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Carbon and its Compounds

Ethane, with the molecular formula C2H6 has

a) 6 covalent bonds.

b) 7 covalent bonds.

c) 8 covalent bonds.

d) 9 covalent bonds.

Solution:

In an ethane molecule, there are six C-H single bonds and one C-C single bond.

Therefore, altogether there are seven single covalent bonds in ethane.

Correct Answer: (b)

Butanone is a four-carbon compound with the functional group

a) Carboxylic acid.

b) aldehyde.

c) ketone.

d) Alcohol.

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Solution:

Butanone is a four-carbon compound with the ketone functional group.

Correct answer: (C)

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.

Solution:

When fuel undergoes incomplete combustion while cooking, then the

bottom of the vessel gets blackened on the outside.

Correct answer: (b)

Explain the nature of the covalent bond using the bond formation in CH3Cl.

Solution:

CH3Cl is chloromethane. In chloromethane, there are one carbon atom, three

hydrogen atoms and one chlorine atom. The carbon atom is at the centre of the



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molecule. The carbon atom has four valance electrons. It shares these electrons

with three hydrogen atoms and one chlorine atom. The hydrogen atom has one

valence electron, while the chlorine atom has seven valence electrons.

Therefore, a chloromethane molecule is formed by sharing of four pairs of

electrons between the lone carbon atom, three hydrogen atoms and one chlorine

atom.

In chloromethane, there are three C-H single bonds and one C-Cl single bond.

Thus, the tetravalaency of carbon is satisfied.

Draw the electron dot structures for

a) ethanoic acid.

b) H2S.

c) Prop none.

d) F2.



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Solution:

What is an homologous series? Explain with an example.

Solution:

Homologous series: A homologous series is a group of organic compound with

the same functional group, in which a member in the group differs from the

succeeding and the preceding members by - CH2 group.

Example: Homologous series of alkanes. The general molecular formula for

alkanes is CnH2n+2 . The homologous series of alkanes is obtained by adding -

CH2 group from one compound to the other.

s.no

Alkane Molecular

formula

Difference in

molecular formula

1 Methane CH4 CH2

2 Ethane C2H6 CH2

3 Propane C3H8 CH2

4 Butane C4H10 CH2

5 Pentane C5H12 CH2

6 Hexane C6H14 CH2



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How can ethanol and ethanoic acid be differentiated on the basis of their

physical and chemical properties?

Solution:

Ethanol Ethanoic acid

Ethanol is a sweet-smelling liquid. Ethanoic acid has a characteristic

smell of vinegar.

The boiling point of ethanol is 351K. The boiling point of ethanoic acid is

391K.

Ethanol has a burning taste. Ethanoic acid has a sour taste.

Ethanol does not react with sodium

hydrogen carbonate.

Ethanoic acid reacts with sodium

hydrogen carbonate giving

brisk effervescence of carbon dioxide

gas.

CH3CH2OH + NaHCO3 →

No reaction

CH3COOH + NaHCO3 →

CH3COONa + H2O + CO2

Why does micelle formation take place when soap is added to water? Will a

micelle be formed in other solvents such as ethanol also?

Solution:

Soap forms micelle with water due to hydrophilic ionic ends and

hydrophobic hydrocarbon chain. Micelles are formed due to the association of

hydrophilic ends of soap molecules, which are insoluble in water.

In ethanol, the hydrophobic part of soap is soluble and therefore, micelle cannot

be formed in ethanol.

Why are carbon and its compounds used as fuels for most applications?

Solution:

Carbon and its compounds are used as fuels because they are highly

combustible, and release large amounts of heat due to the presence of

carbon and hydrogen.



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Example: CH4 + 2O2 → CO2 + 2H2O + Heat

Carbon and its compounds also have high calorific values.

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

Solution:

Soap does not give foam with hard water due to the formation of scum. The

scum is formed by the reaction of soap with calcium and magnesium salts

present in hard water. Scum is an insoluble precipitate of calcium and

magnesium salts of fatty acids formed by the reaction of soap with hard water.

Soap + Hard water → Calcium salt + Magnesium salt

(Scum)

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

Solution:

Soap is a salt of sodium or potassium hydroxide with long chain carboxylic

acids. Soap is, therefore, a salt of strong base and weak acid. The solution of

soap is, therefore, basic in nature. Hence, soap solution turns red litmus blue.

What is hydrogenation? What is its industrial application?

Solution:

The addition of hydrogen to an unsaturated hydrocarbon to get a saturated

hydrocarbon in presence of nickel or palladium as catalyst is called

hydrogenation.

Industrial application : Hydrogenation reaction is industrially used in the

hydrogenation of vegetable oils into Vanaspathy ghee (Dalda)

Vegetable oil + H2→HeatNi Vanaspathy ghee



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Which of the following hydrocarbons undergo addition reactions?

C2H6, C3H8, C3H6, C2H2 and CH4.

Solution:

Unsaturated hydrocarbons undergo addition reactions. In the given

compounds, C3H6 (propane) and C2H2 (ethyne) are unsaturated. Therefore,

C3H6 and C2H2 undergo addition reactions.

Give a test that can be used to differentiate chemically between butter and

cooking oil.

Solution:

Butter is saturated and cooking oil is unsaturated. The test for unsaturation can

be used to differentiate them. Decolourisation of bromine water is a test for

unsaturation. If bromine water is decolourised by a compound, then it is

unsaturated.

a) Cooking oil decolourises bromine water. Therefore, it is unsaturated.

b) Butter does not decolourise bromine water. Therefore, butter is saturated.

Explain the mechanism of the cleaning action of soaps.

Solution:

Soap Molecule: A soap molecule has two parts.

1. Ionic hydrophilic part. This part is soluble in water.

2. Non-polar hydrophobic long hydrocarbon chain.

This part is in soluble in water.

Formation of micelle: When soap is dissolved in water, a large number of soap

molecules associate with their hydrophobic tails pointing towards the inside and

hydrophilic ends in contact with water.

Mechanism of action of soap: The soap solution is a colloidal solution of

micelles. The oil and dirt of the clothes or skin are absorbed by the hydrophobic



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hydrocarbon part of the soap by the mechanical action of rubbing. Layers from

the dirty surface are converted into small globules. A stable emulsion of oil in

water is formed. The emulsified oil globules consisting of dirt can be readily

washed with water.

Thus, soap cleans the dirt from clothes or skin by forming micelles.



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