Chapter 4 – Carbon and its Compounds

Carbon and its Compounds

Q1.   What would be the electron dot structure of carbon dioxide which has the formula CO2?
Ans. The electron dot structure of CO2 is
Q2.   What would he the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur?
Q3.   How many structural isomers can you draw for pentane?
Ans. Three structural isomers can be drawn from pentane.
         Pentane : C5H12
Q4.   What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Ans. Carbon form large number of compounds due to the following properties:
         (a) Catenation ? Carbon shows the property of catenation that is the ability to form bonds with other carbon atoms forming long chains both branched and unbranched chains, and even rings.
         (b) Tetravalency ? Carbon has valency 4, it is capable of bonding with 4 other carbon atoms or atoms of other non-covalent elements, giving rise to compounds with specific properties depending on the elements present in the compound.
         (c) Isomerism ? Carbon compounds show the property of isomerism that is compounds having same molecular formula but different structural formula.
Q5.   What would be the formula and electron dot structure of cyclopentane?
Ans. The formula of cyclopentane is C5H10.
         The electron dot structure is
Q6.   Draw the structures for the following compounds.
         (i) Ethanoic acid         (ii) Bromopentane         (iii) Butanone         (iv) Hexanal
         Are structural isomers possible for bromopentane?
Q7.   How would you name the following compounds:
Ans. (i) Bromo ethane                  (ii) Methanal                  (iii) Hex-l-yne
Q8.   Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Ans. Conversion of ethanol to ethanoic acid is an oxidation reaction because oxygen is added to ethanol to convert it to ethanoic acid.
         In the above reaction alk. KMnO4/acidified K2Cr2O7 add oxygen to ethanol hence they are called oxidising agent.
Q9.   A mixture of oxygen and ethyne is burnt for welding. Cun you tell why a mixture of ethyne and air is not used?
Ans. If air is used, incomplete combustion will take place giving a sooty flame and less heat is produced.
         When pure oxygen is used ethyne burns completely producing large amount of heat and blue flame. This heat is sufficient for a metal to melt and welding is done.
Q10.   How would you distinguish experimentally between an alcohol and a carboxylic acid?
Ans. (a) Acid test: Reaction with carbonates/hydrogen carbonates.
               Take samples of alcohol and carboxylic acid in 2 test tubes, and add sodium carbonate or sodium bicarbonate solution to each. The compound which will produce brisk effervescence of CO2 gas will be acid.
         (b) Alcohol test: Take small amount of ethanol and ethanoic acid in test tube A and B. Add 5% solution of alkaline potassium permanganate drop by drop to this solution and warm the test tube.
               The colour of potassium permanganate will disappear in test tube containing alcohol.
Q11.   What are oxidising agents?
Ans. The compounds which add oxygen to other substance are known as oxidising agent.
         For example, alkaline potassium permanganate solution and acidified potassium dichromate, both can convert alcohol into carboxylic acid, i.e., ethanoic acid.
Q12.   Would you be able to check if water is hard by using detergent?
Ans. No, because detergent forms lather in both, hard and soft water.
Q13.   People use 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. Soap lowers the surface tension of water. The long chain non-ionic hydrocarbon group in soap gets attached to the oil or grease droplets and loosens them from the fibres of cloth along with the dirt. However this loosening is insufficient to remove the grease with dirt completely. Hence the clothes are agitated to remove the grease droplets completely.
Q1.   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.
Q2.   Butanone is a four-carbon compound with the functional group
           (a) carboxylic acid.         (b) aldehyde.
           (c) ketone.         (d) alcohol.
Ans.  (d) ketone.
Q3.   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.
Q4.   Explain the nature of the covalent bond using the bond formation in CH3Cl.
Ans. Bond formation in CH3Cl
           Carbon forms single covalent bond by sharing one electron pair with three hydrogen atoms and one chlorine atom. Chlorine being more electronegative adds polar nature to C-Cl bond.
Q5.   Draw the electron dot structure for
           (a) ethanoic acid         (b) H2S.
           (c) propanone.         (d) F2.
Ans. The electron dot structure are as follows:
           (a) Ethanoic acid – CH3COOH
Q6.   What is art homologous series? Fxplain with an example.
Ans. It is a group of members of same class of organic compound having similar chemical properties, they have same general formula.
           They have same functional group, when arranged in the ascending order of molecular mass they differ by 14 a.m.u. or ?CH2 group.
           Example: Alkane General formula??CnH2n+2
                  Methane              CH4
                  Ethane                  C2H6
                  Propane               C3H8
                  Butane                  C4H10
Q7.   How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Ans. Physical Properties
Q8.   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 molecules have two ends with different properties. One end is hydrophilic, which dissolves in water and other end is hydrophobic, it dissolves in hydrocarbons. When soap is added to water, the ionic end of soap will form a unique orientation and keep the hydrocarbon tail away from it. The cluster of molecules is formed in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. Hence, micelle formation takes place. Soap is soluble in ethanol hence the micelle formation will not take place.
Q9.   Why are carbon and its compounds used as fuels for most applications?
Ans. Carbon and its compounds undergo combustion to produce heat, the amount of heat released can be handled and used so they are used as fuels for most applications.
Q10.   Explain the formation of scum when hard water is treated with soap.
Ans. Hard water contains salts of calcium and magnesium. When soap molecule comes in contact with these salts it forms a curdy white precipitate (compound insoluble in water) called scum. Soap + Hard water ? scum
Q11.   What change will you observe if you test soap with litmus paper (red and blue)?
Ans. Soap is alkaline in nature, hence it will turn red litmus into blue, blue litmus will remain blue.
Q12.   What is hydrogenation? What is its industrial application?
Ans. When unsaturated hydrocarbons (double/triple bond) are reacted with hydrogen in presence of a catalyst like nickel, the hydrogen gets added across the double/triple bond and converts the unsaturated hydrocarbon into saturated hydrocarbon. Such reaction is called addition reaction or hydrogenation.
Q13.   Which of the following hydrocarbons undergo addition reactions?
         C2H6, C3H8, C3H6, C2H2 and CH4.
Ans. Addition reaction takes place in unsaturated hydrocarbons.
         Hence C3H6 and C2H2 are unsaturated hydrocarbons and will show addition reaction.
Q14.   Give a test that can be used to differentiate chemically between butter and cooking oil.
Ans. Butter is saturated compound and oil is unsaturated compound.
         Therefore, when we add oil to a test tube containing alkaline potassium permanganate solution, the pink colour of the solution disappear. Colour of alkaline potassium permanganate will not disappear in the test tube containing butter.
Q15.   Explain the mechanism of cleaning action of soaps.
Ans. Soap molecule has two ends, the charged end that gets attracted towards water is called hydrophilic and the long carbon chain that repels water is called hydrophobic end. When soap is dissolved in water, the carbon chain i.e., hydrophobic end gets attracted towards the oil, dirt and grease. The hydrophilic end stays away from this. The micelle formation takes place.
         The tail entangles dirt, oil or grease, if required the agitation is done. Lot of rinsing is a done with water so that water molecules attract charged (Na+) end and carries the soap molecules with dirt attached to it and clean the clothes, utensils, etc.

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