Carbon and its Compounds Class 10 Notes Science Chapter 4

Overview of Carbon and Covalent Bonding in Carbon - Carbon and its Compounds, Class 10, Science

Carbon & Compound

Introduction :

The compounds obtained from 'Carbon' are widely used as clothes, medicines, books,food, fertilizer, fuel etc. all living structures are carbon based.

The amount of carbon present in the earth's crust and in the atmosphere is quite merge. The earths crust has only 0.02% carbon in the form of mineral (like carbonates, hydrogen-carbonates, coal and petroleum) and the atmosphere has 0.03% of carbon dioxide. In spite of this small amount of carbon available in nature, the importance of carbon seems to be immense.

Carbon forms a large number of compounds with hydrogen which are known as hydrocarbons. In addition to hydrogen, carbon compound may also contain some other element such as oxygen, halogen, nitrogen, phosphorus, sulphur etc.

The number of compounds of carbon is more than three million which is much larger than the compounds formed by all other element put together.

BONDING IN CARBON COMPOUNDS : 

Carbon forms covalent bonds in its compounds with other atoms. In each compound the valency of carbon is four. That is, carbon has tetravalent character. But what is covalent bond and what is meaning of tetravalent ?

Why does a carbon atom form only covalent bond ?

The atomic number of carbon is 6 and first shell contains just two electrons and second shell (Outermost shell) contains four electrons.

Carbon atom can attain the noble gas configuration by sharing its valence electrons with other atoms of carbon or with atoms of other elements and form covalent bond.

COVALENT BOND : 

A chemical bond formed between two atoms of the same element or two atoms of different elements by sharing of electron is called a covalent bond. 

Necessary conditions of the formation of covalent bond : 

The combining atoms should have nonmetallic character.

The combining atoms should contain 4 to 7 electrons in their respective valence shell.

In hydrogen there is only 1 valence electron, but it also forms covalent bond.

The combining atoms need 1, 2, 3 or 4 electrons to complete their octet (hydrogen completes its duplet) 

The combining atoms should contribute equal number of electrons to form pair of electrons to be shared.

After sharing the pair of electrons each combining atoms should attain stable electronic configuration like its nearest noble gas.

CLASSIFICATION OF COVALENT BOND : 

On the basis of the number of electrons shared by two combining atoms, the covalent bond are of three types.

Single Covalent Bond : A single covalent bond is formed by the sharing of one pair of electrons between the two atoms. It is represented by one short line (---) between the two atoms.

Example : H-H, Cl -Cl, H-Cl, CH₃-CH₃.

Double Covalent Bond : A double covalent bond is formed by the sharing of two pairs of electron between the two combining atoms. It is represented by putting (=) two short lines between the two bonded atoms.

Examples : O = O (O₂), CO₂ (O = C = O), H₂C = CH₂  

Triple covalent bond : A triple bond is formed by the sharing of three pair of electrons between the two combining atoms. It is represented by putting three short line (º) betwen two bonded atoms.

Example : N₂ (NºN), CHºCH.

Formation of single covalent compounds : 

Formation of hydrogen molecule (H₂) :

A molecule of hydrogen is composed to two H-atoms. The electronic configuration of H-atom is.

Shell - K

Electron-1 incomplete duplet (unstable)

Electronic configuration of He atom

Shell - K

Electrons-2 complete duplet (stable)

H^• + ^•H → H : H →  H H → H₂

K(1) K(1) Shared electron Covalent Hydrogen

Atom Atom Pair Bond molecule

H H Bond in terms of energy shells (orbits)

Formation of chlorine molecule (Cl₂). The atomic number of chlorine is 17, thus there are 17 electrons in an atom of chlorine.

Electronic configuration of Cl atom

Electronic configuration of Ar atom

Chlorine atom needs one electron more to complete its octet

 +  ¾®  ¾® Cl — Cl ¾® Cl₂

Atom Atom Shared electrons Covalent Bond Chlorine molecule

Cl Cl bond in terms of energy shell orbits

Formation of hydrochloric acid (HCl) : 

H atom has one valence electron. It needs 1 electron more to complete its duplet and chlorine atom has 7 valence electrons. It need 1 electron more to complete its octet and acquire stable electronic configuartion
(2, 8, 8) like noble gas argon.

Formation of oxygen (O₂) :

The atomic number of O atom is 8. There are 6 electron in the valence shell of oxygen atom it needs 2 more electrons to attain the nearest stable inert gas Neon (2, 8) configuration :

 +  ¾®  ¾®

Formation of nitrogen molecule (N₂) :

The atomic number of nitrogen is 7 and its electronic configuration is K(2), L(5). It needs 3 electrons more to complete its octet like noble gas neon (2, 8).

 +  ¾®  ¾®

Formation of ammonia molecule (NH₃) :

The atomic number of N is 7. It's electronic configuration is 2, 5 there are 5 electrons in its valence shell. It needs 3 electrons more to complete its octet like noble gas neon (2, 8).

Formation of H₂O molecule :

The electronic configuration of hydrogen is K (1) and that of oxygen is K(2) L(6) thus each hydrogen require one and oxygen required two electrons to achieve the stable electronic configuration.

Formation of CO₂ molecule :

The atomic number of C is 6 and the electronic configuration of C is K(2), L(4) and that of oxygen is K(2), L(6) thus each carbon require 4 and oxygen require two electrons to achieve the stable electronic configuration.

 +  +  ¾®

CO₂ ¬¾ O = C = O

molecule Double covalent bond

Formation of CH₄ molecule :

Methane is a covalent compound containing 4 covalent bond. It contains one carbon atom and four hydrogen atom covalently bonded to central carbon atom.

 +  ¾®  ¾®

Formation of carbon tetrachloride molecule (CCl₄) :

The electronic configuration of carbon and chlorine atoms are (2, 4) and (2, 8, 7) respectively. Carbon atom needs four electrons and chlorine atom needs one electron to attain the stable electronic configuration.

l +  ¾¾®

Formation of ethylene or ethene molecule (C₂H₄) :

The electronic configuration of carbon atom is 2, 4. There are 4 valence electrons in one C atom. Each H atom contains 1 valence electron. Thus, there are 12 valence electrons present in ethene molecule.

Formation of Acetylene or ethyne molecule (C₂H₂) : 

Q. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur?

Ans. The eight atoms of sulphur are joined together in the form of a puckered ring. [NCERT] 

Non polar and polar covalent compounds : 

Non polar covalent bond : 

A covalent bond formed between two atoms of the same element or same electronegativity is called a
non-polar covalent bond. Example : H₂, N₂, O₂, Cl₂ etc.

Polar covalent bond :

The covalent bond between the atoms of two elements having different electronegativities is called a polar covlaent bond. Molecule in which the atom are bonded by a polar covalent bond are called polar molecules.

Note : In a polar covalent bond, the shared pair of elctrons lies more toward the atom which is more electronegative.

Example : HCl, H₂O & NH₃

Note : d means partial

Characteristics of covalent bond and covalent compounds : 

Characteristics of covalent bond : 

Covalent bond are formed by mutual sharing of electrons

Note : Shared pair of electrons is also called bonding pair of electrons.

Covalent bond is directional in nature because shared pair of electrons remain localized in a definite space between the two atoms.

Characteristics of covalent compounds : 

Physical State : The covalent compounds are generally gases or liquids, but compounds with high molecular masses are solids.

Example : Solid : Urea, Glucose, Naphthalene.

Liquids : Water, ethanol, benzene.

Gases : Methane, chlorine, hydrogen, oxygen

Melting and boiling points : Covalent compounds have low melting and low boiling points because intermolecular forces (cohesive forces) in covalent compounds are weaker than those in ionic compounds.

Note : Some exception like diamond and graphite which are covalent solids have very high M.P. & B.P.

Solubility : 

Covalent compounds generally dissolve readily in organic solvents but they are less soluble in water.

For example : Napthalene which is an organic compound dissolves readily in organic solvents like ether but is insoluble in water. However some covalent compounds like urea, glucose, sugar etc. are soluble in water. Some polar covalent compounds like ammonia and hydrochloric acid are soluble in water.

Conductivity : 

Covalent compounds do not conduct electricity because they contain neither the ions nor free electrons necessary for conduction, So they do not conduct electricity

For example : Covalent compounds like glucose, alcohol, carbon tetrachloride do not conduct electricity.

Differences between ionic and covalent compounds : 

ORGANIC COMPOUNDS :

The chemical compounds which are present in living organisms (plant and animal) are called organic compounds. The belief that formation of organic compounds was possible only in plants and animals led the scientists of early days to propose that Vital Force was necessary for the formation of such compounds. But the experimental work of Friedrich Wohler (German chemist) denied the idea of vital force when he prepared urea in his laboratory. (urea is an organic compound and waste product of urine).

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Allotropes of Carbon - Carbon and its Compounds, Class 10, Science

Allotropy / allotrops of carbon : 

The phenomenon of existance of allotropic forms of an element is called allotropy. Allotrops are the different forms of the same element having different physical properties but almost similar chemical properties. There are three allotrops of carbon these are diamond, graphite and fullerene.

Diamond : Diamond is a crystalline allotrope of carbon. Its atomic symbol & empirical formula is 'C'.
 

Structure of Diamond 

Structure : In diamond, each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. This tetrahedral arrangement of carbon atoms gives a rigid, three dimensional structure to diamond It is due to this rigid structure that diamond.

Is very hard crystalline structure.

Has high melting point.

Is non conductor of heat and electricity.

Properties : Pure diamond is a transparent and colourless solid.

Polished diamond sparkles brightly because it reflects most of the light (referactive index of diamond is 245)

Diamond are not attacked by acids, alkalis and solvents like water, ether, benzene or carbon tetrachloride but diamond is attacked by fluorine at 750°C.

C (Diamond) +2 F₂CF₄

Carbon Fluorine Carbontetrafluoride

The density of diamond is 3.51 g per cm³ at 20°C.

Uses : 

A saw fitted with diamond is used for sawing marbles.

A chip diamond is used for glass cutting.

Black diamonds are used in making drill.

Diamonds are used for making dice for drawing very thin wires of harder metals.

Diamonds are also used for making high precision tools for use in surgery such as, for the removal of cataract.

Diamond are used for making precision thermometers and protective windows for space crafts.

Graphite :

Graphite is also known as black lead it marks paper black. The name graphite has been taken from the greek word ''graphein" (which means to write) in reference to its uses as 'lead' in lead pencils.

Structure : 

Graphite is an opaque and dark grey solid. In a crystal of graphite the carbon atoms are arranged in hexagonal patterns in parallel planes. In a layer of graphite each carbon atom is strongly bonded to three carbon atoms by covalent bonds. Thus, one valence electron of each carbon atom is free in every layer of graphite crystal. The free electron makes graphite a good conductor of electricity.

Each layer is bonded to the adjacent layers by weak forces. As a result, each layer can easily slide over the other.

Properties : 

Graphite is greyish -black, opaque material having metallic (shiny) lustre.

It is soft and has a soapy (slippery) touch.

Graphite is lighter than diamond. The density of graphite is 2.26 g per cm³ at 20°C.

Graphite is a good conductor of heat and electricity.

Graphite has a very high melting point.

Graphite is insoluble in all common solvent.

Uses : 

For making electrodes in dry cells and electric arc furnaces.

Graphite is a good dry lubricant for those parts of machines where grease and oil cannot be used.

For making crucibles for melting metals.

For manufacturing lead pencils.

Graphite is used as neutron moderator in nuclear reactors.

For the manufacture of gramophone records and in electrotyping.

For the manufacture of artificial diamond.

Fullerene : 

Fullerene was discovered in 1985 by Robert F. Curl Jr, Harold Kroto and Richard E. Smally.

This molecule containing sixty atoms of carbon has been named Buckminster fullerene. Fullerens has been named after American architect and engineer R. Buckminster-fuller whose geodesic domes follow similar building principles.

Types of fullerene :

C₆₀, C₇₀, C₇₄ and C₇₈ are the members of the fullerene family. But C₆₀ is the most stable and most studied form of fullerenes.

Structure of fullerene : 

Buckminster fullerene molecule (C₆₀) is nearly spherical.

It consists of 12 pentagonal faces and 20 hexagonal faces giving it 60 corners. Thus, Buckminster fullerene has a hollow, cage-like structure.

In figure, ball like molecules containing C atoms.

Preparation : 

By electrically heating a graphite rod in atmosphere of helium.

By vaporising graphite by using laser.

Properties : 

Fullerene is soluble in benzene and forms deep violet colour solution.

Crystalline fullerene has semiconductor properties.

Compounds of fullerene with alkali metals are called fullerides and they are superconductors.

Uses :

As a superconductor.

As a semiconductor.

As a lubricants and catalyst.

As fibres to reinforce plastics.

Versatile Nature of Carbon : 

About three million (or thirty lakh) compounds of carbon are known. The existence of such a large number of organic compounds is due to the following characteristic features of carbon.

(1) CATENATION : Tendency to form Carbon-Carbon bond : 

"The property of forming bonds with atoms of the same element is called catenation".

Carbon has the maximum tendency for catenation in the periodic table. This is because of strong carbon carbon bonds as compared to other atoms.

l When two or more carbon atoms combine with one another, they form different types of chain such as

(i) Straight chains

(ii) Branched chains

(iii) Closed chain or ring chains

(2) Tetravalency of Carbon : 

The atomic number of carbon is 6.

The electronic configuration of carbon atom is 1s²,2s²,2p² .

It has four electrons in the outermost shell, therefore its valency is four. Thus carbon forms four covalent bonds in its compounds.

(3) Tendency to form multiple bonds : 

Due to small size, carbon can easily form double or triple bonds (called multiple bonds) with itself and with the atoms of other elements as nitrogen, oxygen, sulphur etc.

(4) Isomerism : 

Compounds having same molecular formula but different structural formulae are known as isomers and the phenomenon of existance of isomers is termed as isomersism.

Example : 

Hydrocarbon : 

Compounds formed from combination of carbon and hydrogen are known as hydrocarbon. Hydrocarbon on the basis of chain are mainly classified into two parts.

Saturated and unsaturated hydrocarbon : 

(1) Saturated Hydrocarbon : 

The hydrocarbons which contain only single carbon-carbon covalent bonds are called saturated hydrocarbons.

They are also called alkanes.

General formula for alkanes is C_nH_2n+2 where 'n' is the number of carbon atoms.

General formula of saturated hydrocarbon (C_nH_2n+2) 

No. of 'C' atoms Name Formula Structure 

1 Methane CH₄

2 Ethane C₂H₆

3 Propane C₃H₈

4 Butane C₄H₁₀  

5 Pentane C₅H₁₂

6 Hexane C₆H₁₄ 

(2) Unsaturated hydrocarbons : 

The hydrocarbon in which two carbon atoms are bonded to each other by a double (=) or a triple (º) bond is called an unsaturated hydrocarbon.

Unsaturated hydrocarbons are of two types viz. alkenes and alkynes.

(I) Alkenes : ()

The hydrocarbon in which the two carbon atoms are bonded by a double bond are called alkenes.

Their general formula is C_nH_2n where "n" is the number of carbon atoms.

General formula of alkenes : C_nH_2n 

No. of C atoms Name Formula Structure 

2 Ethene or C₂H₄

Ethylene  CH₂=CH₂ 

3 Propene or C₃H₆

Propylene CH₃-CH=CH₂ 

4. Butene or C₄H₈

Butylene CH₃-CH=CH-CH₃ 

or or

CH₂=CH-CH₂-CH₃  

(II) Alkyne (-CºC-) 

The hydrocarbon in which two carbon atoms are bonded by a triple bond are called alkyne. 

Their general formula is C_nH_2n-2 where 'n' is the number of carbon atoms.

General formula of alkynes : C_nH_2n-2 

No. of 'C'atoms Name Formula Structure 

2 Ethyne or C₂H₂ or H-CºC-H

Acetylene   HCºCH

3 Propyne or C₃H₄ or

Methyl acetylene H₃C-CºC-H

4 Butylene or C₄H₆ or

Dimethyl acetylene H₃C-CºC-CH₃

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Chains,Branches and Rings in Carbon Compounds - Carbon and its Compounds, Class 10, Science

CHAINS, BRANCHES AND RINGS :

The hydrocarbons may also have branched, closed chains or ring or cyclic structures.

Branched structure : 

The alkanes containing three or less carbon atoms do not form branches.

CH₄ CH₃-CH₃ CH₃-CH₂-CH₃

Methane Ethane Propane

l The alkane containing four carbon atoms (C₄H₁₀) has two types of arrangement of carbon atoms.

Closed chains or cyclic hydrocarbon : 

These hydrocarbons contains closed chain or rings of atoms in their molecules. These are of two types :

(A) Alicyclic hydrocarbon : 

These hydrocarbons contain a ring chain of three or more carbon atoms.

These cyclic compounds are named by prefixing cyclo before the name of corresponding straight chain hydrocarbon.

(B) Aromatic hydrocarbon : 

These have at least one benzene ring in their molecules.

It is a special type of ring of six carbon atoms with three double bonds in alternate positions.

Will you be my friend ? (functional group) : 

Carbon forms many compounds with hydrogen. But carbon also forms bonds with other atoms such as halogen, oxygen, nitrogen and sulphur. Therefore, carbon is said to be very friendly element.

These compounds are obtained by replacing one or more hydrogen atoms by other atoms such that the valency of carbon remains satisfied. The atom replacing the hydrogen atom is called heteroatom or Functional group.

Different organic compounds having same functional group have almost same properties these are called families.

Example :

Properties of CH₃-OH and CH₃-CH₂OH are similar and it is due to the presence of -OH (hydroxyl) group.

This group is known as alcoholic group.

Family of compounds having -OH group is called alcohols.

Some Functional Groups in Carbon compounds 

Hetero atom Functional Group Formula of Functional Group

Halogen atom  Halo -X

(F, Cl, Br, I) (Fluoro, Chloro, Bromo, Iodo) (F, -Cl, -Br, -I)

Oxygen 1. Alcohol -OH

2.Aldehydes

3.Ketones

4. Carboxylic acid

Nitrogen  1. Nitro -NO₂ 

2. Amines -NH₂

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Homologous Series and Nomenclature of Carbon Compounds - Carbon and its Compounds, Class 10, Science

HOMOLOGOUS SERIES : 

"A series of organic compounds having similar structures and similar chemical properties in which the successive members differ in their molecular formula by -CH₂ group".

The different members of the series are called homologous.

Characteristics of Homologous Series : 

All the member of a homologous series can be described by a common general formula.

Example : All alkane can be described by the general formula C_nH_2n+2.

Each member of a homologous series differ from its higher and lower neighbouring members by a common difference of -CH₂ group.

Molecular masses of the two adjacent homologues differ by 14 mass units, because molecular mass of -CH₂ group is 12 + 2 = 14.

All the members of a homologous series show similar chemical properties.

All the members of the series can be prepared by similar methods known as the general method of preparation.

Table : Some members of alkane, alkene and alkyne homologous series.

Alkane Alkene Alkyne 

C_nH_2n+2 C_nH_2n C_nH_2n-2 

Homologous series Homologous series Homologous series

Name  Formula Name Formula Name Formula 

Methane CH₄ - - - -

Ethane C₂H₆ Ethene C₂H₄ Ethyne C₂H₂

Propane C₃H₈ Propene C₃H₆ Propyne C₃H₄

Butane C₄H₁₀ Butene C₄H₈ Butyne C₄H₆

Pentane C₅H₁₂ Pentene C₅H₁₀ Pentyne C₅H₈

Hexane C₆H₁₄ Hexene C₆H₁₂ Hexyne C₆H₁₀

Activity : Calculate the difference in the formulae and molecular masses for (a) CH₃OH and C₂H₅OH (b) C₂H₅OH and C₃H₇OH and (c) C₃H₇OH and C₄H₉OH
 

Q. What is homologous series? Explain with an example.  [NCERT] 

Solution : 

Formula Molecular Mass Difference In 

(Calculated)  Formula   Molecular mass 

(a) CH₃OH 12 + 3 + 16 + 1 = 32 -CH₂ 14

C₂H₅OH 24 + 5 + 16 + 1 = 46

(b) C₂H₅OH 24 + 5 + 16 + 1 = 46 -CH₂ 14

C₃H₇OH 36 + 7 + 16 + 1 = 60

(c) C₃H₇OH 36 + 7 + 16 + 1 = 60 -CH₂ 14

C₄H₉OH 49 + 9 + 16 + 1 = 74

Conclusion :

(i) Yes, all these compounds are the members of a homologous series for alcohols.

(ii) CH₃OH, C₂H₅OH, C₃H₇OH and C₄H₉OH -increasing carbon atoms. These four compounds form a
homologous series.

Homologous series containing functional groups. 

Aldehydes : 

HCHO, CH₃CHO, CH₃CH₂CHO, CH₃CH₂CH₂CHO

Carboxylic acids : HCOOH, CH₃COOH, CH₃CH₂COOH,CH₃CH ₂CH₂COOH

Amines : CH₃NH₂, CH₃CH₂NH₂,CH₃ CH₂CH₂NH₂.

Ketones : CH₃COCH₃, CH₃COCH₂CH₃, CH₃COCH₂CH₂CH ₃

Haloalkanes : CH₃X, CH₃CH₂X, CH₃CH₂CH₂X, CH₃CH₂CH₂CH₂ X

How do physical properties change in a homologous series of hydrocarbons. 

The physical properties of the various members of a homologous series change regularly with an increases in the molecular mass.

(i) Melting and boiling points : Melting point and boiling point of hydrocarbon in a homologous series increases with an increase in molecular mass.

(ii) Physical State : 

Hydrocarbons containing lesser number of carbon atoms are gases. 

Hydrocarbons containing large number of carbon atoms are solids. 

Hydrocarbon containing intermediate number of carbon atoms are liquid.

Example : Hydrocarbon containing 1-4 carbon atoms are gases, these containing 513 carbon atoms are liquid and those containing more than 14 carbon atoms are solids.

Nomenclature of carbon compounds : 

Carbon compounds can be called by their common names, but, then remembering millions of compounds by their individual names may be very difficult. Due to this reason, the International Union of Pure and Applied chemistry (IUPAC) has devised a very systematic method of naming these compounds.

Naming a carbon compound can be done by the following methods. 

The number of carbon atoms in the molecule of a hydrocarbon is indicated by the following stems.

No. of carbon atom : 1 2 3 4 5 6 7 8  9 10 

Stem  Meth Eth Prop But Pent Hex Hept Oct Non Dec.

Example : Saturated hydrocarbon.

Alkane → Meth + ane = Methane

Unsaturated hydrocarbon

Alkene → Eth + ene = Ethene

Alkyne → Eth + yne = Ethyne

In case of functional group is present, it is indicated in the name of compound with either a prefix or a suffix.

Identify the longest continuous chain of carbon atoms. This gives the name of parent hydrocarbon.

In the case of any substituent appropriate prefix is added before the name of parent hydrocarbon.

In the case of a functional group, the ending 'e' in the name of the parent hydrocarbon is replaced by the appropriate suffix.

Functional Group : 

"Functional group may be defind as an atom or a group of atoms which is responsible for most of the characteristic chemical properties of an organic compound".

The prefixes and suffixes of some substituents/functional group 

Substituents/ Prefix Suffix Example 

Functional group Structure  Name 

1. Halogen : Chlorine Chloro - CH₃-CH₂-CH₂-Cl Chloropropane

Bromine Bromo - CH₃-CH₂-CH₂-Br Bromopropane

Iodine Iodo - CH₃-CH₂-CH₂-I Iodo propane

2. Alcohol - ol CH₃-CH₂-CH₂-OH propanol

3. Aldehyde - al  propanal

4. Ketone - one   Propanone

5. Carboxylic acid - oic acid  Propanoic acid

6. Single bond (alkane) - ane CH₃-CH₂-CH₃ Propane

7. Double bond (Alkene) - ene CH₃-CH = CH₂ Propene

8. Triple bond (Alkyne) - yne CH₃-CHºCH Propyne

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Chemical Properties of Carbon & its Compounds, Combustion and Oxidation Reactions - Carbon and its Compounds, Class 10, Science

Chemical Properties of Carbon compound :

All carbon compounds show some common characteristic properties. As most of the fuels we use are either carbon or its compounds. Some such properties are described here :

Combustion :

Combustion is a chemical process in which heat and light (in the form of flame) are given out

The process of combustion, is a rapid oxidation reaction of any substance in which heat and light are produced.

Combustion of some common substance : 

Combustion of Carbon : Carbon (or charcoal) burn in air or oxygen to give CO₂ producing heat and light.

C(s) + O₂(g)  CO₂(g) + Heat + light

Carbon Oxygen Carbon dioxide

Combustion of Hydro Carbon : Hydrocarbons burn to produce carbon dioxide (CO₂), water (H₂O) and heat and light.

CH₄(g) + O₂(g)  CO₂(g) + H₂O(g) + Heat + Light

Methane

Note : Natural gas and biogas contain methane. So, burning of natural gas and biogas are also combustion reactions.

Burning of LPG (Butane) produces CO₂, H₂O heat and light.

C₄H₁₀(g) + O₂(g)  4CO₂(g) + 5H₂O(g) + Heat + Light

Butane/LPG

Combustion of cellulose :

Combustion of cellulose (like wood, cotton cloth and paper) gives CO₂, H₂O heat and light. Cellulose is a carbohydrate and can be described by the formula (C₆H₁₀O₅)_n .

(C₆H₁₀O₅)_n (s) + 6nO₂(g)  6nCO₂(g) + 5n H₂O(g) + Heat + light

Cellulose

Combustion of alcohol :

C₂H₅OH(l) + 3O₂(g)  2CO₂(g) + 3H₂O(g) + Heat + light

Ethanol oxygen (in air)

Activity : To observe the combustion of given organic compounds.

Materials : Benzene, naphthalene, Camphor, alcohol (ethanol). Spirit, acetone.

Procedure :

1. Take each compound on iron spatulla and burn them in bunsen burner.

2. Record the type of flame produced.

3. Put a metal plate above the flame and observe whether or not there is black carbon deposition.

Observation :

Compound used Flame Produced Deposit

Benzene Smoky flame Carbon deposited

Naphthalene Smoky flame Carbon deposited

Camphor Smoky flame Carbon deposited

Alcohol Non-Luminous flame No Carbon deposited

Spirit Non-Luminous flame No Carbon deposited

Acetone Non-Luminous flame No Carbon deposited

Conclusion :

Benzene, naphthalene, camphor burn with smoky flame and carbon particles get deposited they undergo
incomplete combustion due to excess of carbon content.

Alcohol, spirit and acetone burn with non-Luminous flame and no carbon gets deposited. They under go complete combustion, therefore produce more heat.

Activity : To study the different types of flames / presence of smoke.

Material required : Bunsen burner.

Procedure :

1. Light the bunsen burner.

2. Close the air hole and observe the colour of the flame.

3. Put a metal plate over it and observe the nature of deposit.

4. Open the air regulator to allow flow of air.

5. Observe the colour of flame.

6. Put a metal plate and observe the nature of deposit.

Observation :

Air Regulator Colour of flame Nature of deposit Nature of flame Temperature

Closed Yellow sooty flame Black carbon deposited Reducing flame low

Open Bluish flame No black carbon deposited Oxidising flame High

Conclusion : Keep the air regulator open to get oxidising, non-sooty flame which has high temperature and does not lead to black deposits.

Combustion and the nature of flame :

(i) Saturated hydrocarbon such as, methane, ethane, propane, butane and natural gas and LPG burn with a
blue flame in the presence of sufficient / excess of air / oxygen.

(ii) In the presence of limited amount of air / oxygen, saturated hydrocarbon, such as, methane, butane. etc
give smoky flame.

(iii) Unsaturated hydrocarbon such as ethene, ethyne etc. burn with a luminous / yellow smoky flame.

(iv) The gas / kerosene stove used at home has inlets for air so that a sufficiently oxygen rich mixture is burnt to give a clean blue flame. If you carefully observe the bottoms of vessels getting blackened, it is clear indication
that the air holes are blocked and the fuel is getting wasted.

(v) Fuels, such as coal and petroleum, have some amount of nitrogen and sulphur in them. Combustion of coal

and petroleum results in formation of oxides of sulphur and nitrogen (such as sulphur dioxide, nitric oxide,
nitrogen peroxide) which are major pollutants in the environment.

Formation of Coal and Petroleum :

Coal and petroleum have been formed from biomass which has been subjected to various biological and geological processes.

Coal is a naturally occurring black mineral and is a mixture of free carbon and compounds of carbon containing hydrogen, oxygen, nitrogen and sulphur. It is not only a good fuel but is also a source of many organic compounds. It is found in coal mines deep under the surface of earth.

Coal is believed to be formed from fossils which got buried inside the earth during earthquakes and volcanoes which occurred about 300 million years ago. Due to huge pressure and temperature inside the earth and in the absence of air, the fossils fuels (vegetable matter or wood, etc.) were converted into coal. The slow chemical processes of the conversion of wood into coal is called carbonisation. Since coal is formed by slow carbonisatiion of plants and fossils, it produces many important carbonisation products like peat, lignite, bituminous and anthracite etc. and is itself known as fossil fuel. Coal is also a non-renewable source of energy.

Petroleum is a complex mixture containing various hydrocarbons (compounds of carbon and hydrogen) in addition to small amounts of other organic compounds containing oxygen, nitrogen, and sulphur. It is a dark coloured, viscous and foul smelling crude oil. The name petroleum is derived from latin words : "petra" meaning rock and "oleum" meaning oil. Since petroleum is found trapped between various rocks, it is also known as rock oil.

Oxidation :

Carbon and its compounds can be easily oxidised on combustion (or burning). During combustion / burning, the compounds gets oxidised completely to different products, depending upon the nature of the oxidising agents.

Carbon gives carbon monoxide or carbondioxide depending upon the oxygen available.

2C(s) + O₂(g) → 2CO(g)

Carbon Oxygen(limited) Carbon monoxide

C(s) + O₂(g) → CO₂(g)

(excess) Carbon dioxide

Hydrocarbon when oxidised give different product as follows :

CH₄(g) + 2O₂(g)  CO₂(g) + 2H₂O(g)

Methane Oxygen(excess)

2CH₄(g) + 3O₂(g)  2CO(g) + 4H₂O(g)

Methane Oxygen(Limited)

Alcohols also give different products on oxidation depending upon the reaction conditions.

Example :

Alcohols on oxidation with certain oxidising agents such as chromic anhydride in acetic acid, yield corresponding aldehydes, where as on oxidation with alkaline potassium permanganate (or acidified potassium dichromate) corresponding carboxylic acid is formed, as given below :

CH₃CH₂OH(l) + [O]  CH₃CHO + H₂O

Ethanol Nascent oxygen Ethanal (an aldehyde)

CH₃CH₂OH(l) + 2[O]  CH₃COOH + H₂O

Ethanoic acid

Activity : To study the reaction of ethanol with alkaline potassium permanganate :

Material required : Ethanol, alkaline KMnO₄, test tube.

Procedure : 

Take about 3 ml of ethanol in a test tube.

Add 5% solution of alkaline KMnO₄ drop by drop into this solution.

Observe the colour of alkaline KMnO₄ after adding initially as well as finally.

Observation : The colour of KMnO₄ gets discharged in the begining. When excess of KMnO₄ is added, the colour of KMnO₄ does not disappear because whole of ethanol gets oxidised to ethanoic acid.

CH₃CH₂OH  CH₃COOH + H₂O

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Addition Reactions, Substitution Reactions and Properties and Reactions of Ethanol (Alcohol) - Carbon and its Compounds, Class 10, Science

Addition reaction :

All unsaturated hydrocarbons (unsaturated carbon compounds) react with a molecule like H₂. X₂. H₂O etc. to form another saturated compounds are called addition reactions.

Unsaturated hydrocarbons add hydrogen, in the presence of catalysts, such as nickel or palladium to give saturated hydrocarbons.

Note : Catalysts are substance that cause a reaction to occur or proceed at a different rate without the
reaction it say being affected.

Addition of hydrogen to ethene :

Addition of hydrogen to ethyne :

Addition of hydrogen to a unsaturated carbon compound is called hydrogenation reaction.

Certain vegetable oils such as ground nut oil, cotton seed oil and mustard oil, contain double bonds (C = C) and are liquids at room temperature. Because of the unsaturation, the vegetable oils undergo hydrogenation, like alkenes, to from saturated products called vanaspati ghee. Which is semi-solid at room temperature.

Vegetable oils (Unsaturated oil) + Hydrogen  Vanaspati Ghee (Saturated ghee)

Substitution reactions :

The reactions in which one or more hydrogen atoms of a hydrocarbon are replaced by some other atoms or groups are called substitution reaction.

Example :

Methane reacts with chlorine (or bromine) in the presence of sunlight and undergo substitution reaction. It is called photochemical reaction because it takes place in presence of sunlight.

CH₄(g) + Cl₂(g)  CH₃Cl(g) + HCl(g)

Chloromethane

CH₃Cl(g) + Cl₂(g) CH₂Cl₂(g) + HCl(g)

Dichloromethane

CH₂Cl₂(g) + Cl₂(g) CHCl₃(g) + HCl(g)

Trichloromethane(chloroform)

CHCl₃(g) + Cl₂(g) CCl₄(l) + HCl(g)

Tetra chloromethane

(carbon tetra chloride)

Some important carbon compounds :

Ethanol (Ethyl alcohol, C₂H₅OH) :

Ethanol is the second member of the homologous series of alcohols.

Preparation : By the fermentation of carbohydrates (sugar or starch).

Ethanol is prepared on commercial scale by fermentation of sugar. Fermentation is allowed to take place at
298 303 K in the absence of air. This is ethanol (ethyl alcohol) gets oxidised to ethanoic acid
(acetic acid) in the presence of air.

C₁₂H₂₂O₁₁ + H₂O  C₆H₁₂O₆ + C₆H₁₂O₆

Sucrose Glucose Fructose

C₆H₁₂O₆ 2C₂H₅OH + 2CO₂(g)

Glucose/Fructose Ethanol (ethyl alcohol) Carbon dioxide

Physical properties : 

Physical state/colour and odour : Pure ethanol is a colourless liquid having a pleasant smell and a burning taste.

Boiling and Freezing points : It is a volatile liquid with a boiling point of 78.1°C, and freezing point is 118°C.

Density : Ethanol is lighter than water as its density is 0.79 g ml¹ at 293 K.

Solubility : Ethanol is miscible with water in all proportions, due to the formation of hydrogen bonds with water molecules.

Conductivity : Ethanol is a covalent compound and does not ionise easily in water, hence it is a neutral compound.

Action on Litmus : Ethanol is a neutral compound. So, it has no effect on the colour of litmus.

Chemical propertIes of ethanol : 

Combustion (or burning) : Ethanol is highly inflammable liquid and readily burn in air with blue flame to form water vapour, carbon dioxide and evolving heat. Thus, combustion of ethanol is an exothermic reaction.

C₆H₅OH (l) + 3O₂(g)  2CO₂(g) + 3H₂O(g) + Heat

Reaction with sodium metal : Ethanol reacts with sodium metal to produce sodium ethoxide and hydrogen gas is evolved.

2C₂H₅OH (l) + 2Na(s)  2C₂H₅ONa + H₂(g)

Ethanol Sodium metal Sodium ethoxide Hydrogen

Activity : To study the reaction of ethanol with sodium metal.

Materials : Ethanol, dry piece of sodium metal test tube.

Procedure : 

Take ethanol in a test tube.

Add a dry piece of sodium metal.

Bring a burning matchstick near the gas evolved to test it and record observation.

Observation : The gas burns in air with a pop sound which is the characteristics of hydrogen gas.

Conclusion : Alcohol react with sodium metal to liberate hydrogen gas.

Reaction with ethanoic acid (Esterification reaction) :

The reaction in which an alcohol reacts with acetic acid in the presence of conc. H₂SO₄ to form an ester is called esterification.

CH₃COOH(l) + C₂H₅OH(l)  CH₃COOC₂H₅(l) + H₂O(l)

ethanoic acid ethanol ehtyl ethanoate

(acetic acid) (ethyl acetate)

sweet smelling compound

Note : Ester are sweet-smelling compounds and are used for making perfumes.

Reaction with conc. sulphuric acid (Dehydration) :

Ethanol when heated with excess of concentrated sulphuric acid at 443 K, gets dehydrated to give ethene.

C₂H₅OH(l) + H₂SO₄(Conc.)  H₂C = CH₂(g) + H₂O(l)

ethanol excess ethene

Note : The concentrated sulphuric acid can be regarded as a dehydrating agent which remove water from ethanol.

Uses of ethanol : 

Ethanol is present in alcoholic beverages such as beer, wine, whisky.

As a solvent for paints, varnishes-dyes, cosmetics, perfumes, soaps and synthetic rubber etc.

Ethanol is used in cough syrups, digestive syrups and tonics.

A mixture of 80% rectified spirit and 20% petrol is called power alcohol. It is used as fuel in cars and aeroplanes.

A mixture of ethanol and water has lower freezing point than water this mixture is known as antifreezing and is used in radiators of vehicles in cold countries and at hill stations.

As an antiseptic to sterilize wounds and syringes in hospitals.

For the manufacture of terylene and polythene.

As a preservative for biological specimens.

Ethyl alcohol is used as hypnotic (induces-sleep).

Harmful effects of Alcohols : 

Consumption of small quantities of dilute ethanol causes drunkenness. Even though this practice is condemned, it is a socially widespread practice. However, intake of even a small quantity of pure ethanol (called absolute alcohol) can be lethal. Also long-term consumption of alcohol leads to many health problems.

When large quantities of ethanol are consumed, it tends to slow metabolic processes and to depress the central nervous system. This results in lack of coordination, mental confusion, drowsiness, lowering of normal inhibitions and finally stupor (unconscious state of wild)

Drinking of alcohol over a long period of time damages liver.

Denatured Alcohol : 

Ethanol to which certain poisonous and nauseating substances like methyl alcohol, pyridine etc. have been added is termed denatured alcohol.

Note : To prevent the misuse of ethanol (Alcohol), industrial alcohol is coloured blue so that it can be recognised easily.

Harmful effects of denatured alcohol : 

Methanol is highly poisonous compound for human beings. Methanol when taken, even in small amount, can cause death.

Methanol gets oxidised to methanal in the liver, which causes coagulation of protoplasm.

Methanol also effects the optic nerve and cause blindness.

Ethanoic acid (acetic acid) CH₃COOH : 

Ethanoic acid is commonly called acetic acid and belongs to the homologous series of carboxylic acid and is represented as CH₃COOH.

5-8% solution of acetic acid in water is called vinegar and is used for preservating foods like sausage, pickles.

Physical properties : 

At ordinary temperature, ethanoic acid is a colourless liquid with a strong pungent smell and sour taste.

Its boiling point is 391 K and its density at 273 K is 1.08 (heavier than water).

It is miscible with water due to the formation of hydrogen bonds with water molecules.

On cooling at 289.6 K, it turns in ice-like crystals, hence named as glacial acetic acid. 

It dissolves sulphur, iodine and many other organic compounds.

It dimerise when dissolved in benzene.

2CH₃COOH  (CH₃COOH)₂

Ethanoic acid Dimer

Activity : To determine pH of acetic acid and hydrochloric acid.

Material : Acetic acid (1M), HCl (1M), blue litmus paper, universal indicator.

Procedure : Take two strips of blue litmus paper.

Put a few drops of HCl on one of them and few drops of acetic acid on the other.

Observe the change in colour.

Take 1 ml of acetic acid in a test tube and add a few drops of universal indicator.

Take 1 ml of HCl in a test tube and add few drops of universal indicator.

Observation : Both acetic acid and HCl turn blue litmus red showing that they are acidic in nature. pH of acetic acid and HCl are not equal.

Conclusion : HCl is strong acid than CH₃COOH, therefore, pH of HCl will be lower than that of acetic acid.

Chemical properties : 

Reaction with alcohols (Esterification reaction) :

Ethanoic acid reacts with ethanol in the presence of conc. H₂SO₄ to form ethyl ethanoate which is an ester.

CH₃COOH(l) + C₂H₅OH(l)  CH₃COOC₂H₅ + H₂O

Ethanoic acid Ethanol Ethyl ethanoate (ester)

the reaction of carboxylic acid with an alcohol to form an ester is called "estrification".

Note : Ester can be hydrolysed in the presence of an acid or a base to give back the parent carboxylic acid and the alcohol.

Example :

(i) Ethyl ethanoate on acid hydrolysis gives ethanoic acid and ethanol.

CH₃COOC₂H₅(l) + H₂O(l)  CH₃COOH(aq.) + C₂H₅OH

(ii) Hydrolysis of ester in the presence of base (alkali) is called "Saponification reactions".

CH₃COOC₂H₅(l) + NaOH(aq)  CH₃COONa + C₂H₅OH

Ethyl ethanoate Sodium Hydroxide Sodium ethanoate Ethanol

Note : Alkaline hydrolysis of higher esters is used in the manufacture of soaps.

Activity : To study the esterification process using ethanol and acetic acid.

Materials : Beaker, water, test tube, ethanol, acetic acid.

Conc. H₂SO₄ etc.

Procedure : Take 2ml of ethanol in a test tube.

Add 2ml of ethanoic acid (acetic acid) in to it.

Add few drops of conc. H₂SO₄.

Warm it in a beaker containing water.

Observation : Pleasant fruity smelling compound (called ester) is formed.

Conclusion : Acetic acid reacts with alcohol in presence of conc. H₂SO₄ which act as a dehydrating agent to form ester.

Reaction with sodium carbonate and sodium hydrogen carbonate :

Ethanoic acid decomposes sodium hydrogen carbonate and sodium carbonate with a rapid evoluation of carbon-dioxide gas.

NaHCO₃(aq) + CH₃COOH(aq)  CH₃COONa(aq) + H₂O(l) + CO₂(g)

Sodium Ethanoic acid Sodium ethanoate hydrogen carbonate

Na₂CO₃(aq) + 2CH₃COOH(aq)  2CH₃COONa(aq) + H₂O(l) + CO₂(g)

Sodium carbonate Ethanoic acid Sodium ethanoate

Note ; Reactions of ethanoic acid with NaOH, NaHCO₃, Na₂CO₃ and active metals show that the hydrogen present in the carboxyl (COOH) group is acidic in nature.

Activity : To study the reaction of carboxylic acid with sodium carbonate and sodium hydrogen carbonate.

Material : Ethanoic acid, Sodium carbonate, Sodium hydrogen carbonate.

Procedure : 

l Take 1g of Na₂CO₃ and add 2ml of ethanoic acid into it.

l Pass the gas formed through lime water and note down the observation.

l Repeat the same procedure with sodium hydrogen carbonate and record observation.

Observation : Brisk effervescence due to carbon dioxide formed which turns lime water milky.

Conclusion : Acetic acid react with Na₂CO₃ and NaHCO₃ to liberate CO₂ gas.

Uses of ethanoic acid : 

Ethanoic acid is used in the manufacture of various dyes, perfumes and rayon.

It is used for making vinegar.

It is used for making white lead [2PbCO₃ . Pb(OH)₂] which is used in white paints.

Its 5% solution is bactericidal (destroys bacteria).

It is used in preparation of cellulose acetate which is used for making photographic film.

It is used for coagulation of the latex.

It is used for preparation of 2, 4-dichloro phenoxy ethanoic acid which is used as herbicide.

Aluminium acetate and chromium acetate are used as mordants in dyeing and water proofing of fabrics.

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Cleansing Action of Soaps and Detergents - Carbon and its Compounds, Class 10, Science

Soap and detergents : 

Soap and detergents are substances whcih are used for cleaning. There are two types of detergents :

1. Soap 2. Synthetic detergents

Soap : A soap is the sodium or potassium salt of a long-chain fatty acids (carboxylic acid or glycerol).

Activity : 

Take about 10mL of water each in two test tubes.

Add a drop of oil (cooking oil) to both the test tubes and label them as A and B.

To test tube B, add a few drops of soap solution. Now shake both the test tubes vigourously for the same period of time.

Can you see the oil and water layers separately in both the test tubes immediately after you stop shaking them.

Leave the test tubes undisturbed for some time and observe. Does the oil layer separate out ? In which test tube does this happen first ?

this activity demonstrate effect of soap in cleasing as we know that most of the dirt is oily in nature and oil does it disolve in water.

But know the question arise what are soap ? What are the detergent which one is more effect. How the work. Soap is sodium or potassium salt a long change fatty acid (Carboxylic acid or Glycerol)

A soap has large non ionic hydrocarbon group and an ionic group. COONa.

Ex.of soap are :

(1) Sodium stearate (C₁₇H₃₅COONa)

(2)Sodium plamitate (C₁₅H₃₁COONa)

Soap are basic in nature so soap solution turn red litmus to blue.

Preparation of Soap : 

The soap is prepared by heating animal fats or vegetable oils (olive oils, castor oil or palm oil) with sodium hydroxide or potassium hydroxide.

The process of formation of soap by the hydrolysis of fat or oil with alkali is called saponification.

Oil or Fat + Sodium hydroxide ® Soap + glycerol

Structure : 

l A soap molecule contains two parts that interact differently with water, one part is a long hydrocarbon (non-polar) chain, and other belongs to the -COONa group (Hydrophillic).

A soap molecule may be represented as :

Cleansing action of soap :

The molecules of soap are sodium or potassium salts of long chain carboxylix acids. The ionic end of soap dissolves in water while the carbon chain dissolves in oil. The soap molecules, thus form structures called micelles where one end of the molecules is towards the oil droplet while the ionic end faces outside. This form an emulsion in water. The soap micelle thus helps in dissolving the dirt in water and we can wash out clothes clean.

Effect of soap in cleaning 
 

Activity : Take two clean test tubes and label them as 'A' and 'B'. Now put 10ml of hard water in each of the two test tubes. Add five drops of soap solution in test tube 'A' and five drops of detergent solution in test tube 'B'. Shake the two test tubes for the same period and observe if both the test tubes have the same amount of foam. Find out in which of the two test tubes a curdy white mass is formed.

In which test tube do you get more form ?

We get more foams in test tube .................... .

A white curdy precipitate is formed in test tube...............

Result (Conclusion) : Soaps are not effective in acidic medium.

When soaps is used for washing clothes with hard water, a large amount of soap is wasted in reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum, before it can be used for the real purpose of washing soap. A large amount of soap is needed for washing clothes. When the water is hard.

Activity : 

Take two test tubes with a about 10 mL of hard water in each.

Add five drops of soap solution to one and five drops of detergent solution to the other.

Shake both test tubes for the same period

Do both test tubes have the same amount of foam ?

In which test tube is a curdy solid formed ?

Observation :

Test tube in which ............................is present contain more amount of foam.

Curdy solids is form in the test tube containing ....................

Conclusion : Detergents have better cleasing action than soap. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water. Detergents are usually used to make shampoos and products for cleaning clothes.  
 

Differences between soaps and synthetic detergents : 

Soaps Synthetic detergents 

1.  Soaps are sodium salts of long chain fatty acid 1. Synthetic detergents are the sodium salts of long-chain

(carboxylic acids) benzene sulphonic acids or the sodium salt of a long -
chain alkyl hydrogen sulphate

2. The ionic part of soap is -COO^-Na⁺ 2. The ionic part in a synthetic detergents is -SO₃^-Na⁺

3. They are prepared from animal fats 3. The are prepared from hydrocarbons

or plant based oils. extracted from coal or petroleum.

4. Their efficiency decreases in hard water 4. Their efficiency is unaffected in hard water.

5. Soaps take more time to dissolve in water. 5. Synthetic detergents dissolve faster than soaps in water

6. They are biodegradable 6. Some synthetic detergents are not biodegradable.

7. Examples :  Sodium sterate, sodium palmitate 7. Example : Sodium lauryl sulphate, sodium dodecyl
benzene sulphonate.

Soap :

Structure : 

The hydrocarbon chain is non-polar and water -hating (hydrophobic), while the other part is polar or water loving (hydrophilic).

Hydrophilic part makes the soap soluble in water and hydrophobic part makes the soap insoluble.

When soap is added to water, the soap molecules assume a configuration which increases the interaction of the water loving heads with the water molecuels, and decreases the interaction between the water hating tails with the water molecules.

The hydrophobic part of the soap molecules traps the dirt and the hydrophilic part makes the entire molecules soluble in water. Thus, the dirt gets washed away with the soap.

The water-hating, non polar tails clump together in a radial fashion with the water-loving, polar heads remaining at the periphery of the clump, these clumps or droplets of soap molecules are called micelles.

Disadvantage of soap : 

Soaps are not effective in hard water : Hard water contains calcium ions (Ca²⁺) and magnesium ions (Mg²⁺). These ions react with the carboxylate ions (RCOO^-) of the soap forming an insoluble precipitate called scum. For example, soap like sodium stearate (C₁₇H₃₅COONa) reacts with calcium and magnesium ions as per the following chemical equation.

2C₁₇H₃₅COONa + Ca²⁺(aq) ® (C₁₇H₃₅COO)₂ Ca ¯ + 2Na⁺ (aq)

Sodium stearate (In hard water) Calcium stearate Sodium ion

2C₁₇H₃₅COONa + Mg²⁺(aq) ® (C₁₇H₃₅COO)₂ Mg ¯ + 2Na⁺ (aq)

Sodium stearate (In hard water) Magnesium stearate(scum) Sodium ion

The scum gets attached to the clothes, utensils and even skin and thus, interferes with the cleansing ability of the additional soap and makes the cleansing of clothes difficult. Moreover, large amount of soap is wasted in reacting with calcium and magnesium ions present in hard water.

Soaps are not effective in acidic medium : In presence of hydrogen ions (H⁺ ions), i.e. in acidic medium, the carboxylate ions of soap (RCOO^- ion) interact with hydrogen ions (H⁺) to form undissociated (free) fatty acid as represented below :

C₁₇H₃₅COO^-(aq) + H⁺ C₁₇H₃₅COOH

carboxylate ion Carboxylic acid (Unionised)

As the fatty acids are weak acids, so they do not get ionised and hence, micelle formation is hindered, thus, adversely affecting the cleansing property of soaps.

You will observe that the amount of foam in the two test tubes in different. The foam is formed to a greater extent in test tube 'B' (containing detergent solution), while formation of a curdy white mass will be observed in test tube 'A'. This activity clearly indicates that detergents can be used for cleansing purpose, even with hard water.

SYNTHETIC DETERGENTS : 

Synthetic detergents are called soapless soap because they are not prepared from fatty acid and alkali.

Synthetic detergents are sodium salts of sulphonic acids, i.e. detergents contain a sulphonic acid group (-SO₃H), instead of a carboxylic acid group (-COOH), on one end of the hydrocarbon chain.

Properties of synthetic detergents : 

Synthetic detergents do not react with the ions present in hard water. Hence, synthetic detergents have no problem in forming lather with hard water, i.e. their efficiency is not affected by hard water.

Synthetic detergents can be used even in acidic solution and sea water, whereas soap cannot be used in the acidic solution (due to precipitation of free acids)

Synthetic detergents do not form insoluble salts of calcium or magnesium with hard water. Hence, lesser amounts of synthetic detergents are required for washing.

Washing powder : 

Washing powders used for washing clothes contain only about 15 to 30 percent detergents by mass. The remaining part is made of the following.

(i) Sodium sulphate and sodium silicate which keep the powder dry.

(ii) Sodium tripolyphosphate or sodium carbonate which maintains alkalinity for removing dirt.

(iii) Carboxymethylcellulose (CM-Cellulose) which keep the dirt particle suspended in water.

(iv) Sodium perborate (a mild bleaching agent) which impart whitenes to the materials (clothes, etc.) being washed.

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PREVIOUS YEARS' BOARD QUESTIONS :

1. An organic compound 'A' has molecular formula C₂H₄O₂ and is acidic in nature. On heating with alcohol and conc. sulphuric acid, vapours with pleasant or fruity smell are given out. What is this chemical compound 'A' and what is the chemical equation involved in the reaction ? (CBSE All India 1999) 

Ans. The compound 'A' with molecular formula C₂H₄O₂ is ethanoic acid (acetic acid). Upon heating with ethanol (ethyl alcohol) and concentrated sulphuric acid, ethyl ethanoate (ethyl acetate) is formed as the product. It is an ester with pleasant or fruity smell. The reaction is known as esterification reaction.

CH₃COOH + C₂H₅OH CH₃COOC₂H₅ + H₂O

Ethanoic acid ('A') Ethanol Ethyl ethanoate (Ester)

2. An organic compound 'A' is a constituent of antifreeze and has the molecular formula C₂H₆O. Upon reaction with alkaline KMnO₄, the compound 'A' is oxidised to another compound 'B' with formula C₂H₆O₂. ldentify the compounds 'A' and 'B'. Write the chemical equation for the reaction which leads to the formation of 'B'.  (CBSE All India 2000 Comptt.) 

Ans. The compound 'A' is ethanol and with alkaline KMnO₄, it is oxidised to ethanoic acid 'B'. The chemical equation for the reaction is :

C₂H₅OH  CH₃COOH

Ethanol (A) Ethanoic acid (B)

3. Name the functional groups present in the following compounds :

(i) CH₃—CH₂—CH₂ —OH (ii) CH₃—CH₂—CH₂ —COOH

(iii) CH₃—CH₂—CHO (iv) CH₃—CO—CH₂—CH ₃

Ans. (i) —OH (ol) (ii) —COON (oic acid) (iii) —CHO (al) (iv) —CO— (one)

4. Write the formulae of the compounds and name the functional groups present in each of them

(i) Ethanoic acid (ii) Propanone (iii) Nitromethane  (C.B.S.E. Delhi 2005) 

Ans. (i) Ethanoic acid : CH₃COOH (oic acid)

(ii) Propanone : CH₃COCH₃ (one)

(iii) Nitromethane : CH₃NO₂ (nitro)

5. Name the enzyme which converts :

(i) milk into curd (yogurt)

(ii) cane sugar into glucose and fructose

(iii) glucose into ethanol.  (C.B.S.E. Foreign 2005) 

Ans. (i) Lactase converts milk into curd

(ii) Invertase converts cane sugar (sucrose) into glucose and fructose

(iii) Zymase converts glucose into ethanol.

6. (i) Name the gas evolved during fermentation process.  (C.B.S.E. Delhi 2006)

(ii) List the two products formed when enzyme invertase acts on sugar present in molasses.

Ans. (i) CO₂ gas is evolved accompanied by brisk effervescence.

(ii) Glucose and fructose are the products when enzyme invertase acts on sucrose (Cl₂H₂₂O₁₁) present in molasses.

7. Complete the following equations and write the names of the products formed. (C.B.S.E. Delhi 2007)

(i) CH₃COOH + NaOH  (ii) C₂H₅OH + O₂

(iii) CH₃COOH + C₂H₅OH

Ans. (i) CH₃COOH + NaOH  CH₃COONa + H₂O

Ethanoic acid Sod. ethanoate

(ii) C₂H₅OH + O₂ CH₃COOH + H₂O

Ethanol Ethanoic acid

(iii) CH₃COOH + C₂H₅OH  CH₃COOC₂H₅ + H₂O

Ethanoic acid Ethanol Ethyl ethanoate

8. Name the organic compound present in vinegar. Write a chemical equation which represents the commercial method for the preparation of this compound from methanol.  (C.B.S.E. All India 2007) 

Ans. The organic compound present in vinegar is ethanoic acid also called acetic acid. For its commercial preparation.

9. (a) Why does carbon form compounds by covalent bonding ?

(b) An organic acid 'X' is a liquid which often freezes during winter time in cold countries. It has the molecular
formula C₂H₄O₂. On warming with ethanol in the presence of a few drops of sulphuric acid, a compound
`Y' with sweet smell is formed.

(i) Identify X and 'Y'. (ii) Write chemical equation for the reaction involved. (C.B.S.E. Delhi 2008) 

Ans. (a) Carbon forms a large number of organic compounds due to the self linking property known as catenation.

(b) The available information suggests that the organic acid X with molecular formula C₂H₄O₂ is ethanoic acid
(CH₃COOH). It reacts with ethanol in the presence of a few drops of sulphuric acid on warming to give
ethyl ethanoate ester with a pleasant smell.

CH₃COOH + C₂H₅OH  CH₃COOC₂H₅ + H₂O

(C₂H₄O₂) Warm Ethyl ethanoate (Y)

Ethanoic acid (X)

10. Why do covalent compounds have low melting and boiling points ? (C.B.S.E. All India 2008) 

Ans. In covalent compounds, the atoms are linked by covalent bonds formed by electron sharing. Since no ions
are present in these, the attractive forces are quite weak. As a result, the covalent compounds have low
melting and boiling points.

11. (i) How are carboxylic acids different from mineral acids from ionisation point of view ?

(ii) Describe an activity to find how ethanoic acid reacts with sodium carbonate. Name the gas evolved. How can it be tested ?  (C.B.S.E. All India 2008) 

Ans. (i) Carboxylic acids (organic acids) are less ionised in solution as compared to mineral acids
(HCI, HNO₃, H₂SO₄ etc.) Due to this reason, these are weaker acids than the mineral acids.

(ii) Take a small volume of ethanoic acid in a tube. Add a few drops of sodium carbonate (Na₂CO₃) solution
prepared in water to the tube. A colourless gas with brisk effervescence will evolve. When the gas
is passed through lime water, it will become milky.

Na₂CO₃(aq) + CH₃COOH(aq) CH₃COONa(aq) + H₂O(l) + CO₂(g)

Ca(OH)₂(aq) + CO₂(g) )  CaCO₃(s) + H₂O(l)

Lime water (Milky)

12. (a) What is a functional group in a carbon compound ? Identify the functional group present in CH₃COOH
and C₂H₅OH.

(b) State the principle on which the cleansing action of soap is based.  (C.B.S.E. Foreign 2008) 

Ans. (a) Functional group may be defined as an atom or group of atoms upon which the properties of a particular
organic compound are based. Different families differ in the functional groups.

Functional group in CH₃COOH : (—COOH)

Functional group in C₂H₅OH : (—OH)

(b) The cleansing action of soap is based on its tendency to act as a bridge between water and oil drops
containing dirt particles. As a result, oil and water get mixed. They form a stable emulsion also called
micelle. This helps in removing oil drops containing dirt particles from clothes. The clothes become clean.

13. (a) Draw the structure of the following compounds

(i) Ethanoic acid (ii) Butanone.

(b) Why is conversion of ethanol to ethanoic acid considered an oxidation reaction? (C.B.S.E. Forigen 2008) 

Ans. (a)

(b) When ethanol (C₂H₅OH) changes with ethanoic acid (CH₃COOH)

• There is a decrease in the number of hydrogen atoms by two.

• There is an increase in the number of oxygen atoms by one. Therefore, the conversion represents
an oxidation reaction.

14. (a) What are esters ? How are they formed ? (b) Write two uses of esters ?  (CBSE Foreign 2008) 

Ans. (a) Esters are the group of organic compounds which contain the function group (COOR) called ester group.
The value of R may change as —CH₃, —C₂H₅, —C₃H₇ etc. A few example of esters are :

Esters are formed as a result of chemical reaction called esterification.

Uses of esters

(i) Esters have pleasent smell. These are used as flavouring agents and also in perfumes.

(ii) Esters of glycerol known as triglycerides are used in the manufacture of soaps.This reaction is called
saponification reaction.

15. Distinguish between esterification and saponification reactions of organic compounds.

(C.B.S.E. All India 2008) 

Ans. (a) In the esterification reaction an acid reacts with alcohol in the pressure of conc. H₂SO₄ to form an ester
with a pleasant or fruity smell. For example,

CH₃COOH + C₂H₅OH  CH₃COOC₂H₅ + H₂O

Ethanoic acid Ethanol Ethyl ethanoate (ester)

Saponification is quite different from esterification because in this case an ester reacts with an alkali
(NaOH or KOH) to form salt of acid and alcohol. For example,

C₃COOC₂H₅ + NaOH  CH₃COONa + C₂H₅OH

Ethyl ethanoate Sod. ethanoate Ethanol

16. (a) In organic compounds, which part largely determines the physical and chemical properties.

(CBSE All India, 2008)

(b) Write chemical equation to represent the reaction of ethanol with acidified solution of potassium dicromate.

Ans. (a) In organic compounds, it is the functional group which largely determines the physical and chemical propertiesnof compounds. Actually, an organic compound is made up of two parts. These are alkyl group and the functional group. Whereas the alkyl group remains the same (size may change) but the functional groups change. These are responsible for the characteristics of the compounds. For example, the properties of alkanols (OH is the functional group) are different from those of alkanoic acid (COON is the functional group). For more details, consult text part.

(b) Acidified solution of potassium dichromate (K₂O₂O₇) forms chromic acid (H₂CrO₄). It releases oxygen to
bring about the oxidation of ethanol first to ethanal and then to ethanoic acid.

CH₃ — CH₂ — OH CH₃ — = O  CH₃ — = O

Ethanol Ethanal Ethanoic acid

17. Give reason for the following:

(a) Air holes of the gas burners have to be adjusted when heated vessels get blackened by the flame.

(b) Use of synthetic detergents causes pollution problems. (C.B.S.E. Delhi, 2009) 

Ans. (a) In case the vessel where cooking is done gets blackened from outside, this means that combustion is incomplete.
As a result, the carbon particles in the form of soot get deposited and the vessel becomes black from outside. In order to check this, oxygen or air supply must be increased. This can be done only by adjusting the air holes of the gas burner.

(b) The pollution problems caused by the synthetic detergents is due to their non-biogradable nature. These are actually long chain organic compounds which do not break or decompose in water. Naturally, this will result in pollution problems. Some of the detergents are even of toxic nature and will make water unfit for drinking.