Science
(Chapter – 4) (Carbon and its Compounds)
(Class – X)
Exercises
Question 1:
Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.
Answer 1:
(b) Ethane has 7 covalent bonds.
Question 2:
Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.
Answer 2:
(c) The functional group of butanone is ketone.
Question 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.
Answer 3:
(b) While cooking, if the bottom of the vessel is getting blackened on the outside, then it
means that the fuel is not burning completely.
9
,Question 4:
Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer 4:
Carbon can neither lose four of its electrons nor gain four electrons as both the processes
require extra amount of energy and would make the system unstable. Therefore, it
completes its octet by sharing its four electrons with other carbon atoms or with atoms of
other elements. The bonds that are formed by sharing electrons are known as covalent
bonds. In covalent bonding, both the atoms share the valence electrons, i.e., the shared
electrons belong to the valence shells of both the atoms.
Here, carbon requires 4 electrons to complete its octet, while each hydrogen atom requires
one electron to complete its duplet. Also, chlorine requires an electron to complete the
octet. Therefore, all of these share the electrons and as a result, carbon forms 3 bonds
with hydrogen and one with chlorine.
Question 5:
Draw the electron dot structures for
(a) ethanoic acid.
(b) H2S.
(c) propanone.
(d) F2.
Answer 5:
(a) Ethanoic acid
10
,(b) H2S
(c) Propanone
(d) F2
Question 6:
What is a homologous series? Explain with an example.
Answer 6:
A homologous series is a series of carbon compounds that have different numbers of
carbon atoms but contain the same functional group.
For example, methane, ethane, propane, butane, etc. are all part of the alkane
homologous series. The general formula of this series is CnH2n+2.
Methane CH4
Ethane CH3CH3
Propane CH3CH2CH3
Butane CH3CH2CH2CH3
It can be noticed that there is a difference of −CH2 unit between each successive
compound.
11
,Question 7:
How can ethanol and ethanoic acid be differentiated on the basis of their physical and
chemical properties?
Answer 7:
Ethanol is a liquid at room temperature with a pleasant odour while ethanoic acid
has vinegar-like smell. The melting point of ethanoic acid is 17°C. This is below
room temperature and hence, it freezes during winters.
Ethanoic acid reacts with metal carbonates and metal hydrogencarbonates to form
salt, water, and carbon dioxide gas while ethanol does not react with them.
For example,
For example,
Question 8:
In the electrolytic refining of a metal M, what would you take as the anode, the cathode
and the electrolyte?
Answer 8:
In the electrolytic refining of a metal M:
Anode → Impure metal M
Cathode → Thin strip of pure metal M
Electrolyte → Solution of salt of the metal M
12
,Question 9:
Why are carbon and its compounds used as fuels for most applications?
Answer 9:
Most of the carbon compounds give a lot of heat and light when burnt in air. Saturated
hydrocarbons burn with a clean flame and no smoke is produced. The carbon compounds,
used as a fuel, have high calorific values. Therefore, carbon and its compounds are used
as fuels for most applications.
Question 10:
Explain the formation of scum when hard water is treated with soap.
Answer 10:
Soap does not work properly when the water is hard. A soap is a sodium or potassium salt
of long chain fatty acids. Hard water contains salts of calcium and magnesium. When soap
is added to hard water, calcium and magnesium ions present in water displace sodium or
potassium ions from the soap molecules forming an insoluble substance called scum. A lot
of soap is wasted in the process.
Question 11:
What change will you observe if you test soap with litmus paper (red and blue)?
Answer 11:
Since soap is basic in nature, it will turn red litmus blue. However, the colour of blue litmus
will remain blue.
Question 12:
What is hydrogenation? What is its industrial application?
Answer 12:
Hydrogenation is the process of addition of hydrogen. Unsaturated hydrocarbons are
added with hydrogen in the presence of palladium and nickel catalysts to give saturated
hydrocarbons.
This reaction is applied in the hydrogenation of vegetables oils, which contain long chains
of unsaturated carbons.
13
,Question 13:
Which of the following hydrocarbons undergo addition reactions:
C2H6, C3H8, C3H6, C2H2 and CH4.
Answer 13:
Unsaturated hydrocarbons undergo addition reactions. Being unsaturated hydrocarbons,
C3H6 and C2H2 undergo addition reactions.
Question 14:
Give a test that can be used to differentiate chemically between butter and cooking oil.
Answer 14:
Butter contains saturated fats. Therefore, it cannot be hydrogenated. On the other hand,
oil has unsaturated fats. That is why it can be hydrogenated to saturated fats (solids).
Question 15:
Explain the mechanism of the cleaning action of soaps.
Answer 15:
Cleansing action of soaps:
The dirt present on clothes is organic in nature and insoluble in water. Therefore, it cannot
be removed by only washing with water. When soap is dissolved in water, its hydrophobic
ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of
soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster.
These micelles remain suspended in the water. Hence, the dust particles are easily rinsed
away by water.
14
, Page 61
Question 1:
What would be the electron dot structure of carbon dioxide which has the formula CO 2?
Answer 1:
Electron dot structure of CO2 is
Question 2:
What would be the electron dot structure of a molecule of sulphur which is made up of
eight atoms of sulphur? (Hint − the eight atoms of sulphur are joined together in the form
of a ring.)
Answer 2:
Electron dot structure of a sulphur molecule
1
, Page 68 - 69
Question 1:
How many structural isomers can you draw for pentane?
Answer 1:
Three structural isomers are possible for pentane.
(i)
(ii)
(iii)
Question 2:
What are the two properties of carbon which lead to the huge number of carbon
compounds we see around us?
Answer 2:
The two features of carbon that give rise to a large number of compounds are as follows:
(i) Catenation: It is the ability to form bonds with other atoms of carbon.
(ii) Tetravalency: With the valency of four, carbon is capable of bonding with four other
atoms.
2
,Question 3:
What will be the formula and electron dot structure of cyclopentane?
Answer 3:
The formula for cyclopentane is C5H10. Its electron dot structure is given below.
Question 4:
Draw the structures for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal
*Are structural isomers possible for bromopentane?
Answer 4:
(i)
(ii) There are many structural isomers possible for bromopentane. Among them, the
structures of three isomers are given.
3
, (iii)
(iv)
4
(Chapter – 4) (Carbon and its Compounds)
(Class – X)
Exercises
Question 1:
Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.
Answer 1:
(b) Ethane has 7 covalent bonds.
Question 2:
Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.
Answer 2:
(c) The functional group of butanone is ketone.
Question 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.
Answer 3:
(b) While cooking, if the bottom of the vessel is getting blackened on the outside, then it
means that the fuel is not burning completely.
9
,Question 4:
Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer 4:
Carbon can neither lose four of its electrons nor gain four electrons as both the processes
require extra amount of energy and would make the system unstable. Therefore, it
completes its octet by sharing its four electrons with other carbon atoms or with atoms of
other elements. The bonds that are formed by sharing electrons are known as covalent
bonds. In covalent bonding, both the atoms share the valence electrons, i.e., the shared
electrons belong to the valence shells of both the atoms.
Here, carbon requires 4 electrons to complete its octet, while each hydrogen atom requires
one electron to complete its duplet. Also, chlorine requires an electron to complete the
octet. Therefore, all of these share the electrons and as a result, carbon forms 3 bonds
with hydrogen and one with chlorine.
Question 5:
Draw the electron dot structures for
(a) ethanoic acid.
(b) H2S.
(c) propanone.
(d) F2.
Answer 5:
(a) Ethanoic acid
10
,(b) H2S
(c) Propanone
(d) F2
Question 6:
What is a homologous series? Explain with an example.
Answer 6:
A homologous series is a series of carbon compounds that have different numbers of
carbon atoms but contain the same functional group.
For example, methane, ethane, propane, butane, etc. are all part of the alkane
homologous series. The general formula of this series is CnH2n+2.
Methane CH4
Ethane CH3CH3
Propane CH3CH2CH3
Butane CH3CH2CH2CH3
It can be noticed that there is a difference of −CH2 unit between each successive
compound.
11
,Question 7:
How can ethanol and ethanoic acid be differentiated on the basis of their physical and
chemical properties?
Answer 7:
Ethanol is a liquid at room temperature with a pleasant odour while ethanoic acid
has vinegar-like smell. The melting point of ethanoic acid is 17°C. This is below
room temperature and hence, it freezes during winters.
Ethanoic acid reacts with metal carbonates and metal hydrogencarbonates to form
salt, water, and carbon dioxide gas while ethanol does not react with them.
For example,
For example,
Question 8:
In the electrolytic refining of a metal M, what would you take as the anode, the cathode
and the electrolyte?
Answer 8:
In the electrolytic refining of a metal M:
Anode → Impure metal M
Cathode → Thin strip of pure metal M
Electrolyte → Solution of salt of the metal M
12
,Question 9:
Why are carbon and its compounds used as fuels for most applications?
Answer 9:
Most of the carbon compounds give a lot of heat and light when burnt in air. Saturated
hydrocarbons burn with a clean flame and no smoke is produced. The carbon compounds,
used as a fuel, have high calorific values. Therefore, carbon and its compounds are used
as fuels for most applications.
Question 10:
Explain the formation of scum when hard water is treated with soap.
Answer 10:
Soap does not work properly when the water is hard. A soap is a sodium or potassium salt
of long chain fatty acids. Hard water contains salts of calcium and magnesium. When soap
is added to hard water, calcium and magnesium ions present in water displace sodium or
potassium ions from the soap molecules forming an insoluble substance called scum. A lot
of soap is wasted in the process.
Question 11:
What change will you observe if you test soap with litmus paper (red and blue)?
Answer 11:
Since soap is basic in nature, it will turn red litmus blue. However, the colour of blue litmus
will remain blue.
Question 12:
What is hydrogenation? What is its industrial application?
Answer 12:
Hydrogenation is the process of addition of hydrogen. Unsaturated hydrocarbons are
added with hydrogen in the presence of palladium and nickel catalysts to give saturated
hydrocarbons.
This reaction is applied in the hydrogenation of vegetables oils, which contain long chains
of unsaturated carbons.
13
,Question 13:
Which of the following hydrocarbons undergo addition reactions:
C2H6, C3H8, C3H6, C2H2 and CH4.
Answer 13:
Unsaturated hydrocarbons undergo addition reactions. Being unsaturated hydrocarbons,
C3H6 and C2H2 undergo addition reactions.
Question 14:
Give a test that can be used to differentiate chemically between butter and cooking oil.
Answer 14:
Butter contains saturated fats. Therefore, it cannot be hydrogenated. On the other hand,
oil has unsaturated fats. That is why it can be hydrogenated to saturated fats (solids).
Question 15:
Explain the mechanism of the cleaning action of soaps.
Answer 15:
Cleansing action of soaps:
The dirt present on clothes is organic in nature and insoluble in water. Therefore, it cannot
be removed by only washing with water. When soap is dissolved in water, its hydrophobic
ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of
soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster.
These micelles remain suspended in the water. Hence, the dust particles are easily rinsed
away by water.
14
, Page 61
Question 1:
What would be the electron dot structure of carbon dioxide which has the formula CO 2?
Answer 1:
Electron dot structure of CO2 is
Question 2:
What would be the electron dot structure of a molecule of sulphur which is made up of
eight atoms of sulphur? (Hint − the eight atoms of sulphur are joined together in the form
of a ring.)
Answer 2:
Electron dot structure of a sulphur molecule
1
, Page 68 - 69
Question 1:
How many structural isomers can you draw for pentane?
Answer 1:
Three structural isomers are possible for pentane.
(i)
(ii)
(iii)
Question 2:
What are the two properties of carbon which lead to the huge number of carbon
compounds we see around us?
Answer 2:
The two features of carbon that give rise to a large number of compounds are as follows:
(i) Catenation: It is the ability to form bonds with other atoms of carbon.
(ii) Tetravalency: With the valency of four, carbon is capable of bonding with four other
atoms.
2
,Question 3:
What will be the formula and electron dot structure of cyclopentane?
Answer 3:
The formula for cyclopentane is C5H10. Its electron dot structure is given below.
Question 4:
Draw the structures for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal
*Are structural isomers possible for bromopentane?
Answer 4:
(i)
(ii) There are many structural isomers possible for bromopentane. Among them, the
structures of three isomers are given.
3
, (iii)
(iv)
4
