Revision Notes for Class 10 Science Carbon And Its Compounds
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Carbon And Its Compounds Notes Class 10 Science
CARBON AND ITS COMPOUNDS
Organic compounds: The compounds like urea, sugars, fats, oils, dyes, proteins vitamins etc., which were isolated directly or indirectly from living or indirectly from living organism such as animals and plants were called organic compounds. The branch of chemistry which deals with the study of these compounds is called ORGANIC CHEMISTRY.
BONDING IN CARBON = THE COVALENT BOND :
Most carbon compounds are poor conductors of electricity. The boiling and melting points of the carbon compounds are low. Forces of attraction between these molecules of organic compounds are not very strong/ As these compound are largely non conductors of electricity hence the bonding in these compound does not give rise to any ions.
The reactivity of elements if explained at their tendency to attain a completely filled outer shell, that is, attain noble gas configuration. Element forming ionic compounds achieve this by either gaining or losing electrons from the outermost shell. In the case of carbon, it has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration. It is were to gain or lose electrons –
(i) It could gain four electrons forming C4- anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.
(ii) It could lose four electrons forming C4+ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.
(a) Some Simple Molecules Formed by the Sharing of Valence Electrons are s follows:
(i) Hydrogen molecules: This is the simplest molecule formed by sharing of electrons. The atomic number of hydrogen is 1 and it has only one electron is its outermost K shell. It required only one more electron to complete the K shell. So, when two hydrogen atoms approach each other, the single electron of both the atoms form a shared pair. This may be represented as:
According to Lewis notation, the electrons in the valence shell are represented by dots and crosses. This method was proposed by G.N.Lewis and is known as Lewis representation or Lewis structure. The shared pair of electron (show x) is said to constitute a single bond between the two hydrogen atoms and is represented by a line between the two atoms. Pictorially, the molecule can be represented by drawing two overlapping circles around the symbols of the atoms and showing the shared pair of electrons in the overlapping part.
(ii) Chlorine molecule : Each chlorine atom has seven electrons in its outermost shell. When the two chlorine atoms come close together, an electron of both the atoms is shared between them.
(iii) Hydrogen chloride molecule: It may be note that a covalent bond is not only formed between two similar atoms, but it may be formed between dissimilar atoms also. For example, hydrogen and chlorine form a covalent bond between their atoms. In HCI, hydrogen atom (1) has only one electron in its valence shell and chlorine atom (2,8,7) has seven electrons in its valence shell. Therefore, by mutual sharing of electron pair between hydrogen and a chlorine atom. Both the atoms acquit nearest noble gas configuration.
(iv) Formation of water molecule (H2O) : Each hydrogen atom has only one electron in its outermost shell. Therefore, each hydrogen atom required one more electron to achieve the stable configuration of helium (nearest noble gas). The oxygen atom has the electronic configuration 2,6 and has six electrons in its outermost shell. It needs two electrons to complete its octet. Therefore, one atom of oxygen shares its electrons with two hydrogen atoms.
(v) Formation of methane molecule (CH4) : Methane (CH4) is a covalent compound containing covalent bonds. Carbon atom has atomic number 6. Its electronic configuration is 2,4. It has four electrons in its valence shell and needs 4 more electrons to get the stable noble gas configuration. Hydrogen atom has one electron and needs one more electron to get stable electronic configuration of nearest noble bas, helium. Therefore, one atom of carbon shares its four electrons with four atoms of hydrogen to form four covalent bonds.
(b) Different Kinds of Covalent Bonds :
Electron pair shared between two atoms results in the formation of a covalent bond. This shared pair is also called bonding pair of electron.
1.If two atoms share one electron pair, bond is known as single covalent bond and is represented by one dash (-)
2.If two atoms share two electron pairs, bond is known as double covalent bond and is represented by two dashed (=).
3.If two atoms share three electron pairs, bond is known as triple covalent bond and is represented by three dashes (=).
(i) Formation of double bond (oxygen molecule) : Two oxygen atoms combine to form oxygen molecule by sharing two electron pairs. Each oxygen atom (2, 6) has six electrons in the valence shell. It required two electrons to acquire nearest noble gas configuration. Therefore, both the atoms contribute two electrons each for sharing to form oxygen molecule. In the molecule, two electron pairs are shared and hence there is a double bond between the oxygen atoms.
(ii) Formation of triple bond (Nitrogen molecule) : Nitrogen atom has five electrons in its valence shell. In the formation of a nitrogen molecule, each of the following atoms provide three electrons to form three electrons pairs for sharing. Thus, a triple bond is formed between two nitrogen atoms.
(c) Characteristic Properties of Covalent Compounds:
The important characteristic properties of covalent compounds are :
(i) Covalent compounds consist of molecules: The covalent compounds consist of molecules. They do not have ions. For example - hydrogen, oxygen, nitrogen etc. consist of H2, O2 and N2 molecules respectively.
(ii) Physical state : Weak Vanderwaal’s forces are present between the molecules of covalent compounds. So, covalent compounds are in gaseous or liquid state at normal temperature and pressure.
For example: Hydrogen, chlorine, methane, oxygen, nitrogen are gases while carbon tetrachloride, ethyl alcohol, ether, bromine etc. are liquids. Glucose, sugar, urea, iodine etc. are some solid covalent compounds.
(iii) Crystal structure - Covalent compounds exhibit both crystalline and non crystalline structure.
(iv) Melting point and boiling point: Energy required to break the crystal is less due to the presence of weak Vanderwaal’s force, so their melting and boiling points are less.
(v) Electrical conductivity - Covalent compounds are bad conductors of electricity due to the absence of free electrons or free ions.
(vi) Solubility : Due to the non - polar nature of covalent compounds they are soluble in non - polar solvents like benzene, carbon tetrachloride etc. and insoluble in polar solvents like water etc.
ALLOTROPIC FORMS OF CARBON :
Allotropy is the property by virtue of which an element exist in more than one form and each form has different physical properties but identical chemical properties. These different forms are called allotropes. The two common allotropic forms of carbon are diamond and graphite.
(i) Structure of Diamond: Diamond crystals found in nature are generally octahedral (eight faced). In the structure of diamond, each carbon i linked to four other carbon atoms forming regular and tetrahedral arrangement and this network of carbon atoms extends in three dimensions and is very rigid. This strong bonding is the cause of its hardness and its high density. This regular, symmetrical arrangement makes the structure very difficult to break. To separate one carbon atom from the structure, we have to break four strong covalent bonds.
Elements in which atoms are bonded covalently found in solid state. For example diamond, graphite, sulphur etc.
(ii) Properties of Diamond :
(A) It occurs naturally in free state and has octahedral shape.
(B) It is the hardest natural substance known.
(C) It has high specific gravity (about 3.5).
(D) It is transparent, colourless and brittle solid.
(E) It has a high refractive index (about 2.4).
(F) It is non-conductor of electricity.
(iii) Uses of Diamond:
(A) They are used in jewellery because of their ability to reflect and refract light.
(B) Diamond is used in cutting glass and drilling rocks.
(C) Diamond has an extraordinary sensitivity to heat rays and due to this reason, it is used for making high precision thermometers.
(D) Diamond has the ability to cut out harmful radiations and due to this reason it is used for making protective windows for space probes.
(E) Diamond dies are used for drawing thin wires. Very thin tungsten wires of diameter less than one-sixth of the diameter of human hair have been drawn using diamond dies.
(F) Surgeons use diamond knives for performing delicate operations.
Graphite is an allotrope of carbon, which is black or bluish grey with a metallic lustre and or greasy feel. It occurs in igneous and metamorphic rocks, such as marble.
(i) Structure of Graphite :
Each carbon is bonded to only three neighboring carbon atoms in the same plane forming layers of hexagonal networks separated by comparatively larger distance. The different layers are held together by weak forces, called vanderwaal’s forces. The layers can therefore, easily slide over one another. This makes graphite lubricating, soft and greasy to touch.
Within each layer of graphite, every carbon atom is joined to three others by strong covalent bonds. This forms a pattern of interlocking hexagonal rings. The carbon atoms are difficult to separate from one another. So graphite also has high melting point.
However, the bonds between the layers are weak. The layers are able to slide easily over one another, rather like pack of cards. This makes graphite soft and slippery. When we write with a pencil, layers of graphite flake off and stick to the paper.
(ii) Properties of Graphite:
(A) It is soft and greasy in touch.
(B) Its specific gravity is 2.25 (generally).
(C) It is grayish black and opaque.
(D) It is a good conductor of heat and electricity.
(E) It occurs in hexagonal layers.
(F) It is stable and has high melting point.
(iii) Uses of graphite:
(A) It is used for making pencil lead, printer’s ink, black paint etc.
(B) It is used as dry lubricant for heavy machinery.
(C) It is used in making crucibles for melting substances.
(D) It is used as an electrode in batteries and electric furnaces.
(E) It is used in nuclear reactors as moderator to regulate nuclear reactions.
(F) It is also used in making artificial diamonds.
(i) Structure: Fullerene is naturally occurring allotrope of carbon in which 60 carbon atoms are linked to form a stable structure. Previously, only two forms of carbon (diamond and graphite) were known. The third allotrope of carbon, called fullerene was discovered in 1985 by Robert Curl, Herald Kroto and Richard Smalley.
The correctly suggested the cage structure as shown in the figure and named the molecule Buckminster fullerene after the architect Buckminster Fuller, the inventor of the Geodesic dome, which resembles the molecular structure of C60. Molecules of C60 have a highly symmetrical structure in which 60 carbon atoms are arranged in a closed net with 20 hexagonal faces and 12 pentagonal faces. The pattern in exactly like the design on the surface of a soccer ball. C60 has been found to form in sooting flames when hydrocarbons are burned.
All the fullerenes have even number of atoms, with formulae ranging upto C400 and higher. These materials offer exacting prospects for technical application. For example, because C60 readily accepts and donates electrons, it has possible application in batteries.
(ii) Uses of Fullerenes : It is hoped fullerenes or their compounds may find used as -
(E) as highly tensile fibres for construction industry.
(F) inhibiting agents in the activity of the AIDS virus.
(d) Explaining Conduction in Carbon :
In diamond, all four electrons in the outer shell of each carbon atom are used to make covalent bonds. This means that there are no free electrons and so diamond is an insulator. In graphite, only three of the outer shell electrons are used in bonding to other carbon atoms. This leaves on electrons per atom free to move, so graphite acts as an electrical conductor.
(e) Difference Between Properties of Diamond and Graphite :
VERSATILE NATURE OF CARBON :
About 3 million organic compounds are known today. The main reasons for this huge number of organic compounds are =
(i) Catenation : The property of self linking of carbon atoms through covalent bonds to form long straight or branched chains and rings of different sizes is called catenation. Carbon shows maximum catenation in the periodic table due to its small size, electronic configuration and unique strength of carbon - carbon bonds.
(ii) Tetravalency of carbon : Carbon belongs to group 14 of periodic table. Since the atomic number of carbon is 6. The electronic configuration of carbon atom is 2,4. It has four electrons in the outermost shell. Therefore, its valency is four. Thus carbon forms four covalent bonds in its compounds. A methane molecule (CH4) is formed when four electrons of carbon are shared with four hydrogen atoms are shown below.
(iii) Tendency to form multiple bond : Due to small size of carbon it has a strong tendency to form multiple bond (double & triple bonds) by sharing more than one electron pair. As a result, it can form a variety of compound. For example -
VITAL FORCE THEORY OF BERZELIUS HYPOTHESIS :
Organic compounds cannot by synthesized in the laboratory because they require the presence of a mysterious force (called vital force ) which exists only in living organisms.
WOHLER’S SYNTHESIS :
In 1828, Friedrich Wohler synthesized urea (a well known organic compound) in the laboratory by heating ammonium cyanide. Urea is the first organic compound synthesized in the laboratory.
(a) Introduction :
The organic compounds containing only carbon and hydrogen are called hydrocarbons. These are the simplest organic compounds an are regarded as parent organic compounds. All other compounds are considered to be derived form them by the replacement of one or more hydrogen atoms by other atoms or groups of atoms. The major source of hydrocarbons is petroleum.
(b) Types of Hydrocarbons:
The hydrocarbons can be classified as :
(I) Saturated hydrocarbons.
(A) Alkanes : Alkanes are saturated hydrocarbons containing only carbon - carbon and carbon - hydrogen single covalent bonds.
For e.g. : CH4 (Methane)
(ii) Unsaturated hydrocarbons:
(A) Alkenes: These are unsaturated hydrocarbons which contain carbon - carbon double bond. They contain two hydrogen less than the corresponding alkanes.
General formula: CnH2n+2
For e.g.: C2H4 (Ethane)
(B) Alkynes: They are also unsaturated hydrocarbons which contain carbon - carbon triple bond. They contain four hydrogen atoms less than the corresponding alkanes.
General formula: CnH2n
For e.g. : C2H2 (Ethane)
(c) Classifications of Organic Compounds:
The organic compounds are very large in number on account of the self - linking property of carbon called catenation. These compounds have been further classified as open chain and cyclic compounds.
(i) Open chain compounds: These compounds contain an open chain of carbon atoms which my be either straight chain or branched chain in nature. Apart from that, they may also be saturated or unsaturated based upon the nature of bonding in the carbon atoms. For example.
Butane is a straight chain alkane while 2- Methyl propane is branched chain in nature.
(ii) Closed chain or Cyclic compounds : Apart form the open chains, the organic compounds can have cyclic or ring structures. A minimum of three atoms are needed to form a ring. These compounds have been further classified into following types.
(A) Alicyclic compounds : Those carboxylic compounds which resemble aliphatic compounds in their properties are called alicyclic compounds.
(B) Aromatic compounds : Organic compounds which contain one or more fused or isolated benzene rings are called aromatic compounds
HOMOLOGOUS SERIES :
Homologous series may be defined as a series of similarly constituted compounds in which the members possess similar chemical characteristics and the two consecutive members differ in their molecular formula by - CH2.
(a) Characteristics of Homologous Series :
(i) All the members of series can be represented by the same generally formula.
For eg. General formula for alkane series is CnH2n+2.
(ii) Any two consecutive members differ in their formula by a common difference of - CH2 and differ in molecular mass by 14.
(iii) Different member in a series have a common functional group.
For eg. All the members of alcohol family have - OH group.
(iv) The members in any particular family have almost identical chemical properties. Their physical properties such as melting point, boiling point, density etc. show a regular gradation with the increase in the molecular mass.
(v) The members of a particular series can be prepared almost by the identical methods.
(b) Homologues :
The different members of a homologous series are known as homologues.
For example :
(i) Homologous series of alkanes
NOMENCLATURE OF ORGANIC COMPOUNDS :
Nomenclature means the assignment of names to organic compounds. There are two main systems of nomenclature of organic compounds –
2.IUPAC system (International Union of Pure and Applied Chemistry)
(a) Basic Rules of Nomenclature or Compounds in IUPAC System :
For naming simple aliphatic compounds, the normal saturated hydrocarbons have been considered as the parent compounds and the other compounds as their derivatives obtained by the replacement of one or more hydrogen atoms with various functional groups.
Each systematic name has first two or all three of the following parts :
(i) Word root : The basic unit is a series of word rot which indicate linear or continuous number of carbon atoms.
(ii) Secondary suffix : Suffixes added after the primary suffix to indicate the presence of a particular functional group in the carbon chain are known as secondary suffixes.
14.1 (b) Name of Straight Chain Hydrocarbons
The name of straight chain hydrocarbon may be divided into two parts
(i) Word root (ii) Primary suffix
(i) Word roots for carbon chain lengths :
(c) Names of Branched Chain Hydrocarbon :
The carbon atoms in branched chain hydrocarbons are present as side chain. These side chain carbon atoms constitute the alkyl group or alkyl radicals. An alkyl group is obtained from an alkane by removal of a hydrogen. General formula of an alkyl group = CnH2n+1
An Alkyl group is represented by R.
(d) A Branched Chain Hydrocarbon is Named Using the Following General IUPAC Rules :
Rule 1 : Longest chain rule : Select the longest possible continuous chain of carbon atoms. If some multiple bond is present, the chain selected must contain the multiple bond.
(i) The number of carbon atoms in the selected chain determines the word root.
(ii) Saturation or unsaturation determines the primary suffix (P. suffix(.
(iii) Alkyl substituents are indicated by prefixes .
Rule 2 : Lowest number Rule : The chain selected in numbered in terms of arabic numerals and the position of the alkyl groups are indicated by the number of the carbon atom to which alkyl group is attached.
(i) The numbering is done in such a way that the substituents carbon atom has the lowest possible number.
(ii) If some multiple bond is present in the chain, the carbon atoms involved in the multiple bond should get lowest possible numbers.
The name of the compound, in general, is written in the following sequence. (Position of substituents) - (prefixes) (word root) (p - suffix)
Rule 3: Use of prefixed di, tri etc. : If the compound contains more than one similar alkyl groups, their positions are indicated separately and an appropriate numerical prefix, di, tri, etc., is attached to the name of the substituents. The positions of the subsistent are separated by commas.
Rule 4: Alphabetical arrangement of prefixes: If there are different alkyl substituents present in the compound their names are written in the alphabetical order. However, the numerical prefixes such as di, tri etc. are not considered for the alphabetical order.
Rule 5: Naming of different alkyl substituents at the equivalent positions :
If two alkyl substituents are present at the equivalent position then numbering of the chain is done is such a way that the alkyl group which comes first in alphabetical order gets the lower position.
(e) Some More Example:
An atom or group of atoms in an organic compound or molecule that is responsible for the compound’s characteristic reactions and determines its properties is known as functional group. An organic compound generally consists of two parts -
(i) Hydrocarbon radical (ii) Functional group
Hydrocarbon radical Functional group
- Functional group is the most reactive part of the molecule.
- Functional group determines the chemical properties of an organic compound.
- Hydrocarbon radical determines the physical properties of the organic compound.
(b) Main Functional Groups:
(i) Hydroxyl group (-OH): All organic compounds containing - OH group are known as alcohols.
For e.g. Methanol (CH3OH), Ethanol (CH3 - CH2 - OH) etc.
(ii) Aldehyde group (-CHO) : All organic compounds containing CHO group are known as aldehydes.
For e.g. Methanol (HCHO), Ethanol (CH3CHO) etc.
(iii) Ketone group (-CO-) : All organic compounds containing -CO- group are known as ketones.
For e.g. 2- Propanone (CH3COH3), 2-Butanone (CH3COCH2CH3) etc.
(iv) Carboxyl group ( -COOH) : All organic acids contain carboxyl group. Hence they are also called carboxylic acids.
For e.g. CH3COOH (Ethanoic acid)
CH3CH2COOH (Propanoic acid)
(v) Halogen group (x= F, CI, Br, I) : All organic compounds containing - X(F, CI, Br or I) group are known as halides.
For e.g. Chloromethane (CH3CI), Bromomethane (CH3Br) etc.
Nomenclature of Compounds Containing Functional Group :
In case come functional group (other than C = C and C C) is present, it is indicated by adding secondary suffix after the primary suffix. The terminal ‘e’ of the primary suffix is removed if it is followed by a suffix beginning with ‘a’, ‘e’, ‘i’, ‘o’, ‘u’. Some groups like - F, - CI, - Br and - I are considered as substituents and are indicated by the prefixes.
(d) Naming of an Organic Compound Containing Functional Group :
Step 1 : Select the longest continuous chain of the carbon atoms as parent chain. The selected chain must include the carbon atom involved in the functional groups like - COOH, - CHO etc., or those which carry the functional groups like - OH, - CI etc.
Step 2 : The presence of carbon - carbon multiple bond decides the primary suffix.
Step 3 : The secondary suffix is decided by the functional group.
Step 4 : The carbon atoms of the parent chain are numbered in such a way so that the carbon atom of the functional group gets the lowest possible number. In case the functional group does not have the carbon atom, then the carbon atom of the parent chain attached to the functional group should get the lowest possible number.
Step 5 : The name of the compound is written as -
Prefixes - word root - primary suffix - secondary suffix
The number of carbon atoms in the parent chain decides the word root.
(e) Some More Example:
ISOMERS & ISOMERSISM:
Such compounds which have same molecular formula but different in some physical or chemical properties are known as isomers and the phenomenon is known as isomerism.
(b) Structural Isomerism:
Such compounds which have same molecular formula but different structural arrangement of atoms in their molecules are known as structural isomers and the phenomenon is known as structural isomerism.
(i) Chain isomerism: The isomerism in which the isomers differ from each other due to the presence of different carbon chain skeletons in known as chain isomerism.
(iii) Functional group isomerism: In this type of isomerism, isomers differ in the structure due to the presence of different functional groups.
CHEMICAL PROPERTIES OF CARBON COMPOUNDS:
The important chemical properties of organic compounds are discussed below:
Carbon in all its allotropic forms burns in air or oxygen to give carbon dioxide and releases energy in the form of heat and light.
Most carbon compound also release a large amount of heat and light on burning.
Saturated hydrocarbons will generally give a clean flame while unsaturated carbon compounds will give a yellow flame with lots of black smoke. This results in a sooty deposit on the metal plate. However, limiting the supply of air results in incomplete combustion of even saturated hydrocarbons giving a sooty flame.
(b) Oxidation :
Oxidation is a process in which oxygen is added to a substance. The substances which add oxygen to other substances are called oxidising agents. There are many oxidising agents such as alkaline potassium permanganate (alk. KMnO4), acidified potassium dichromate (K2Cr2O7), nitric acid (HNO3) etc. which are commonly used in organic chemistry. Some common reactions of oxidation are-
(c) Substitution Reaction:
The reaction in which an atom or group of atoms in a molecule is replaced or substituted by different atoms or group of atoms are called substitution reactions. Saturated hydrocarbons are fairly uncreative. For example, chlorine does not react with methane at room temperature. However, in the presence of sunlight the reaction of chlorine and hydrocarbons is fairly fast reaction. It gives a variety of products
The reactions in which two molecules react to form a single product having all the atoms of the combining molecules are called addition reactions. Unsaturated compounds such as alkenes contain double bond between carbon atoms. Because of the presence of double bond, they undergo addition reaction.
This reaction is called hydrogenation. Hydrogenation reaction is used in the manufacture of vanaspati ghee from vegetable oils. The vegetable oil such as ground nut oil, cotton speed oil and mustard oil contain bonds (C = C) in their molecules. When reacted with hydrogen in the presence of nickel as catalyst, they are converted into vanaspati ghee which is solid at room temperature like butter or ghee.
BURNING OF SUBSTANCES WITH OR WITHOUT SMOKE FLAME :
When coal or charcoal burns n an ‘angithi’, sometimes it just glows red and gives out heat without a flame. This is because a flame is only produced when gaseous substances burn. When wood or charcoal is ignited, the volatile substances present vapourise and burn with a flame in the beginning.
A luminous flame is also observed when the atoms of the gaseous substances are heated and start to glow. The colour of the flame is characteristic of that element. For example, when a copper wire is heated in the flame of the a gas stove, a bluish green colour is obtained.
The incomplete combustion gives soot or smoke which is due to carbon. Saturated hydrocarbons burn with blue non-sooty flame. This is because the percentage of carbon in these compounds is low which gets oxidised completely by the oxygen present in the air.
On the other hand, unsaturated hydrocarbons burn with yellow sooty flame. This is because the percentage of carbon in these compounds is comparatively higher (than saturated compounds). Therefore, all the carbon does not get oxidised completely in the oxygen of the air. Due to incomplete combustion, the flame is sooty due to the presence of unburnt carbon particles.
The fuels such as coal, petroleum have some amount of nitrogen and sulphur in them. On heating, they are burnt to oxides of nitrogen and sulphur, which are released in the atmosphere. These are the major pollutants in the environment.
FORMATION OF COAL AND PETROLEUM:
Coal and petroleum are the fossil fuels. These are believed to be formed from biomass which has been subjected to various biological and geological processes inside the earth. Coal is formed from the remains of plants and animals (fossils) which died about millions of years ago. These remains gradually got buried deep in the earth during earthquakes, volcanoes etc. These remains were covered with sand, clay and water. Due to high temperature and high pressure and the absence of air inside the earth, the fossils got converted into coal. This process of conversion of plants and animals buried inside the earth under high temperature and pressure to coal is called carbonisation. It is a very slow process and may have taken thousands of years.
Petroleum is formed form the bacterial decomposition of the remains of animals and plants which got buried under the sea millions of years ago. When these organisms died, they sank to the bottom and got covered by sand and clay. Over a period of millions of years, these remains got converted into hydrocarbons by heat, pressure and catalytic action. The hydrocarbons formed rose though porous rocks and got trapped between two layers of impervious rock forming an oil trap.
SOME IMPORTANT CARBON COMPOUNDS:
(a) Ethanol or (Ethyl alcohol):
- Ethanol is the second member of the homologous alcoholic series.
- It is also known as methyl carbinol.
- Structural formula.
(i) Properties of Ethanol:
(A) Physical properties.
- Ethanol is colourless liquid having a pleasant smell.
- Ethanol boils at 351 K.
- It is miscible with water in all proportions.
- It is a non-conductor of electricity (it does not contain ions)
- It is neutral to litmus.
(iv) Reaction with carboxylic acids: [ESTERIFICATION] The process of formation of an ester by the combination of an alcohol with carboxylic acid is known as etherification/
Esters are sweet smelling substances and thus are used in making perfumes.
(v) Acton with concentrated sulphuric acid : Ethanol reacts with concentrated sulphuric acid at 443 K to produce ethylene. This reaction is known as acidic dehydration of ethanol because in this reaction, water molecule is removed from ethanol.
The concentrated sulphuric acid may be regarded as a dehydrating agent because it removes water from ethanol
(b) Some Important Terms :
(i) Denatured alcohol : To prevent the misuse for drinking purpose, the alcohol supplied for industrial purpose is rendered unfit by mixing it with some poisonous substances like methanol, pyridine, copper sulphate etc. It is known as denatured alcohol.
(ii) Rectified spirit : Ethanol cottoning 5 percent water is known as rectified spirit.
(iii) Absolute alcohol : Rectified spirit is heated under reflux over quicklime for about 5 to 6 hours and then allowed to stand for 12 hours. One distillation, pure alcohol (C2H5OH = 100%) is obtained. This is called absolute alcohol.
(iv) Power alcohol : Alcohol, which is used for generating power is called power alcohol. It consists of a mixture of absolute alcohol petrol roughly in the ratio 20 : 80. Since alcohol itself, does not mix with petrol, therefore, a third solvent such as benzene, ether etc. is added as a co-solvent.
(c) Uses of Ethanol:
(I) Ethanol is a constituent of beverages like beer, wine, whisky and other liquors.
Beer = 3 - 6% Ethanol
Whisky = 50% Ethanol
Wine = 10 - 20% Ethanol
(ii) Ethanol is used to sterilize wounds and syringes.
(iii) Antifreeze: It is a mixture of ethanol and water which has a much lower freezing point than that of water. It is used in radiators of vehicles in cold countries.
(iv)It is used in manufacture of paints, des, medicines, soaps and synthetic rubber. Solution of ethanol prepared in pharmaceutical industry are known as tinctures.
(d) Harmful effects of drinking alcohol:
(i) If ethanol is mixed with CH3OH and consumed, it may cause serious poisoning and loss of eyesight.
(ii) It causes addiction (habit forming) and mixes with blood. It damages liver if taken regularly.
(iii) Higher amount of consumption of ethanol leads to loss of body control & consciousness. It may even cause death.
ETHANOIC ACID (OR ACETIC ACID):
(iii) It dissolves in water, alcohol and ether. Its dissolution in water takes place with the evolution of heat and decrease in volume of the solution.
(iv) The melting point of ethanoic acid in 290 K and hence it often freezes during winter in cold climates. Therefore, it is names as glacial acetic acid.
(b) Chemical properties :
(i) Acidic character : Ethanoic acid is a monobasic acid. It has a replaceable hydrogen atom in its - COOH group. Therefore, it neutralizes alkalies.
(A) It reacts with a solution of sodium hydroxide to form sodium ethanoate and water.
Sodium ethanoate is an ionic compound which dissolves in polar solvents such as water, but does not dissolves in non polar solvents such as alcohol, propanone etc.
The term’ decarboxylation ‘ is used when the elements of carbon dioxide are removed from a molecule.
(c) Uses :
(i) Dilute aqueous solution (5-8%) of ethanoic acid is called vinegar, which is used to preserve food (sausage, pickles, etc.)
(ii) Pure ethanoic acid is used as a solvent and chemical reagent.
(iii) As cellulose ethanoate, it is used in making photographic films and rayon.
(iv) Ethanoic acid finds application in the preparation of propanone, choroethanoic acid, ethanoates of metals etc.
(v) It is widely used in the manufacture of textiles.
(vi) It is used in the preparation of white lead.
(d) Tests for Ethanoic Acid :
(i) Litmus test : Add small amount of blue litmus solution to the given compound. If the blue litmus solution turns red, it indicates that the organic compound is ethanoic acid.
(ii) Sodium bicarbonate test: Take a small portion of the organic compound in a test tube and add a pinch of solid sodium bicarbonate. Evolution of carbon dioxide with brisk effervescence shows the presence of carboxylic acid.
(iii) Ester formation : When a mixture of ethanoic acid and ethanol is heated in the presence of concentrated sulphuric acid, a fruity smelling ester, ethyl ethanoate, is produced.
SOAPS AND DETERGENT :
The word ‘detergent’ means’ cleansing agent and so the detergents are substances which remove dirt and have cleansing action in water. According to this definition of detergents, soap is also a detergent and has been used for more than two thousand years. There are two types of detergents :
(a) Soapy detergents or soaps
(b) Non - soapy detergents or soapless soaps.
A soap is a sodium or potassium salt of some long chain carboxylic acids (fatty acid). Sodium salts of fatty acids are known as hard soaps and potassium salts of fatty acid are known as soft soaps. A soap has a large non-ionic hydrocarbon group and an ionic COO-Na+ group. The structure of soap can be represented as:
where represents the hydrocarbon group and represents negatively charged carboxyl group. Some example so soaps are sodium stearate, C17H35COO- Na+, sodium palmitate, C15H31COO- Na+ and sodium oleate, C17H33COO- Na+.
Hard water, which contains salts of magnesium and calcium, reacts with soap to form magnesium and calcium salts of fatty acid
(i) Preparation of soap : Soap is prepared by heating oil or fat of vegetable or animal origin with concentrated sodium hydroxide solution (caustic soda solution). Hydrolysis of fat takes place and a mixture of sodium salt of fatty acids and glycerol is formed. Since the salt of fatty acids thus formed are used as soap so alkaline hydrolysis of oils and fats is commonly known as saponification.
(ii) Limitation of soaps: Soap is not suitable for washing clothes with hard water because of the following reasons.
(A) Hard water contains salts of calcium and magnesium. When soap is added to hard water, calcium and magnesium ions of hard water react with soap forming insoluble calcium and magnesium salts of fatty acids.
Therefore, a lot of soap is wasted if water is hard.
(B) When hard water is used, soap forms insoluble precipitates of calcium and magnesium salts, which stick to the cloth being washed. Therefore, it interferes with the cleaning ability of the soap and makes the cleaning process difficult.
These calcium and magnesium salts of fatty acid are insoluble in water and separate as cruddy white precipitate.
These are also called synthetic detergents or soap less soaps. A synthetic detergent is the sodium salt of a long chain benzene sulphonic acid or the sodium salt of a long chain alkyl hydrogen sulphate.
(i) Preparation of Synthetic Detergents : Synthetic detergents are prepared by reacting hydrocarbons from petroleum with conc. sulphuric acid and converting the product into its sodium salt.
Washing powders available in the market contain about 15 to 30 percent detergents by weight.
Alkaline hydrolysis of oils and fats is commonly known as saponification.
(c) Comparison Between Properties of Soaps and Detergents :
(d) Advantages of Synthetic Detergents Over Soap :
Synthetic detergents are widely used as cleaning agents these days. Some of their advantages over soaps are :
(i) Synthetic detergents can be used for washing even in hard water. On the other, soaps are not suitable for use with hard water.
(ii) Synthetic detergents can be used even in acidic solutions because they are not readily decomposed in acidic medium. On the other hard, soaps cannot be used in acidic medium because they are decomposed into carboxylic acids in acidic medium.
(iii) Synthetic detergents are more soluble in water than soaps.
(iv) Synthetic detergents have a stronger cleaning action than soaps.
(e) Cleaning Action of Soaps and Detergents:
A molecule of soap is made up of two parts: a non-polar part consisting of a long chain 12 - 18 carbon atoms and a polar part, COO- Na+. The polar end in water soluble and is thus hydrophilic whereas hydrocarbon part is insoluble in water and is thus hydrophobic. In a soap solution, the hydrocarbon portions of several soap molecules huddle together to form aggregates of molecules (or ions) called micelles. The soap micelles are negatively charged due to the presence of carboxylate ions at the surface. Repulsion between similarly charged micelles keeps them dispersed in the solution.
The hydrocarbon part is however soluble in non-polar solvents and is sometimes called lipophilic.
(i) Cleansing action of soap: Mostly the dirt is held to any surface such as cloth by the oil or grease which is present there. Now since the oil and grease are not soluble in water, the dirt particles cannot be removed by simply washing the cloth with water. However, when soap is applied, the non polar hydrocarbon part of the soap molecules dissolves in oil droplets while the polar - COO- NA+ groups remain attached to water molecules. In this way, each oil droplet gets surrounded by negative charge.
These negatively charged oil droplets cannot coalesce and continue breaking into small droplets. These oil droplets (containing dirt particles) can be washed away with water along with dirt particles. So, the action of soap or detergents in to emulsify oil or grease, this loosens the soil particles of dirt and they are removed.
In a soap molecule hydrophilic polar end in water soluble and hydrophobic hydrocarbon part is insoluble in water.
Soap or detergent helps in cleansing in another way. Not only it emulsifies oil or grease but it also lowers the surface tension of water. As a result of this water wets things more effectively.
When water is added on to the surface of the cloth then water molecules tend to stay as close to each other as possible because of the strong forces of attraction (hydrogen bonding) for each other and do not wet the cloth properly. If some soap solution is added to this away then polar end of soap dissolves in water and non polar hydrocarbon end remains away from the water. Thus, soap molecules arrange themselves between the water molecules on the surface of water and decrease the forces of attraction between the water molecules. Water can now spread on the surface of cloth and can make it wet effectively.
(f) Synthetic Detergent: A Serious Problem :
It may be noted that in the past, the widespread use of detergents caused pollution of rivers and other water bodies. Earlier the synthetic detergents were made from long chain of hydrocarbons having a lot of branched chains in them. These branched chain detergent molecules were degraded very slowly by the micro-organisms present in water bodies like lakes or rivers.
Therefore, they tend to remain in water bodies for a long time and make water unfit for aquatic life. For example, detergents containing phosphates can cause rapid growth of algae and therefore, deplete the dissolved oxygen present in the water of lakes and rives. As a result of lack of oxygen, fish and other aquatic animals may die. To solve these problems, now-a-days, the detergents are prepared from hydrocarbons which have minimum branching. These are degraded more easily than branched chain detergents. Therefore, these are biodegradable and create less problems.
Carbon and its compounds
1. Covalent bond: A covalent bond is a bond formed by sharing of electrons between atoms. In a covalent bond, the shared pair of electrons belongs to the valence shell of both the atoms.
2. Conditions for formation of covalent bond:
a. The combining atoms should have 4 to 7 electrons in their valence shell.
b. The combining atoms should not lose electrons easily.
c. The combining atoms should gain electrons readily.
d. The difference in electronegativities of two bonded atoms should be low.
3. Properties of covalent compounds:
a. Physical states: They are generally liquids or gases. Some covalent compounds may exist as solids.
b. Solubility: They are generally insoluble in water and other polar solvents but soluble in organic solvents like benzene, toluene etc.
c. Melting and boiling point: They generally have low melting and boiling points.
d. Electrical conductivity: They do not conduct electrical current.
4. Steps for writing the Lewis dot structures of covalent compounds:
a. Write the electronic configuration of all the atoms present in the molecule.
b. Identify how many electrons are needed by each atom to attain noble gas configuration.
c. Share the electrons between atoms in such a way that all the atoms in a molecule have noble gas configuration.
d. Keep in mind that the shared electrons are counted in the valence shell of both the atoms sharing it.
5. Electronic configuration of some non- metals:
6. Carbon forms covalent bonds.
7. Electronegativity – It is the ability of an atom to attract a shared pair of electrons towards itself.
8. If the atoms forming a covalent bond have different electronegativities, the atom with higher electronegativity pulls the shared pair of electron towards itself. Thus, the atom with the higher electronegativity develops a partial negative charge and the atom with the lower electronegativity develops a partial positive charge. This covalent bond with some polarity is called polar covalent bond.
9. Carbon forms a large number of compounds because of two unique properties:
10.Tetravalency of carbon: Atomic number = 6
Electronic configuration: 2, 4
Valence electrons = 4
Valency = 4
So, carbon needs four electrons to attain noble gas configuration. Or in other words, carbon has the ability to form four bonds with carbon or atoms of other mono-valent elements.
11.Catenation: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.
12.Steps for writing the Lewis dot structures of Hydrocarbons:
a. Write the electronic configuration of all the atoms present in the molecule.
b. Identify how many electrons are needed by each atom to attain noble gas configuration.
c. First complete the noble gas configuration of all the hydrogen atoms by bonding each hydrogen atom with a carbon atom by a single bond.
d. The remaining valency of each carbon is completed by forming carbon – carbon single, double or triple bonds.
e. Keep in mind that the shared electrons are counted in the valence shell of both the atoms sharing it.
13.Classification of hydrocarbons:
a. Aliphatic or open chain hydrocarbons: These are the carbon compounds which have carbon carbon long open chains. They are classified as:
i. Saturated hydrocarbons: These hydrocarbons have all carbon – carbon single bonds.
ii. Unsaturated hydrocarbons: These hydrocarbons have at least one carbon – carbon double or triple bonds.
* Hydrocarbons with at least one carbon-carbon double bond are called alkenes.
General formula = CnH2n where n = number of carbon atoms
* Hydrocarbons with at least one carbon-carbon triple bond are called alkynes.
General formula = CnH2n-2 where n = number of carbon atoms
b. Cyclic or closed chain hydrocarbons: These are the hydrocarbons which have carbon carbon closed chain. They are classified as:
i. Alicyclic hydrocarbons: These are the hydrocarbons which do not have benzene ring in their structure.
ii. Aromatic hydrocarbons: These are the hydrocarbons which have benzene ring in their structure. When hydrogen bonded to carbon of benzene is substituted with halogens, radicals or other functional groups, the derivatives are called aromatic compounds.
14.Benzene: It is an aromatic hydrocarbon which has the molecular formula C6H6. It has alternating carbon - carbon single and double bonds.
Benzene can also be represented as:
15.IUPAC name of hydrocarbon consists of two parts:
a. Word root:Number of carbons in the longest carbon chain
b. Suffix: Depends on the type of carbon – carbon bond: for single bond, suffix is –ane ; for double bond, suffix is –ene, and for triple bond suffix is –yne
16.Steps to write the IUPAC nomenclature of hydrocarbons:
a. Select the parent carbon chain:
i. Select the longest carbon chain as the parent chain.
ii. If a double or a triple bond is present in the carbon chain, it should be included in the parent chain.
b. Number the parent carbon chain from that carbon end such that the double bond, triple bond or side chain gets the lowest number.
c. Identify and name the side chain if any: -CH3 is named as methyl, -C2H5 is named as ethyl etc. Also identify the position of the side chain.
Write the name of the hydrocarbon as:
d. Position number-name of the side chain word root – Position number- suffix
Example: 2-Methyl but-1-ene
e. Remember if the hydrocarbon is an alkane, the position number of suffix is not written.
17.Types of formula for writing hydrocarbons:
a. Molecular formula: The actual number of each type of atom present in the compound.
b. Structural formula: The actual arrangement of atoms is written
c. Condensed formula: It is the shortened form of the structural formula
18.Conditions for Isomerism:
a. Only alkanes with more than three carbon atoms can have isomers.
b. The side chains cannot be present on the terminal carbons.
19. How to write different chain isomers of hydrocarbons:
a. First draw the different carbon chains keeping in mind the conditions for isomerism.
b. Complete the tetravalency of carbon by forming single covalent bonds with hydrogens.
c. In the end, check that the molecular formula of each isomer should be same.
20. How to write different position isomers of unsaturated hydrocarbons:
a. First draw the different carbon chains keeping in mind the conditions for isomerism
b. If it is an alkene draw the first isomer always by drawing a double bond between C1 and C2 or if it is an alkyne draw the first isomer always by drawing a triple bond between C1 and C2
c. The next isomers will be dawn by drawing the same chain and changing the positions of the double and triple bonds in alkenes and alkynes respectively.
d. Complete the tetravalency of carbon by forming single covalent bonds with hydrogens.
e. In the end, check that the molecular formula of each isomer should be same.
21.Homologous Series: A series of organic compounds in which every succeeding member differs from the previous one by –CH2 or 14 u. The molecular formula of all the members of a homologous series can be derived from a general formula.
22.Properties of a homologous series: As the molecular mass increases in a series, so physical properties of the compounds show a variation, but chemical properties which are determined by a functional group remain the same within a series.
23.Homologous series of alkanes: General formula: CnH2n+2 where n = number of carbon atoms
24. Homologous series of alkenes: General formula: CnH2n where n = number of carbon atoms
25.Homologous series of alkynes: General formula: = CnH2n-2 where n = number of carbon atoms
26.Functional group: An atom or a group of atoms which when present in
a compound gives specific properties to it, regardless of the length and nature of the carbon chain is called functional group.
a. Free valency or valencies of the group are shown by the single line.
b. The functional group is attached to the carbon chain through this valency by replacing one hydrogen atom or atoms.
c. Replacement of hydrogen atom by a functional group is always in such a manner that valency of carbon remains satisfied.
d. The functional group, replacing the hydrogen is also called as hetero atom because it is different from carbon, and can be nitrogen, sulphur, or halogen etc.
27.Some functional groups in carbon compounds:
28. Steps to write the IUPAC name of organic compounds:
i. Select the parent carbon chain:
1. Select the longest carbon chain as the parent chain.
2. If a double or a triple bond is present in the carbon chain, it should be included in the parent chain.
3. If a functional group is present, the carbon chain should include the functional group.
ii. Number the parent carbon chain from that carbon end such that the functional group, double bond, triple bond or side chain gets the lowest number.Remember here that the aldehyde and carboxylic acid functional group are present on the terminal carbon atom.
iii. Identify the name and position of the functional group, double bond, triple bond or side chain.
iv. The name of the functional group is written with either a prefix or a suffix as given in the above table.
v. If the name of the functional group is to be given as a suffix, the name of the carbon chain is modified by deleting the final ‘e’ and adding the appropriate suffix. For example, a three-carbon chain with a ketone group would be named in the following manner – Propane – ‘e’ = propan + ‘one’ = propanone.
vi. Remember that in the compounds which have carbon containing functional groups, the name of the word root includes the functional group carbon atom also.
vii. If the carbon chain is unsaturated, then the final ‘ane’ in the name of the carbon chain is substituted by ‘ene’ or ‘yne’ as given in the table above. For example, a threecarbon chain with a double bond would be called propene and if it has a triple bond, it would be called propyne.
29. Difference between chemical properties of saturated and unsaturated hydrocarbons:
30.Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction being affected.
31.Oxidizing agents are substances which are capable of providing oxygen to other compounds for their oxygen. Example: Alkaline KMnO4, acidified K2Cr2O7 etc.
32.Reactions of ethanol:
33.Reactions of ethanoic acid:
34. Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction being affected.
35. Soaps are sodium or potassium salts of long chain carboxylic acids.
36. Structure of soap molecule: The structure of soap molecule consists of a long hydrocarbon tail at one end which is hydrophobic in nature. The other end is the ionic part which is hydrophilic in nature.
37. Cleansing action of soap: When soap is at the surface of water, the ionic end of soap orients itself towards water and the hydrocarbon ‘tail’ orients itself aligns itself along the dirt. Thus, clusters of molecules are formed in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle.
Soap in the form of a micelle is able to clean, since the oily dirt will be collected in the centre of the micelle. The micelles stay in solution as a colloid and will not come together to precipitate because of ion-ion repulsion. Now, when water is agitated, the dirt suspended in the micelles is also easily rinsed away.
38. When hard water is treated with soap, scum is formed. This is caused by the reaction of soap with the calcium and magnesium salts, which cause the hardness of water.
39. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids.
40. Detergents do not form scum with hard water. This is because 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.
CARBON AND ITS COMPOUNDS
Carbon is a versatile element.
In earth’s crust, carbon is 0.02% and found in form of minerals.
Atmosphere has 0.03% of Carbon dioxide.
All living structures are carbon based.
Covalent Bond in Carbon
– The atomic number of carbon is 6 and its electronic configuration is 2, 4. To attain a noble gas configuration it can
1. Gain 4 electrons. But it would be difficult for nucleus to hold 4 extra electrons.
2. Lose 4 electrons. But it would require a large amount of energy to remove
– It is difficult thus for an atom of carbon to either gain or lose electrons.
– Carbon attains the noble gas configuration by sharing its valence electrons with other atoms. Atoms of other elements like hydrogen, oxygen, nitrogen,
chlorine also show sharing of valence electrons.
TETRAVALENCY : Having a valency of 4, carbon atom is capable of bonding with atoms of oxygen, hydrogen, nitrogen, sulphur, chlorine and other elements.
The smaller size of carbon atom enables nucles nucleus to hold the shared pair of electrons strongly, thus carbon compounds are very stable in general.
Saturated and Unsaturated Carbon Compounds
– It is a series of compounds in which the same functional group substitutes for hydrogen in a Carbon chain.
– For instance, the ALCOHOLSs: CH3 OH, C2H5 OH, C3H7 OH, C4H9 OH.
– The successive member differs by –CH2-; unit and 14 units of mass.
– The chemical properties are imparted by the functional group thus allmembers have similar chemical properties. But the members have different physical properties.
– The physical properties vary among the members of homologous series due to difference in their molecular mass.
– Melting point and boiling point increases with increasing molecular mass.
Nomenclature of Carbon Compounds:
1. Identify the number of carbon atoms in the compound.
2. Functional group is indicated either by prefix or suffix.
3. If a suffix is added, then final ‘e’ is removed from the name eg. methanol (methane-e = methan + ol).
Chemical properties of Carbon compounds :
1. COMBUSTION :
*Carbon compounds generally burn (oxidize) in air to produce carbon dioxide and water, and release heat and light energy.
CH4 + O2 → CO2 + H2O + heat and light
*Saturated hydrocarbon burns generallywith a blue flame in good supply or air and with a yellow sooty flame in limited supply of air.
*Sooty flame is seen when unsaturated hydrocarbons are burnt.
*Burning of coal and petroleum emits oxides of sulphur and nitrogen which are responsible for acid rain.
2. OXIDATION :
*Alcohols can be converted to carboxylic acids by oxidizing them using alkaline potassium permanganate or acidified poatassium dichromate (they add oxygen to the reactant, thus are called oxidizing agents).
CH3 - CH2 OH Alkaline KMnO4 + heat/Acidified K2 Cr2 O7 + heat CH3 COOH
3. ADDITION REACTION:
Hydrogen is added to unsaturated hydrocarbon in presence of palladium or nickel as catalyst.
Vegetable oils are converted into vegetable ghee using this process.
Saturated fatty acids are harmful for health and oils with unsaturated fatty acids should be used for cooking.
4. SUBSTITUTION REACTION :
In saturated hydrocarbons, the hydrogen attached to carbon can be replaced by another atom or group of atoms in presence of sunlight.
CH4 + Cl2 → CH3Cl + HCl (sunlight required)
IMPORTANT CARBON COMPOUNDS : Ethanol and Ethanoic Acid Ethanol :
Carboxylic acids react with alcohols in presence of few drops of concentrated sulphuric acid as catalyst and form sweet smelling compounds called ester.
On heating with an acid or a base the ester forms back the original alcohol and carboxylic acid.
Soaps and Detergents
– Soap is sodium and potassium salt of carboxylic acids with long chain.
– Soaps are effective with soft water only and ineffective with hard water.
– Detergents are ammonium or sulphonate salts of carboxylic acids with long chain. They are effective with both soft as well as hard water.
An ionic part (hydrophilic) and a long hydrocarbon chain (hydrophobic) part constitutes the soap molecule.
Structure of a Soap Molecule
Cleansing Action of Soaps :
– Most dirt is oily in nature and the hydrophobic end attaches itself with dirt, while the ionic end is surrounded with molecules of water. This result in formation of a radial structure called micelles.
– An emulsion is thus formed by soap molecule. The cloth needs to be mechanically agitated to remove the dirt particles from the cloth.
– Scum : The magnesium and calcium salts present in hard water reacts with soap molecule to form insoluble products called scum, thus obstructing the cleansing action. Use of detergents overcome this problem as the detergent molecule prevents the formation of insoluble product and thus clothes get cleaned.
Carbon and its compounds
Important terms and conditions
Versatility of carbon :Carbon is known metal and occurs in free as well combined state in nature.
Free state: Diamond ,graphite and coal.
Bond angle: The angle that is formed between two adjacent bonds on the same atom.
Bond length: The equilibrium distance between the nuclei of two groups or atoms that are bonded to each other.
Hydrocarbons: An organic compound containing only carbon and hydrogen atoms.
Saturated hydrocarbons: A substance in which the atoms are linked by single bonds.
Unsaturated hydrocarbons: A substance in which atoms are linked by double or triple bond.
Allotropy: The phenomenon of existence of two or more different physical forms of a chemical element.
Catenation: The property of self linking of elements to form a long chain.
Homologous series: A homologous series is a group of organic chemical compounds, usually listed in order of increasing size, that have a similar structure (and hence also have similar properties) and whose structures differ only by the number of CH2 units in the main carbon chain.
Tetravalency: Tetravalency is the state of an atom in which there are four electrons available with the atom for covalent chemical bonding.
Isomers: Compounds having similar molecular formula but different chemical structure.
Isomerism: The phenomenon in which the compounds have the same molecular formula and different structural formula.
Combined state :1.Solid state: All animals and plants products.
2.Liquid state: Petroleum and vegetable oil .
3.Gaseous state: In air has CO3 .
Carbon has 4 valance electrons carbon can form an anion c-4 by gain of electons.It can also form
of cations C+4 by loss of electron.IT can share its balanced electrons with other carbon atoms or
atoms of non metal and forms covalent bonding.
Compounds of carbon: Simplest compounds of carbon are hydro carbon and simplest hydro carbonis methane.
CH3COOH+C2H5OH → CH3COOC2H5+H2O
Saponfication reaction : Alkaline hydrolysis of ester produces soaps.
CH3COOC2H5+NaOH → CH3COONa+C2H5OH
Reaction with carbonates and hydrogen carbonates: reaction of ethanoic acid with carbonates or bi carbonate evolves carbon di oxide gas.
2CH3COOH+Na2CO3 → 2CH3COONa+CO2+H2O
SOAP AND DETERGENT: Soap is sodium and potassium salt of long chain of carboxylic acid .They foam lather with soft water only.
Detergent are ammonium or sulphonate salts of long chain carboxylic acid .they even remain effective in hard water and foam lather.
Carbon is the most important and widely distributed element on the earth. It is present in the bodies of all living organisms, plant and animals and also in several non-living things (e.g. limestone, marble, chalk, etc.). It is present in air as CO2. It forms the largest number of compounds and above 85% of known compounds contain carbon. Compounds of carbon are studied as a separate branch of chemistry known as Organic Chemistry. Its name is derived from the Latin word "Carbo" meaning coal. Carbon constitutes about 0.02 percent of the earth's crust.
Carbon has a unique property that it can join with other carbon atoms to form carbon-carbonbonds This can result in the formation of compounds with long chains. This property is called catenation.
This most important combination of carbon is with hydrogen to form a set of compounds known as Hydrocarbons.
*Limestone : Marble or chalk is calcium carbonate (CaCO3)
* Magnesite : Is magnesium, carbonate (MgCO3)
* Dolomite : Is calcium carbonate and magnesium carbonate (MgCO3 · CaCO3)
* Calamine : Is Zinc Carbonate (ZnCO3).
* Petroleum, Air contains about 0.03% by volume of carbon dioxide.
Carbon is the essential constituent of food for all living beings. This carbon comes essentially from the non-living world, mainly in the form of carbon dioxide converted into starch during photosynthesis and to a small extent, from carbonates and bicarbonates dissolved in water. For life to contiune, this carbon has to go back to the nonliving world. This happens mainly through respiration and combustion, and to a smaller extent by the decay of
dead remains of living matter. Thus, there is constant transfer of carbon between living and non-living matter. This continuous cycling of carbon between the living and the non-living world is called the carbon cycle, as shown in fig.
There are some element which can exist in different forms in the same physical state. The different forms of the element in the same state are known as allotropes and the phenomenon is known as allotropy. Thus, Oxygen (O2) and ozone (O3) are allotropes of oxygen ; rhombic Sulphur and monoclinic sulphur are allotropes of sulphur.
The phenomenon of existance of an element in two or more different forms in the same physical state is known as allotropy.
DO YOU KNOW?
Q. Define organic chemistry.
Q. Write the percentage of carbon which is present in earth crusts.
Q. What is catenation?
Q. How carbondioxide is released from calcium carbonate rocks.
Q. What is allotropy? What are the different allotropic forms of carbon?
It is one of the purest forms of carbon. In India diamond are found in panna mines in Madhya Pradesh and Golkonda mines in Karnataka and also at Vajrakarur (Andhra Pradesh).
The weight of diamond is expressed in carats 1 Carat = 200 mg
Structure of Diamond : Diamond is a sparkling material though it is made up of carbon, which is a black substance (Fig). The shine in diamond is on account of its definite crystalline arrangement, where each carbon atom is bonded to four carbon atoms, as shown in fig. These are in turn bonded to four carbon atoms each. This arrangement results in a closely packed, hard, three-dimensional structure. This makes diamond the hardest natural substances.
All the electrons in the carbon atoms in diamond are used up in bonding. No electrons are thus available for conduction of electricity. Diamond is therefore a poor conductor of electricity.
Formation of Diamond : It is belived that diamond crystals are formed when carbon is trapped in molten lava, about 150 km below the Earth's surface. The conditions of extermely high temperature and pressure at this depth convert carbon into diamond. Diamond reaches the upper surface of the Earth alongwith Kimberlite rocks. It is also possible to convert Graphite into Diamond. The process requires temperature of about 2000°C and pressure of about 1,00,000 atmosphere in presence of catalyst. The gem-quality diamond made in this manner are, however, too expensive.
Properties of Diamond
• Diamond is a transparent, colourless solid. Most naturally occuring diamonds contain small amount of impurities, which impart colour to them.
• Diamond has a high refractive index. Hence, it sharply bends the light rays passing through it. it is because of this property that properly cut and polished diamond sparkles brightly.
• It has a high density of 3.5 g/cm3.
• It has high melting point of about 3500°C.
• It is the hardest natural substance. Only a diamond can cut another diamond.
• It is a poor conductor of heat and electricity.
• Diamond is extermely unreactive. However, since it is pure carbon, it burns at about 800°C to give carbon dioxide.
Uses of Diamond
• They are used in jewellery because of their ability to reflect and refract light.
• Black diamonds called carbonado are used in cutting glass and drilling rocks.
• Diamond has extraordinary sensitivity to heat rays and due to this reason, it is used for making high precision thermometers.
• Diamond has the ability to cut out harmful radiations and due to this reason, it is used for making protective windows for space probes.
• Diamond dies are used for drawing thin wires. Very thin tungsten wires of diameter of less than one sixth of the diameter of human hair have been drawn using diamond dies.
Graphite is one of the softest materials known. A form of carbon, graphite, is black or bluish grey with a metallic lustre and a greasy feel, as shown in figure. It occurs in igneous and metamorphic rocks, such as marble.
It is found in Srilanka, Mexico, Austria, North Korea, China and India.
In India, Graphite is found in Rajasthan, Andhra Pradesh, Uttar Pradesh, Jammu and Kashmir, Bihar and Tamil Nadu.
Structure of Graphite : The atoms of carbon in a single Graphite crystal are arranged in the form of a hexagon and all of them are in the same plane. The bonds between the carbon atoms of two single crystals in the parallel lines are weak, as illustrated in fig. Thus, one plane of Graphite crystals can easily slip over another plane by applying presure. This accounts for the softness of Graphite.
Why is Graphite a good conductor of electricity?
In case of Graphite, every carbon atom in a single crystal is covalently bonded to three neighbouring atoms of carbon. As you know that carbon atom has four valence electrons, therefore, one electron in each carbon atom is free. These free electrons can be easily made to flow within the structure of graphite by applying potential difference. Thus, graphite is a good conductor of electricity.
Properties of Graphite
• It is a dark grey solid having a metallic lustre.
• It has a soft greasy touch. It makes the paper grey.
• It density ranges from 1.5 to 2.3 gm/cm3.
• It is good conductor of heat and electricity.
• It is insoluble in ordinary solvents.
• Graphite when heated in the absence of air, melts at about 3730°C
• Graphite catches fire at 700°C in the presence of oxygen and forms carbon dioxide gas.
C + O2 700°C→ CO2
Graphite Oxygen Carbon dioxide
Uses of Graphite
• As pencil lead : Graphite is mixed with clay or finely powdered sand. It is then moulded to form thin rods, which are called pencil lead. The hardness of pencil lead depends upon the amount of clay in it, i.e, more the clay, the harder is ther pencil lead.
• As electrodes : Graphite is a good conductor of electricity. Moreover, it does not react with acids or alkalis. Thus, it is used for making electrodes for electrolytic cells, which are not affected by acids and alkalis
• As a dry lubricant : Graphite powder suspended in oil is used as a lubricant in those part of machinery, where oil cannot be applied easily.
• As heat resistant crucibles : When graphite mixed with clay is moulded and baked, it forms heat resistant crucibles. The crucibles can with stand high temperatures on account of clay and are good conductors on account of graphite.
• In making light weight composite material : The graphite fibres are very strong. These fibres are used to reinforce plastic. The reinforced plastic with carbon fibres form a composite material. It used formaking (i) tennis rackets, (ii) fishing rods, (iii) bicycle frame, (iv) aircraft frames (v) parts of the spacecraft, and (vi) dish antennas.
• In making artificial diamonds : Graphite is heated to a temperature of 2000°C in the presence of some noble gas at a pressure of 100,000 times the atmospheric pressure. The high pressure and temperature breaks the carbon atoms in graphite, which rearrange themselves into diamond structure. Roughly 90% of the diamonds required for making tools are made artifically from graphite.
Fullerence are the crystalline forms of carbon with 30 to 960 atoms in their molecules. These are the clusters of hollow shells arranged in cage shaped molecules. It has extraordinary strength and stability. The structure of a fullerence looks like a spherical base ball. In 1985, prof. Harold Kroto of Sussex University (U.K.) and Richard E. Smalley of Rice University (U.S.A.) discovered this useful allotrope of carbon consisting of clustered carbon atoms by vapourising graphite in helium with lasers. When the scientists tried to vapourise graphite, they noticed that some of the vapourised atoms clustered together containing 60 carbon atoms. These were called C-60 fullerene. These were also called Bucky balls. This allotrope family was named after R. Buckminster fuller a genious architect of twentith century. Later on, bigger fullerences such as C70, C76, C78 were produced.
Research is still going on to prepare more and more compounds of fullerences of to use them for various purposes. The research done so far has suggested that in future, fullerences and their compounds many prove to be of great use as semiconductors, superconductors, lubricants, catalysts, electric wires and as fibres to reinforce plastic (to make plastic strong). Some of the compounds of fullerences appear to be active against diseases like Cancer and AIDS. This can lead to finding cure for cancer and AIDS.
Amorphus Forms of Carbon : The word 'amorphous' means 'non crystalline'. So, the non-crystalline form of carbon is called amorphus carbon. In amorphous carbon, the carbon atoms are not arranged in an ordered manner. The packing of carbon atoms in amorphous carbon is quite haphazard. The three amorphous forms of carbon made by man are :
1. Charcoal 2. Coke 3. Lampblack
When a solid organic compound is heated in a controlled supply of air, it leaves behind a grey porous residue, commonly called charcoal. We can obtain charcoal from any solid organic substance from plant or animal origin.
However, we will consider three kinds of charcoal, which are obtained from wood, bones of animals, and sugar.
Wood Charcoal : Wood charcoal is prepared locally by piling logs of wood one upon another, leaving a gap in the centre. The pile is then covered with wet clay so as to prevent the entry of air. A few holes are left at the bottom of the pile. The wood is then set on fire from the central hole. When the fire builds up, the top hole is covered with an iron sheet and then wet clay. The wood now burns in limited supply of air. The heat of burning wood chars the rest of wood. When the fire dies out, a skeleton of wood pieces in the form of grey brittle solid
is left behind. This is called wood charcoal.
Physical properties of wood charcoal :
• It is a grey brittle solid, porous in nature.
• It density is about 1.5 g/cm3. However, it floats on the surface of water because a large amount of air is traped
in its pores. If a piece of charcoal, floating on water, is boiled, it sinks in water because the heat expels out air from its pores and hence, makes it heavy.
• It is a bad conductor of heat and electricity.
• It adsorbs gases, liquids and solids. Adsorption is the property due to which a substance accumulates gases, liquids or solids on its outer surface.
Uses of wood charcoal
• Wood charcoal is used in gas-masks to remove poisonous gases and fumes.
• It is used as a decolourising agent and for purification of water.
• It is used as a fuel.
• It is used as a reducing agent in some metallurgical processes.
Animal Charcoal : It is obtained by destructive distillation of animal bones. It is an impure form of carbon and contains only 10–12% carbon.
Uses of animal charcoal
• Animal charcoal has the property of removing colouring matter from solution. It is therefore, used in the purification of brown coloured sugarcane juice in the manufacture of sugar.
• It is also used a black pigment for rubber and plastics.
Sugar charcoal : It is purest form of amorphous carbon. It is prepared by heating sugar in the absence of air which removes the water from sugar leaving behind the carbon content.
It can also be prepared by treating sugar with concentrated sulphuric acid. Concentrated H2SO4 is a dehydrating agent and removes water from sugar.
Uses of sugar charcoal
• It is used as a reducing agent for obtaining metals from their oxides.
• It is used as a fuel.
Lamp black is a fine, black pigment containing 98-99% carbon. It is prepared by burning substances rich in carbon, such as kerosene, petroleum, turpentine oil, paraffin wax, mustard oil etc. in a limited supply of air. it is also known as carbon black.
Uses of Lamp Black
• It is used in making black paints, printing ink and shoe polish.
• It is used as a black pigment for carbon papers.
• It is used for hardening natural rubber which is then used for making tyres.
CARBON DIOXIDE - CO2
Carbon combines with oxygen to form two oxides – carbon monoxide (CO) and carbon dioxide (CO2). Carbon dioxide occurs to the extent of about 0.03 –0.05% in the atmosphere. It is formed during respiration in animals, decay of plant matter, burning of fossil fuels and volcanic eruptions.
Preparation of Carbon Dioxide
PROPERTIES OF CARBON DIOXIDE
1. Physical properties
• It is colourless and odourless gas.
• It is heavier than air, having a density 1.977 g/L (About 1.5 times denser than air).
• It is slightly souble in water. Its solubility increases with an increase in the pressure. Aerated drinks contain CO2 gas dissolved under pressure. On opening the bottle, CO2 gas escapes in the form of fizz.
• If carbon dioxide is cooled and then pressurised, it changes directly into a solid called 'dry ice'. When dry ice is heated, it does not melt, but sublimes to give carbon dioxide gas.
• Solid carbon dioxide, i.e., dry ice causes blisters if rubbed against the skin. Therefore, it should be handled carefully.
2. Chemical Properties
• CO2 dissolves slightly in the water to form carbonic acid. The solution, thus formed, is weakly acidic and turns blue litmus red. This shows that CO2 is an acidic oxide.
Uses of Carbon dioxide
1. As a refrigerant : Solid carbon dioxide, also known as dry ice, is used for refrigerating.
• It can provide a temperature as low as – 75°C and thus, can slow down the bacterial growth.
• It is not poisonous.
2. In the manufacture of effervescent drinks : Various types of effervescent drinks, e.g. Coca cola, Limca, etc. are obtained by adding sugar flavours and colouring agents. By dissolving the gas in water under high pressure.
3. In fire extinguisher : Carbon dioxide produced through fire extinguishers is used for extinguishing fires because it does not support combustion.
4. In the manufacture of Urea :
5. In hospitals for artifical respiration : Carbogen, a mixture of 5% carbon dioxide and 95% oxygen, is used for artifical respiration on patients suspected of carbon monoxide poisoning, drowning and pneumonia.
Compounds containing only carbon and hydrogen are called hydrocarbons. The simplest hydrocarbon is methane having the molecular formula CH4. Most important source of methane is natural gas which contains about 80% methane.Fuel gases obtained from petroleum and coal, that is, petroleum gas and coal gas contain methane in small amounts. methane is formed during the decay of plant and animal matter in marshes and is, therefore, known as marsh gas.
Preparation of methane : In the laboratory, methane is prepared by heating sodium acetate with soda-lime which is a mixture of sodium hydroxide (caustic soda) and calcium oxide (quick lime).
Properties of methane
1. Physical Properties
• It is a colourless and odourless gas.
• It is insoluble in water and is lighter than air.
2. Chemical Properties
• Methane burns in air with a clear, blue flame and releases a large amount of heat. It is, therefore, used as a fuel.
CH4(g) + 2O2(g) ⎯→ CO2(g) + 2H2O(g) + Heat
• It reacts with chlorine in the presence of sunlight. In this reaction, hydrogen atoms of methane are replaced by chlorine atoms.
Uses of Methane
• Methane is used as a fuel in homes and industries.
• Methane (in the form of Compressed Natural Gas, CNG) is used as a fuel for automobiles like buses, cars and autorickshaws.
• Methane is used for preparing carbon black.
• Methane is used for preparing several important chemicals such as dichloromethane, chloroform, carbon tetrachloride, methyl alcohol and formaldehyde.
• Methane is used for making hydrogen gas needed for making ammonia for the fertiliser industry.
♦ C12 (Carbon–12) is used as a standard for atomic weights.
♦ C14 finds use as a radioactive tracer.
♦ Diamond and graphite are allotropes of carbon and occur naturally.
♦ Carbon shows a covalency of four.
♦ Graphite and diamond are pure forms of carbon and are crystalline forms.
♦ Coke is a form of amorphous carbon and is used as a smokeless fuel and to make water gas.
♦ Coke and coaltar are products of destructive distillation of coal.
♦ Fractional distillation of coaltar produces asphalt (pitch) and creosote, a wood preservative.
♦ A lustrous coal, called anthracite is the preferred domestic fuel.
♦ Diamond is the hardest known substance.
♦ Diamond has Mohs hardness of 10 and refractive index 2.4.
♦ Synthetic graphite is produced by heating anthracite (carbon) to 2500°C in an electrical furnace in the absence of air.
♦ Carbon black is a fine carbon powder which is obtained by burning hydrocarbons in unsufficient air and is used as a pigment and a filler (e.g., for rubber).
♦ Charcoal is a solid porous high-carbon product which is obtained by heating wood in the absence of air, often used
in the manufacture of gunpowder. Charcoal (wood charcoal) is used in gas masks to absorb poisonous gases in air.
♦ Bone charcoal is obtained by heating bones in the absence of air. It contains about 10% carbon. It is used for
decolourising substances, e.g., raw sugar is decolourised to white sugar by bone charcoal.
♦ Coke, coal, charcoal and carbon are inorganic in nature.
♦ Carbon forms vast number of compounds, as such is unique among elements.
♦ C14 (Carbon-14) is continuously formed in the atmosphere by cosmic ray bombardment and is used in Radiocarbon Dating.
♦ Dry ice (solid carbon dioxide) is often used to create artificial rain (cloud seeding).
♦ Carbon monoxide is injurious to health.
♦ Fossils are organic compounds of animals and plants which have remained preserved in rocks.
Question. Which of the following forms of carbon occurs naturally?
Question. Graphite differs from diamond because graphite is –
(a) Slippery to touch and good conductor of electricity.
(b) Slippery to touch and very good conductor of heat
(c) Greyish black in colour and bad conductor of electricity.
(d) Greyish black in colour and very good conductor of heat.
Question. Which of the following is incombusitable?
(a) Carbon monoxide
(c) Carbon dioxide
Question. Which of the following is the hardest substance?
Question. Which of the following is used to cut glasses?
Question. Which of the following are allotropes of carbon?
(a) Coal and charcoal
(b) Graphite and diamond
(c) Coke and coaltar
(d) All the above
Question. Diamond and graphite are :
(a) Non-crystalline forms of carbon
(b) Isotopes of carbon
(c) Allotropes of carbon
(d) Isomeric forms of carbon
Question. Which of the following is crystalline form of carbon?
(a) Bone charcoal
Question. Due to weak binding forces and less distance between the layers, graphite :
(a) Shows lubricating property
(b) Is good conductor of elecricity
(c) Has lustre
(d) is hexagonal
Question. Graphite is used :
(a) In the instruments for drilling in rocks
(b) In making electrodes
(c) As a reducing agent in metallurgy
(d) In making carbon paper
Question. Which one of the following is a good conductor of electricity :
Question. Which is non-crystalline form of carbon?
(d) None of the above
Question. Pencil - lead is made from :
(a) Carbon black
(c) Bone charcoal
Question. Refractive index of diamond is :
Question. Which of the following is used as moderator in Nuclear Reactors?
(b) Diamond Gem
Question. Temperature, hardness of water is due to the presence of :
(a) Calcium bicarbonate
(b) Calcium carbonate
(c) Sodium sulphate
(d) All of the above
Question. Baking soda is :
(a) Calcium carbonate
(b) Sodium carbonate
(c) Magnesium carbonate
(d) Sodium bicarbonate
Question. Washing soda is :
(a) Sodium sulphate
(b) Sodium carbonate
(c) Calcium carbonate
(d) Sodium bicarbonate
Question. Which of the following is used in medicine as antacids?
(a) Calcium carbonate
(b) Sodium bicarbonate
(c) Calcium bicarbonate
(d) magnesium carbonate
Question. Carbon monoxide is toxic as it combines with RBC to form :
(d) None of the above
Question. The air contains carbon dioxide :
(a) 2 %
Question. Which gas is produced when calcium carbonate is heated with dilute hydrochlorice acid?
(a) Carbon monoxide
(b) Carbon dioxide
(c) Carbon disulphide
(d) Carbon tetrachloride
Question. Which of the following is used in cloud seeding?
(a) Carbon dioxide gas
(b) Carbon monoxide gas
(c) Dry ice
(d) Carbonic acid
Question. Which of the following causes greenhouse effect on earth?
(a) Carbon monoxide
(b) Carbon disulphide
(c) Carbon tetrachloride
(d) Carbon dioxide
Question. Liquid carbon dioxide is used in :
(b) Food preservation
(c) Cloud seeding
(d) All the above
Question. The charcoal used to decolourise raw sugar is :
(a) Wood charcoal
(b) Coconut charcoal
(c) Sugar charcoal
(d) Bone charcoal
Question. Anthracite is a
(a) Inferior type of coal
(b) Superior type of coal
(c) Cheapest form of coal
(d) None of these
Question. Graphite is used :
(a) as a lubricant
(b) In making electrodes
(c) In pencil lead
(d) All of these
Question. Diamond is
(a) The soft form of carbon
(b) The hardest known substance
(c) Slippery in nature
(d) None of these
Question. Coking of coal yields
(a) Solution of ammonia
(b) Coal gas
(c) Coal tar
(d) All of these
Question. Soot is
(a) Lamp black
(c) Coal tar
(d) All of these
Question. Which of the following elements exhibit allotropy?
(d) All of these
Question. Charcoal is
(a) Crystalline carbon
(b) Amorphus carbon
(c) Both of these
(d) None of these
FILL IN THE BLANKS:
Question. The form of carbon which is known as black lead is _____
Question. The form of carbon which is used as a lubricant at high temperature is _____
Question. _____ is present in both living and non-living things.
Question. The tendency of an element to exist in two or more forms but in the same physical state is called _____
Question. _____ chemistry deals exclusively with carbon compounds.
Question. _____ and _____ are the major allotropes of carbon.
Answer: Diamond , Graphite
Question. _____ is the hardest substance known.
TRUE OR FALSE :
Question. Charcoal is a good adsorbent.
Question. Graphite has a layer structure.
Question. Bone charcoal is the purest form of amorphous carbon.
Question. Wood charcoal is used in gas masks and cigarette filters.
Question. Coke is obtained by the destructive distillation of bones.
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