which contain one or more double bonds between the carbon atoms are
called alkenes. Their general formula is CnH2n.
Hydrocarbons which contain one or more triple bonds between the carbon atoms are
called alkynes. Their general formula is CnH2n-2.
Functional group An atom or group of atoms present in a molecule which determines its
functions or chemical properties is called a functional group. It is the most reactive site of a
carbon compound.
Homologous series The family of organic compounds having same functional group, similar
chemical properties and the successive members of which differ by CH2 group is called a
homologous series.
Characteristics of a homologous series
1. All the members can be represented by same general formula.
2. The molecular formulae of two successive members differ by CH2 group or by 14u.
3. All the members have same functional group.
4. All the members show similar chemical properties.
The melting and boiling points of the members of homologous series increase gradually
because their molecular masses increase.
Allotropy The phenomenon in which one element exists in two or more forms having same
chemical properties but different physical properties is called allotropy. The substances that
show allotropy are carbon, sulphur, etc.
Allotropes The different forms of an element having same chemical properties but different
physical properties are called allotropes.
Isomerism The phenomenon in which a compound can be represented by different structures
having different properties is called isomerism.
Isomers The compounds which can be represented by different structures having different
properties are called isomers.
IUPAC – International Union of Pure and Applied Chemistry.
Combustion The process of heating a substance strongly in the presence of excess of oxygen or
air is called combustion.
Carbon and carbon compounds release carbon dioxide, water and a large amount of heat
and light on burning.
C + O2 CO2 + Heat and Light
CH4 + O2 CO2 + H2O + Heat and Light
C2H5OH + O2 CO2 + H2O + Heat and Light
Saturated hydrocarbons generally give a clean blue flame because complete combustion
of these substances takes place.
Saturated hydrocarbons burn with a yellow flame with lots of black smoke due to the
incomplete combustion of carbon contents.
Condition in which saturated carbon compounds burn with sooty flame – If a saturated
carbon compound is burnt in limited (insufficient) supply of air, it burns with sooty flame
due to incomplete combustion.
The gas/kerosene stoves used at homes have inlets for air so that a sufficient oxygen
rich mixture is burnt to give a clean blue flame with a lot of heat.
Sometimes bottoms of cooking vessels get blackened due to incomplete combustion of
gas/kerosene. It means the holes are blocked. This problem can be removed by cleaning
the burner by opening holes.
The pollutants released in the environment by burning coal and petroleum are oxides of
sulphur and nitrogen e.g. SO2 , NO, NO2 , etc.
Combustion of hydrocarbons is regarded as oxidation reaction because during
combustion, carbon is oxidised to CO2 and hydrogen is oxidised to water by addition of
oxygen.
Only the gaseous substances produce flame on burning.
Wood and charcoal are solid but they produce flame when ignited because when they are
ignited the volatile substances present vaporize and burn with a flame in the beginning
only.
Fossil fuels The fuels formed by the dead animals and plants buried under the earth
millions of years ago due to intense heat and pressure are called fossil fuels. E.g. coal
and petroleum.
When an alcohol is heated in the presence of alkaline KMnO4 (or acidified K2 Cr2 O7 )
then corresponding carboxylic acid is formed.
Addition reaction The reaction which involves addition of two reactants to form a single
product is called an addition reaction. Only unsaturated hydrocarbons perform addition
reactions.
CH2 = CH2 + Cl2 CH2Cl – CH2Cl
Industrial application of addition reaction Addition reaction is commonly used in the
hydrogenation of vegetable oils using a nickel catalyst to form vegetable ghee.
Vegetable oil (liquid) + H2 Ni (473K) Vegetable ghee (solid)
Saturated fatty acids are harmful for health so oils containing unsaturated fatty acids should be
used for cooking because Saturated fats increase the level of bad cholesterol (low density
lipoprotein LDL) in blood which sticks to the walls of arteries and causes heart diseases.
Substitution reaction The reaction which involves direct replacement of an atom or group of
atoms in an original molecule is called substitution reaction. Only saturated hydrocarbons
perform substitution reactions.
CH4 + Cl2 CH3Cl + HCl
Functional group Symbol/formula Prefix/suffix Compound name
Halo -Cl, -Br, - I Halo (prefix) Haloalkane
Alcohol -OH -ol Alkanol
Aldehyde -CHO -al alkanal
Ketone - CO - -one Alkanone
Carboxylic -COOH -oic acid Alkanoic acid
Simplest compound Common name IUPAC name Formula
Alcohol Methyl alcohol Methanol CH3OH
Aldehyde Formaldehyde Methanal HCHO
Ketone Acetone Propanone CH3COCH3
Carboxylic acid Formic acid Methanoic acid HCOOH
alkane Methane Methane CH4
Alkene Ethylene Ethene C2H4
alkyne Acetylene Ethyne C2H2
ETHANOL (CH3CH2OH or C2H5OH)
Physical properties
1. It is liquid at room temperature.
2. It is colourless and has distinct smell and burning taste.
3. It is soluble in water in all proportions.
Chemical properties
1. It reacts with sodium to form sodium ethoxide and hydrogen gas.
2CH3CH2OH + 2Na 2CH3CH2ONa + H2
2. It reacts with hot concentrated H2SO4 to give ethene.
CH3CH2OH CH2=CH2 + H2O
USES
1. It is used in all alcoholic drinks like wine, beer, etc.
2. In the form of rectified spirit (95% alcohol + 5% water), it is used as an antiseptic for
wounds.
3. It is used in medicines like tincture iodine, cough syrups, tonics etc because it is a good
solvent.
4. In cold countries it is used as antifreeze in automobiles.
Harmful effects of ethanol
1. Consumption of its small quantity causes drunkenness.
2. It depresses the central nervous system which results in mental confusion and
drowsiness.
3. It damages liver and kidney.
4. It decreases the sense of judgment and sense of timing.
5. It increases crime in the society.
Denatured alcohol To prevent the misuse of ethanol produced for industrial use, it is made unfit
for drinking by adding poisonous substances like methanol, copper sulphate, etc. it is called
denatured alcohol.
ETHANOIC ACID (acetic acid or vinegar, CH3COOH)
Physical properties.
1. It is a colourless and pungent smelling liquid.
2. Its melting point is 290K so it often freezes during winter and looks like glacier.
Therefore, it is also known as glacial acetic acid.
3. It is soluble in water in all proportions.
5% to 8% solution of Ethanoic acid in water is called vinegar.
Chemical properties
1. Reaction with alcohol. Ethanoic acid reacts with ethanol in the presence of an acid to
give ester.
CH2COOH + C2H5OH Acid CH3COOC2H5 + H2O
2. Reaction with base. Ethanoic acid reacts with sodium hydroxide to give sodium
ethanoate (sodium acetate) and water.
CH3COOH + NaOH CH3OONa + H2O
3. Reaction with carbonates and bicarbonates. Ethanoic acid reacts with carbonates and
bicarbonates to salt carbon dioxide and water.
2CH3COOH + Na2CO3 2CH3COONa + CO2 + H2O
CH3COOH + NaHCO3 CH3COONa + CO2 + H2O
Esterification The reaction between a carboxylic acid and an alcohol to form an ester is called
Esterification reaction.
CH2COOH + C2H5OH Acid CH3COOC2H5 + H2O
The reaction between the ester and hot base to give original alcohol and carboxylic acid
back is called saponification reaction because this reaction is used in preparing soaps.
CH3COOC2H5 NaOH CH2COOH + C2H5OH
The product formed when a carboxylic acid reacts with an alcohol having the formula R-COO-R’
is called an ester. Esters are sweet smelling substances. They are widely spread in nature. The
smell of fruits and flowers is due to the presence of esters. Esters are used as flavorings agents
and in making perfumes.
Cleansing action of soap The molecules of soap are sodium or potassium salts of long chain of
carboxylic acids. The hydrocarbon tail being hydrophobic reacts with oil or grease while the ionic
end being hydrophilic reacts with water. As a result micelles are formed. They form an emulsion
in water.
When the surface of clothes is beaten or agitated, micelles are thrown away and the cloth is
cleaned.
Micelle The cluster of about 100 – 200 molecules with hydrophilic ends on the surface of cluster
and hydrophobic ends towards the centre, is called a micelle.
Soaps Detergents
Soaps are sodium salts of long chain carboxylic
acids.
Detergents are sodium salts of long chain
sulphonic acids.
Soaps do not form leather with hard water. Detergents form leather with hard water.
Soaps are biodegradable. They are non biodegradable.
Soaps do not have strong cleansing action. They have strong cleansing action.
These are prepared from animal fats.
They are prepared from hydrocarbons of
petroleum.
Advantage of soaps over detergents Soaps are biodegradable so they do not produce pollution.
While detergents being non biodegradable produce pollution.
Advantage of detergents over soaps Detergents can be used in hard water. Also, they have
strong cleansing action. While soaps have weak cleansing action and they cannot be used in
hard water.
Extra Knowledge
Properties of Alkanes/ Alkenes/ Alkynes (10th Carbon and its compounds)
Properties of Alkanes/ Alkenes/ Alkynes
(a) Alkanes are gas (C1to C4) ; liquid (C5to C17) and rest are solid at room temperature.
(b) The melting and boiling point of Alkanes increases with increase in number of C – atom in
Alkanes.
Reason: Alkanes experience inter-molecular van der Waals forces. Stronger inter-molecular van
der Waals forces give rise to greater boiling points of alkanes.
A straight-chain alkane will have a boiling point higher than a branched-chain alkane due to the
greater surface area in contact.
Note: In Chemistry the Van der Waals forces include attractions and repulsions between atoms,
molecules, and surfaces, as well as other intermolecular forces.
(c) The density of the alkanes usually increases with increasing number of carbon atoms
Alkane Formula Density
Pentane C5H12 0.626 (liquid)
Hexane C6H14 0.659 (liquid)
Heptane C7H16 0.684 (liquid)
Octane C8H18 0.703 (liquid)
Nonane C9H20 0.718 (liquid)
(d) Solubility: Alkanes are generally insoluble in polar compound like water but dissolve in
organic solvents (Non polar compound) like benzene. The liquid alkanes are good solvents for
many other covalent compounds.
Reason: Alkanes do not conduct electricity, nor are they polarized by electricity. For this reason
they do not form hydrogen bonds and are insoluble in polar solvents such as water.
(e) Reactivity: Alkanes are stable and less reactive than alkenes
Reason: This is because saturated hydrocarbons contain only single bonds which are very stable
and difficult to break. On the other hand, unsaturated hydrocarbons contain pie bonds, which
can be easily broken as they are more strained.
(f) Combustion: Alkanes are generally good combustible material due presence of the good
percentage of Hydrogen.
Since Alkanes burn with non smoky and non sooty flame due to presence of the good
percentage of Hydrogen, It is used as a fuel like LPG and CNG
2CH4 + 2O2 ----------- CO2 + H2O + Heat and light
2C2H6 + 7O2 ----------- 4CO2 + 6H2O + Heat and light
C2H4 + 3O2 ----------- 2CO2 + 2H2O + Heat and light
2C2H2 + 5O2 ----------- 4CO2 + 2H2O + Heat and light
2CH3 CH2OH + 3O2 ----------- 2CO2 + 3H2O + Heat and light
However, if the supply of air or oxygen is not sufficient for complete combustion, carbon
monoxide is formed. Carbon monoxide (CO) is highly poisonous.
2CH4 + 3O2 ----------- 2CO + 4H2O
2CH4 + 3O2 ----------- 2CO + 4H2O
2C4H10 + 9O2 ----------- 8CO + 10H2O
Q. What is the difference between Oxidation and combustion?
Answer: Combustion is the complete oxidation of organic compound into carbon dioxide and
water molecules in presence of oxygen gas while oxidation is the addition of oxygen in a organic
compound or with an element the loss of electron from an atom or ion is also oxidation.
Hence, all Oxidation reactions are not combustion reaction but all combustion reactions are
Oxidation. Oxidation reaction does not involve heat where as combustion reactions do.
(g) Substitution reaction: Alkanes do not undergo addition reaction due to strong van der wall
force but take part in substitution reaction:
Alkanes undergo substitution reaction because hydrogen attached to carbon easily replaced by
atom more reactive than hydrogen like halo atom Cl , Br ,I etc.
Sunlight
CH4 + Cl2 ---------- CH3Cl + HCl
Sunlight
CH4Cl + Cl2 ----------- CH2Cl2 + HCl
Sunlight
CH2Cl2 + Cl2 ----------- CHCl3 + HCl
Sunlight
CHCl3 + Cl2 ----------- CH3Cl + HCl
If chlorine present in excess, then reaction does not stop in between but keep on reacting till it
form carbon tetra chloride.
(h) Addition reaction:
Unlike alkane, generally alkene Undergo addition reaction with hydrogen gas in the presence of
Palladium or nickel at (473 k) catalyst and gives saturated hydrocarbon.
Example: Ethene Undergo addition reaction with hydrogen gas in the presence of Palladium or
nickel at (473 k) catalyst and gives saturated hydrocarbon Ethane
Ni
CH2 = CH2 + H2 ---------- CH3 - CH3
473 k
Ethyne Undergo addition reaction with hydrogen gas in the presence of Palladium or nickel at
(473 k) catalyst and gives saturated hydrocarbon Ethane . This reaction is known as
Hydrogenation Reaction.
Pd
CH2 CH2 + 2H2 ----------- CH3 - CH3
This addition reaction of hydrogen is helpful in converting vegetable Oil into saturated fat like
vanaspati gee. This reaction is commonly called Hydrogenation of Oil. This test helps to
distinguish between saturated and saturated fats.
Note: Butter contain saturated compound where as cooking oil contain unsaturated compound.
If Alkaline KMno4 added to both, pink color of KMno4 disappear in cooking oil but remain in pink
in butter.
Bromine and chlorine react with alkene to form vicinal dihalides (iodine does not undergo
addition reaction under normal conditions).
CCl4
CH2 = CH2 + Cl2 ----------- CH2 - CH2
I I
Cl Cl
Ethene 1,2- Dichloroethane
CCl4
CH2 = CH2 + Br2 ----------- CH3 - CH - CH2
I I
Br Br
Ethene Bromine water 1,2-Dibromoethane
Bromine water test: Solution of Bromine in water is reddish brown in colour but 1, 2-
Dibromoethane formed from the addition reaction is colourless. This helps us to identify
unsaturated carbon compound. If an organic compound is unsaturated Solution of Bromine in
water became colourless.
Note: In Alkanes, the four valencies of carbon atom are saturated and they have stable
(sigma) bonds. Any nuleophile comes; one hydrogen atom is replaced to accommodate the
nucleophile.
e.g. CH4 + Cl2 CH3Cl + HCl
In case of Alkene or Alkyne, Carbon atom has double or triple bonds. In this, one is stable
(sigma) bond and the rests are unstable (or weak) bonds. When nucleophile approaches to
the carbon atom that has double or triple bonds, they easily break to accommodate it.
e.g., H2C=CH2 + Cl2 H2ClC-CH2Cl.
(i) Cracking (or pyrolysis):
When heated to a sufficiently high temperature in the absence of oxygen, alkanes decompose to
produce hydrocarbons of shorter chain length. This reaction is called thermal cracking or
pyrolysis.
For example, when octane is heated to 6500C in the absence of oxygen, it forms ethene and
exane.
6500C
C8H18 -------> C6H14 + C2H4
Octane Hexan
e
Ethene
In this process, vapour of higher alkanes is passed through a hot metal tube (5000C – 7000C).
Propane on cracking gives
C3H6 + H2
C3H8ca ----------
CH4 + C2H4
Cracking of hexane gives butane and ethane.
C6H14 ---------- C4H10 + C2H4
Cracking is used to convert some of the less volatile fraction of petroleum containing high
moleculer mass into compounds of lower molecular masses of higher volatility. Such
hydrocarbons with lower molecular masses are more suitable as fuels for automobiles.
C16 H34 → C8H18 + C8H16
n - Hexadecane n-octane octene (unsaturated)
Q. What's the difference between cracking and Pyrolysis?
Pyrolysis: The decomposition of a compound on heating in absence of air is known as pyrolysis.
Cracking: is the breakdown of large organic compounds by use of a catalyst and low
temperature to form fewer different compounds
Q. In cracking will the decomposed hydrocarbon always be a saturated and a unsaturated
hydrocarbons? Can they both be either unsaturated or saturated hydrocarbons?
Cracking is defined as the process of breaking or decomposition of large hydrocarbons into
smaller compounds. This process is widely used in the petroleum industry. Usually, we get a
mixture of alkane and alkenes by the process of cracking of hydrocarbons. This is because the
bonds in the hydrocarbons can be cleared in any way. As a result, we will not get alkane and
alkene exclusively but a mixture of both.
(j) Oxidation: The chemical reaction in which oxygen added to substance is called oxidation of
substance. The substance which donate oxygen to other substance during chemical reaction is
called oxidizing agent like K2Cr2O7, HNO3 and KMnO4 . Alkane on oxidation produces heat and
light known as combustion.
(a) Ethene on treating with alkaline KMnO4 oxidized to Ethylene Glycol
H H H H
I I Alk. KMnO4 I I
H - C = C - H + H2O + O ----------- H – C – C - H
I I
OH OH
Ethene Ethylene Glycol
(b) Ethyne on treating with alkaline KMnO4 oxidized to Oxalic Acid
Alk. KMnO4 COOH
H – C C – H + 4O ----------- I
COOH
Ethyne Oxalic Acid
(c) Ethanol on treating with alkaline KMnO4 or acidified K2Cr2O7 oxidized to Ethanoic Acid.
During oxidation of Ethanol alkaline KMnO4 losses its purple colour .
Alk. KMnO4 + Heat
CH3 CH2 OH + 4O ------------------------ CH3COOH
Ethanol Ethanoic Acid
Ethanol is highly inflammable and catches fire readily. This is why during oxidation it should
never be heat directly on a burner. it should be heated on a water bath.
1. Ethanol (C2H5OH)
Ethanol or ethyl alcohol or simply alcohol is one of the most important members of the family
of alcohols.
Physical properties
(i) Ethanol is a clear liquid with burning taste.
(ii) Its boiling point is 351K which is higher than corresponding alkane.
(iii) It is completely miscible with water in all proportions.
Chemical properties
(i) Dehydration
(a) Intra molecular dehydration :
Ethanol, when heated with excess conc. H2SO4 at 443 K undergoes intra molecular dehydration
(i.e. removal of water within a molecule of ethanol).
CH3CH2OH -------Conc.H2SO4/443K-----> CH2 = CH2 +H2O
(b) Inter molecular dehydration :
When excess of alcohol is heated with conc. H2SO4 at 413K two molecules condense by losing a
molecule of water to form ether (i.e. removal of water from two molecules of ethanol).
C2H5- OH + HO- C2H5 -------Conc.H2SO4/413K----> C2H5-O-C2H5 (Diethyl ether)+H2O
(ii) Reaction with sodium :
Ethanol reacts with sodium metal to form sodium ethoxide and hydrogen gas.
2C2H5OH + 2Na ------------> 2C2H5ONa (sodium ethoxide) + H2 ↑
(iii) Oxidation:
Ethanol is oxidized to Ethanoic acid with alkaline KMnO4 or acidified K2Cr2O7
CH3CH2OH ----Oxidation---> CH3COOH (Ethanoic acid) + H2O
During this reaction, orange colour of K2Cr2O7 changes to green. Therefore, this reaction can
be used for the identification of alcohols.
(iv) Esterificaiton :
Ethanol reacts with ethanoic acid in the presence of conc.H2SO4 (catalyst) to form ethyl
ethanoate and water. The compound formed by the reaction of an alcohol with carboxylic acid is
known as ester (fruity smelling compound) and the reaction is called esterification.
C2H5OH + CH3COOH ---conc.H2SO4-----> CH3COOC2H5 (Ethyl ethanoate) + H2O
(v) Dehydrogenation :
When the vapour of ethanol is passed over reduced copper catalyst at 573 K, it is
dehydrogenated to acetaldehyde.
CH3CH2OH -----------Cu/573K ------> CH3CHO (Acetadehyde) +H2
Ethanol is used
1. As an anti-freeze in automobile radiators.
2. As a preservative for biological specimen.
3. As an antiseptic to sterilize wounds in hospitals.
4. As a solvent for drugs, oils, fats, perfumes, dyes, etc.
5. In the preparation of methylated spirit (mixture of 95% of ethanol and 5% of
methanol),rectified spirit (mixture of 95.5% of ethanol and 4.5% of water), power alcohol
(mixture of petrol and ethanol) and denatured sprit (ethanol mixed with pyridine).
6. In cough and digestive syrups.
Evil effects of consuming alcohol
• If ethanol is consumed, it tends to slow down metabolism of our body and depresses the
central nervous system.
• It causes mental depression and emotional disorder.
• It affects our health by causing ulcer, high blood pressure, cancer,brain and liver damage.
• Nearly 40% accidents are due to drunken drive.
• Unlike ethanol, intake of methanol in very small quantities can cause death.
• Methanol is oxidized to methanal (formaldehyde) in the liver and methanol reacts rapidly with
the components of cells.
• Methanal causes the protoplasm to get coagulated, in the same way an egg is coagulated by
cooking. Methanol also affects the optic nerve, causing blindness.
2. Ethanoic acid (CH3COOH)
Ethanoic acid is most commonly known as acetic acid and belongs to a group of acids called
carboxylic acids. Acetic acid is present in many fruits and sour taste of fruits is because of this
acid.
1. Preparation of Ethanoic acid
Ethanol on oxidation in the presence of alkaline potassium permanganate or acidified potassium
dichromate gives Ethanoic acid.
CH3CH2OH (Ethanol) ------ Oxidation ------> CH3COOH (Ethanoic acid) + H2O
2. Physical properties
(i) Ethanoic acid is a colourless liquid and has a sour taste.
(ii) It is miscible with water in all proportions.
(iii) Boiling point (391 K) is higher than corresponding alcohols, aldehydes and ketones.
(iv) On cooling, pure ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it
is called glacial acetic acid.
3. Chemical properties
(i) Ethanoic acid is a weak acid but it turns blue litmus to red.
(ii) Reaction with metal
Ethanoic acid reacts with metals like Na, K, Zn, etc to form metal Ethanoate and hydrogen gas.
2CH3COOH + Zn --------------> (CH3COO)2 Zn + H2 ↑
2CH3COOH + 2Na ----------------> 2CH3COONa + H2 ↑
(iii) Reaction with carbonates and bicarbonates.
Ethanoic acid reacts with carbonates and bicarbonates and produces brisk effervescence due to
the evolution of carbon dioxide.
2CH3COOH + Na2CO3 ------------> 2CH3COONa + CO2 ↑ + H2O
CH3COOH + NaHCO3 -------------> CH3COONa + CO2 ↑ + H2O
(iv) Reaction with base
Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water
CH3COOH + NaOH ------------> CH3COONa + H2O
(v) Decarboxylation (Removal of CO2)
When sodium salt of Ethanoic acid is heated with soda lime (Solid mixure of 3 parts of NaOH
and 1 part of CaO) methane gas is formed
CH3COONa ------NaOH / CaO-------> CH4 ↑ + Na2CO3
Ethanoic acid is used
1. For making vinegar which is used as a preservative in food and fruit juices.
2. As a laboratory reagent.
3. For coagulating rubber from latex.
4. In the preparation of dyes, perfumes and medicine.
Important Questions
Question: Why does Ethanoic acid called glacial acetic acid? (Imp.)
Ans. On cooling, pure Ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it
is called glacial acetic acid.
Question: Why is the conversion of ethanol to ethanoic acid an oxidation reaction? (Imp.)
Ans. When ethanol is oxidized, hydrogen is removed from its molecule and oxygen is added so
as to form ethanoic acid. Thus, conversion of ethanol into acetic acid is an oxidation reaction.
Question: A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of
ethyne and air is not used? (Imp.)
Ans. Ethyne has only two hydrogen atoms and two carbon atoms in its molecule. It burns in air
with a sooty flame, because the oxygen from air is insufficient to burn the carbon completely.
Thus, pure oxygen is used which completely burns carbon and hydrogen and produces a very
hot flame.
Question: Why is the conversion of ethanol to Ethanoic acid considered an oxidation reaction?
Ans. Conversion of ethanol to Ethanoic acid is considered an oxidation reaction since it involves:
(i) addition of oxygen to the ethanol molecule
(ii) removal of hydrogen from the ethanol molecule
Q. An organic compound burns with a sooty flame. Is it saturated or unsaturated compound?
Justify
Answer: it is unsaturated compound. Unsaturated compound have low percentage of hydrogen
so incomplete combustion takes palace and produce sooty flame.
Q. (a) Differentiate between saturated and unsaturated hydrocarbons. Write any tow points of
difference.
(b) Why are carbon compounds (i) poor conductors of electricity (ii) have low melting and
boiling points?
(c) Name the simplest hydrocarbon and write its formula
Ans: (a) Compounds of carbon, which are linked by only single bonds between the carbon
atoms are called saturated compounds. Compounds of carbon having double or triple bonds
between their carbon atoms are called unsaturated compounds.
Saturated hydrocarbons will generally give a clean flame without soot while unsaturated carbon
compounds will give a yellow flame with lots of black smoke and soot on combustion.
(b)(i) carbon compounds are poor conductors of electricity because they do not have any free
electrons or an overall electric charge
(ii) Carbon compounds have low melting and boiling points this is because the weak
intermolecular forces break down easily.
(iii) The simplest hydrocarbon is methane CH4
Q. (a) Explain with the help of chemical equation the following properties of carbon compounds-
(i) Combustion (ii) Oxidation
(b) How do saturated and unsaturated hydrocarbons can be differentiated on the basis of their
combustion?
(c) What are oxidizing agents ?
Answer: (i) carbon compounds burns in oxygen to give carbon dioxide along with the release of
heat and light.
For example : C + O2 → CO2 + heat and light : CH4 + O2 → CO2 + H2O + heat and light
CH3CH2OH + O2 → CO2 + H2O + heat and light
(ii) Carbon compounds easily oxidised on combustion or in the presence of oxidising agents like
Alkaline potassium permanganate or acidified potassium dichromate. For example : alcohols are
converted to carboxylic acids .
CH3 – CH2OH Alkaline KMnO 4
𝐻𝑒𝑎𝑡
→ CH3COOH
(b) Saturated hydrocarbons will generally give a clean flame without soot while unsaturated
carbon compounds will give a yellow flame with lots of black smoke and soot on combustion.
(c) Any substances that add oxygen to others substance is called oxidising agents
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