Class 10 Science Chapter 4 Carbon and Its Compounds
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NCERT Solutions For Class 10 Science Chapter 4 Carbon and Its Compounds
Class 10 Science Chapter 4 Carbon and Its Compounds
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
Ans . Correct option : ( b )
Explanation : Ethane has 7 covalent bonds . One bond is between two carbon atoms and rest of the six are between hydrogen atoms .
Q. 2. Butanone is a four – carbon compound with the functional group :
( a ) carboxylic acid
( b ) aldehyde
( c ) ketone
( d ) alcohol
Ans . Correct option : ( c )
Explanation : The functional group of butanone is 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 .
Ans . Correct option : ( b )
Explanation : While cooking , if the bottom of the vessel is getting blackened on the outside , then it means that the fuel is not burning completely .
Q. 4. Explain the nature of the covalent bond using the bond formation in CH3Cl .
Ans . Carbon completes its octet by sharing its four electrons with other carbon atoms or with atoms of other elements , because losing and gaining of four electrons requires extra amount of energy which makes the system unstable . In covalent bonding , both the atoms share the valence electrons , that is , 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 .
Q. 5. Draw the electron dot structures for :
( a ) ethanoic acid .
( b ) H₂S .
( c ) propanone .
( d ) F₂ .
Q. 6. What is a homologous series ? Explain with an example .
Ans . A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series . In this series carbon atoms can be linked together to form chains of varying lengths . In addition , hydrogen atom or atoms on these carbon chains 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 : 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 observed that there is a difference of -CH₂ unit between each successive compound .
As the molecular mass increases in any homologous series , the melting points and boiling points also increases . Other physical properties such as solubility in a particular solvent also show a similar gradation . But the chemical properties , which are determined by the functional group , remain similar in a homologous series .
Q. 7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties ?
Ans . 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 hydrogen carbonates to form salt , water , and carbon dioxide gas while ethanol does not react with them .
Metal Carbonate / Hydrogen carbonate + Carboxylic acid → Salt + Water + Carbon dioxide
For Example :
2CH3COOH + Na₂CO3 → 2CH3COONa + H₂O + CO₂
Metal Carbonates / Metal Hydrogen carbonates + Alcohols → No reaction
CH3CH₂OH + Na₂CO3 → No reaction
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 ?
Ans . 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 ?
Ans . 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 .
Q. 10. Explain the formation of scum when hard water is treated with soap .
Ans . 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 .
Q. 11. What change will you observe if you test soap with litmus paper ( red and blue ) ?
Ans . Since soap is basic in nature , it will turn red litmus blue . However , the colour of blue litmus will remain blue .
Q.12 . What is hydrogenation ? What is its industrial application ?
Ans . 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 .
Q. 13. Which of the following hydrocarbons undergo addition reactions :
C₂H6 , C3H8 , C3H6 , C₂H₂ and CH4 .
Ans . Unsaturated hydrocarbons undergo addition reactions . Being unsaturated hydrocarbons , C3H6 and C₂H₂ undergo addition reactions .
Q. 14. Give a test that can be used to differentiate chemically between butter and cooking oil.
Ans . 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 ) .
Q. 15. Explain the mechanism of the cleaning action of soaps .
Ans . Cleaning action of soaps :
The dirt ( oil and grease ) present on clothes is organic in nature , and insoluble in water . Therefore , it cannot be removed only by washing with water . When soap molecules are present in water , the molecules arrange themselves in the form of a clusters in such a manner that their hydrophobic ends are away from the water molecules and their hydrophilic or ionic ends are towards the water molecules .
The molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster . These micelles remain suspended in water like particles in a colloidal solution . The various micelles present in water do not come together to form a precipitate as each micelle repels the others because of ion – ion repulsion . Thus , the dust particles remain trapped in the micelles ( which remain suspended ) , and are easily washed away by water .
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Q. 1. What would be the electron dot structure of carbon dioxide which has the formula CO₂ ? [ NCERT Q. 1 , Page 61 ]
Ans . Electron dot structure of CO₂ :
Atomic number of carbon ( C ) = 6
Electronic configuration of carbon ( C ) = 2,4
Valence electrons of carbon ( C ) = 4
Atomic number of oxygen ( O ) = 8
Electronic configuration of oxygen ( O ) = 2,6
Valence electrons of oxygen ( O ) = 6
Q. 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 . ) [ NCERT Q. 2 , Page 61 ]
Ans . Electron dot structure of a sulphur molecule :
Atomic number of sulphur ( S ) = 16
Electronic configuration of sulphur ( S ) = 2 , 8 , 6
Valence electrons of sulphur ( S ) = 6
Q. 3. How many structural isomers can you draw for pentane ? [ NCERT Q. 1 , Page 68 ]
Ans . Three structural isomers are possible for pentane .
Q. 4. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us ? [ NCERT Q. 2 , Page 68 ]
Ans . The two properties of carbon which 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 . The compounds may have long chains of carbon , branched chains of carbon or even carbon atoms arranged in rings . Also the carbon atoms may be linked by single , double or triple bonds .
( ii ) Tetravalency : With the valency of four , carbon is capable of bonding with four other atoms . A carbon atom has four valence electrons . So , it has an ability to bond with four other atoms of carbon or atoms of any other mono – valent element .
Q. 5. What will be the formula and electron dot structure of cyclopentane ? [ NCERT Q. 3 , Page 68 ]
Ans . The formula for cyclopentane is C5H₁0 . Its electron dot structure is given below :
Q. 6. Draw the structures for the following compounds .
( i ) Ethanoic acid
( ii ) Bromopentane *
( iii ) Butanone
( iv ) Hexanal
* Are structural isomers possible for bromopentane ? [ NCERT Q. 4 , Page 69 ]
There are many structural isomers possible for bromopentane . Among them , the structures of three isomers are given .
Q. 7. How would you name the following compounds ?
[ NCERT Q. 5 , Page 69 ]
Ans . ( i ) Bromoethane
( ii ) Methanal
( iii ) Hexyne
Q. 8. Why is the conversion of ethanol to ethanoic acid an oxidation reaction ?
[ NCERT Q. 1 , Page 71 ]
Ans . Since the conversion of ethanol to ethanoic acid involves the addition of oxygen to ethanol , it is an oxidation reaction .
Q. 9. A mixture of oxygen and ethyne is burnt for welding . Can you tell why a mixture of ethyne and air is not used ? [ NCERT Q. 2 , Page 71 ]
When ethyne is burnt in air , it gives a sooty flame . This is due to incomplete combustion caused by limited supply of air . However , if ethyne is burnt with oxygen , it gives a clean flame with temperature 3000 ° C because of complete combustion . This oxy – acetylene flame is used for welding . It is not possible to attain such a high temperature without mixing oxygen . This is the reason why a mixture of ethyne and air is not used .
Q.10 . How would you distinguish experimentally between an alcohol and a carboxylic acid ? [ NCERT Q. 1 , Page 74 ]
Ans . We can distinguish between an alcohol and a carboxylic acid on the basis of their reaction with carbonates and hydrogen carbonates . Acid reacts with carbonate and hydrogen carbonate to evolve CO₂ gas that turns lime water milky .
Metal Carbonate / Hydrogencarbonate + Carboxylic acid → Salt + Water + Carbon dioxide
Alcohols , on the other hand , do not react with carbonates and hydrogen carbonates .
Q. 11. What are oxidising agents ? [ NCERT Q. 2 , Page 74 ]
Ans . Some substances such as alkaline potassium permanganate and acidified potassium dichromate are capable of adding oxygen to others . These are known as oxidizing agents .
Q. 12. Would you be able to check if water is hard by using a detergent ? [ NCERT Q. 1 , Page 76 ]
Ans . Detergents are generally sodium salts of sulphonic acids or ammonium salts with chlorides or bromides ions , etc. Unlike soap , they do not react with calcium and magnesium ions present in hard water to form scum . They give a good amount of lather irrespective of whether the water is hard or soft . This means that detergents can be used in both soft and hard water . Therefore , it cannot be used to check whether the water is hard or not .
Q. 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 ? [ NCERT Q. 2 , Page 76 ]
Ans . A soap molecule has two parts hydrophobic and hydrophilic . With the help of these , it attaches to the grease or dirt particle and forms a cluster called micelle . These micelles remain suspended as a colloid . To remove these micelles ( entrapping the dirt ) , it is necessary to agitate clothes .
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