206
Carbon and Its Compounds
11. Carboxylic acids are used as solvent for resins, medicines , as
vinegar as coagulant for rubber etc.
Intext�Exercises
Intext Questions
On�Page�61
Question 1. What would be the electron dot structure of carbon dioxide
which has molecular formula CO2 ?
Answer Atomic number of C = 6
Atomic number of O = 8
Electronic configuration of C and O are
K L
K L
C 2 4
O 2 6
Electron dot structure
••
•
•
•O •
+
•
•
•C•
••
•
•
•O •
+
→
••
•
•O
• •
• •
• •
• •
C
••
O ••
or O == C ==O
Question 2. What would be the electron dot structure of a molecule of
sulphur which is made up of 8 atoms of sulphur?
Answer Atomic number of S = 16
Electronic configuration = K L M
2 8 6
Electron dot structure of S8
S
S
S
S
S
S
S
S
S
S
S
S
9
S
S
S
S
Crown shaped S8
molecule
On�Page�68
Question 1. How many structural isomers can you draw for pentane?
Answer
Pentane (C5H12 ) has a skeleton of five carbon atoms. It can exist as
straight chain as well as two branched chains. The possible structural isomers
have been shown below.
207
H H H H H
    
H C C C C C H
    
H H H H H
(n-pentane)
H H
4
H
3
H
2
1
H—C—C—C—C—H
H H
H
H—C—H
H
(2-methylbutane)
H

H C H

H  H
3 2 1
H C C C H
  
H  H
H C H

H
(2,�2-dimethyl�propane)
Question 2. What are the two properties of carbon which lead to the
huge number of carbon compounds we see around us?
Answer Two main reasons why carbon forms a huge number of carbon
compounds are (i) catenation (2) tetravalency of carbon.
(i) Catenation The self linking of carbon atoms through covalent bonds is
called catenation. Due to the property of catenation, C forms straight and
branched chains of varying lengths and rings of different sizes. This
increases the number of carbon compounds.
(ii) Tetravalency Due to tetravalency of C, it can form bonds either with
other carbon atoms or some other elements. Infact, due to its small size,
C forms strong bonds with many elements such as H, O, N, S and
208 halogens etc. In addition to this, C forms both double and triple bonds
with itself or with other elements like O, N etc. This further increases the
number of carbon compounds.
Question 3. What will be the formula and dot structure
cyclopentane?
of
Answer General formula of cycloalkane = Cn H2n
In cyclopentane n = 5,
∴ Formula of cyclopentane, C5H5 × 2 = C5H10
Electron dot structure of cyclopentane
Science-X
H
H
H
×
×
C
H
×
Carbon and Its Compounds
Question 3. What will be the formula and dot structure
cyclopentane?
of
Answer General formula of cycloalkane = Cn H2n
In cyclopentane n = 5,
∴ Formula of cyclopentane, C5H5 × 2 = C5H10
Electron dot structure of cyclopentane
H
H
×
×
×
H
C
×
H
H
×
H
×
C
C
×
C
C
×
×
×
H
H
H
H
Question 4. Draw the structure of the following compounds.
(a) Ethanoic�acid
(b) Bromopentane
(c) Butanone
(d) Hexanal
Are�structural�isomer�possible�for�bromopentane?
Answer
(a) Ethanoic acid,
H O
 
CH3 COOH, H  C  C OH

H
(b) Bromopentane, CH3 CH2 CH2 CH2 CH2Br
H H H H H
    
H  C  C  C  C  C Br
    
H H H H H
O

(c) Butanone,
CH3 CH2 C  CH3
H H O H
   
H  C  C  C  C �—H
 

H H
H
(d) Hexanal,
209
CH3 CH2 CH2 CH2 CH2 CHO
H H H H H O
     
H  C  C  C  C  C  C H
    
H H H H H
Yes, isomers of bromopentane are
(i) CH3 CH2 CH2 CH2 CH2Br
1-bromopentane
(ii) CH3 CH2 CH2CHCH3

Br
Science-X
2-bromopentane
(iii) CH3 CH2CHCH2CH3

Br
Carbon and Its Compounds
 
H H
Yes, isomers of bromopentane are
(i) CH3 CH2 CH2 CH2 CH2Br

H

H

H
1-bromopentane
(ii) CH3 CH2 CH2CHCH3

Br
2-bromopentane
(iii) CH3 CH2CHCH2CH3

Br
3-bromopentane
Question 5. How would you name the following compounds?
H

(a) CH3 CH2 Br
(b) H  C == O
H H H H
   
(c) H  C  C  C  C C ≡≡ C H
   
H H H H
Answer (a) CH3  CH2 Br, Bromoethane (because for two carbons, root
word is ‘eth’)
H

(b) H  C == O, Formaldehyde or methanal (because for single carbon, root
word is ‘meth’)
(c) CH3 CH2 CH2 CH2 C≡≡ CH , 1-hexyne (because for 6 carbons, root word is
‘hex’ and for triple bond suffix is ‘yne’.)
On�Page�71
Question 1. Why is conversion of ethanol to ethanoic acid an
oxidation reaction?
Answer Oxidation is the addition of oxygen to and removal of hydrogen from
any compound. During the conversion of ethanol to ethanoic acid we are
actually removing two hydrogen and adding oxygen to ethanol, so it is an
oxidation reaction.
O
210

CH3 CH2OH + O2 → CH3 C OH + H2O
Question 2. A mixture of oxygen and ethyne is used for welding. Why
do you think a mixture of ethyne and air is not used?
Answer We need a high temperature for welding but when ethyne is burnt in
air, it undergoes incomplete combustion and releases a lot of smoke and the
temperature is also not very high.
In order to ensure complete oxidation and to obtain the high temperature
needed for welding, a mixture of ethyne and oxygen is used.
2CH ≡≡ CH +5O2 → 4CO2 + 2H2O + heat + light
On�Page�74
Question 1. How would you distinguish experimentally between an
alcohol and a carboxylic acid?
Science-X
Carbon and Its Compounds
Answer Sodium bicarbonate test (NaHCO3 test)
Alcohol + NaHCO3 → No�effervescence
temperature is also not very high.
In order to ensure complete oxidation and to obtain the high temperature
needed for welding, a mixture of ethyne and oxygen is used.
2CH ≡≡ CH +5O2 → 4CO2 + 2H2O + heat + light
On�Page�74
Question 1. How would you distinguish experimentally between an
alcohol and a carboxylic acid?
Answer Sodium bicarbonate test (NaHCO3 test)
Alcohol + NaHCO3 → No�effervescence
Acid + NaHCO3 → Brisk�effervescence
The sample which produces brisk effervescence when treated with NaHCO3
due to release of CO2 is a carboxylic acid.
Question 2. What are oxidising agents?
Answer Those substances which are capable of providing oxygen to other
substances are called oxidising agents. e.g., alk. KMnO4 and acidified K 2 Cr2O7
can both behave as oxidising agents.
Acidic K 2 Cr 2O 7 + ∆
CH3 CH2OH → CH3 COOH + H2O
alk. KMnO4 + ∆
On�Page�76
Question 1. Would you be able to check if water is hard by using a
detergent?
Answer No, because detergent does not form scum with hard water either.
Question 2. People use a variety of methods to wash clothes. Usually
after adding soap, they beat the clothes or beat them with a paddle or
scrub with a brush or agitate the mixture in a washing machine. Why is
this agitation necessary to get clean clothes?
Answer When soap solution is made and dirty clothes soaked in it then
micelle formation occurs. This results in the formation of an emulsion. To wash
away the loosened dirt particles in the form of micelles from the surface of the
cloth, it is either scrubbed mechanically or beaten or agitated in washing
211
machine.
Exercises
Exercises
Question 1. Ethane, with molecular formula C 2H 6 has
(a) 6�covalent�bonds
(c) 8�covalent�bonds
(b) 7�covalent�bonds
(d) 9�covalent�bonds
H H
 
Answer (b) Structure of C2H6 is H  C  C H
 
H H
It is clear that it has 7 covalent bonds.
Question 2. Butanone is a four carbon compound with functional group
(a) carboxylic�acid
(c) ketone
(b) aldehyde
(d) alcohol
Science-X
Carbon and Its Compounds
Answer (c) In butanone, the function group is ketone (one) C == O.
Question 3. While cooking, if the bottom of the vessel is getting
blackened on the outside, it means that


Answer (b) Structure of C2H6 is H  C  C H
 
H H
It is clear that it has 7 covalent bonds.
Question 2. Butanone is a four carbon compound with functional group
(a) carboxylic�acid
(c) ketone
(b) aldehyde
(d) alcohol
Answer (c) In butanone, the function group is ketone (one)
C == O.
Question 3. While cooking, if the bottom of the vessel is getting
blackened on the outside, it means that
(a)
(b)
(c)
(d)
food�is�not�cooked�completely
the�fuel�is�not�burning�completely
fuel�is�wet
fuel�is�burning�completely
Answer (b) The unburnt particles of the fuel present in smoke blacken the
vessel from outside.
Question 4. Explain the formation of covalent bond in CH3Cl.
Answer Atomic number of
C = 6; H = 1; Cl = 17
Electronic configuration
K L
K LM
K
C2 4
Cl 2 8 7
H 1
C needs 4 electrons to complete its octet, H needs 1 and Cl needs 1
electron.
∴C shares its 4 electrons with each of the 3 H-atoms and 1 with chlorine
atom. It thus forms 4 covalent bonds as shown.
H
H
××
× ×
× ×
×
H
×
H—C—Cl
212
×
C
Cl
×
H
H
Question 5. Draw electron dot structure for
(a) ethanoic�acid
(c) propanone
(b) H2 S
(d) F2
Answer (a) Ethanoic acid, CH4 COO or CH3 COOH
H
O
C
C
H O
(a)
H—C—C—O—H
H
O
H
H
H
××
(b)
H2S, H—S—H
H ×
S
×
H
××
H
O
C
C
Science-X
H
Carbon and Its Compounds
(c) Propanone, CH3COCH3
H
H
C
H
H
H
××
(b)
H2S, H—S—H
H ×
S
×
H
××
(c) Propanone, CH3COCH3
H
H
O
H
C
C
C
H
H
××
××
F
××
F
××
F2, F—F
××
××
(d)
H
××
Question 6. What is a homologous series? Explain with an example.
Answer Homologous series-A series of similarly constituted compounds in
which the members present have the same functional group and similar
chemical properties and any two succesive members in a particular series differ
in their molecular formula by —CH2 unit is called homologous series.
Example of homologous series
Alkane series Cn H2n + 2
Methane, C2H6 Ethane
CH4
Propane, C4H10 Butane
C3H8
C5H12 Pentane
Question 7. How can ethanol and ethanoic acid be differentiated on
the basis of their physical and chemical properties?
Answer
I. Distinction based on physical properties
1. Smell Ethanoic acid has a pungent smell.
Ethanol has a pleasant smell.
213
2. Melting point Ethanol has lower melting point (150 K) than ethanoic acid
(290 K).
3. Physical state Ethanoic acid is solid (glacial acetic acid) in winters but
ethanol is always a liquid.
II. Distriction based on chemical properties
(i) Action with sodium hydrogen carbonate On adding a small amount of
sodium hydrogen carbonate to ethanoic acid, carbon dioxide gas is
evolved with brisk effervescence. However, no such reaction noticed in
case of ethanol.
CH3 COOH + NaHCO3 → CH3 COONa + CO2 ↑ + H2O
(ii) Action with caustic alkalies Ethanoic acids reacts with both sodium
hydroxide (NaOH) and potassium hydroxide (KOH) to form corresponding
salt and water. Ethanol fails to react with either of these.
CH3 COOH + NaOH → CH3 COONa + H2O
CH3 COOH + KOH → CH3 COOK + H2O
Question 8. Why does micelle formation take place when soap is added
to water? Will a micelle be formed in other solvents like ethanol also?
Answer Soaps are the molecules in which the two ends have different
properties, one is hydrophilic, that is, dissolved in water, while the other end is
hydrophobic, that is, dissolved in hydrocarbons. When soap
is atand
the Its
surface
of
Science-X
Carbon
Compounds
water, the hydrophobic ‘tail’ of soap will not be soluble in water and the soap will
align along the surface of water with the ionic end in water and the hydrocarbon
‘tail’ protruding out of water. Inside water, these molecules have a unique
CH3 COOH + KOH → CH3 COOK + H2O
Question 8. Why does micelle formation take place when soap is added
to water? Will a micelle be formed in other solvents like ethanol also?
Answer Soaps are the molecules in which the two ends have different
properties, one is hydrophilic, that is, dissolved in water, while the other end is
hydrophobic, that is, dissolved in hydrocarbons. When soap is at the surface of
water, the hydrophobic ‘tail’ of soap will not be soluble in water and the soap will
align along the surface of water with the ionic end in water and the hydrocarbon
‘tail’ protruding out of water. Inside water, these molecules have a unique
orientation that keeps the hydrocarbon portion out of the water. This is achieved
by forming clusters of molecules 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. Thus, the dirt suspended in the micelles is also easily rinsed away.
No, because ethanol is a polar covalent compound,so it acts as a solvent for
hydrophilic as well as hydrophobic end of the soap. Other such compounds
also do not form micelle with soaps due to similar reason.
Question 9. Why are carbon and its compounds used as fuels for most
applications?
Answer Carbon burns in oxygen (air) to form carbon dioxide and water.
During this reaction a large amount of heat and light are released. Further, once
ignited carbon and its compounds keep on burning without the requirement of
additional
214 energy. Hence, they are used as fuels.
C + O2 → CO2 + heat + light
Question 10. Explain the formation of scum when hard water is
treated with soap.
Answer Hard water contains calcium and magnesium salt and hence, their
ions. Soap is basically sodium or potassium salt of higher fatty acids. When
soap is added to water corresponding calcium and magnesium salts are
formed. These form scum.
Reaction taking place are shown below.
Ca 2+ + 2RCOONa → (RCOO)2 Ca + 2Na +
(Hard water)
(Soap)
(Calcium salt ppt.)
Mg2 + + 2RCCONa → (RCOO)2 Mg + 2Na +
(Hard water)
(Soap)
(Magnesium salt ppt.)
Question 11. What change will you observe if you test soap with
litmus (red or blue)?
Answer Soap is alkaline in nature and hence turns red litmus blue.
It will have no effect on blue litmus.
Question 12. What is hydrogenation? What is its industrial application?
Answer Hydrogenation The addition of hydrogen to unsaturated
hydrocarbon in the presence of catalyst is known as hydrogenation.
Industrial application When hydrogen gas is made to pass through vegetable
oil in the presence of nickel catalyst, it changes to solid fat (ghee).
Ni
Heat
Vegetable oils + H2 → Fats (ghee)
Science-X
(Unsaturated)
(Saturated)
Carbon and Its Compounds
Question 13. Which of the following hydrocarbons undergo addition
reaction?
Question 12. What is hydrogenation? What is its industrial application?
Answer Hydrogenation The addition of hydrogen to unsaturated
hydrocarbon in the presence of catalyst is known as hydrogenation.
Industrial application When hydrogen gas is made to pass through vegetable
oil in the presence of nickel catalyst, it changes to solid fat (ghee).
Ni
Heat
Vegetable oils + H2 → Fats (ghee)
(Unsaturated)
(Saturated)
Question 13. Which of the following hydrocarbons undergo addition
reaction?
C 2H 6 , C 3H 8 , C 3H 6 , C 2H2 and CH4
Answer Unsaturated hydrocarbons containing double/ triple bond undergo
addition reactions.
H H
H H
H
H
 
 


C2H6 , H  C  C H
C3H6 , H  C  C == C == C H
 

H H
H
H H H
H
  

C3H8 , H  C  C  C— H C2H2 , H —C≡≡ C — H CH4 , H  C H
  

H H H
H 215
So, C3H6 and C2H2 will undergo addition reactions.
Question 14. Give a test that can be used to differentiate between
butter and cooking oil.
Answer Butter contains saturated compounds while cooking oil contains
unsaturated compounds. Since unsaturated compounds are oxidised by
alkaline KMnO4 with disappearance of its pink colour.
∴ When cooking oil is treated with a few drops of alkaline KMnO4 , pink colour of
KMnO4 disappears. With butter however, the pink colour KMnO4 does not
disappear.
Question 15. Explain the mechanism of the cleansing action of soaps.
Answer Refer to Ans. No. 8.
Selected�NCERT�Exemplar�Problems
Multiple�Choice�Questions
Question 1. Carbon exists in the atmosphere in the form of
(a)
(b)
(c)
(d)
carbon�monoxide�only
carbon�monoxide�in�traces�and�carbon�dioxide
carbon�dioxide�only
coal
Answer (b)
Question 2. Which of the following statements are usually correct for
carbon compounds? These
(i) are�good�conductors�of�electricity
(ii)�are�poor�conductors��of�electricity
Science-X(iii)�have�strong�forces�of�attraction�between�their�molecules
Carbon and Its Compounds
(iv)�do�not�have�strong�forces�of�attraction�between�their�molecules
(a) (i)�and�(iii)
(b)�(ii)�and�(iii)
(c)�(i)�and�(iv)
(d) (ii) and (iv)