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Chemistry 10th Class Chemistry

10th Class Chemistry Chapter 11  Organic Chemistry Notes

10th Class Chemistry Chapter 11  Organic Chemistry Notes

 

Question 1: Write a note on history of organic and inorganic chemistry?

Answer: History of Organic and Inorganic chemistry: Initially (before 1828), the name organic chemistry was given for the chemistry of compounds obtained from plants and animals, i.e., from living organism. The word organic signifies life. Lavoisier showed that compounds obtained from plants were often made of C, H and O elements while compounds obtained from animals contain elements C, H, N, O, S, P…. Etc. While the study of all other elements and their compounds are termed as inorganic compounds and are studied in inorganic chemistry.

In early 19th century, Swedish chemist Jacob Berzellius put forward the “Vital Force Theory”. According to this theory, organic compounds could not be prepared in laboratories because they were supposed to be synthesized under the influence of a mysterious force called Vital Force, inherent only in living things.

The Vital Force theory suffered death blow in 1828 when Wohler synthesized the first organic compound urea from inorganic substance by heating ammonium cyanate (NH4CNO):

NH4CNO ⇒ NH2CONH2

 

Later on Vital Force theory was further negated by Kolbe (1845) when he prepared acetic acid in laboratory.

Organic compounds include carbohydrates, proteins, lipids, enzymes, vitamins, drugs, pharmaceutical products, fertilizers, pesticides, paints, dyes, synthetic rubbers, plastics, artificial fibres and many polymers, etc.

 

Question 2: Write a note on organic compounds and organic chemistry? Why some of the compounds of carbon are excluded from organic compounds?

 

ORGANIC COMPOUNDS:

 

Old definition of organic compounds: Compounds obtained from living organisms, I,e plants and animals are called organic compounds.

Today, there are about ten millions of organic compounds and thousands of new organic compounds are being prepared every year in the laboratory , so the old definitions of organic compounds that these are obtained from organisms has been rejected.

 

New Definition of Organic compounds:

A detailed investigation of organic compounds revealed that all of them contain covalently bonded carbon and hydrogen as their essential constituent. Hence, Scientists put forward a new definition of organic compounds.

“Hydrocarbons (compounds of carbon and hydrogen) and their derivatives, in which covalently bonded carbon is an essential constituent are called organic compounds.”

Organic chemistry: The branch of chemistry which deals with the study of hydrocarbons and their derivatives is known as organic chemistry.

Though, the oxides of carbon like carbon monoxide and carbon dioxide, carbonates, bicarbonates and carbides are also carbon compounds, they are not treated as organic compounds because their properties are quite different from those of organic compounds.

 

Question 3: What are the different formulas of organic compounds? Explain each with a proper example.

Answer: Each organic compound has specific formula.

There are four types of formulae of organic compounds:

  • Molecular formula
  • Structural formula
  • Condensed formula
  • Dot and cross formula (Electronic Formula)

(i) Molecular Formula

The formula which represents the actual number of atoms in one molecule of the organic compound is called the molecular formula, e.g., molecular formula of butane is C4H10. It shows:

  • Butane is made up of carbon and hydrogen atoms.
  • Each molecule of butane consists of 4 carbon atoms and 10 hydrogen atoms.

(ii) Structural Formula

Structural formula of a compound represents the exact arrangement of the different atoms of various elements present in a molecule of a substance.

In a structural formula, single bond is represented by a single line (-), a double bond by two lines (=) and a triple bond by three lines (≡ ) between the bonded atoms.

Organic compounds may have same molecular formulae but different structural formulae, e.g., structural formulae of butane C4H10 are:

 

(iii) Condensed Formula

The formula that indicates the group of atoms joined together to each carbon atom in a straight chain or a branched chain is called the condensed formula.

 

(iv) Electronic or Dot and Cross Formula

The formula which shows the sharing of electrons between various atoms in one molecule of the organic compound is called dot and cross formula or electronic formula.

 

 

 

Table : Presentsthe names, molecular, condensed and structural formulas of the first ten Hydrocarbons

 

Question 4: Write a detailed note on classification of organic compounds.

Classification of Organic Compounds

All known organic compounds have been broadly divided into two categories depending upon their carbon skeleton. These are:

  • Open chain or acyclic compounds.
  • Closed chain or cyclic compounds.

 

(i) Open chain or Acyclic compounds

Open chain compounds are those in which the end carbon atoms are not joined with each other, in this way they form a long chain of carbon atoms. These chains may be either straight or branched. Open chain compounds are also called aliphatic compounds.

 

Types of Open chain compounds:

(a) Straight chain compounds

(b) Branched chain compounds

 

Straight chain compounds: Straight chain compounds are those in which carbon atoms link with each other through a single, double or triple bonds forming a straight chain such as; n-Butane. C-C-C-C. The following diagram straight chain for a compound hexane.

 

 

 

Branched chain compounds: Branched chain compounds are those in which there is a branch along a straight chain, such as:

 

 

(ii) Closed chain or Cyclic compounds

Closed chain or cyclic compounds are those in which the carbon atoms at the end of the chain are not free. They are linked to form a ring. They are further divided into two classes:

  • Homocyclic or carbocyclic compounds.
  • Heterocyclic compounds.

(a) Homocyclic or Carbocyclic compounds.

Homocyclic or carbocyclic compounds contain rings which are made up of only one kind of atoms, i.e., carbon atoms. These are further divided into two classes:

 

  • Aromatic compounds
  • Alicyclic compounds

 

  • Aromatic compounds (Benzenoid) :

These organic compounds contain at least one benzene ring in their molecule. A benzene ring is made up of six carbon atoms with three alternating double bonds. They are called aromatic because of aroma or smell they have. They are also called benzenoid compounds.  Examples are Benzene and Naphthaline.

 

 

  • Alicyclic or non-benzenoid compounds:

Carbocyclic compounds which do not have benzene ring in their molecules are called alicyclic or non-benzenoid compounds. For example,

(b) Heterocyclic compounds

Cyclic compounds that contain one or more atoms other than that of carbon atoms in their rings are called heterocyclic compounds.

 

The classification may be summarized as follows:

 

Question 5: Why are organic compounds numerous?

Diversity and Magnitude of Organic Compounds

There are a total of 118 elements known today. The number of organic compounds (carbon compounds) is more than ten million. This number is far more than the number of compounds of all the remaining elements taken together. The existence of such a large number of organic compounds is due to the following reasons:

 

(i) Catenation: The ability of carbon atoms to link with other carbon atoms to form long chains and large rings is called catenation. carbon atoms can link with one another by means of covalent bonds to form long chains or rings of carbon atoms. The chains can be straight or branched. This is the main reason for the existence of a large number of organic compounds.

Two basic conditions for an element to exhibit catenation are:

  • Element should have valency two or greater than two.
  • Bonds made by an element with its own atoms should be stronger than the bonds made by the element with other atoms especially oxygen.

Both silicon and carbon have similar electronic configurations but carbon shows catenation whereas silicon does not. It is mainly due to the reason that C-C bonds are much stronger (355 kJ mol-1) than Si-Si (200 kJ mol) bonds. On the other hand, Si – O bonds are much stronger (452 kJ mol-1) than C-O bonds (351 kJ mol-1). Hence, silicon occurs in the form of silica (SiO2) and silicates in nature.

(ii) Isomerism: The compounds are said to be isomers if they have the same molecular formula but different arrangement of atoms in their molecules or different structural formulae. The phenomenon is called isomerism.

Isomerism is Another reason for the abundance of organic compounds. Number of isomers increases with the increase in number of carbon atoms in the given molecular formula.

Isomerism also adds to the possible number of structures, e.g., molecular formula C5H12 can be represented by three different structures. Thus, C5H12 has three isomers, as shown below:

(iii) Strength of covalent bonds of carbon: Due to its very small size, carbon can form very strong covalent bonds with other carbon atoms, hydrogen, oxygen, nitrogen and halogens. This enables it to form a large number of compounds.

(iv) Multiple bonding: In order to satisfy its tetravalency, carbon can make multiple bonds (i.e., double and triple bonds). This further adds to the possible number of structures. For example, two carbons in ethane are linked by a single covalent bond, by a double covalent bond in ethylene and a triple covalent bond in acetylene.

 

Question 6: What are the general properties of organic compounds?

Answer: General Characteristics of Organic Compounds:

Organic compounds have the following general characteristics:

 

(i) Origin: Naturally occurring organic compounds are obtained from plants and animals. On the other hand, inorganic compounds are obtained from minerals and rocks.

 

(ii) Composition: Carbon is an essential constituent of all organic compounds. They are made up of few elements such as carbon, hydrogen, nitrogen, oxygen, halogen, sulphur, etc. On the other hand, inorganic compounds are made up of almost all the elements of the Periodic Table known so far.

 

(iii) Covalent linkage: Organic compounds contain covalent bonds, that may be polar or non-polar, while the inorganic compounds mostly contain ionic bonds.

(iv) Solubility: Organic compounds having non-polar linkages are generally soluble in organic solvents like alcohol, ether, benzene, carbon disulphide etc. On the other hand, the inorganic compounds with ionic bonds are soluble in polar solvents like water.

 

(v) Electrical conductivity: Due to the presence of covalent bonds, organic compounds are poor conductor of electricity. Whereas inorganic compounds being ionic in nature, are good conductors of electricity in molten state or in aqueous solution.

 

(vi) Melting and boiling points: Generally, organic compounds have low melting and boiling points and are volatile in nature. Inorganic compounds, on the other hand, have comparatively high melting and boiling points.

 

(vii) Stability: Since organic compounds have low melting and boiling points, they are less stable than inorganic compounds.

 

(viii) Combustibility: Organic compounds with high percentage of carbon are generally combustible. On the other hand, inorganic compounds are mostly non-combustible.

 

(ix) Isomerism: A main characteristics of organic compounds which differentiate them from inorganic substances is their tendency to exhibit the phenomenon of isomerism. Isomerism is rare in inorganic substance.

 

(x) Rate of reaction: Due to the presence of covalent linkages, the reactions of organic compounds are molecular in nature. They are often slow and require specific conditions such as temperature, pressure or catalyst.

 

Question 7: What are different sources of organic compounds?

 

Answer: SOURCES OF ORGANIC COMPOUNDS

Organic compounds are prepared naturally by animals and plants. Animals synthesize two main groups of organic compounds: proteins and fats. Proteins are meat, mutton, chicken and eggs, etc. Fats are present in milk, butter, etc. Plants synthesize; carbohydrates, proteins, fats, vitamins, etc

Moreover, dead plants buried under Earth’s crust are converted through biochemical processes to coal, petroleum and gas. These materials are the main sources of organic compounds. We can get thousands of organic compounds by the destructive distillation of coal and fractional distillation of petroleum. Detail for each source is given in figure below:

 

 

Fig: Source of organic compounds

 

Question 8: (a) How is coal formed? What are the different types of coal?

(b) Write down the composition and uses of different types of coal.

(c) What is destructive distillation of coal?

(d) Name the different types of the products obtained by the destructive distillation of coal.

 

Answer: Coal

Coal is blackish, complex mixture of compounds of carbon, hydrogen and oxygen. It also consists of small amounts of nitrogen and sulphur compounds.

Formation of Coal: Coal was formed by the decomposition of dead plants buried under the Earth’s crust millions of years ago.

 

Carbonization: Conversion of wood into coal is called carbonization.

 

Explanation : It is a very slow biochemical process. It takes place in the absence of air under high pressure and high temperature over a long period of time (about 500 millions of years) as shown in figure below. Wood contains about 40% carbon, so depending upon the extent of carbonization process, four types of coal are found. These types differ with respect to carbon content, volatile matter and moisture. Table below shows the detail of contents of different types of coals and their uses in daily life and industry.

 

Fig. Formation of coal in different stages with the increase of pressure.

 

 

 

Table  Different types of coal

 

Type of Coal

Carbon ContentsUses 

 

Peat60 %It is interior quality coal used in kiln 
Lignite70 %It is soft coal used in thermal power stations. 
Bituminous80 %It is common variety of coal used as household coal. 
Anthractle90 %It is superior quality hard coal that is used in industry. 

 

 

Destructive distillation: The strong heating of coal in the absence of air is called destructive distillation.

Products obtained by destructive distillation of coal: Coal has become a major source of organic compounds because of destructive distillation. As we know, coal contains elements like carbon, hydrogen, oxygen, nitrogen and sulphur. So destructive distillation of coal provides a large number of organic compounds along with a few inorganic compounds. These products are:

 

Coal Gas: Coal Gas is mixture of hydrogen, methane and carbon monoxide.

Uses: It produces heat when burnt in air. Therefore, it is mainly used as a fuel in industry. It is also used to provide an inert or reducing atmosphere in various metallurgical processes.

 

Ammonical Liquor : Ammonical Liquor is a solution of ammonia gas in water.

Uses: It is used to prepare nitrogenous fertilizers. For example, when it is treated with sulphuric acid, it produces ammonium sulphate, fertilizer.

 

Coal Tar: Coal Tar is a thick black liquid.

Components of coal tar: It is a mixture of more than 200 different organic compounds, mostly aromatic. These compounds are separated by fractional distillation. Some of the important aromatic compounds are benzene, phenol, toluene, aniline, etc.

Uses of coal tar and its components: These chemicals are used to synthesize drugs, dyes, explosives, paints, varnishes, plastics, synthetic fibre and pesticides. Besides these valuable chemicals, the black residue of the coal tar called pitch is obtained. It is used for surfacing of roads and roofs.

(iv) Coke: Coke is 98% carbon. It is left behind residue of coal. When coal is subjected to destructive distillation, it loses all its volatile components and leaves behind a solid residue called coke.

 

Uses: It is mainly used as a reducing agent in the extraction of metals especially iron. It is also used as fuel.

 

Question 9: What is petroleum? What are main components of petroleum?

Petroleum

Petroleum is a dark brownish or greenish black coloured viscous liquid. It is a complex mixture of several solid, liquid or gaseous hydrocarbons in water mixed with salts and earth particles. Petroleum is a main source of organic compounds. It consists of several compounds mainly hydrocarbons. These compounds are separated by fractional distillation (separation of fractions or components depending upon their boiling point ranges).

 

Table: Fractions of Petroleum
NameCompositionBoiling rangeUses
Petroleum GasC1 to C4up to 25 0CAs a fuel, as such in the form of LPG, used for the production of carbon black (needed in tyre industry) and hydrogen gas (needed to form NH3 used to manufacture fertilizer).
Petroleum EtherC5 to C730 to 80 0CUsed as laboratory solvent and for dry cleaning purposes.
Gasoline or PetrolC7 to C1080 to 170 0CUsed as a fuel in motor cycles, motor cars and other light vehicles. It is more volatile than kerosene oil. It is also used for dry cleaning.
Kerosene oilC10 to C12170 to 250 0CUsed as domestic fuel, a special grade of it is used as jet fuel.
Diesel oilC13 to C15250 to 350 0CFuel for buses, trucks railway engines, tubewell engines and other heavy vehicles.
Fuel oilC15 to C18350 to 400 0CUsed in ships and industries to heat boilers and furnaces.

 

Question 10: Write a short note on natural gas?

Answer: Natural Gas:

It is a mixture of low molecular mass hydrocarbons. The main component about 85% is methane, along with other gases: ethane, propane and butane. Its originis similar to that of coal and petroleum. Therefore, it is found with their deposits. Natural gas is used as fuel in homes as well as in industries. It is used as fuel in automobiles as compressed natural gas (CNG). Natural gas is also used to make carbon black and fertilizer.

Fig. Occurrence and drilling of gas.

 

Question 11: Give some uses of organic compounds in our daily life?

Answer: USES OF ORGANIC COMPOUNDS:

No doubt, thousands of organic compounds are synthesized naturally by animals and plants. But millions of organic compounds are being prepared in the laboratories by the chemists. Because these compounds are part of everything from food we eat to the various items we use in daily life to fulfill our needs.

 

  • Uses as Food:The food we eat daily such as milk, eggs, meat, vegetables, etc., contain carbohydrates, proteins, fats, vitamins, etc., are all organic stuff.
  • Uses as Clothing:All types of clothing (we wear, we use as bed sheets etc.) are made up of natural fibres (cotton, silk and wool, etc.) and synthetic fibres (nylon , dacron and acrylic, etc.) all these are organic compounds.
  • Uses as Houses:Wood is cellulose (naturally synthesized organic compound). It is used for making houses and furniture of all kinds.
  • Uses as Fuel:The fuels we use for automobiles and domestic purposes are coal, petroleum and natural gas. These are called fossil fuels. All of these are organic compounds.
  • Uses as Medicines:A large number of organic compounds (naturally synthesized by plants) are used as medicines by us. Most of the life saving medicines and drugs such as antibiotics (inhibit or kill microorganisms which cause infectious diseases) are synthesized in laboratories.
  • Uses as Raw Material:Organic compounds are used to prepare a variety of materials, such as rubber, paper, ink, drugs, dyes, paints, varnishes, pesticides, etc.

 

Question 12: What are alkanes and alkyl radicals? Write down the characteristics of homologous series?

 

ALKANES: SATURATED HYDROCARBONS IN WHICH CARBON ATOMS ARE LINKED WITH OTHER CARBON ATOMS OR HYDROGEN ATOMS BY SINGLE BONDS ONLY ARE CALLED ALKANES.

Alkanes are saturated hydrocarbons or paraffins (para means little, affin means affinity). Their general formula is C nH2n+2 where ‘n’ is number of carbon atoms. In case of alkanes ‘n’ ranges from 1 to 40. In this way, alkanes form the most important homologous series of compounds.

 

Formation of Alkyl Radicals:

Alkyl radicals are derivatives of alkanes and they are formed by the removal of one of the hydrogen atom of an alkane and are represented by a letter ‘R’. Their name is written by replacing “ane” of alkane with ‘yl’. Following table represents first ten alkanes and their alkyl radicals. Their general formula is CnH2n+1.

 

 

Table: Names and Molecular Formulae of Alkanes and their Alkyl Radicals

 

 

Examples: Propane has a straight chain structure. When terminal H is removed, it is called n-propyl. When hydrogen from central carbon is removed, it is called isopropyl, as explained below:

 

 Similarly, different structures of butyl radicals are explained:

 

 

 

Homologous Series:

Organic compounds are divided into groups of compounds having similar chemical properties. Each group is known as a homologous series. Organic compounds of the same homologous series have the following properties in common:

  1. All members of a series can be represented by a general formula for example general formulae of alkane, alkenes and alkynes are CnH2n+2 , CnH2n and CnH2n-2 , respectively.
  2. Successive members of the series differ by one unit of -CH2– and 14 units in their relative molecular mass.
  3. They have similar chemical properties (because they contain the same functional group).
  4. There is a regular change in their physical properties; the melting and boiling points increase gradually with the increase of molecular masses.
  5. They can be prepared by similar general methods.

 

Question 13: Write a detailed note on functional groups of alkenes and alkynes. How they are identified from other compounds?

What are amines? Explain the different types of amines giving an example of each type. How primary amino group is identified?

Describe the functional group of an alcohol. How alcoholic groups are identified?

Differentiate between aldehydic and ketonic functional groups. How both are identified from each other?

 

Answer: FUNCTIONAL GROUPS: An atom or group of atoms or presence of double or triple bond which determines the characteristic properties of an organic compound is known as the functional group. The remaining part of the molecule mainly determines the physical properties such as melting point, boiling point, density, etc. For example, -OH group is the functional group of alcohols, which gives characteristics properties of alcohols.

The characteristic properties of carboxylic acids are due to the presence of -COOH group in them. Therefore, functional group of carboxylic acids is -COOH group.

 

 

Functional Groups Containing Carbon, Hydrogen and Oxygen:

The organic compounds containing carbon, hydrogen and oxygen as functional group are alcohols, ethers, aldehydes, ketones, carboxylic acids and esters.

 

(i) Alcoholic Group

The functional group of alcohol is -OH. Their general formula is ROH. Where R is any alkyl group.

 Methyl Alcohol CH3-OH

 

(ii) Ether Linkage: The functional group of ether is C – O – C. Their general formula is R – O – R` where R and R’ are alkyl groups. R and R’ may be same or different, such as:

H3C – O – CH3 Dimethyl ether C2H5 – O – C2H5 Diethyl ether

H3C – O – C2H5 Ethyl methyl ether

(iii) Aldehydic Group: Aldehyde family consists of functional group

Their general formula is RCHO. Where R stands for H or some alkyl group, such as:

 

(iv) Ketonic Group: Compounds containing the functional group C=O 10th Class Chemistry Chapter 11  are called ketones.

They have the general formula

where R and R’ are alkyl groups.

They may be same or different, such as:

 

(v) Carboxyl Group: Compounds containing functional group

are called carboxylic acids.

Their general formula is

where R stands for — H or some alkyl group. Such as:

 

(vi) Ester Linkage: Organic compounds consisting of RCOOR’ functional group are called esters.

Their general formula is

where R and R’are alkyl groups. They may be same or different, such as:

 

Table Functional groups containing carbon, hydrogen and oxygen

 

Functional Group Containing Carbon, Hydrogen and Nitrogen:

 

The organic compounds containing carbon, hydrogen and nitrogen as functional group are called as amines. Their functional group is -NH2 and their general formula is R-NH2. Examples of amines are:

Functional Group Containing Carbon, Hydrogen and Halogens:

The organic compounds having functional group containing carbon, hydrogen and halogens are called alkyl halides. Their functional group is R-X. ‘X’ may be F, CI, Br or I.

 

 

Table: Functional group containing carbon, hydrogen and halogens.

 

Double and Triple Bond: Hydrocarbon compounds consisting of double bonds between two carbon atoms in their molecules are called as alkenes, such as:

Hydrocarbon compounds consisting of triple bonds between two carbon atoms in their molecules are called as alkynes, such as:

 

 

TESTS OF FUNCTIONAL GROUPS:

 

Test for Unsaturation

(i) Bromine water test:

Dissolve a pinch of the given organic compound in 2.0 cm3 of carbon tetrachloride (CCI4). Add 2 cm3 of bromine water in it and shake.
Result: Bromine will be decolourised.

(ii) Baeyer’s test:

Dissolve about 0.2 g of the organic compound in water. Add to it 2-3 drops of alkaline KMnO4 solution and shake.

Result: Pink colour will disappear.

 

Test for Alcoholic Group (-OH)

 

(i) Sodium metal test:

Take about 2-3 cm3 of the given organic liquid in a dry test tube and add a piece of sodium metal.

Result: Hydrogen gas will evolve.

 

(ii) Ester formation test:

Heat about 1.0 cm3 of the organic compound with 1.0 cm3 of acetic acid and 1-2 drops of concentrated sulphuric acid.

Result: Fruity smell will be given out.

 

Test for Carboxyl Group

(i) Litmus test:

Shake a pinch of the given compound with water and add a drop of blue litmus solution.

Result: Litmus paper will turn red.

(ii) NaHCO3 solution test:

Take about 2.0 cm3 of 5% NaHCO3 solution and add a pinch of given compound.

Result: CO2 gas with effervescence evolves.

 

Detection of Aldehydic Group: (RCHO)

(i) Phenyl hydrazine test:

Shake a pinch of the given organic compound with about 2.0 cm3 of phenyl hydrazine solution.

Result: Orange red precipitate will be formed.

(ii) Sodium bisulphite test:

Shake about 0.2 g or 0.5 cm3 of the given compound with 1-2 cm3 of saturated solution of sodium bisulphite.

Result: A crystalline white precipitate will be formed.

 

(iii) Fehling’s solution test:

Mix equal volumes of Fehling’s solution A and B in a test tube. Add a pinch of organic compound and boil for five minutes.

Result: Red precipitate will be formed.

 

Test for Ketonic Group

(ii) Sodium nitroprusside test:

Take about 2.0 cm3 of sodium nitroprusside solution in a test tube and add 2-3 drops of NaOH solution. Now add a pinch of the given compound and shake.

Result: Red colour will be formed.

(iii) With Fehling’s solution:

No reaction

Test for Primary Amino Group (-NH2)

(i) Carbyl amine test:

Heat about 0.2 g of the given compound and add 0.5 cm3 of chloroform and add 2-3 cm3 of alcoholic KOH.

Result: Extremely unpleasant odour will be given out.

 

Test for Ester:

They are recognized by their fruity smell.

 

 

Science , Society and Technology

 

Pharmaceutical chemists work towards the partial and total synthesis of effective drugs

Synthesise of effective drugs to control the epidemics and fatal diseases is the need of the society. The responsibility to synthesize effective drugs is of pharmaceutical chemists. They can evaluate the efficiency and safety of these drugs. They make the drugs more and more effective by reducing their side effects and enhancing potency.

 

Concept Diagram:

 

 

Short Questions:

  1. What is meant by the term catenation? Give an example of a compound that displays catenation.

Answer: Catenation: The ability of carbon atoms to link with other carbon atoms to form long chains and large rings is called catenation. carbon atoms can link with one another by means of covalent bonds to form long chains or rings of carbon atoms.

 

Silicon and carbon have similar electronic configurations but carbon shows catenation whereas silicon does not. It is mainly due to the reason that C-C bonds are much stronger (355 kJ mol-1) than Si-Si (200 kJ mol) bonds. On the other hand, Si – O bonds are much stronger (452 kJ mol-1) than C-O bonds (351 kJ mol-1). Hence, silicon occurs in the form of silica (SiO2) and silicates in nature.

 

Example:

c-c-c-c-c-c-c-c

 

  1. How is coal formed?

Answer: Formation of Coal: Coal was formed by the decomposition of dead plants buried under the Earth’s crust millions of years ago.Conversion of wood into coal is called carbonization. It is a very slow biochemical process. It takes place in the absence of air under high pressure and high temperature over a long period of time (about 500 millions of years)

 

  1. What is importance of natural gas?

Answer: Natural gas is used as fuel in homes as well as in industries. It is used as fuel in automobiles as compressed natural gas (CNG). Natural gas is also used to make carbon black and fertilizer.

 

  1. Justify that organic compounds are used as food?

Answer: Uses of organic compounds as Food: The food we eat daily such as milk, eggs, meat, vegetables, etc., contain carbohydrates, proteins, fats, vitamins, etc., are all organic stuff.

  1. How are alkyl radicals formed? Explain with examples.

Answer: Formation of Alkyl Radicals:

Alkyl radicals are derivatives of alkanes and they are formed by the removal of one of the hydrogen atom of an alkane and are represented by a letter ‘R’. Their name is written by replacing “ane” of alkane with ‘yl’. Following table represents first ten alkanes and their alkyl radicals. Their general formula is CnH2n+1.

 

  1. What is the difference between n-propyl and isopropyl? Explain with structure.

Answer: Propane has a straight chain structure. When terminal H is removed, it is called n-propyl. When hydrogen from central carbon is removed, it is called isopropyl.

 

  1. Explain different radicals of butane.

Answer: Different radicals of butane are as follows.

 

 

 

  1. Define functional group with an example.

Answer: FUNCTIONAL GROUPS:

An atom or group of atoms or presence of double or triple bond which determines the characteristic properties of an organic compound is known as the functional group. The remaining part of the molecule mainly determines the physical properties such as melting point, boiling point, density, etc. For example, -OH group is the functional group of alcohols, which gives characteristics properties of alcohols.

The characteristic properties of carboxylic acids are due to the presence of -COOH group in them. Therefore, functional group of carboxylic acids is -COOH group.

 

  1. What is an ester group? Write down the formula of ethyl acetate.

Answer: Ester Linkage: Organic compounds consisting of RCOOR’ functional group are called esters.

Their general formula is

 

where R and R’are alkyl groups. They may be same or different, such as:

 

  1. Write classification of coal.

Answer:

Table  Different types of coal

 

Type of Coal

Carbon ContentsUses 

 

Peat60 %It is interior quality coal used in kiln 
Lignite70 %It is soft coal used in thermal power stations. 
Bituminous80 %It is common variety of coal used as household coal. 
Anthractle90 %It is superior quality hard coal that is used in industry. 

 

  1. What are heterocyclic compounds? Give two examples.

Answer: Heterocyclic compounds:

Cyclic compounds that contain one or more atoms other than that of carbon atoms in their rings are called heterocyclic compounds.

 

  1. Why are benzene and other homologous compounds of benzene called aromatic compounds?

Answer: Benzene and other homologous compounds of benzene posses aroma or smell so they are called aromatic compounds.

 

Extensive Questions:

 

  1. (a) How is coal formed? What are the different types of coal?

(b) Write down the composition and uses of different types of coal.

Answer: Please see answer of question no.8.

 

  1. (a) What is destructive distillation of coal?

(b) Name the different types of the products obtained by the destructive distillation of coal.

Answer: Please see answer of question no.8.

 

  1. Write a detailed note on functional groups of alkenes and alkynes. How they are identified from other compounds?

Answer: Related to question no. 13.

 

  1. Give some uses of organic compounds in our daily life.

Answer: Please see answer of question no. 11.

 

 

  1. Write down the characteristics of homologous series.

Answer: Please see answer of question no. 12.

 

  1. Why are organic compounds numerous?

Answer: Please see answer of question no. 5.

 

  1. What are amines? Explain the different types of amines giving an example of each type. How primary amino group is identified?

Answer: Please see answer of question no. 13.

 

  1. Describe the functional group of an alcohol. How alcoholic groups are identified?

Answer: Please see answer of question no. 13.

 

  1. Differentiate between aldehydic and ketonic functional groups. How both are identified from each other?

Answer: Please see answer of question no. 13.

 

  1. What are the general properties of organic compounds?

Answer: Please see answer of question no. 6.

 

  1. Write a detailed note on classification of organic compounds.

Answer: Please see answer of question no. 4.

 

Test yourself 11.1

1. Why and how carbon completes its octet?

Answer: Each and every atom wants to gain stability or attain octet role. For this purpose they gain, loss or share electrons. Carbon attain stability or complete its octet by sharing four electrons. Carbon forms multiple bonds (single, double or triple).

Example: In ethane carbon atom is bonded with other carbon or hydrogen atoms by single bonds.

 

2. Point out the properties of carbon which are responsible for formation of long chains of carbon atom compounds.

Answer: Catenation: The ability of carbon atoms to link with other carbon atoms to form long chains and large rings is called catenation. carbon atoms can link with one another by means of covalent bonds to form long chains or rings of carbon atoms. The chains can be straight or branched. This is the main reason for the existence of a large number of organic compounds.

Two basic conditions for an element to exhibit catenation are:

 

Element should have valency two or greater than two.

Bonds made by an element with its own atoms should be stronger than the bonds made by the element with other atoms especially oxygen.

 

3. Why is the melting and boiling points of organic compounds low?

Answer: Generally organic compounds have low melting and boiling points due to weak attractive forces in between their molecules (Weak intermolecular forces).

 

4. Why are the organic compounds poor conductors of electricity?

Answer: Organic compounds are weak conductors of heat and electricity due to their non-polar nature or due to the presence of non polar covalent bond.

 

 

5. What are the reasons for the formation of millions of organic compounds?

Answer: Organic compounds are basically hydrocarbons and their derivatives. Carbon is the main constituent of these compounds. Carbon has million of organic compounds in nature due to the following reasons.

a) Catenation.

b) Isomerism.

c) Strength of cavalent bond.

d) Multiple bonding.

 

 

 

 

Test Yourself 11.2

i. Name the gases which are found in coal gas?

Answer: Coal gas is a mixture of hydrogen, methane and carbon monoxide gases.

 

ii. Is coal tar a compound. What is importance of coal tar?

Answer: No, Coal tar is not a compound. Coal Tar is a thick black liquid. It is a mixture of more than 200 different organic compounds, mostly aromatic. These compounds are separated by fractional distillation. Some of the important aromatic compounds are benzene, phenol, toluene, aniline, etc.

 

iii. What is coke? For what purpose it is used?

Answer: Coke: Coke is 98% carbon. It is left behind residue of coal. When coal is subjected to destructive distillation, it loses all its volatile components and leaves behind a solid residue called coke.

Uses: It is mainly used as a reducing agent in the extraction of metals especially iron. It is also used as fuel.

 

iv. Which is the best quality of coal?

Answer: Anthracite is considered as the best quality of coal and is used in industries.

 

v. What is destructive distillation?

Answer: Destructive distillation: The strong heating of coal in the absence of air is called destructive distillation. OR  Destructive distillation is the process of separation of solid components from a mixture by heating in absence of air.

 

 

 Read Also Noun and types of Nouns

 

Test Yourself 11.3

1. Define petroleum.

Answer: Petroleum:

Petroleum is a dark brownish or greenish black coloured viscous liquid. It is a complex mixture of several solid, liquid or gaseous hydrocarbons in water mixed with salts and earth particles. Petroleum is a main source of organic compounds. It consists of several compounds mainly hydrocarbons. These compounds are separated by fractional distillation (separation of fractions or components depending upon their boiling point ranges).

 

2. What types of compounds are synthesized by plants?

Answer: Plants synthesize macromolecules like carbohydrates, proteins, fats, vitamins, etc Moreover, dead plants buried under Earth’s crust are converted through biochemical processes to coal, petroleum and gas. These materials are the main sources of organic compounds.

 

3. What is the basic unit of carbohydrates and how it is synthesized?

Answer: The basic unit of carbohydrates is glucose, which is synthesized by plants through the process of photosynthesis.

6CO2 + 6H2O à C6H12O6 + 6O2 + Energy.

 

4. CNG stands for ….

Answer: CNG stands for Compressed natural gas. CNG is used as fuel in automobiles.

 

5. Our existence owe to organic compounds, comment.

Answer: Organic compounds are the basic part of our food, our clothes, medicines and other useful items that we use in our daily life. Organic compounds fulfill our basic needs in various ways. That is why we can say our existence owe to organic compounds.

 

 

 

 

 

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