Organic Chemistry Class-10 Goyal Brothers ICSE Solutions Ch-11

Answer :Ethene and bromine are an addition reaction because ethene is an alkene – it has a double bond. It is easier for new atoms to open the double bond and react there than to remove the hydrogen already attached, and then bond to it, which would be a substitution reaction

Question 7. What do you understand by hydrogenation? Give the necessary conditions and chemical equation for the hydrogenation of ethene.

Answer : Hydrogenation is a chemical reaction between molecular hydrogen and other compounds and elements. Hydrogenation is used in many applications such as the food industry, petrochemical industry and the pharmaceutical manufacturing industry

The hydrogenation of ethene


Ethene reacts with hydrogen in the presence of a finely divided nickel catalyst at a temperature of about 150°C. Ethane is produced.

Question 8. What do you mean by polymerization? How can polyethene be prepared by ethene?

Answer :

Polymerization, any process in which relatively small molecules, called monomers, combine chemically to produce a very large chainlike or network molecule, called a polymer. The monomer molecules may be all alike, or they may represent two, three, or more different compounds.

Poly(ethene) (polythene or polyethylene)

Question 9. How will you bring about the following conversion?
(i) Ethene into ethyl alcohol (ii) Ethene into acetaldehyde

Answer : conversion

(i) Ethene into ethyl alcohol–Ethanol is manufactured by reacting ethene with steam. The reaction is reversible, and the formation of the ethanol is exothermic. Only 5% of the ethene is converted into ethanol at each pass through the reactor

(ii) Ethene into acetaldehyde–The catalytic conversion of ethane to acetaldehyde has been achieved using nitrous oxide as the oxidant. Water vapor is essential for high selectivity to acetaldehyde.

Question 10.  Give molecular formula and names of first four homologous members of alkenes.


Answer :

Alkene Homologous Series
Name Number of Carbon atoms Molecular Formula CnH2n
ethene 2 C2H2(2) = C2H4
Propene 3 C3H2(3) = C3H6
Butene 4 C4H2(4) = C4H8
Pentene 5 C5H2(5) = C5H10

Question 11.  Starting from ethylene, how will you obtain acetic acid?

Answer  –  ethylene is oxidized into acetaldehyde with a PdCl2–CuCl2 catalyst, which is subsequently oxidized to acetic acid with a manganese acetate catalyst.

Exercise 5 Page –211

Organic Chemistry Class-10 Goyal Brothers ICSE Solutions Ch-11

Question 1. How is acetylene gas prepared in the laboratory?

Answer :Acetylene is prepared in the laboratory from calcium carbide. Calcium carbide is decomposed to acetylene with water as per the following reaction. Acetylene is collected in a glass jar by the downward displacement of wate

Question 2. How does acetylene gas react with chlorine?

Answer :The chlorine gas reacts with the acetylene (as well as many other hydrogenated compounds). This reaction is not what one might first expect, since it is not the product of the addition of the halogen across the carbon-carbon triple bond. The product is formed by the abstraction of hydrogen from the hydrocarbon

Question 3.  How will you distinguish between alkanes, alkenes and alkynes?

Answer :

Alkanes have single bonds between carbons in a hydrocarbon. Saturated hydrocarbons are saturated with hydrogen and are the simplest. They are represented in general as CnH2n+2 in case of non-cyclic structures or straight-chain structures. They are also called paraffins. In alkanes, there are four bonds for each carbon atom; it could be either C-H or C-C bond. Each hydrogen atom has to be bonded with a carbon atom. The simplest alkane is CH4. Alkane compounds are not very reactive; this is because the carbon bonds are stable and do not break easily. They have no functional groups attached to the carbon atoms

.Alkenes are unsaturated hydrocarbons which have at least one double bond. They are represented as CnH2n in general when there is no other functional group. They are also called olefin or olefine . they are more reactive than alkanes but relatively stable as compared to alkynes.


Alkynes are also unsaturated hydrocarbons; they have one or more triple bonds between the carbon atoms. Their general formula is CnH2n-2, in the case of any non-cyclic compound. They are also known as acetylenes. Alkynes are more reactive than alkenes and alkanes; They are highly reactive due to the presence of triple, unsaturated bonds and readily undergo addition reactions

Question 4.  Write names and structural formulas of isomers of third and fourth homologous members of alkynes.

Answer :

names and structural formulas of isomers of third homologous members of alkynes.
CH3-CH2-C≡CH  But-1-yne
CH3-C≡C-CH   But-2-yne

Chain isomerism 

Alkynes having or five or more carbon atoms show isomerism due to different structures of the carbon chain.

CH3-CH2-CH2-C≡CH Pent-1-yne

Functional isomerism 

Alkynes are functional isomers of dienes i.e. compounds containing two double bonds.

CH3-CH2-C≡CH But-1-yne

CH2=CH-CH=CH2 But-1,3-dienes

CH2=C=CH-CH3 But-1,2-diene

Question 5. How does acetylene gas react with alkaline KMn04?

Answer :Ethyne or acetylene on reaction with cold KMnO4 adds 4 OH− to the triple bond. It is oxidised by a dilute aqueous solution of potassium permanganate to form oxalic acid.

Question 6. Write four uses of acetylene gas.

Answer :The welding process that uses acetylene is known as oxy-fuel cutting or gas cutting. This method is used to cut or weld materials that require temperatures as high as 3,500 °C (6,330 °F). Among all other gasesacetylene is capable of producing the hottest flame

Question 7. What is the characteristic chemical reaction for unsaturated hydrocarbon?

Answer :Addition reaction is a characteristic of unsaturated hydrocarbons like alkenes and alkynes. An unsaturated hydrocarbon combines with another substance to produce a single product (saturated hydrocarbon), in the presence of a catalyst

Question 8. How will you distinguish between saturated and unsaturated hydrocarbons on the basis of chemical reaction?

Answer : Bromine water test – is used to differentiate between the unsaturated compounds (like alkenes and alkynes) and the saturated compounds. For this purpose, bromine is used in the form of bromine water. A solution of bromine in water is called bromine water. Bromine water has a red-brown color due to the presence of bromine in it. When bromine water is added to an unsaturated compound, then bromine gets added to the unsaturated compound and the red-brown color of bromine water is discharged. So, if an organic compound decolorizes bromine water, then it will be an unsaturated hydrocarbon (containing a double bond or a triple bond), but saturated hydrocarbon (alkanes) do not decolorize bromine water

Exercise 6 Page –216

Organic Chemistry Class-10 Goyal Brothers ICSE Solutions Ch-11

Question 1. State four industrial uses of alcohol.
Answer :  four industrial uses of alcohol.

Uses of Alcohols
  • Alcoholic Drinks.
  • Industrial methylated spirits.
  • Use of ethanol as a fuel.
  • Ethanol as a solvent.
  • Methanol as a fuel.
  • Methanol as an industrial feedstock.

Question 2. What is spurious liquor? What makes it harmful?
(a) What is the common name of the first member of the aldehyde group of compounds?
(b) State the IUPAC name and the structural formula of the above compound.

Answer : Spurious liquors include: illicit liquor (un-authorized preparation, not fit for human consumption and not complying with the BIS standards) and denatured alcohol (prepared for industrial uses and is rendered entirely unfit for human consumption by adding denaturants).

(a) the common name of the first member of the aldehyde group of compounds: formaldehyde,
(b)  the IUPAC name – Methanal

the structural formula – HCHO

structural formula - HCHO

Question 3. Complete the following chemical equation :

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