Carbon and it's compounds
NCERT Solutions
NCERT Exercises
1. Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds
(b) 7 covalent bonds
2. Butanone is a four-carbon compound with the functional group
(a) carboxylic acid
(b) aldehyde
(c) ketone
(d) alcohol
(c) Ketone
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.
(b) the fuel is not burning completely.
4. Explain the nature of the covalent bond using the bond formation in CH3Cl.
CH_3Cl – Chloromethane.
Number of outermost electrons for following atoms
Carbon atom – 4
Hydrogen atom – 1
Chlorine – 7
Carbon shares its four outermost electrons with three hydrogen atoms and one chlorine atom to form CH_3Cl . Since, bonds are formed because of sharing of electrons, hence these are covalent bonds.
5. Draw the electron dot structures for
(a) ethanoic acid
(b) H2 S
(c) propanone
(d) F2
6. What is a homologous series? Explain with an example.
It is a group of organic compounds with similar structure and chemical properties. Different organic compounds present in the homologous series are called homologues. The successive compounds are differ by CH_2 group. The general molecular formula for homologous series is C_nH_{2n+2} .
Example:
7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
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?
Micelle formation takes place when soap is added to water. Soap molecule is made up of two parts: A long hydrocarbon chain which is insoluble in water and small ionic part which is soluble in water. In water soap molecules are clustered to form a micelle in spherical shape.
Micelle formation does not occur in ethanol, because the soap is soluble in ethanol.
9. Why are carbon and its compounds used as fuels for most applications?
Its because of the heat energy it liberated when carbon and it’s compound burnt in the oxygen in atmosphere.
10. Explain the formation of scum when hard water is treated with soap?
Soap does not give form easily with the hard water. When soap reacts with the magnesium ion and calcium ions in the soap, an insoluble precipitate called scum is formed.
11. What change will you observe if you test soap with litmus paper (red and blue)?
Soap is a salt of sodium hydroxide which is a strong base and carboxylic acid which is a weak salt. So soap in water is basic in nature. The solution changes the colour of the red litmus to blue, and no effect will be there for the blue litmus.
12. What is hydrogenation? What is its industrial application?
It is the process in which hydrogen is added to an unsaturated hydrocarbon in the presence of a catalyst like nickel or palladium.
Application: It is used to convert vegetable oil into vegetable ghee.
13. Which of the following hydrocarbons undergo addition reactions: C2H6, C3H8, C3H6, C2H2 and CH4.
Unsaturated hydrocarbons undergo addition reactions. Here C3H6 and C2H2 are unsaturated hydrocarbons. So they undergo addition reactions.
14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.
All Carbon atoms are bonded to other carbon atoms through carbon – carbon single bonds in Saturated hydrocarbons. While in unsaturated hydrocarbons, there exist double bond or triple bond between carbons.
By using Bromine water test or Baeyer’s Reagent we can differentiate the unsaturated compounds (like alkenes and alkynes) and the saturated compounds.
15. Explain the mechanism of the cleaning action of soaps.
As you all know, we use soaps and detergents to remove dirt from our clothes but there is an interesting mechanism behind this. Most dirt is oily in nature and oil does not dissolve in water. Soap molecules have two ends, one is hydrophilic, that is, it interacts with the water while the other end is hydrophobic, as it interacts with hydrocarbons. The ionic end (hydrophilic end) interacts with the water while the hydrophobic end interacts with oil. Thus, the soap molecules form a structure called micelles. In micelles, the hydrophilic end is towards the oil droplet while the hydrophobic end (ionic end) faces outside. As a result, an emulsion is formed in water. Thus, the soap micelle helps in removing the dirt from our clothes.
Intext Exercises
Pg. No. 61
1. What would be the electron dot structure of carbon dioxide which has the formula CO2?
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).
Pg. No. 68
1. How many structural isomers can you draw for pentane?
3 Structural isomer of pentane can be drawn
2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
i. Catenation: It is the ability of a carbon atoms to form bonds with other carbon atoms.
ii. Tetravalency: Due to 4 valence electrons of carbon, it can make bonding with four other atoms.
3. What will be the formula and electron dot structure of cyclopentane?
4. Draw the structures for the following compounds.
(i) Ethanoic acid
(ii) Bromopentane*
(iii) Butanone
(iv) Hexanal
5. How would you name the following compounds?
Pg. No. 71
1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
It’s because the oxygen is added to it during the conversion.
2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
A mixture of oxygen and ethyne is burnt for welding because it produce a high temperature and hot blue flame. When oxygen and ethyne are burnt, it burns completely. But air and ethyne gives out a sooty flame which is the resultant of unburnt particles, resulting in lesser heat.
Pg. No. 74
1. How would you distinguish experimentally between an alcohol and a carboxylic acid?
By using Sodium bicarbonates test or by litmus test.
Example: Take alcohol ( Ethyl alcohol) in one test tube and carboxylic acid ( acetic acid) in another test tube. Now add a small amount of sodium bicarbonate into two test tubes. Evolution of CO_2 can be noticed in the test tube containing acetic acid. We can find brisk effervescence when CO_2 is evolved. But no such effervescence can be noticed in the tustube containing Ethyl alcohol.
CH_3COOH + NaHCO_3 → CH_3COONa + H_2O + CO_2 \uparrow
C_2H_5OH+ NaHCO_3 → No reaction
2. What are oxidising agents?
The substance that provide oxygen for oxidation are called as oxidising agents. Ex: Alkaline potassium permanganate and acidified potassium dichromate.
Pg. No. 76
1. Would you be able to check if water is hard by using a detergent?
Detergent cannot be used to check whether water is hard or not. Both in hard and soft water, detergent gives lather. Detergents are salts of ammonium or sulphonates of long chain carboxylic acids.
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 a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
Agitation is necessary to get clean clothes as agitation aid soap micelles to trap the oil, grease or any other impurities that have to be removed. When they are being beaten or agitated, the particles are removed from the clothes’ surfaces and go into the water, thus cleaning the clothes.