NCERT In Text Solution
Question: 1. What would be the electron dot structure of carbon dioxide which has the formula CO2?
Answer:
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:
Question: 3. How many structural isomers can you draw for pentane?
Answer: Pentane has three structural isomers. These are n-pentane, Iso-pentane and neo-pentane. Structures of all the three isomers are given here.
Question: 4. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Answer: Carbon can form huge number of carbon compounds because of the following properties:
Answer: Carbon can form huge number of carbon compounds because of the following properties:
- Catenation: Carbon can form bond with other carbon atoms. This property is called catenation. Because of catenation, carbon can form long chains, branched chains and closed chains.
- Carbon can form compounds with elements of many other elements.
- Ethanoic acid
- Bromopentane*
- Butanone
- Hexanal
- 6 covalent bonds
- 7 covalent bonds
- 8 covalent bonds
- 9 covalent bonds
- carboxylic acid
- aldehyde
- ketone
- alcohol
- the food is not cooked completely
- the fuel is not burning completely
- the fuel is wet
- the fuel is burning completely
- Compounds of same the homologous series have same general formula.
- Compounds of same homologous series differ from their consecutive members by one carbon atom and two hydrogen atoms, i.e. by CH2.
- Compounds of same homologous series have same chemical properties.
- Compounds of same homologous series differ by molecular mass of 14u from their consecutive members.
- Compounds of same homologous series differ by physical properties with increase or decrease in molecular mass.
Question: 5. What will be the formula and electron dot structure of cyclopentane?
Answer: Formula of cyclopentane is C5H10
Question: 6. Draw the structures for the following compounds.
Answer:
(i) Ethanoic acid
(ii) Bromopentane
(iii) Butanone
(iv) Hexanal
Question: 7. Are structural isomers possible for bromopentane?
Answer:Yes, isomer of bromopentane is possible. Structure of one of the isomers of bromopentane is given above.
Question: 8. How would you name the following compounds?
Answer:
(i) Bromoethane
Explanation: There is a bromo group with two carbon atoms.
(ii) Methanal
Explanation: There is an aldehyde group in this compound with one carbon atom.
(iii) Hexyne
Explanation: There is a triple bond with six carbon atoms.
Question: 9. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Answer: The conversion of ethanol to ethanoic acid is as follows:
CH3CH2OH + (Alkaline KMnO4 ) ⇨ CH3COOH
Since, in this reaction one oxygen is added to ethanol, hence it is an oxidation reaction.
Question: 10. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Answer: When mixture of oxygen and ethyne is burnt, it gives high temperature because of complete combustion and gives clean flame. But when ethyne is burnt with air, it results in incomplete combustion. Incomplete combustion will not give a high temperature simultaneously it will give sooty flame. This is the reason, oxygen is used; instead of air; to burn ethyne.
Question: 11. How would you distinguish experimentally between an alcohol and a carboxylic acid?
Answer: When acid reacts with carbonate and hydrogen carbonate, it gives carbon dioxide which turns lime water milky. On the other hand, alcohol does not give carbon dioxide on reaction with carbonate or hydrogen carbonate. Thus, the reaction with carbonate or hydrogen carbonate; can be used to distinguish between carboxylic acid and alcohol.
Question: 1 - Ethane, with the molecular formula C2H6 has
Answer: (b) 7 covalent bonds
Question: 2 - Butanone is a four-carbon compound with the functional group
Answer: (c) ketone
Question: 3 -While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
Answer: (b) the fuel is not burning completely
Question: 4 - Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer: Carbon has 4 valence electrons. In order to make octet, it shares each of the four electrons with each of the three hydrogen atoms and one chloride atom. Since, bonds are formed because of sharing of electrons, hence these are covalent bonds.
Question: 5 - Draw the electron dot structures for
(a) Ethanoic acid
Answer:
(b) H2S
Answer:
(c) Propanone
Answer:
(d) F2
Answer:
Question: 12. What are oxidising agents?
Answer:Substances which give oxygen or replace hydrogen on reaction with other compounds are called oxidising agents, example; potassium permanganate.
Question: 13. Would you be able to check if water is hard by using a detergent?
Answer: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.
Question: 14. 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:Molecules of soap form micelles with dirt, such as grease. Micelles remain suspended as colloid. To remove dirt in the form of micelles from clothes agitation is necessary to get clean clothes.
Question: 6 - What is an homologous series? Explain with an example.
Answer: The compounds of a homologous series can be represented by the same general formula. Compounds of homologous series differ by CH2 from their consecutive members. All the compounds of a homologous series show similar chemical and physical properties. Example: Alkanes; such as, Methane, Ethane, Propane, Butane, etc. belong to the same homologous series. Similarly, all alkenes belong to a particular homologous series and all alkynes belong to another homologous series.
Properties of homologous series:
Question: 7 - How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Answer:
| Physical Properties | |
|---|---|
| Ethanol | Ethanoic acid |
| Is a liquid at room temperature and has a pleasant fruity smell. | Is a liquid at room temperature and has vinegar like smell. |
| It does not freeze in winter. | It freezes in winter at 17° |
| It evaporates at room temperature. | It does not evaporate at room temperature. |
| It does not react with carbonate or metal carbonate. | It reacts with carbonate and metal carbonate to give salt, carbon dioxide and water |
Question: 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: 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.
Question: 9 - Why are carbon and its compounds used as fuels for most applications?
Answer: Carbon and its compounds have maximum number of carbon and hydrogen, which makes them of high calorific value. Thus, most of the carbon compounds release high amount of energy. This is the cause that 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: Hard water often contains salts of calcium and magnesium. Soap molecules react with the salts of calcium and magnesium and form a precipitate. This precipitate begins floating as an off-white layer over water. This layer is called scum. Soaps lose their cleansing property in hard water because of formation of scum.
Question: 11 - What change will you observe if you test soap with litmus paper (red and blue)?
Answer:Since soaps are basic in nature, thus it turns red litmus paper blue. When blue litmus paper is dipped in soap solution it remains blue.
Question: 12 - What is hydrogenation? What is its industrial application?
Answer: Hydrogenation is the chemical reaction between hydrogen and other compounds in the presence of catalyst. Hydrogenation is used mainly to reduce saturated hydrocarbons. Hydrogenation is an addition reaction.
Example: When ethene is heated with the catalyst nickel it is reduced to ethane.
Industrial application: Hydrogenation is used in many industrial applications. For example; in Petrochemical Industry, hydrogenation is used to convert alkenes into alkanes (paraffins) and cycloalkanes. Hydrogenation is also used to prepare vegetable ghee from vegetable oils.
Question: 13 - Which of the following hydrocarbons undergo addition reactions: C2H6, C3H8, C3H6, C2H2 and CH4
Answer: Formation of larger molecules by addition of more radicals is known as addition reaction. Thus, unsaturated hydrocarbons undergo addition reactions. Since, C3H6 and C2H2 are unsaturated hydrocarbons, thus these undergo addition reactions.
Question: 14 - Give a test that can be used to differentiate chemically between butter and cooking oil.
Answer: Butter is saturated carbon compound while cooking oil is unsaturated carbon compound. An unsaturated carbon compound decolorizes bromine water while a saturated hydrocarbon does not decolorize bromine water. Thus, with reaction with bromine water; butter and cooking oil can be differentiated. If the given sample does not decolorize the bromine water, it is butter and the one which decolorizes bromine water, is cooking oil.
Question: 15 - Explain the mechanism of the cleaning action of soaps.
Answer:Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. In other words, one end is lipophobic (hydrophilic) and another end is lipophilic (hydrophobic). When soap is dissolved in water and clothes are put in the soapy solution, the hydrophobic ends of soap molecules entrap dirt and converge in a typical fashion to make a structure; called micelle. Micelle is a spherical structure. In the formation of micelle, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. Micelle is rinsed away from clothes.
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