# Carbon and Its Compounds : NCERT Exercise Questions

Q.1       Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.
Sol.         (b) 7 covalent bonds.

Q.2       Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.
Sol.         (c) ketone

Q.3       While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
(a) the food is not cooked completely.
(b) the fuel is not burning completely.
(c) the fuel is wet.
(d) the fuel is burning completely.
Sol.         (b) the fuel is not burning completely.

Q.4       Explain the nature of the covalent bond using the bond formation in CH3Cl.
Sol.

Carbon has 4 valence electrons. In order to make octet, it shares each of the four electrons with each of the three hydrogen atoms and one chloride atom. Since, bonds are formed because of sharing of electrons, hence these are covalent bonds.

Q.5       Draw the electron dot structures for
(a) ethanoic acid.
(b) H2S.
(c) propanone.
(d) F2 .
Sol.
(a) Ethanoic Acid

(b) H2S

(c) Propanone

(d) F2

Q.6       What is an homologous series? Explain with an example.

Sol.

The compounds of a homologous series can be represented by the same general formula. Compounds of homologous series differ by CH2 from their consecutive members. All the compounds of a homologous series show similar chemical and physical properties.
Example:
Alkanes; such as, Methane, Ethane, Propane, Butane, etc. belong to the same homologous series.

Similarly, all alkenes belong to a particular homologous series and all alkynes belong to another homologous series.
Properties of homologous series:
(a) Compounds of same the homologous series have same general formula.
(b) Compounds of same homologous series differ from their consecutive members by one carbon atom and two hydrogen atoms, i.e. by CH2.
(c) Compounds of same homologous series have same chemical properties.
(d) Compounds of same homologous series differ by molecular mass of 14u from their consecutive members.
(e) Compounds of same homologous series differ by physical properties with increase or decrease in molecular mass.

Q.7       How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Sol.

Difference in chemical properties:
Ethanol does not react with metal carbonate or metal hydrogen carbonate.

Ethanol +Metal carbonate $\rightarrow$ No Reaction

Ethanoic acid gives carbon dioxide when it reacts with metal carbonate or metal hydrogen carbonate.
Ethanoic Acid +Metal carbonate $\rightarrow$ Carbon Dioxide + Salt +Water

Q.8       Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Sol.

Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. When soap is dissolved in water and clothes are put in the soapy solution, soap molecules converge in a typical fashion to make a structure; called micelle. The hydrophobic ends of different molecules surround a particle of grease and make the micelle; which is a spherical structure. In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. This is why micelle formation takes place when soap is added to water.
Micelle is not formed in other solvent such as ethanol.

Q.9      Why are carbon and its compounds used as fuels for most applications?
Sol.

Carbon and its compounds have maximum number of carbon and hydrogen, which makes them of high calorific value. Thus, most of the carbon compounds release high amount of energy. This is the cause that carbon and its compounds are used as fuels for most applications.

Q.10     Explain the formation of scum when hard water is treated with soap.
Sol.

Hard water often contains salts of calcium and magnesium. Soap molecules react with the salts of calcium and magnesium and form a precipitate. This precipitate begins floating as an off-white layer over water. This layer is called scum. Soaps lose their cleansing property in hard water because of formation of scum.

Q.11     What change will you observe if you test soap with litmus paper (red and blue)?
Sol.

Since soaps are basic in nature, thus it turns red litmus paper blue. When blue litmus paper is dipped in soap solution it remains blue.

Q.12     What is hydrogenation? What is its industrial application?
Sol.

Hydrogenation is the chemical reaction between hydrogen and other compounds in the presence of catalyst. Hydrogenation is used mainly to reduce saturated hydrocarbons. Hydrogenation is an addition reaction.
Example:
When ethene is heated with the catalyst nickel it is reduced to ethane.
Industrial application:
Hydrogenation is used in many industrial applications. For example; in Petrochemical Industry, hydrogenation is used to convert alkenes into alkanes (paraffins) and cycloalkanes.
Hydrogenation is also used to prepare vegetable ghee from vegetable oils.

Q.13     Which of the following hydrocarbons undergo addition reactions:
C2H6, C3H8, C3H6, C2H2 and CH4.
Sol.

Thus, unsaturated hydrocarbons undergo addition reactions. Since, C3H6 and C2H2 are unsaturated hydrocarbons, thus these undergo addition reactions.

Q.14     Give a test that can be used to differentiate chemically between butter and cooking oil.
Sol.

Butter is saturated carbon compound while cooking oil is unsaturated carbon compound.
An unsaturated carbon compound decolorizes bromine water while a saturated hydrocarbon does not decolorize bromine water.
Thus, with reaction with bromine water; butter and cooking oil can be differentiated.
If the given sample does not decolorize the bromine water, it is butter and the one which decolorizes bromine water, is cooking oil.

Q.15     Explain the mechanism of the cleaning action of soaps.

Sol.

Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. In other words, one end is lipophobic (hydrophilic) and another end is lipophilic (hydrophobic). When soap is dissolved in water and clothes are put in the soapy solution, the hydrophobic ends of soap molecules entrap dirt and converge in a typical fashion to make a structure; called micelle. Micelle is a spherical structure. In the formation of micelle, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. Micelle is rinsed away from clothes.

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