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?
|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 reason 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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