The fourth chapter in the NCERT Book for Class 10 Science focuses on Carbon and its various compounds. The chapter talks about covalent bonding in carbon and the versatility of carbon and further discusses the different saturated and unsaturated carbon compounds, their structures, the homologous series, and the nomenclature used for carbon compounds. You will also get to learn about the chemical properties of carbon compounds, and the properties of important compounds like Ethanol and Ethanoic Acids. The chapter also elaborates on how Soaps and Detergents work.
The topics in Chapter 4 include:
Get introduced to the world of Carbons and Carbon Compounds with Home Revise.
Q.1 What would be the electron dot structure of carbon dioxide which has the formula CO2?
Ans: The electron dot structure of carbon dioxide can be shown in this way.
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.)
Ans: The electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur will appear like this
Q.3 How many structural isomers can you draw for pentane?
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?
Ans: The two properties of carbon that give rise to a large number of compounds are as follows:
→ Catenation - It is the ability to form bonds with other atoms of carbon.
→ Tetra-valency - With the valency of four, carbon is capable of bonding with four other atoms.
Q.5 What will be the formula and electron dot structure of cyclo-pentane?
Ans: The formula for cyclo-pentane is C5H10. So electron dot structure can be given in this way
Q.6 Draw the structures for the following compounds.
(i) Ethanoic acid
(ii) Bromopentane
(iii) Butanone
(iv) Hexane
Ans: i) This is structure of ethanoic acid
Ans: ii) This is structure of Bromopentane
(iii) This is structure of Butanone.
(iv) This is structure of Hexane
Q.7 How would you name the following compounds?
(i) Bromoethane
(ii) Methanal (formaldehyde)
(iii) Hexyne
Ans: Given chemical compounds:
(i) Bromoethane:Longest carbon chain has two carbon atoms and it is an example of haloalkane.
CH3 – CH2 – Br
Ethyl bromide or bromo ethane(ii) Methanal (formaldehyde):The compound has 1 carbon atom and an aldehyde is present.
H−CHO
Formaldehyde or methanal(iii) Hexyne:Longest carbon chain has six carbon atoms, so suffix end is used and double bond present at the first carbon atom.
CH3− (CH2)3 − CH = CH2
1- HexeneQ.8 Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Ans: CH3CH2OH + (Alkaline KMnO4) → CH3COOH
Since, in this reaction one oxygen is added to ethanol; hence 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?
2HC ≡ CH + 5O2 → 4CO2 + 2H2O + Heat
Q.10 How would you distinguish experimentally between an alcohol and a carboxylic acid?
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.
Alcohols, on the other hand, do not react with carbonates and hydrogen carbonates.
Q.11 What are oxidizing agents?
Ans: Oxidizing agents are the substances that gain electrons in redox reaction and whose oxidation number is reduced.
Q.12 Would you be able to check if water is hard by using a detergent?
Ans: Detergent gives lather with hard and soft water both, while a soap gives lather with soft water only. Thus, it is not possible to check if water is hard; by using a detergent.
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?
Ans: A soap molecule has two parts namely 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, it is necessary to agitate clothes.
Q.14 How many structural isomers can you draw for pentane?
Ans: Three structural isomers are possible for pentane:
(i) CH3 - CH2 - CH2 - CH2 - CH3
n-Pentane(ii) 
iso-Pentane
(iii) 
neo-Pentane
Q.15 What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Ans: The two features of carbon that give rise to a large number of carbon compounds are as follows:
(i) Catenation - It is the ability of carbon to form bonds with other atoms of carbon.
(ii) Tetravalency - With the valency of four, carbon is capable of bonding with four other atoms.
Q.16 What will be the formula and electron dot structure of cyclopentane?
Ans: The formula for cyclopentane is C5H10.
Its electron dot structure is given below.
Q.17 How would you name the following compounds?
(i) CH3-CH2-Br
(ii)
(iii)
Ans: (i) Bromoethane
This compound has 2 carbon atoms so its parent name is ethane and it has also a bromo group; hence its name will be bromoethane.
(ii) Methanal (formaldehyde)
This compound has 1 carbon atom so its parent name is methane and it has also a functional group -CHO (aldehyde) so its name will be methanal.
(iii) Hexyne
This compound has 6 carbon atoms so its parent name is hexane and it has also a triple bond hence its name will be hexyne.
Q.18 Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Ans:
Since the conversion of ethanol to ethanoic acid involves the addition of oxygen to ethanol, it is an oxidation reaction.
Q.19 A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Ans:
When ethyne is burnt in air, it gives a sooty flame due to incomplete combustion caused by limited supply of oxygen by air. This is the reason, why a mixture of ethyne and air is not used. However, if ethyne is burnt with oxygen, because of complete combustion, it gives a clean flame with a temperature of about 3000oC. Thus, oxy-acetylene flame is used for welding.
Q.20 How would you distinguish experimentally between an alcohol and a carboxylic acid?
Ans: We can distinguish between an alcohol and a carboxylic acid on the basis of their reaction with sodium carbonate and sodium hydrogen carbonate. Carboxylic acids react with sodium carbonate and sodium hydrogen carbonate to evolve CO2 gas that turns lime water milky.
Sodium carbonate / Sodium hydrogen carbonate + Carboxylic acid
Salt + Water + Carbon dioxide
Alcohols, on the other hand, do not react with sodium carbonate and sodium hydrogen carbonate.
Q.21 What are oxidising agents?
Ans: Substances which are capable of adding oxygen to the starting material are called oxidising agents.They provide oxygen for oxidizing other substances.
Q.22 Would you be able to check if water is hard by using a detergent?
Detergents cannot be used to check whether the water is hard or not because they give a good amount of lather irrespective of whether the water is hard or soft.
Q.23 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?
Ans: A soap molecule has two parts namely hydrophobic hydrocarbon chain and hydrophilic ionic head, COO-Na+.
When the soap is added to dirty clothes, which contains grease and oily substances, the greasy and oily dirt particles attach themselves to the hydrocarbon part and ionic part remains attached to the water forming clusters of molecules. In these clusters, 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.
When the dirty clothes are agitated in soap or detergent solution, the dirt particles attached to the hydrocarbon part get washed away in water and the clothes get cleaned.
Q.24 Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds
Ans: (b) 7 covalent bonds
Q.25 Butanone is a four-carbon compound with the functional group
(a) carboxylic acid
(b) aldehyde
(c) ketone
(d) alcohol
Ans: (c) ketone
Q.26 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: (b) the fuel is not burning completely
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.27 Explain the nature of the covalent bond using the bond formation in CH3Cl.
Ans: Carbon can neither lose four valence 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, carbon shares one electron with each of the three atoms of hydrogen and one electron with the atom of chlorine. As a result, carbon forms 3 single covalent bonds with hydrogen and one with chlorine to form CH3Cl.
Q.28 Draw the electron dot structures for
(a) Ethanoic acid
(b) H2S
(c) Propanone
F2
Ans: (a) Ethanoic acid
(b) H2S
(c)Propanone
(d)F2
Q.29 What is a homologous series? Explain with an example.
Ans: A homologous series is a series of carbon compounds having similar structures and chemical properties and contain the same functional group. The successive compounds differ by -CH2 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.
Q.30 How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Ans:
Q.31 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: A soap is a sodium or potassium salt of long chain fatty acids.
A soap molecule has two parts namely the non polar (hydrocarbon) hydrophobic chain and polar (ionic) hydrophilic head, COO-Na+.
The long hydrocarbon chain being hydrophobic is insoluble in water but soluble in oil and grease. On the other hand, the ionic part of soap being hydrophilic is soluble in water but insoluble in oil and grease.
When soap is added to water, soap molecules arrange them in a cluster to keep the non-polar hydrophobic tail are towards the interior of the cluster and the polar hydrophilic head towards water. Since the dirt present on clothes is organic in nature and insoluble in water, the hydrophobic ends of the clusters attach themselves to the dirt. This cluster formation in which the dirt is entrapped is the micelle.The micelles stay in solution as a colloid and does not come together to precipitate because of ion-ion repulsion.Micelle formation does not occur in alcohol because the alkyl chain of soap becomes soluble in alcohol.
Q.32 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.33 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 carboxylic acids. Hard water contains salts of calcium and magnesium. When soap is added to hard water, calcium and magnesium ions, which are present in hard water, readily react with the carboxylate ion of the soap to form insoluble substance called scum. A lot of soap is wasted in the process.
Q.34 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.35 What is hydrogenation? What is its industrial application?
Ans: Hydrogenation is the process of addition of hydrogen. Unsaturated hydrocarbons are reacted with hydrogen in the presence of palladium or nickel catalysts to give saturated hydrocarbons.
This reaction is applied in the hydrogenation of vegetables oils, which contain long chains of unsaturated carbons.
Q.36 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.37 Give a test that can be used to differentiate chemically between butter and cooking oil.
And: Butter contains saturated fats. Therefore, it burns with a blue flame while oil has unsaturated fats and therefore burns with yellow flame.
Q.38 Explain the mechanism of the cleaning action of soaps.
Ans: A soap is a sodium or potassium salt of long chain fatty acids.A soap molecule has two parts namely the non polar (hydrocarbon) hydrophobic tail and polar (ionic) hydrophilic head, COO-Na+.
The long hydrocarbon chain being hydrophobic is insoluble in water but soluble in oil and grease. On the other hand, the ionic part of soap being hydrophilic is soluble in water but insoluble in oil and grease.
When soap is added to water, soap molecules arrange them in a cluster to keep the non-polar hydrophobic tail are towards the interior of the cluster and the polar hydrophilic head towards water. Since the dirt present on clothes is organic in nature and insoluble in water, the hydrophobic ends of the clusters attach themselves to the dirt. This cluster formation in which the dirt is entrapped is the micelle. The micelles stay in solution as a colloid and does not come together to precipitate because of ion-ion repulsion.
When the dirty clothes are agitated, the dirt particles attached to the hydrocarbon part get washed away in water and the clothes get cleaned.