Carbon and its Compounds (Question Answer)
QUESTIONS
1. What would be the electron dot structure of carbon dioxide which has
the formula CO2?
Answer:
OR 
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:
3. How many structural isomers can you draw for pentane?
Answer: Three structural isomers can be drawn for pentane.
n-pentane
iso-pentane
neo-pentane
4. What are the two properties of carbon which lead to the huge number
of carbon compounds we sea around us?
Answer: The numbers
of carbon compounds whose formulae are known to chemists was
recently estimated to be about three million. This outnumbers by a
large margin the compounds formed by all the other elements put
together.The nature of the covalent bond enables carbon to form a
large number of compounds. Two properties of carbon which lead to the huge number of carbon compounds are-
(i) Catenation: Carbon has the unique ability to form bonds with other atoms of
carbon, giving rise to large molecules. This property is called
catenation. These compounds may have long chains of carbon,
branched chains of carbon or even carbon atoms arranged in rings.
In addition, carbon atoms may be linked by single, double or triple
bonds. No other element exhibits the property of catenation to the extent
seen in carbon compounds. The carbon-carbon bond is very strong
and hence stable. This gives us the large number of compounds
with many carbon atoms linked to each other.
(ii) Tetra-valency: Since carbon has a valency of four, it is capable of bonding with
four other atoms of carbon or atoms of some other mono-valent
element. Compounds of carbon are formed with oxygen, hydrogen,
nitrogen, sulphur, chlorine and many other elements giving rise to
compounds with specific properties which depend on the elements
other than carbon present in the molecule.
5. What will be the formula and electron dot structure of cyclopentane?
Answer: Formula of cyclopentane is C5H10 . Its electron dot structure is -
6. Draw the structures for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal.
*Are structural isomers possible for bromopentane?
Answer:
(i) Structure of ethanoic acid is-
(ii) Structure of bromopentane is-
(iii) Structure of butanone is-
(iv) Structure of hexanal is-
Structural isomers of bromopentane are-
1-bromopentane
2-bromopentane
3-bromopentane
7. How would you name the following compounds?
(i) CH3—CH2—Br (ii) 
(iii) 
Answer:
(i) Bromorthane (ii) Methanal (iii) 1- hexyne
8. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Answer: Alkaline potassium permanganate or acidified potassium dichromate can convert alcohol to acids. In the process of conversion of ethanol to ethanoic acid oxygen is added to ethanol. hence this reaction is called an oxidation reaction.
CH3-CH2OH Alkalline KMnO4+ Heat→ CH3 COOH
9. A mixture of oxygen and ethyne is burnt for welding. Can you tell why
a mixture of ethyne and air is not used?
Answer: The amount of heat generated during the welding of iron is very important. When a mixture of ethyne and oxygen is burned, it burns completely and produces more heat than a mixture of ethyne and air. Therefore, a mixture of oxygen and ethyne is burned during welding and mixture of ethyne and air is not used.
10. How would you distinguish experimentally between an alcohol and
a carboxylic acid?
Answer: We can distinguish experimentally between an alcohol and a carboxylic acid by following ways-
(1) With the help of blue litmus paper: Carboxylic acids can change the color of blue litmus paper to red but alcohol cannot.
(2) With the help of Sodium Hydrogen Carbonate (NaHCO3): Sodium Hydrogen Carbonate will react with carboxylic acid with the evolution of a gas, but the alcohol does not react in any way.
11. What are oxidising agents?
Answer: Some substances are capable of adding oxygen to others.
These substances are known as oxidising agents.
CH3-CH2OH alkalline KMnO4/ acidified K2Cr2O7+ Heat → CH3 COOH
In the above reaction, alkaline potassium permanganate or acidified potassium dichromate
are oxidising alcohols to acids, that is, adding oxygen to the starting
material. Hence they are oxidising agents.
12. Would you be able to check if water is hard by using a detergent?
Answer: No, we cannot check if the water is hard or not by using detergent because detergents give froth in hard water also.
13. People use a variety of methods to wash clothes. Usually after adding
the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle,
scrub with a brush or the mixture is agitated in a washing machine.
Why is agitation necessary to get clean clothes?
Answer: Most dirt is
oily in nature and as you know, oil does not dissolve in water. The soap molecules along with dirt particles form structures called micelles where one end of the molecules is towards the oil droplet
while the ionic-end faces outside. This forms an emulsion in water. The
soap micelle thus helps in dissolving the dirt in water and we can wash
our clothes clean. To remove dirt particles along with micelles, people beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine.
EXERCISES
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: (b) 7 covalent bonds.
2. Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.
Answer: (c) ketone.
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: (b) the fuel is not burning completely.
4. Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer: CH3Cl is a covalent compound formed due to the sharing of electron among all the atoms present in the compound. It contains carbon (Z=6), hydrogen (Z=1) and Chlorine (Z=17). Valency of carbon is 4, while that of hydrogen and chlorine is 1. Carbon will share one electron each with three hydrogen atoms and one chlorine atom to satisfy its remaining tetra-valency. In this way the remaining valencies of hydrogen and chlorine will also be satisfied and all three atoms will attain stable octet. Formation of CH3Cl can be easily depicted with electron dot structure.
5. Draw the electron dot structures for
(a) ethanoic acid.
(b) H2S.
(c) propanone.
(d) F2 .
Answer:
(a)
Or 
(b)
Or 
(c)
Or 
(d)
Or 
6. What is an homologous series? Explain with an example.
Answer: A series of compounds in
which the same functional group substitutes for hydrogen in a carbon
chain is called a homologous series. Hydrogen atom or atoms on a carbon
chain can be replaced by any of the functional groups. The presence of a functional group such as alcohol dictates the
properties of the carbon compound, regardless of the length of the carbon
chain. For example, the chemical properties of CH3OH, C2H5OH, C3H7OH
and C4H9OH are all very similar.
7. How can ethanol and ethanoic acid be differentiated on the basis of their physical
and chemical properties?
Answer: Difference between ethanol and ethanoic acid on the basis of their physical properties:
1. Ethanol has a sweet smell, ethanoic acid has a pungent smell.
2. Melting point of ethanol is 156 K while that of ethanoic acid is 290 K.
3. Boiling point of ethanol is 351 K and boiling point of ethanoic acid is 391 K.
Difference between ethanol and ethanoic acid on the basis of their chemical properties :
1. Ethanoic acid can change the colour of blue litmus paper to red, while ethanol cannot change the colour of litmus paper.
2. Ethanoic acid reacts with sodium hydrogen carbonate to form effervescence due to evolution of CO2. But ethanol does not react with sodium hydrogen carbonate.
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?
Answer: In soap molecules the two ends have different properties, one is hydrophilic,
that is, it dissolves in water, while the other end is hydrophobic, that is, it dissolves in
hydrocarbons. When soap is added to 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.
Such micelle formation will not be possible in other solvents like ethanol in which sodium salt of fatty acids do not dissolve.
9. Why are carbon and its compounds used as fuels for most applications?
Answer: Combustion of carbon compounds produces huge amount of heat along with light. So, in most cases carbon compounds are used as fuels.
10. Explain the formation of scum when hard water is treated with soap.
Answer: Soaps cannot form leather in hard water. Hard water contains salts of calcium and magnesium. Calcium and magnesium on reacting with soap form insoluble precipitate called scum. The scum formation lessens the cleansing property of soaps in hard water.
2C17H35COONa + CaCl2 → (C17H35COO)2Ca + 2NaCl
Soap White precipitate
11. What change will you observe if you test soap with litmus paper (red and blue)?
Answer: Soaps are basic in nature. Hence, soap can change the colour of red litmus paper to blue. But it cannot change the colour of blue litmus paper.
12. What is hydrogenation? What is its industrial application?
Answer: Hydrogen can be added to unsaturated hydrocarbons in the presence of catalysts
such as palladium or nickel to give saturated hydrocarbons. This reaction is commonly
used in the hydrogenation of vegetable oils using a nickel catalyst.
Vegetable oils generally have long unsaturated carbon chains while
animal fats have saturated carbon chains. Hydrogenation reaction can be used to convert unsaturated vegetable oil to saturated oil.
13. Which of the following hydrocarbons undergo addition reactions:
C2H6, C3H8, C3H6, C2H2 and CH4.
Answer: C3H6 and C2H2 undergo addition reaction.
14. Give a test that can be used to differentiate chemically between butter and
cooking oil.
Answer: Bromine water test can be used to differentiate chemically between butter and cooking oil. This test is performed to differentiate between the unsaturated compounds (like alkenes and alkynes) and the saturated compounds. When bromine water is added to an unsaturated hydrocarbon red brown color of bromine solution is discoloured. So if there is dis-coloration then the compound will be an unsaturated Hydrocarbon. As butter is a saturated fat and cooking oil is a unsaturated fat hence bromine water test can be used to differentiate between butter and cooking oil.
15. Explain the mechanism of the cleaning action of soaps.
Answer: Most dirt is
oily in nature and as you know, oil does not dissolve in water. The
molecules of soap are sodium or potassium salts of long-chain carboxylic
acids. The ionic-end of soap dissolves in water while the carbon chain
dissolves in oil. The soap molecules, thus form structures called micelles
(see Fig. below) where one end of the molecules is towards the oil droplet
while the ionic-end faces outside. This forms an emulsion in water. The
soap micelle thus helps in dissolving the dirt in water and we can wash
our clothes clean.
Micelle
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