Intext Questions Solved

Page 61

Question 1 : What would be the electron dot structure of carbon dioxide which has 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?

Answer :

Pages 68-69

Question 1 : How many structural isomers can you draw from pentane?

Answer : There are three possible structural isomers of pentane.

Question 2 : What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

Answer : i) Catenation and Tetravalency of carbon
ii) Isomerism

Question 3 : What will be the formula and electron dot structures of cyclopentane?

Answer : C5H10

Question 4 : Draw the structures for the following compounds.
i) Ethanoic acid
ii) Structural isomers of bromopentane
iii) Butanone
iv) Hexanal

Answer :

Question 5 : How would you name the following compounds?

Answer : i) Bromoethane
ii) Methanal
iii) Hex-1-yne or Hexyne

Page 71

Question 1 : Why is the conversion of ethanol to ethanolic acid an oxidation reaction?

Answer : It involves addition of oxygen and removal of hydrogen, therefore, it is oxidation process.

Question 2 : A mixture of oxygen and ethylene is burnt for welding. Can you tell why a mixture of ethylene and air is not used?

Answer : It is because air containing nitrogen as well as oxygen , and N2 is non-supporter of combustion.

Page 74

Question 1 : How would you distinguish experimentally between an alcohol and a carboxylic acid?

Answer : Add sodium bicarbonate solution to each of them. If we get brisk effervescence due to CO2, it is carboxylic acid. Alcohol will react.

Question 2 : What are oxidising agents?

Answer : Oxidising agents are those compounds which can supply oxygen or can remove hydrogen , e.g. alkaline KMnO4 is oxidising agent.

Page 76

Question 1 : Would you be able to check if water is hard by using a detergent?

Answer : No, we cannot determine whether the water is hard or not by using a detergent.

Question 2 : 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 paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?

Answer : It is because dirt and grease are strongly attracted towards the clothes, therefore, beating or scrubbing with a brush or agitation in machine is necessary to overcome the force of attraction between fibre and dirt. Secondly it will produce heat, which helps in removing dirt and grease from fibres.

Text Book Questions Solved

Question 1 : Ethane, with the molecular formula C2H6, has

a) 6 covalent bonds
b) 7 covalent bonds
c) 8 covalent bonds
d) 9 covalent bonds

Answer :

Question 2 : Butanone is four-carbon compound with the functional group.

a) carboxylic acid
b) aldehyde
c) ketone
d) alcohol

Answer : c) ketone

Question 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.

Answer : b) the fuel is not burning completely.

Question 4 : Explain the nature of covalent bond using the formation in CH3Cl.

Answer : Carbon has four valence electrons. It shares one electron with chlorine and one electron each with three hydrogen atoms.

Question 5 : Draw the electron dot structures for

a) Ethanoic acid
b) H2S
c) Propanone
d) F2

Answer : a) Ethanoic acid CH3COOH

Question 6 : What is the homologous series? Explain with an example.

Answer : It is series of organic compounds having a general formula, same functional group, having general methods of preparation, having similar chemical properties and gradation in physical properties , e.g.

Question 7 : How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Answer : Ethanol has specific smell whereas ethanoic acid has vinegar like smell.

Ethanol does not react with sodium hydrogen carbonate whereas ethanoic acid liberates CO2 on treatment with NaHCO3.

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 has hydrophilic and hydrophobic part. Hydrocarbon portion is hydrophobic which forms clusters called micelle.

Micelle formation will not take place in ethanol.

Question 9 : Why are carbon and its compounds used as fuels for most applications?

Answer : It is because they are inflammable and have high calorific value.

Question 10 : Explain the formation of scum when hard water is treated with soap.

Answer : Soap is sodium or potassium salt or fatty acids. Hard water contains Ca2+ and Mg2+ which react with soap to form calcium and magnesium salt of fatty acid which is insoluble and is called scum.

Question 11 : What change will you observe if you test soap with litmus paper (red and blue)?

Answer : Soap solution will turn red litmus blue but it will not affect blue litmus.

Question 12 : What is hydrogenation? What is its industrial application?

Answer : Hydrogen is a process in which a substance reacts with hydrogen in presence of nickle asĀ  catalyst.

Industrial application:

Hydrogen is used to prepare vegetable ghee from vegetable oils.

Question 13 : Which of the following hydrocarbons will undergo addition reactions?
C2H6, C3H8, C3H6, C2H2 and CH4

Answer : C3H6 and C2H2 are unsaturated hydrocarbons, therefore, they will undergo addition reactions.

Question 14 : Give a test that can be used to differentiate chemically between butter and cooking oil.

Answer : Add Br2 (aq) to each of them. Cooking oil will decolourise bromine water showing that it is unsaturated. Butter will not react with Br2 (aq) showing that it is saturated.

Question 15 : Explain the mechanism of the cleansing action of soaps.

Answer : Soap has hydrophobic and hydrophilic part. Hydrophobic part is hydrocarbon which forms cluster of molecules called micelle. They attract dirt, grease, etc. , whereas hydrophilic part attracts water. Dirt, grease, etc., is washed away with the help of water.