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Class 10 LAKHMIR SINGH AND MANJIT KAUR Solutions Chemistry Chapter 4 - Carbon And Its Compounds

Carbon And Its Compounds Exercise 220

Solution 1

Carbon

Solution 2

Catenation (Self linking of carbon atoms to form long chains) and Tetravalency.

Solution 3

False

Carbon And Its Compounds Exercise 221

Solution 4

Friedrich Wohler.

Solution 5

Carbon.

Solution 6

n-butane and iso-butane.

Solution 7

(a) 20 hexagons

(b) 12 pentagons

Solution 8

Graphite

Yes, current will flow through the circuit since graphite is a good conductor of electricity.

Solution 9

Graphite is used as a lubricant in the form of graphite powder or mixed with petroleum jelly or with any lubricant oil to form graphite grease.

Solution 10

Diamond

Solution 11

C60 is called buckminsterfullerene

Solution 12

Methyl

Solution 13

(a) Ethane

(b) Ethene

(c) Ethyne

Solution 14

Ethane.

Solution 15

Solution 16

Solution 17

Solution 18

Isomers.

Solution 19

Isopentane and neopentane.

Solution 20

(i) Isomer of hexane: 2-methylpentane

(ii)

Solution 21

(a) Graphite

(b) Graphite

(c) Hydrocarbons

(d) Alkene

(e) Alkynes

(f) Unsaturated

(g) Two

(h) Low; covalent

(i) Catenation

(j) Alkenes

(k) Ethene

(l) Ethyne

Solution 22

(a) The atomic number of carbon is 6. Its electronic configuration is 2,4.

(b) Carbon forms covalent bonds because it can achieve the inert gas electron arrangement only by sharing of electrons.

(c) Diamond, graphite and buckminsterfullerene.

Solution 23

(a) Hydrocarbons

(b) Carbon forms covalent bonds because it can achieve the inert gas electron arrangement only by sharing of electrons.

Solution 24

(a) The property of self combination of carbon atoms to form long chains is called catenation. Carbon and Silicon exhibit the property of catenation.

(b)

 

Solution 25

(a) Buckminsterfullerene is an allotrope of carbon containing clusters of 60 carbon atoms joined together to form spherical molecules. It burns on heating to form carbon dioxide and nothing is left behind. This shows that it is made up of carbon only like diamond and graphite.

(b) Diamond used for making cutting tools but graphite is not because diamond is a very hard substance and graphite is a soft substance.

(c) Graphite is used for making dry cell electrodes but diamond is not because graphite is a good conductor of electricity whereas diamond is a bad conductor of electricity.

Carbon And Its Compounds Exercise 222

Solution 35

(a)

Diamond

Graphite

(i) Each carbon atom is linked to four other carbon atoms.

(ii) A diamond crystal has a tetrahedral arrangement of carbon atoms.

(i) Each carbon atom is joined to only three other carbon atoms.

(ii) A graphite crystal has flat hexagonal rings structure.

(b) Due to its softness, powdered graphite can be used a lubricant whereas diamond being extremely hard can not be used as lubricant.

(c) Due to its rigid structure, diamond is the hardest known substance to man. Hence, it is used in rock drilling equipments but graphite is soft and hence not used in rock drilling equipments.

(d) Diamonds are used for making jewellery.

     Graphite is used for making pencil cores or 'pencil leads'.

Solution 36

(a) Diamond is a colourless transparent substance having extraordinary brilliance. It is made up of carbon.

(b) A diamond crystal is a giant molecule of carbon atoms. Each carbon atom in the diamond crystal is linked to four other carbon atoms by strong covalent bonds. The four surrounding carbon atoms are at the four vertices of a regular tetrahedron. This rigid structure of diamond makes it a very hard substance.

(c) Diamond has a high melting point because a lot of heat energy is required to break the network of strong covalent bonds in the diamond crystal.

(d) (i) Used in rock drilling equipment (ii) Used in making jewellery.

Solution 37

(a) Graphite is a greyish-black opaque substance. It is made up of carbon.

(b) The structure of graphite is very different from that of diamond. A graphite crystal consists of layers of carbon atoms or sheets of carbon atoms.  Each carbon atom in a graphite layer is joined to other three carbon atoms by strong covalent bonds to form flat hexagonal rings. The various layers of carbon atoms in graphite are held together by weak Van der Waals forces. Due to this sheet like structure, graphite is a comparatively soft substance.

(c) Due to the presence of free electrons in a graphite crystal, it conducts electricity however; a diamond crystal does not have free electrons so it does not conduct electricity.

(d) (i) Used as a lubricant (ii) Used for making pencil leads.

Solution 38

(a) The organic compounds having the same molecular formula but different structures are known as isomers for ex: n-butane and iso-butane are isomers.

(b) Isomer of n-heptane: 2-methylhexane


(c) Butane

(d) (i) 2-methylpropane

     (ii) 2-methylbutane

     (iii) Propene

     (iv) Propyne

Solution 26

(a) (i) CnH2n+2 (ii) CnH2n (iii) CnH2n-2

(b) Alkanes: C5H12, C3H8

     Alkenes: C2H4, C4H8

     Alkynes: C3H4, C5H8

Solution 27

(a) (i) Ammonium cyanate, NH4CNO

(ii) Urea, CO(NH2)2

(b) The molecular formula of butane is C4H10; Its isomers are n-butane and 2-methylpropane; LPG.

Solution 28

(a) Methane (single bond): CH4

     Ethyne (triple bond): C2H2

(b) Benzene: C6H6

(c) Isobutene

Solution 29

Carbon forms strong bonds among themselves and with other elements and this makes the carbon compounds stable whereas silicon shows catenation property due to which it forms compounds with hydrogen having chains of up to 7 or 8 silicon atoms; but due to weak bonds, these compounds are unstable.

Solution 30

(a) Diamonds can be made artificially by subjecting pure carbon to very high pressure and temperature. The synthetic diamonds are small whereas natural diamonds are big.

(b) (i) Diamond is hard whereas graphite is soft.

(ii) Diamond is a non-conductor of electricity whereas graphite is a good conductor of electricity.

The difference in the physical properties of diamond and graphite arises because of the different arrangements of carbon atoms in them.

Solution 31

(a) Carbon forms a large number of carbon compounds because carbon atoms can link with one another by means of covalent bonds to form long chains of carbon atoms.

(b) Isomers of butane (C4H10)

Solution 32

(i) (ii)

(iii) (iv)

(b) (i) Acetylene (ii) Ethylene

(c) C6H6;

Solution 33

(a) The most unique property of carbon atom is its ability to combine itself, atom to atom to form long chains. This property of self combination is useful to us because it gives rise to an extremely large number of carbon compounds (or organic compounds).

(b) A diamond crystal is a giant molecule of carbon atoms. Each carbon atom in the diamond crystal is linked to four other carbon atoms by strong covalent bonds. The four surrounding atoms are at the four vertices of a regular tetrahedron. This rigid structure of diamond makes it a very hard substance.

The structure of graphite is very different from that of diamond. A graphite crystal consists of layers of carbon atoms or sheets of carbon atoms and these layers are held together by weak Van der Waals forces. Due to this sheet like structure, graphite is a comparatively soft substance.

Solution 34

(a) (i) Ethyne:- Single bonds: Two; Triple bond: One

     (ii) Ethene:- Single bonds: Four; Double bond: One

     (iii) Ethane:- Single bonds: Nine; Double bonds: Three

(b) Molecular formula of cyclohexane: C6H12;

 

No. of covalent bonds: 18

Carbon And Its Compounds Exercise 223

Solution 39

(a) A compound made up of hydrogen and carbon only is called a hydrocarbon (Hydrogen + Carbon= Hydrocarbon). For exampe: methane (CH4), ethane (C2H6), ethene (C2H4), and ethyne (C2H2), all are hydrocarbons as they are made up of only two elements: carbon and hydrogen.

(b) Saturated Hydrocarbons: These are the ones in which the carbon atoms are connected by only single bonds. They are also known as alkanes.

Example: Methane (CH4) and ethane (C2H6)

Unsaturated Hydrocarbons: These are the ones in which two carbon atoms are connected by a double bond or a triple bond.

Example: Ethene (C2H4) and ethyne (C2H2)

(c) Saturated cyclic hydrocarbon: Cyclohexane, C6H12

     Unsaturated cyclic hydrocarbon: Benzene, C6H6

(d) Hexane, C6H14

(e) (i) None (ii) Two (iii) Three (iv) Five

Carbon And Its Compounds Exercise 224

Solution 60

(a) Element X: Carbon

(b) Allotrope Y: Graphite

(c) Y is a good conductor of electricity.

(d) Y is used for making graphite electrodes or carbon electrodes in dry cells.

(e) Allotropes of X: Diamond and buckminsterfullerene

Solution 61

(a) A is cyclohexane, C6H12

     

(b) B is hexene, C6H12

(c) B

(d) A

Solution 62

(a) Element A: Carbon

(b) Gas B: Carbon dioxide

(c) Allotrope C: Diamond

(d) Used for making jewellery

(e) Buckminsterfullerene

(f) Graphite

Solution 63

(a) Element E: Carbon

(b) Allotrope A: Buckminsterfullerene

(c) Allotrope B: Graphite

(d) Allotrope C: Diamond

(e) C

(f) B

Solution 64

(a) C6H12

(b) C6H6

(c) C7H14; C5H10; C6H12

(d) C5H8; C7H12

(e) C7H14; C5H10; C6H12

Carbon And Its Compounds Exercise 225

Solution 65

C3H4

Solution 66

Molecular formula: C8H16


Solution 67

Molecular formula: C4H8

Solution 68

(i) C20H42 (ii) C20H40 (iii) C20H38

Solution 69

C5H10

Solution 70

C3H4

Carbon And Its Compounds Exercise 239

Solution 1

C2H5OH

Solution 2

Ethanol (C2H5OH)

Solution 3

Alcohol group; Methanol

Solution 4

Common name: formaldehyde

IUPAC name: methanal

Solution 5

Formaldehyde

Solution 6

(i) Alkyne

(ii) Alkene

Solution 7

Propanone

Solution 8

Acetone

Solution 9

(i) Propanone

(ii) Butanone

Carbon And Its Compounds Exercise 240

Solution 10

Formic acid; HCOOH

Solution 11

IUPAC name

Common name

Formula

(i) Methanoic acid

Formic acid

HCOOH

(ii) Ethanoic acid

Acetic acid

CH3COOH

Solution 12

(a) Methanoic acid - Formic acid

(b) Ethanoic acid - Acetic acid

Solution 13

(a) 

(b)

Solution 14

Formula

IUPAC name

Common name

(i) HCOOH

Methanoic acid

Formic acid

(ii) CH3COOH

Ethanoic acid

Acetic acid

 

Solution 15

Ethanoic acid; CH3COOH

Solution 16

(a) Methanoic acid: HCOOH

(b) Ethanoic acid: CH3COOH

Solution 17

Common name: Ethyl alcohol

IUPAC name: Ethanol

Solution 18

Propanol, C3H7OH

Solution 19

Ethanol; C2H5OH

Solution 20

(a) Butanol, C4H9OH

(b) Pentanol, C5H11OH

Solution 21

Methyl alcohol

Solution 22

(i) 14 u

(ii) Two consecutive homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.

Solution 23

(a) Fuels which vaporise on heating, burn with a flame.

(b) Fuels which do not vaporise on heating, burn without a flame.

Solution 24

False

Solution 25

(a) Propanol

(b) C3H7OH

(c) Propane

(d) -OH (alcohol)

(e) Carboxylic acids

Solution 26

(a) Alkynes, CnH2n-2

     First member: Ethyne

(b) Second member: C3H6

      Fourth member: C5H10

(c) Third member: C3H8

     Fifth member: C5H12

Solution 27

(a)

(b) Alkyne; CnH2n-2

(c) Alkanes: C3H8, C4H10

     Alkenes: C5H10, C8H16

     Alkynes: C6H10, C7H12

Solution 28

(a) (i) C4H8   (ii) C3H8     (iii) C3H4

(b) 14 u

(c) 1 carbon atom and 2 hydrogen atoms i.e. a CH2 group.

Carbon And Its Compounds Exercise 241

Solution 29

Solution 30

(a) IUPAC name: Chloromethane

     Common name: Methyl chloride

(b) Chlorobutane:

(c) Bromopentane:

Yes, structural isomers are possible for bromopentane.

Solution 31

(a) Acetone - CH3COCH3

(b) (i) Chloromethane - CH3Cl

      (ii) Chloroethane - C2H5Cl

      (iii) Chloropropane - C3H7Cl

(c) Ethylbromide

Solution 32

(a) Ketones

(b) CH3COOH

(c) Formaldehyde

Solution 33

(a) A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH2 group.

Ethyl alcohol: C2H5OH

(b) C3H7OH

(c) Coal and petroleum

Solution 34

(a) (i) Propanone

(ii) Butanone

(b) (i) Methanal       (ii) Ethanal     (iii) Propanal       (iv) Butanal

(c) Alcohol group, -OH; C4H9OH

Solution 35

(a) CH3COOH: Ethanoic acid

      CH3CHO: Ethanal

      CH3OH: Methanol

(b)

(c) Ethanoic acid.

Solution 36

(a) Carboxylic acid group, -COOH; C4H9COOH

(b) (i) Ethanal - CH3CHO

     (ii) Methanol - CH3OH

     (iii) Ethanoic acid - CH3COOH

     (iv) Chloromethane - CH3Cl

Solution 37

(a) C5H12O or C5H11OH

(b) (i) Aldehyde group

     (ii) Alcohol group

     (iii) Carboxylic acid group

      (iv) Ketone group

      (v) Halo group

(c) When a candle is lighted, the wax melts, rises up the wick and gets converted into vapours. In a candle, there is no provision for the proper mixing of oxygen (of air) for burning wax vapours. So, the wax vapours bum in an insufficient supply of oxygen (of air) which leads to incomplete combustion of wax. This incomplete combustion of wax produces small unburnt carbon particles. These solid carbon particles rise in the flame, get heated and glow to give out yellowish light. This makes the candle flame yellow and luminous.

Exercise

Solution

Solution

Carbon And Its Compounds Exercise 242

Solution 39

(a) An 'atom' or 'a group of atoms' which makes a carbon compound (or organic compound) reactive and decides its properties (or functions) is called a functional group. The alcohol group, -OH, present in ethanol, C2H5OH, is an example of a functional group.

(b) (i) Halo group: -X

     (ii) Alcohol group: -OH

     (iii) Aldehyde group: -CHO

(c) (i) Carboxylic acid group

     (ii) Aldehyde group

     (iii) Alcohol group

     (iv) Ketone group

(d) Ketone group, -CO-

(e) (i) 

(ii)

(iii)


(iv)

Solution 40

(a) When carbon is burned in air, it forms carbon dioxide gas and releases a large amount of heat and some light:

(b) Coal and petroleum are called as fossil fuels because they were formed by the decomposition of the remains of the pre-historic plants and animals (fossils) buried under the earth long, long, ago.

(c) Coal was formed by the decomposition of large land plants and trees buried under the earth millions of years ago. It is believed that millions of years ago, due to earthquakes and volcanoes, etc., the forests were buried under the surface of the earth and got covered with sand, clay and water. Due to high temperature and high pressure inside the earth, and in the absence of air, wood was converted into coal.

(d) Petroleum oil (and natural gas) was formed by the decomposition of the remains of extremely small plants and animals buried under the sea millions of years ago. It is believed that millions of years ago, the microscopic plants and animals which lived in seas, died. Their bodies sank to the bottom of the sea and were soon covered with mud and sand. The chemical effects of pressure, heat and bacteria, converted the remains of microscopic plants and animals into petroleum oil and natural gas just as they converted forest trees into coal. This conversion took place in the absence of oxygen or air. The petroleum thus formed got trapped between two layers of impervious rocks (non-porous rocks) forming an oil trap.

(e) Natural gas.

Carbon And Its Compounds Exercise 243

Solution 56

(a) Propanone (or Acetone)

(b)

(c) Propanal

(d)


(e) Methanal (or Formaldehyde) is used in preserving biological specimens.

Solution 57

(a) X is coal; Y is wax; Z is natural gas

(b) (i) Y (wax)

     (ii) X (coal)

     (iii) Z (natural gas)

Solution 58

(a) B; Butanol, C4H9OH

(b) A; Butanoic acid, C3H7COOH

(c) C4H8O

Aldehyde : Butanal, C3H7CHO

Ketone: Butanone, CH3COCH2CH3

Solution 59

(a) Liquid X is ethanoic acid; it belongs to homologous series of carboxylic acids. Methanoic acid is another member of this homologous series.

(b) Liquid Y is Propanone; it belongs to homologous series of ketones. Butanone is another member of this homologous series.

(c) Propanal; it belongs to homologous series of aldehydes.

(d) Liquid Z is ethanol; it belongs to homologous series of alcohols. Methanol is another member of this homologous series.

Solution 60

(a) Chloropropane, CH3-CH2-CH2-Cl

(b) Propanol, CH3-CH2-CH2-OH

(c) Butanal, CH3-CH2-CH2-CHO

(d) Butanoic acid, CH3-CH2-CH2-COOH

(e) Propanone, CH3-CO-CH3

Carbon And Its Compounds Exercise 262

Solution 1

Carbon dioxide (CO2) gas is evolved in the reaction. When passed through lime water, it turns lime water milky.

Solution 2

CH3COOH will give brick effervescence. Being acid, it reacts with sodium hydrogencarbonate to produce carbon dioxide gas.

 

Solution 3

Carboxylic acid group, -COOH gives brisk effervescence with NaHCO3.

Solution 4

Ethene is formed when ethanol is heated with conc. H2SO4 at 170oC. This reaction is called dehydration.

Solution 5

Ethyne (acetylene) burn with a sooty flame because ethyne is an unsaturated hydrocarbon and the percentage of carbon in these hydrocarbons is comparatively higher which does not get oxidised completely in oxygen of air.

Solution 6

Ethane is formed when hydrogen is added to ethene.

Solution 7

Ethene decolourises bromine water because ethene is an alkene. And all alkenes and alkynes are unsaturated compounds which decolourise bromine water. On the other hand, ethane being an alkane is a saturated compound which does not decolourise bromine water.

Solution 8

Nickel or palladium can be used as catalyst in the hydrogenation of unsaturated compounds.

Solution 9

Disadvantages of incomplete combustion:

(i) It leads to the formation of soot which is nothing but unburnt carbon which pollutes the atmosphere, blackens cooking utensils.

(ii) It leads to the formation of an extremely poisonous gas called carbon monoxide.

Solution 10

When Sodium reacts with ethanol (ethyl alcohol), hydrogen gas is evolved.

Solution 11

Ethanol reacts with sodium metal to form sodium ethoxide and hydrogen gas. This reaction is used as a test for ethanol. When a small piece of sodium metal is put into ethanol in a dry test tube, rapid effervescence is produced due to evolution of hydrogen gas.

Solution 12

Ethanol is used as an additive in petrol.

Solution 13

(i) Vegetable oil (like castor oil, cottonseed oil or soyabean oil)

(ii) Sodium hydroxide (caustic soda)

(iii) Sodium chloride (common salt)

Solution 14

No, we would not be able to check the hardness of water by using a detergent because a detergent forms lather easily even with hard water.

Solution 15

Litmus test: Some blue litmus solution is added to the organic compound (to be tested). If the blue litmus solution turns red, it shows that the organic compound is acidic in nature and hence it is a carboxylic acid.

Solution 16

Oxidation means controlled combustion. When ethanol is heated with alkaline potassium permanganate solution (or acidified potassium dichromate solution), it gets oxidised to ethanoic acid. It is called an oxidation reaction because oxygen is added to it during this conversion.

Solution 17

Alkanes burn in air to produce a lot of heat due to which they are known to be excellent fuels.

Solution 18

Sodium hydrogencarbonate can be used to distinguish between ethanol and ethanoic acid.

Solution 19

Carbon And Its Compounds Exercise 263

Solution 20

Solution 21

(a) Combustion

(b) Soap

(c) Detergent

(d) Ethanoic acid

Solution 22

CH4, C3H8 and C5H12; all these are saturated hydrocarbons (Alkanes) and hence will give substitution reactions.

Solution 23

C2H4 and C3H4 will give addition reactions because these are unsaturated hydrocarbons (Alkene and Alkyne) and unsaturated hydrocarbons give addition reactions.

Solution 24


(b) Since, ethanol burns with a clear flame giving a lot of heat, therefore, it is used as a fuel.

(c) Uses of ethanol:

(i) It is used in the manufacture of paints, varnishes, lacquers, medicines, perfumes, dyes, soaps and synthetic rubber.

(ii) It is used as a solvent. Many organic compounds which are insoluble in water are soluble in ethyl alcohol.

Solution 25

(a) Propanoic acid will react with the alcohol in the presence of concentrated sulphuric acid to form esters.

(b) Red litmus paper turns blue in soap solution and no change occurs on blue litmus paper because soap is basic in nature.

(c) Denatured alcohol is ethyl alcohol which has been made unfit for drinking purposes by adding small amounts of poisonous substances like methanol, pyridine, copper sulphate etc. This is done to prevent the misuse of industrial alcohol for drinking purposes or black marketing (as it is supplied duty free for industrial purposes by the government).

Solution 26

(a) Sodium metal test: Add a small piece of sodium metal to the organic liquid (to be tested), taken in a dry test tube. If bubbles (or effervescence) of hydrogen gas are produced, it indicates that the given organic liquid is an alcohol.

(b) Harmful effects of drinking alcohol:

(i) Alcohol slows down the activity of the nervous system and brain due to which the judgement of a person is impaired and his reaction becomes slow.

(ii) Heavy drinking of alcohol on a particular occasion leads to staggered movement, slurred speech and vomiting.

(c) Unlike ethanol, drinking methanol, even in a small quantity can be fatal leading to permanent blindness and even death. Methanol damages the optic nerve causing permanent blindness in a person. This happens because methanol is oxidised to methanal in the liver of a person. This methanal reacts rapidly with the components of the cell causing coagulation of their protoplasm. Due to this, the cells stop functioning normally.

Solution 27

(a) Dehydration: conversion of ethanol into ethene

(b) Oxidation: conversion of propanol to propanoic acid

Solution 28

(a) Air holes of a gas burner have to be adjusted because blackening of vessels show that the air holes of the gas stove are getting blocked and hence the fuel is not burning completely (due to insufficient supply of oxygen).

(b) Some of the detergents (synthetic) are not bio-degradable, that is they cannot be decomposed by micro organisms like bacteria and hence cause water pollution.

Solution 29

(a) On adding 5% alkaline potassium permanganate solution drop by drop to some warm ethanol, we would observe that the purple color of potassium permanganate starts disappearing; the product formed by this process; ethanoic acid can turn blue litmus red.

(b) A carboxylic acid reacts with sodium hydrogencarbonate to give brisk effervescence of carbon dioxide gas but an alcohol does not react with sodium hydrogencarbonate.

Solution 30

Alkenes can be hydrogenated.

The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation.

Example: Ethene reacts with hydrogen in the presence of finely divided nickel as catalyst to form ethane.


Liquid vegetable oils are hydrogenated into vegetable ghee (solid fat).

Solution 31

(a) Hydrogen gas is evolved when ethanol reacts with sodium.

(b) Esters are formed when a carboxylic acid reacts with an alcohol in the presence of conc. H2SO4.

(c) Dilute ethanoic acid turns universal indicator paper to orange, showing that its pH is about 4 which tell us that ethanoic acid is a weak acid. On the other hand, dilute hydrochloric acid turns universal indicator paper to red, showing that its pH is about 1. This shows us that hydrochloric acid is a strong acid.

Solution 32

(a) CH3COOH is a carboxylic acid.

(b) Ethanol, CH3CH2OH should be oxidised to prepare CH3COOH.

(c) Liquid state

(d) Soaps are biodegradable whereas detergents are non-biodegradable.

Carbon And Its Compounds Exercise 264

Solution 34

(a) When ethanol is oxidised with alkaline potassium permanganate (or acidified potassium dichromate), it gets oxidised to form ethanoic acid.


(b) CH3COOH and HCOOH can turn blue litmus solution red. These are organic acids.

Solution 35

(a) Soap can be prepared in the laboratory as follows:

1. Take about 20 ml of castor oil (cottonseed oil, linseed oil or soya bean oil) in a beaker.

2. Add 30 ml of 20% sodium hydroxide solution to it.

3. Heat the mixture with constant stirring till a paste of soap is formed.

4. Then add 5 to 10 grams of common salt (sodium chloride).

5. Stir the mixture well and allow it to cool. On cooling the solution, solid soap separates out.

6. When the soap sets, it can be cut into pieces called 'soap bars'.

(b) Common salt is added to the mixture to make the soap come out of solution. Though most of the soap separates out on its own but some of it remains in solution. Common salt is added to precipitate out all the soap from the aqueous solution.

(c) When soap is used for washing clothes with hard water, a large amount of soap in water is reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum, before it can be used for the real purpose of washing.

Solution 36

(a) Carbon dioxide and water vapour are formed when methane burns in air.


(b) Ethanoic acid reacts with sodium carbonate to form sodium ethanoate and carbon dioxide.


(c) Add bromine water to a little of cooking oil and butter taken in separate test tubes:

(i) Cooking oil decolourises bromine water (showing that it is an unsaturated compound).

(ii) Butter does not decolourise bromine water (showing that it is a saturated compound).

Solution 37

(a) Substitution reaction of methane with chlorine: Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.


(b) An oxidising agent is one which oxidises other substances by providing oxygen or removing hydrogen. Alkaline potassium permanganate and acidified potassium dichromate can be used as oxidising agents.

(c) Reaction with alcohols: Ethanoic acid reacts with alcohols in the presence of a little of conc. sulphuric acid to form esters.

Solution 38

(a) (i) Single bond: Methane, CH4. They are quite unreactive hence they undergo substitution reaction with chlorine in presence of sunlight.

     (ii) Double bond: Ethene, CH2=CH2. They undergo addition reaction in the presence of a catalyst like nickel or palladium.

(b) A detergent is the sodium salt of long chain benzene sulphonic acid which has cleansing properties in water. Ex: Sodium n-dodecyl benzene sulphonate.

(c) Detergents are better cleansing agents than soaps because they do not form insoluble calcium and magnesium salts with hard water, and hence can be used for washing even with hard water.

Solution 39

(a) Ethanoic acid reacts with sodium hydrogencarbonate to evolve brisk effervescence of carbon dioxide gas.

(b) Carbon and its compounds used as fuels because they burn in air releasing a lot of heat energy.

(c) Detergent is better for washing clothes with hard water. They are better cleansing agents than soaps because they do not form insoluble calcium and magnesium salts with hard water, and hence can be used for washing even with hard water.

Solution 40

(a) The reaction in which one (or more) hydrogen atoms of a hydrocarbon are replaced by some other atoms (like chlorine), is called a substitution reaction.

Example: Substitution reaction of methane with chlorine:-

Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.


(b) Soap is made by heating animal fat or vegetable oil with concentrated sodium hydroxide solution.

Solution 41

(a) Ethanoic acid is obtained from ethanol by the means of oxidation reaction. When ethanol is heated with alkaline potassium permanganate solution (or acidified potassium dichromate solution), it gets oxidised to ethanoic acid. It is called an oxidation reaction because oxygen is added to it during this conversion.


(b) Litmus test: Some blue litmus solution is added to the organic compound (to be tested). If the blue litmus solution turns red, it shows that the organic compound is acidic in nature and hence it is a carboxylic acid (ethanoic acid). Ethanol has no effect on any litmus solution.

(c) When soap is used for washing clothes with hard water, a large amount of soap in water reacts with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum. This makes the cleaning of clothes difficult.

Solution 42

(a) Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride. This reaction is called substitution reaction.

 

(b) The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation.

Application: Vegetable oils are hydrogenated to form vegetable ghee (or vanasapati ghee).

(c)

Soaps

Detergents

(i)Soaps are biodegradable.

(ii)Soaps have relatively weak cleansing action.

(i) Detergents are not biodegradable.

(ii) Detergents have a strong cleansing action.

 

Solution 43

(a) Ethanoic acid reacts with sodium hydroxide to form a salt called sodium ethanoate and water.


(b) On hydrogenation, the liquid vegetable oils change into solid fat (vanasapati ghee). Nickel or palladium can be used as the catalyst.

(c) Advantage: Detergents can be used even with hard water and have stronger cleaning action.

   Disadvantage: Detergents are not biodegradable and hence cause water pollution.

Solution 44

(a) Ethanoic acid, CH3COOH gives brisk effervescence with sodium hydrogencarbonate.

(b) A mixture of ethyne and air is not used for welding because burning of ethyne in air produces a sooty flame (due to incomplete combustion) which is not hot enough to melt metals for welding.

(c) Addition reactions are a characteristic of unsaturated hydrocarbons.

Solution 45

(a) The reaction in which an unsaturated hydrocarbon combines with another substance to give a single product is called an addition reaction.

Example: Ethene reacts with hydrogen when heated in the presence of nickel catalyst to form ethane:


(b) Hydrogen is added to groundnut oil when it is to be converted to vanaspati ghee.

(c) Vegetable oil is better because it has unsaturated fatty acids which are good for our health.

Carbon And Its Compounds Exercise 265

Solution 46

(a) Salt X is sodium ethanoate, CH3COONa; Gas Y is carbon dioxide, CO2

Activity: Take a boiling tube and put about 0.5 g of sodium carbonate in it. Add 2 ml of dilute ethanoic acid to the boiling tube (through a thistle funnel). We will observe that brisk effervescence of carbon dioxide gas is produced. Let us pass this gas through lime water taken in a test tube. We will find that lime water turns milky. Only carbon dioxide gas can turn lime water milky. So, this experiment proves that when ethanoic acid reacts with sodium carbonate, then carbon dioxide gas is evolved.


(b) (i) Dilute ethanoic acid (in the form of vinegar) is used as a food preservative in the preparation of pickles and sauces.

     (ii) It is used in the manufacture of acetone and esters used in perfumes.

Solution 47

(a) Activity:

(i) Take 1 ml of pure ethanol (absolute alcohol) in a test-tube and add 1 ml of glacial ethanoic acid to it. Then add 2 or 3 drops of concentrated sulphuric acid to the mixture.

(ii) Warm the test-tube containing above reaction mixture in hot water bath (a beaker containing hot water) for about 5 minutes.

 

(iii) Pour the contents of the test-tube in about 50 ml of water taken in another beaker and smell it.

(iv) A sweet smell is obtained indicating the formation of an ester.

Reaction:

 

(c) Uses of esters:

(i) Esters are used in making artificial flavours and essences. These are used in cold drinks, ice-creams, sweets and perfumes.

(ii) Esters are used as solvents for oils, fats, gums, resins, cellulose, paints, varnishes, etc.

Solution 48

(a) Catalytic hydrogenation is usually used in conversion of vegetable oils to fats.

Hydrogenation of oils: Vegetable oils are unsaturated fats having double bonds between some of their carbon atoms and can undergo addition reactions. When a vegetable oil (like groundnut oil) is heated with hydrogen in the presence of finely divided nickel as catalyst, then a saturated fat called vegetable ghee (or vanaspati ghee) is formed. This reaction is called hydrogenation of oils and it can be represented as follows:

 

(b) The process of making soap by the hydrolysis of fats and oils with alkalis is called saponification.

(c) Soap are sodium or potassium salts of long-chain carboxylic acids. When soap is added to the water, the hydrophilic end (acid end) will align along the surface of water and the hydrophobic tail (carbon chain) remains out of water.

 When a soap is dissolved in water, it forms a colloidal suspension in water in which the soap molecules cluster together to form spherical aggregates called micelles. In a soap micelle, soap molecules are arranged radially with hydrocarbon ends directed towards the centre and ionic ends directed outwards.

No, micelle will not be formed in other solvents such as ethanol because hydrocarbon chains of soap molecules are soluble in organic solvents like ethanol.

Solution 49

(a) A soap is the sodium salt (or potassium salt) of a long chain carboxylic acid (fatty acid) which has cleansing properties in water.

Example: Sodium stearate, C17H35COO-Na+

(b) A soap molecule has two parts: the long chain organic part and the ionic part containing the -COO-Na+ group.  It has to be remembered that this is not an ion, the atoms are all covalently bonded, the electrical charges show how the charges get polarized in the group. A soap molecule has a tadpole like structure shown below:

 

(c) Cleaning action of soap has been explained with the help of the image below:

Soaps are molecules in which the two ends have differing properties, one is hydrophilic, that is it dissolves in water, while the other end is hydrophobic, that is it dissolves in hydrocarbons. When soap is at the surface of water, the hydrophobic 'tail' of soap will not be soluble in water and the soap will align along the surface of water with the ionic end in water and the hydrocarbon 'tail' protruding out of water.

 

Inside water, these molecules have a unique orientation that keeps the hydrocarbon portion inside the water. This is achieved by forming clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle. When a dirty cloth is put in water containing dissolved soap, then soap in the form of a micelle is able to clean. The hydrocarbon ends of the soap attach to the oily dirt particles and entrap them at the centre of the micelle. the ionic ends in the micelles remain attached to water. When the dirty cloth is agitated in soap solution, the oily dirt particles entrapped by soap micelles get dispersed in water and the cloth gets cleaned.

Carbon And Its Compounds Exercise 266

Solution 66

X is ethanol

Y is ethanoic acid

Z is ethyl ethanoate

Ethanol reacts with ethanoic acid to form ethyl ethanoate ester.

Solution 67

C2H5OH and CH3COOH react in the presence of conc. H2SO4 to form an ester. Ethyl ethanoate, CH3COOC2H5 is formed in the reaction.

Solution 68

Alcohol group, -OH. Acids react with alcohols to form sweet smelling esters.

Solution 69

Acid: Ethanoic acid

Alcohol: Ethanol

CH3-CH2-OH

Solution 70

(a) C4H9COOC2H5; Ester

(b) C2H5OH; Alcohol forms ethene, C2H4

(c) CH4; Methane

(d) CH3OH; Methanol

(e) CH3COOH; Acetic acid

(f) C2H5OH; Ethanol

Solution 71

(a) X is ethanoic acid, ; Y is methyl ethanoate,

(b)

Solution 72

(a) A is propanol, CH3-CH2-CH2OH

(b) B is propene, CH3CH=CH2

(c) Dehydration reaction 

(d) C is propane, CH3CH2-CH3

(e) Addition reaction

Solution 75

(a) X is butanol, C4H9OH

(b) Y is butanoic acid, C3H7COOH

(c) Z is butyl butanoate, C3H7COOC4H9

(d) Sweet smell is given by the compound Z.

(e) Esters

(f) Esterification reaction.

Carbon And Its Compounds Exercise 267

Solution 73

A is ethanoic acid, CH3COOH

B is sodium ethanoate, CH3COONa

C is methanol, CH3OH

D is methyl ethanoate, CH3COOCH3

Solution 74

C6H12 and C6H10 can decolourise bromine water since these are unsaturated hydrocabons.

C6H14 cannot decolourise bromine water since it is a saturated hydrocarbon.

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