Home » Lakhmir Singh Class 10 Chemistry » Lakhmir Singh Class X Chemistry Chapter 4 – Carbon and its Compounds

Lakhmir Singh Class X Chemistry Chapter 4 – Carbon and its Compounds


Exercise : Solution of Questions on page Number : 220


Answer 1:
Carbon has buckminsterfullerene as one of its allotropes.


Answer 2:
Following are the two properties of carbon which lead to the formation of a large number of carbon compounds:
(i) Catenation (self combination of carbon atoms to form long chains), and
(ii) Tetravalency (4 valence electrons in its outer most shell that help carbon to form four bonds with other atoms).


Answer 3:
False
Diamond and graphite are the allotropic forms of carbon (C) with covalent bonding between different carbon atoms.


Exercise : Solution of Questions on page Number : 221


Answer 22:
(a) The atomic number of carbon is 6.
Its electronic configuration is K L.
2 4ethene​.
(b) Carbon always forms covalent bonds. This is because it is tetravalent and attain the inert gas configuration of 8 electrons in its outermost shell by sharing electrons.
(c) The three allotropic forms of carbon are:
(i) Diamond
(ii) Graphite
(iii) Buckminsterfullerene


Answer 4:
Friedrich Wohler is the scientist who disproved the ‘vital force theory’ for the formation of organic compounds.


Answer 5:
Carbon is the element whose allotropic form is graphite.


Answer 6:
n-butane and iso-butane are the two isomers of butane found in LPG cylinders.
The condensed structural formulas of n-butane and iso-butane are as follows:
n-butane :       CH3CH2CH2CH3
iso-butane :     CH3CHCH3ethene​.

CH3


Answer 7:
(a) In one molecule of buckminsterfullerene, 20 hexagons of carbon atoms are present.
(b) In one molecule of buckminsterfullerene, 12 pentagons of carbon atoms are present.


Answer 8:
The black substance inside a pencil is graphite.
Yes, current will flow through the electrical circuit if we use the sharpened ends of the pencil to complete the circuit, as graphite is a good conductor of electricity.


Answer 9:
Graphite has a hexagonal structure and weak van der Waals for<>ce between the layers of the carbon atoms in its crystal. Due to this weak force, the layers of carbon atoms in graphite can slide over one another, making graphite slippery in nature and capable of acting as a lubricant.


Answer 10:
Diamond is the hardest natural substance known.


Answer 11:
C60 is called buckminsterfullerene.


Answer 12:
The general formula of an alkyl group is CnH2n+1 where n is an integer. A methyl group (-CH3) is a derivative of methane (CH4) with the structural formula as shown below:


Answer 13:
(i) Ethane:

(ii) Ethene:

(iii) Ethyne:


Answer 14:
The IUPAC name of C2H6 is ethane.


Answer 15:
The structural formula of propene is as follows:


Answer 16:
The structural formula of propyne is as follows:


Answer 17:
The structural formula of butane (C4H10) is as follows


Answer 18:
Isomers are the forms of compounds with the same molecular formula but different structural arrangements of atoms.


Answer 19:
2-methylbutane and 2,2-dimethylpropane are the two isomers represented by the molecular formula C5H12.


Answer 20:
2 -methylpentane is an isomer of hexane (C6H14).
(i) Structural formula:

(ii) Electron-dot formula :


Answer 21:
(a) The form of carbon which is known as black lead is graphite.
(b) The form of carbon which is used as a lubricant at high temperature is graphite.
(c) Compounds of carbon with hydrogen alone are called hydrocarbons.
(d) CnH2n is the general formula of alkene hydrocarbons.
(e) Hydrocarbons having the general formula CnH2n−2 are called alkynes​.
(f) Ethene and ethyne are examples of unsaturated hydrocarbons.
(g) Ethyne has two carbon-hydrogen single bonds.
(h) Carbon compounds have usually low melting points and boiling points because they are covalent in nature.
(i) The property of carbon atoms to form long chains in compounds is called catenation.
(j) The general formula CnH2n for cycloalkanes is the same as that of alkenes​.
(k) The IUPAC name of ethylene is ethene​.
(l) The IUPAC name of acetylene is ethyne​.


Answer 22:
(a) The atomic number of carbon is 6.
Its electronic configuration is K L.
2 4
(b) Carbon always forms covalent bonds. This is because it is tetravalent and attain the inert gas configuration of 8 electrons in its outermost shell by sharing electrons.
(c) The three allotropic forms of carbon are:
(i) Diamond
(ii) Graphite
(iii) Buckminsterfullerene


Answer 23:
(a) The general name for all the compounds made up of hydrogen and carbon is hydrocarbon.
(b) Carbon has the property of tetravalency, so it mainly forms covalent bonds. Since carbon is an element with atomic number 6, its electronic configuration is (2,4). This means there are 4 valence electrons in its outermost shell, and it can either gain 4 electrons or lose 4 electrons to attain the inert gas configuration for becoming stable. As the atoms of carbon are of extremely small size, the nucleus exerts a great force of attraction on the outermost electrons to hold them tightly. This makes it difficult to remove or add electrons to its structure. Therefore, it attains the inert gas configuration by the sharing of electrons in the outermost shell. As the inert gas configuration is attained by the sharing of electrons, carbon forms compounds always by covalent bonding.


Answer 24:
(a) Catenation is the unique property exhibited by the carbon atoms. It is the ability of one carbon atom to combine with its other atoms to form long chains, and give rise to a large number of carbon compounds.
Carbon and silicon are the two elements which exhibit the property of catenation.
(b)

Isomer of hexane (C6 H14 ) Structural formula
1) Hexane
2) 2-methyl pentane
3) 3-methyl pentane
4) 2,2-dimethyl butane
5) 2,3-dimethyl butane  

Answer 25:
(a) Buckminsterfullerene is an allotrope of carbon. It is a spherical shaped molecule containing 60 carbon atoms, arranged in interlocking 20 hexagonal and 12 pentagonal rings of carbon atoms. Buckminstterfullerene along with diamond and graphite are allotropes of the element carbon with symbol C.
(b) Diamond is the hardest, naturally occuring material known. Owing to its rigid structure, it can be used as glass cutters. Whereas graphite is a layered structure of carbon atoms and is very soft so, it cannot be used for making cutting tools.
(c) Graphite is a good conductor of electricity. Therefore, it is used for making dry cell electrodes. Whereas, diamond does not conduct electricity, as it has no free electrons and all its valence electrons go into the formation of strong covalent bonds.


Answer 26:
(a)
(i) The general formula of an alkane is CnH2n+2.​
(ii) The general formula of an alkene is CnH2n.​
(iii) The general formula of an alkyne is CnH2n-2.​
(b) Alkanes: C5H12 and C3H8
Alkenes: C2H4 and C4H8
Alkynes: C3H4 and C5H8


Answer 27:
(a) (i) The name of the inorganic compound is ammonium cyanate, and its formula is NH4CNO.
ii) The name of the organic compound formed is urea, and its formula is CO(NH2)2.
(b) The molecular formula of butane is C4H10. The names of two of its isomers are normal-butane (n-butane) and iso-butane. The butane fuel present in cooking gas cylinders contains both n-butane and iso-butane.


Answer 28:
(a) The IUPAC name of the compound, comprising four carbon and hydrogen single bonds, is methane. And, the IUPAC name of the compound, comprising one triple bond between the carbon atoms and two single bonds between the carbon and hydrogen atoms, is ethyne.
(b) C6H6 is the molecular formula of benzene.
(c) Iso-butane has a branched chain, while normal butane has a single chain of carbon atoms.


Answer 29:
Catenation is the ability of an element to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. The ability of catenation in carbon is greater than in silicon, as carbon atoms are smaller than silicon atoms. Hence, the nucleus of carbon exerts a greater force of attraction on the shared pair of electrons, and holds them firmly to form strong covalent bonds. This is also the reason behind the ability of carbon to hold n number of atoms (form lengthy compounds). On the other hand, silicon can only hold seven or eight atoms to form weaker covalent bonds.


Answer 30:
(a) Artificial diamonds are made by subjecting pure carbon to extreme temperature and pressure. The diamonds prepared artificially are called synthetic diamonds. Synthetic diamonds differ from natural diamonds in terms of their hardness and brightness. Synthetic diamonds are more bright and less harder than natural diamonds.
(b)

Sl.No  Diamond Graphite
1. Diamond has a rigid structure that makes it a hard material. Graphite has a layered structure that makes it a soft material.
2. Diamond does not conduct electricity. Graphite is a good conductor of electricity.

The differences in their properties is due to the different arrangement of carbon atoms in both the allotropes. In diamond, one carbon atom is linked to four other carbon atoms by strong covalent bonds to form regular tetrahedron. While in graphite, one carbon atom is joined to three other carbon atoms by covalent bonds to form a flat hexagonal ring. In graphite, the various layer of carbon atoms are held together by a weak van der Waals force.
Graphite is a good conductor, as in its crystal, only three valence electrons of a carbon atom are used in the bond formation, while the fourth valence electron is free. The free movement of these electrons in the graphite crystal allows the conductivity of electric current.


Answer 31:
(a) The element, carbon, forms a large number of carbon compounds because of its property of self combination (catenation). The ability of one carbon atom to combine with the many other carbon atoms to form long chains produces a large number of carbon compounds. This long chain of carbon atoms supports the other atoms to get attached to it in a number of ways due to which a large number of carbon compounds are obtained.
(b) The structure and names of two isomers of butane are:

i) normal-butane:


Answer 32:
(a) (i) Methane is an alkane with the molecular formula CH4.
Structural formula is:

(ii) Ethene is an alkene with the molecular formula C2H4.
Structural formula is :

(iii) Ethyne is an alkyne with the molecular formula C2H2.
Structural formula is :

(iv) Cyclohexane is a cycloalkane with the molecular formula C6H12.
Structural formula is:

(b) Common name of
(i) Ethyne is acetylene
(ii) Ethene is ethylene
(c) The molecular formula of benzene is C6H6.
Its structural formula is :


Answer 33:
(a) Self combination (catenation) is the most unique property of a carbon atom. This property is extremely as it gives rise to a large number of carbon compounds or organic compounds. Other atoms get attached to the long chain of carbon atoms in a number of ways to produce a large number of carbon compounds.
Note: Tetravalency is the other property which supports this unique characteristic of carbon to produce a large number of carbon or organic compounds.
(b) Even if diamond and graphite are made up of carbon, the former is extremely hard while the latter is soft. Diamond is hard because of the strong covalent bond between its carbon atoms forming a regular tetrahedron which is hard to break. Graphite, on the other hand, consists of flat hexagonal ring forming layers of carbon atoms. The various layers of the carbon atoms are far apart from each other; hence, the covalent bond cannot exist. The layers are held together by weak van der Waals forces, thereby allowing them to slide over each other. Due to this layered structure, graphite is softer than diamond.


Answer 34:
(a) (i) Structure of ethyne (C2H2) is as follows:

Ethyne has one triple bond between its carbon atoms, and two single bonds between its carbon and hydrogen atoms.
(ii) Structure of ethene (C2H4) is as follows:

Ethene has a double bond between its carbon atoms, and four single bonds between its carbon and hydrogen atoms.
(iii) Structure of benzene (C6H6 ) is as follows:

A benzene molecule has three carbon-carbon double bonds, three carbon-carbon single bonds and six carbon-hydrogen single bonds.
(b) Molecular formula of cyclohexane is C6H12.
Its structure is as follows:

A cyclohexane molecule has six carbon-carbon single bonds and twelve carbon-hydrogen single bonds. Therefore, there are 18 covalent bonds in one molecule of cyclohexane.


Answer 35:

Sl.No Structure of Diamond  Structure of Graphite
1. Each carbon atom is joined to four other carbon atoms by strong covalent bonds to form a regular tetrahedron. Each carbon atom is joined to three other carbon atoms by strong covalent bonds to form flat hexagonal rings.
2. Compact and rigid structure (hard)  Layered structure (soft)

(b) Because of its softness and non-volatile nature, graphite is used as a lubricant in the fast moving parts of a machinery. It is used for lubricating the parts of machinery which operate at high temperatures. Diamond, on the other hand, is an extremely hard substance; therefore, it cannot be used as a lubricant.
(c) As diamond is extremely hard, it can be used to cut and grind other hard materials or metals. Hence, it is used in rock-drilling equipment to drill holes in the rocky layers of the Earth. Graphite being soft cannot be used to cut or grind.
(d)1. Diamonds are used in making jewellery because of their extraordinary shine and texture.
2.Graphite is used in making pencil leads (black core of pencils) because of its black colour and softness.


Answer 36:
(a) Diamond, which is a colourless and transparent substance, is an allotrope of carbon. It is the hardest natural substance known. Diamonds are purely made of carbon and the symbol is C. When we burn diamond in oxygen, only carbon dioxide is evolved showing that diamond is made up of carbon.
(b) A crystal of diamond is a molecule of carbon atoms in which each carbon atom is connected to four other carbon atoms by strong covalent bonds forming a regular tetrahedron. As the carbon atoms are held together firmly by covalent bonds, diamond forms a very rigid structure.
The arrangement of carbon atoms in a diamond crystal is shown below:

(c) Diamonds has a very high melting point, as a huge amount of heat energy is required to break the strong covalent bonds in one crystal of a diamond. The melting point of diamonds is above 3500oC.
(d) Uses of diamonds:
(i) As diamonds have an extraordinary shine, they are used in making jewellery.
(ii) Diamonds, due to their hardness, are used in instruments like glass cutters, grinders. They are also used as abrasives for polishing.


Answer 37:
(a) Graphite is an allotrope of carbon, and is a soft, greyish black and opaque substance. The graphite is made up of carbon atoms. On burning graphite in the presence of oxygen, only carbon dioxide gas is evolved proving that graphite is only made of carbon.
(b) The structure of graphite consists of layers or sheets of carbon atoms which form flat hexagonal rings. In a graphite layer or sheet, each carbon atom is connected to three other carbon atoms by covalent bonds. Each layer of carbon atoms is at a distance with no covalent bonds existing between them. As the various layers of carbon atoms in a graphite crystal are held by weak Van der Waals forces, the layers can slide over each other smoothly.
The following diagram represents the structure of a graphite crystal:

(c) Graphite is a good conductor of electricity because of the presence of free electrons in its crystal. As we know that an atom of carbon has 4 valence electrons, in a graphite crystal, each carbon atom is connected to only three other carbon atoms by covalent bonds. This means that the fourth valence electron of each carbon atom is free. These free moving electrons are responsible for the conduction of electricity in a graphite crystal. But in the case of diamond these free electrons are not available due to its structure. Hence, diamond is a non-conductor.
(d) Uses of graphite:
(i) As graphite is a good conductor of electricity, it is used in making carbon electrodes in dry cells.
(ii) Graphite is used in making pencil leads and black paints.


Answer 38:
(a) Isomers: Isomers are compounds with the same molecular formula but different arrangements of carbon atoms in them. The existence of two or more organic compounds with the same molecular formula but different arrangement of carbon atoms is called isomerism. Isomerism can only exist in hydrocarbons comprising 4 or more carbon atoms.
An example of an isomer is the compound Butane (C4H10)​. As the number of carbon atoms are four, two isomers of butane are possible, and they are n-butane (normal butane with a straight chain arrangement) and iso-butane (three carbon atoms put in a straight chain, and the fourth carbon atom is joined in the side chain to form a different structure).
The structural formula for the isomers of butane are as follows:

(b) (i) Heptane (C7H16) has 7 carbon atoms in its molecule. An isomer other than n-heptane will be 2-methylhexane.The structural formula is shown below :

(ii) The electronic dot structure is as follows:

(c) The IUPAC name of n-C4H10 is butane.
This is because the compound is a saturated hydrocarbon and has 4 carbon atoms in its molecule. If it has four carbon atoms in a single chain, it is represented by the word “but”, and as it comprises all single bonds, it is represented by the ending “ane”. Again, as the carbon atoms are in a single continuous chain, it is represented by n-Butane (where, n is normal).
(d) (i) 2-methylpropane
(ii) 2-methylbutane
(iii) Propene
(iv) Propyne


Exercise : Solution of Questions on page Number : 223


Answer 39:
(a) Hydrocarbon is a compound of hydrogen and carbon. Examples for hydrocarbons are methane (CH4), ethane (C2H6) and ethyne (C2H2). All these compounds are hydrocarbons as they are only made of hydrogen and carbon elements which is evident from their respective molecular formulae.
(b) (i) Saturated hydrocarbons are hydrocarbons in which the carbon atoms are connected by single bonds only. They are also called alkanes, and their general formula is CnH2n+2, where n is the number of carbon atoms in each of their molecules.
Examples: Methane (CH4) and butane (C4H10) are saturated hydrocarbons with 1 and 4 carbon atoms respectively, and their names end with ‘ane’. The atoms are only connected by single covalent bonds.
The structures are represented below:

ii) Unsaturated hydrocarbons are hydrocarbons in which two carbon atoms are either connected by a double bond or triple bond. If the two carbon atoms are connected by a double bond, then it is called an alkene, and its general formula is CnH2n.
Example: Ethene (C2H4) is an alkene in which two carbon atoms are connected by a double bond.
The structure is as follows:

If two carbon atoms are connected by a triple bond, then it is called an alkyne, and its general formula is CnH2n-2.
Example: Ethyne (C2H2) is an alkyne in which two carbon atoms are connected by a triple bond.
The structure of ethyne is as follows:

(c) Name of one saturated cyclic hydrocarbon is cyclohexane. It’s molecular formula is C6H12.
Structure of cyclohexane is as follows:

Name of one unsaturated cyclic hydrocarbon is benzene. It’s molecular formula is C6H6.
Structure of benzene is as follows:
(d) Hexane (C6H14) is a hydrocarbon having 5 structural isomers. They are hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane.

(e)
(i) C3H8 doesn’t have isomers, as isomerism is only possible if the number of carbon atoms is 4 or more.
(ii) C4H10 – Two isomers are possible for this compound, butane. They are butane and 2-methylpropane.
(iii) C5H12 – Three isomers are possible for this compound, pentane. They are pentane, 2-methylbutane and 2,2-dimethylpropane.
(iv) C6H14 – Five isomers are possible for this compound, hexane. They are hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane.


Answer 40:
(c) carbon
Buckminsterfullerene is an allotropic form of the element carbon, and contains 60 carbon atoms joined in a spherical structure.


Answer 41:
(c) C4H6 and C6H12
C4H6 and C6H12 are unsaturated compounds as they correspond to the formula CnH2n-2 and CnH2n. They belong to the group alkyne and alkene respectively.


Answer 42:
(d) 16
The number of covalent bonds in pentane is 16.
This is clear from the structure of pentane shown below:


Answer 43:
(d) catenation
The property of atoms of an element to self-combine and form long chains is known as catenation.


Answer 44:
(c) C6H6
Benzene (C6H6) is the cyclic hydrocarbon having carbon-carbon single bonds as well as carbon-carbon double bonds in its molecule.


Answer 45:
(a) n-pentane
The hydrocarbon 2-methylbutane is an isomer of n-pentane.


Answer 46:
(c) 26
The general formula for unsaturated hydrocarbons with triple bond, is CnH2n-2. Where ‘n’ is the number of atoms in one molecule. If the number of hydrogen atoms in its molecule is 50, then the number of carbon atoms should be 26 (2n-2 = 50; therefore, n = 26).


Answer 47:
(b) 148
The number of hydrogen atoms in an alkyne that has 75 carbon atoms in its molecule is 148. The general formula of the alkynes is CnH2n-2, where ‘n’ is the number of carbon atoms in each molecule. Substituting n = 75 in the formula of alkynes, we get the number of hydrogen atoms to be 148.


Answer 48:
(c) marble slabs
A diamond-toothed saw is usually used for cutting marble slabs.


Answer 49:
(b) urea
Urea is the organic compound prepared by Wohler from an inorganic compound called ammonium cyanate.


Answer 50:
(c) cumene
Cumene is not an allotrope of carbon. Allotropes of carbon are diamond, graphite and buckministerfullerene.


Answer 51:
(b) five
The number of carbon atoms in the organic compound 2,2-dimethylpropane (C5H12) is 5. 2,2-dimethylpropane is one of the three isomers of pentane.


Answer 52:
(d) silicon and carbon
Silicon and carbon exhibit the property of catenation.


Answer 53:
(b) twenty four
Alkanes are saturated hydrocarbons that have the general formula CnH2n+2. According to the question, the number of hydrogen atoms is 50, i.e., 2n+2=50.
∴ n = 48/2 = 24


Answer 54:
(a) 200
Alkenes have double bonds and are represented by the formula CnH2n. Here, ‘n’ is the number of carbon atoms in its molecule. Therefore, substituting ‘n’ with 100 in the formula of the alkenes, we get 200 hydrogen atoms.


Exercise : Solution of Questions on page Number : 224


Answer 55:
(b) benzene
Benzene is the hydrocarbon which has alternate single and double bonds arranged in the form of a ring.


Answer 56:
(c) C3H8
C3H8 is the compound which cannot exhibit isomersim, as it contains only 3 carbon atoms. Isomerism is possible only with hydrocarbons containing 4 or more carbon atoms.


Answer 57:
(d) graphite
The pencil leads are mainly made of graphite.


Answer 58:
(c) 3
The number of isomers formed by the hydrocarbon pentane, with molecular formula C5H12, is 3. They are n-pentane, isopentane and neopentane.


Answer 59:
(b) sixty
The number of carbon atoms joined in a spherical molecule of buckminsterfullerene is 60.


Answer 60:
(a) The solid element ‘X’ is carbon, which has four electrons in the outermost shell of its atom.
(b) Graphite is the allotrope ‘Y’ of carbon which is used as a dry lubricant in machinery, and also in making pencil leads.
(c) Graphite (Y) is a good conductor of electricity because of the presence of free electrons in its crystal.
(d) Graphite (Y) is used in making carbon electrodes or graphite electrodes in dry cells and electric arcs.
(e) Diamond and buckminsterfullerene are the two other allotropes of carbon.


Answer 61:
(a) If A is a cyclic compound, then C6H12 is the molecular formula of the compound named cyclohexane.
The structural formula is as follows:

(b) If B is an open chain compound, then C6H12is the molecular formula of the compound named hexene.
The structural formula is shown below:

(c) Hexene (B) is an unsaturated hydrocarbon comprising both single-bonded and double-bonded carbon atoms.
(d) Cyclohexane is an alkane which contains only single-bonded carbon atoms.


Answer 62:
(a) Carbon is the element A which exhibits the property of catenation.
(b) Carbon dioxide is the gas B which is utilised by the plants for photosynthesis.
(c) Diamond is the allotrope C of carbon which is used in glass cutters.
(d) Diamond is used in making jewellery.
(e) Buckminsterfullerene is an allotrope of carbon which exists as spherical molecules.
(f) Graphite is another allotrope of carbon which conducts electricity.


Answer 63:
(a) Carbon is the element ‘E’ which exists in three allotropic forms A, B and C.
(b) Buckminsterfullerene is the allotrope, A, of carbon in which the atoms are joined to form spherical molecules.
(c) Graphite is the allotrope, B, of carbon which is surrounded by three other carbon atoms to form a sheet like structure.
(d) Diamond is the allotrope, C, of carbon in which each atom is surrounded by four other carbon atoms to form a rigid structure.
(e) The allotrope C (Diamond) is used to make jewellery.
(f) The allotrope B (Graphite) is used in making anode of a dry cell.


Answer 64:
(a) C6H12 is the molecular formula which represents cyclohexane as well as hexene. The molecular formula for both hexene and cyclohexane is the same in which there are 6 carbon atoms. However, their structure differs, as in a cyclic compound, the carbon atoms form closed chains while hexene has an open chain structure.
(b) C6H6 represents is the molecular formula of benzene. Benzene is an unsaturated cyclic hydrocarbon made up of 6 carbon atoms and 6 hydrogen atoms.
(c) C7H14, C5H10 ,C6H12 are the molecular formulae for the open chain unsaturated hydrocarbons having double bonds, as they correspond to the general formula of alkenes, i.e. CnH2n,​ where n is the number of carbon atoms in its one molecule.
(d) C5H8 and C7H12 are the molecular formulae for the unsaturated hydrocarbons comprising triple bonds, as they correspond to the general formula of alkynes, i.e. CnH2n-2, where n is the number of carbon atoms in its one molecule.
(e) C7H14, C5H10, C6H12 are the three molecular formulae which represent cyclic hydrocarbons, as they correspond to the general formula CnH2n, where n is the number of carbon atoms in its one molecule. The closed chains of cyclic hydrocarbons contain as many carbon atoms as denoted by their molecular formulae. Therefore, a cyclic hydrocarbon containing 7 carbon atoms will be a closed cycloheptane, a cyclic hydrocarbon with 5 carbon atoms will form a pentagonal ring called cyclopentane and a cyclic hydrocarbon with 6 carbon atoms will form a cyclohexane.


Exercise : Solution of Questions on page Number : 225


Answer 65:
Among the given compounds, only C3H4 has a triple bond as it corresponds to the general formula for alkynes CnH2n-2, where n = 3.


Answer 66:
The molecular formula of the cyclic hydrocarbon is C8H16, as it satisfies the general formula of a cyclic hydrocarbon, i.e. CnH2n, where n is the number of carbon atoms in its one molecule. Also, it is already given that the hydrocarbon contains 8 carbon atoms (n = 8) arranged in the form of a closed ring; therefore, it will be called a cyclooctane.
The structural formula of cyclooctane (C8H16 ) is as follows:


Answer 67:
The molecular formula of a cyclic hydrocarbon is C4H8, as it satisfies the general formula of a cyclic hydrocarbon, i.e. CnH2n. Here, the number of hydrogen atoms is already given as 8, i.e. 2n = 8.
Therefore, n = 8/2 = 4. Here, n represents the number of carbon atoms. Therefore, the molecular formula is C4H8.
The structural formula of the cyclic hydrocarbon C4H8 is as follows​:


Answer 68:
(i) An alkane comprising 20 atoms of carbon (n = 20):
C20H2×20+2=C20H42
(ii) An alkene comprising 20 atoms of carbon (n=20):
C20H20×2= C20H40
(iii) An alkyne comprising 20 atoms of carbon (n=20):
C20H2×20-2=C20H38


Answer 69:
C5H10 can have a double bond because it satisfies the general formula for alkenes i.e., CnH2n. Here, there are 5 carbon atoms; hence, n is 5. Substituting n in the formula CnH2n, we get, C5H2×5=C5H10.


Answer 70:
C3H4 (CnH2n-2) is an unsaturated hydrocarbon. It has three carbon atoms, of which two carbon atoms are connected by a triple bond. Here, is 3. Now, substituting in the formula of the alkynes, we get, C3H2×3-2=C3H4. This compound is called propyne. C2H6 is a saturated hydrocarbon with two carbon atoms bonded by a single bond.


Exercise : Solution of Questions on page Number : 220


Answer 1:
The molecular formula of ethanol is C2H5OH.


Answer 2:
The next higher homologue of methanol (CH3OH) is ethanol (C2H5OH).


Answer 3:
The functional group present in the compound CH3OH, is alcohol (OH). The IUPAC name of the given compound is methanol.


Answer 4:
The common name of the simplest aldehyde is formaldehyde (HCHO), and its IUPAC name is methanal.


Answer 5:
Formaldehyde is the common name for methanal.


Answer 6:
(a) The functional group of the given compound is a triple bond or an alkyne group.
(b) The functional group of the given compound is a double bond or an alkene group.


Answer 7:
Propanone (acetone) is the simplest ketone.


Answer 8:
The common name of propanone is acetone.


Answer 9:
(i) IUPAC name of CH3COCH3 is propanone.
(ii) IUPAC name of CH3COCH2CH3 is butanone.


Exercise : Solution of Questions on page Number : 240


Answer 10:
The simplest organic acid is formic acid (methanoic acid) with the chemical formula HCOOH.


Answer 11:
The IUPAC names, common names and formula for the first two members of the homologous series of carboxylic acid are:
1) IUPAC name: Methanoic acid; Common name: Formic acid; Formula: HCOOH
2) IUPAC name: Ethanoic acid; Common name: Acetic acid; Formula: CH3COOH


Answer 12:
(a) The common name of methanoic acid is formic acid.
(b) The common name of ethanoic acid is acetic acid.


Answer 13:
(a) Structure of ethanoic acid:

(b) Structure of propanoic acid:


Answer 14:
(a) Common name and IUPAC name of HCOOH are formic acid and methanoic acid respectively.
(b) Common name and IUPAC name of CH3COOH are acetic acid and ethanoic acid respectively.


Answer 15:
Ethanoic acid (CH3COOH) is the name of the compound which is a homologue of HCOOH (methanoic acid).
The structural formula is:


Answer 16:
(a) The formula of methanoic acid is HCOOH.
(b) The formula of ethanoic acid is CH3COOH.


Answer 17:
The common name of C2H5OH is ethyl alcohol, and its IUPAC name is ethanol.


Answer 18:
The IUPAC name of the compound C3H7OH is propanol.


Answer 19:
Ethanol (C2H5OH) is a member of the alcohol group.
Its structural formula is as follows:


Answer 20:
(a) The IUPAC name of C4H9OH is butanol.
(b) The IUPAC name of C5H11OH is pentanol.


Answer 21:
The common name of methanol is methyl alcohol.


Answer 22:
(i) 14 u is the difference between two consecutive homologues in terms of molecular mass.
(ii) The two consecutive homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.


Answer 23:
(a) Gaseous fuels like cooking gas (LPG) burn with a flame.
(b) Solid and liquid fuels (coal, charcoal, etc.) burn without a flame.


Answer 24:
False, as there cannot be a ketone with less than three carbon atoms in it. Propanone or acetone (CH3COCH3) is the first member of the ketone family.


Answer 25:
(a) The next higher homologue of ethanol is propanol.
(b) The next homologue of C2H5OH is C3H7OH.
(c) The next higher homologue of ethane is propane.
(d) The functional group present in ethanol is alcohol (OH).
(e) Organic compounds having   functional group are known as carboxylic acids.


Answer 26:
(a) The general name for the class of compounds having the formula CnH2n-2 is alkynes. Ethyne is the first member of the homologous series of alkynes.
(b) CnH2n is the general formula for the homologous series of alkenes. The second and the fourth member of this series will have the molecular formulae C3H6 and C4H8 respectively.
c) The third and fifth member of the series having the general formula CnH2n+2 (alkanes) will have the molecular formula C3H8 and C5H12 respectively​.


Answer 27:
(a) Ethane (C2H6) and propane (C3H8) are the names of the successive homologues of methane.
Their structural formulae are as follows:
(b) The homologous series of a hydrocarbon with the molecular formula C10H18 is alkynes (CnH2n-2).
(c)
(i) C3H8 and​ C4H10 are the hydrocarbons belonging to the homologous series of alkanes.
(ii) C5H10 and​ C8H16 are the hydrocarbons belonging to the homologous series of alkenes.
(iii) C6H10 and​ C7H12 are the hydrocarbons belonging to the homologous series of alkynes.


Answer 28:
(a)
(i) The molecular formula of a homologue of C3H6 is C4H8.​ It belongs to the homologous series of alkenes having the general formula CnH2n.
(ii) The molecular formula of a homologue of C2H6 is C3H8. It belongs to the homologous series of alkanes having the general formula CnH2n+2.
(iii) The molecular formula of a homologue of C2H2 is C3H4. I​t belongs to the homologous series of alkynes having the general formula CnH2n-2.
(b) The difference in the molecular masses of any two adjacent homologues is 14u.
(c) Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae.


 Exercise : Solution of Questions on page Number : 241


Answer 29:
(a) The formula of the functional group present in carboxylic acids is RCOOH (where, R is an alkyl group)
(b) The functional group present in is the alkyne group (triple bond).
(c)
(i) The functional group present in CH3CHO is the formyl group (-CHO).
(ii) The functional group present in CH3CH2COOH is the group of carboxylic acids (-COOH).
(iii) The functional group present in CH3COCH3 is the carbonyl group (-CO-).
(iv) The functional group present in CH3CH2CH2OH is the alcohol (hydroxyl) group (-OH).


Answer 30:
(a) The IUPAC name of CH3Cl is chloromethane, and its common name is methyl chloride.
(b) The structure of chlorobutane is as follows:

(c) The structure of bromopentane is as follows:

Yes, structural isomers are possible for bromopentane. Some of its isomers are 1-bromopentane, 2-bromopentane and 3-bromopentane.


Answer 31:
(a) Propanone (CH3COCH3) is one of the organic compounds comprising a ketone functional group (CO).
(b) The general formula of chloroalkanes (haloalkanes) is CnH2n+1-X (where, X is Cl, Br or I).
Therefore, the first three members of the chloroalkane series will be:
Chloromethane (CH3Cl)
Chloroethane (C2H5Cl)
Chloropropane (C3H7Cl)
(c) The name of the compound is bromoethane, as the structure has the parent alkane. It contains 2 carbon atoms, and its one hydrogen atom is replaced by a halogroup (-X or bromine) atom. So, the name of the compound is bromoethane.


Answer 32:
(a) The general name for the organic compounds comprising -CO- is ketones.
(b) CH3COOH is the compound which contains a carboxylic acid group (-COOH).
(c) The name of the compound is methanal, as the structure contains one carbon atom and an aldehyde group (-CHO), which is indicated by using ‘al’ as the suffix. Hence, replacing the last letter ‘e’ of methane with ‘al’ we get the name methanal.


Answer 33:
(a) Homologous series: A series of organic compounds having similar structures and chemical properties and in which the successive compounds differ by CH2 group is called a homologous series. A homologue of CH3OH will differ by the -CH2 group; therefore, methanol’s successive homologue will be ethanol (C2H5OH).
The structural formula of ethanol is as follows:

(b) The molecular formula of the third member of the homologous series, comprising the general formula CnH2n+1OH, is C3H7OH (propanol).
(c) Coal and petroleum are the two fossil fuels.


Answer 34:
(a) The molecular structures for propanone (C3H6O) and butanone (C4H8O) are as follows:
Propanone:

Butanone:

(b) Formula IUPAC                           name
(i) HCHO                                          Methnal
(ii) CH3CHO                                    Ethanal
(iii) CH3CH2CHO                           Propanal
(iv) CH3CH2CH2CHO                    Butanal
(c) The functional group, likely to be present in an organic compound having the molecular formula C4H10O, is the alcohol group (-OH). The formula of the compound will be C4H9OH (butanol).


Answer 35:
(a)

Sl.No Group A Group B
1. CH3COOH Ethanoic acid
2. CH3CHO Ethanal
3. CH3OH Methanol

(b) Structure of butanoic acid (C3H7COOH) is as follows:

c) The IUPAC name of acetic acid (CH3COOH) is ethanoic acid.


Answer 36:
(a) Carboxylic group (-COOH) can be present as the functional group in an organic compound having the molecular formula C5H10O2. The formula of the organic compound will be C4H9COOH.
(b)
(i) Methanal (HCHO) is a compound containing an aldehyde group (-CHO).
(ii) Ethanol (C2H5OH) is a compound containing the alcohol group (-OH).
(iii) Propanoic acid (C2H5COOH) is a compound containing the carboxylic acid group (-COOH).
(iv) Chlorobutane (C4H9Cl) is a compound containing the halo group (-X).
(c)
(i) Propene (C3H6) is a compound having the functional alkene group as it satisfies the general formula of alkenes, i.e. CnH2n.
(ii) Ethyne (C2H2) is a compound having the functional alkyne group as it satisfies the general formula of alkynes, i.e. CnH2n-2.


Answer 37:
(a) The molecular formula of the alcohol which can be derived from pentane will be C5H11OH (pentanol).
Structure of pentanol is as follows:

(b) The names for the functional groups are as follows:
(i) Aldehydes
(ii) Alcohols
(iii) Carboxylic acids
(iv) Ketones
(v) Halo group
(c) A candle burns with a yellow, luminous flame due to the incomplete combustion of wax in the air. When we light a candle, we observe the wax melt and rise up to the wick in the form of vapours. As there is no proper way for the oxygen to mix with these wax vapours, the latter burns with insufficient oxygen, thereby resulting into the incomplete combustion of wax. This incomplete combustion produces small unburnt carbon particles that rise in the flame, get heated up and make the flame yellow and luminous.


Answer 38:
(a) A group of compounds having similar structures and chemical properties but their successive compounds differ by a CH2 group is called a homologous series.
Example: Alkanes have similar structures and similar chemical properties, so they can be grouped together to form a homologous series. The general formula of the homologous series of alkanes is CnH2n+2, where n is the number of carbon atoms in each molecule.
The first five members of the homologous series of alkanes are as follows:
1. Methane CH4 ( First member, contains 1 carbon atom)
2. Ethane C2H6 (Second member, contains 2 carbon atoms)
3. Propane C3H8 (Third member, contains 3 carbon atoms)
4. Butane C4H10 (Fourth member, contains 4 carbon atoms)
5. Pentane C5H12 (Fifth member, contains 5 carbon atoms)
(b) Characteristics of a homologous series are as follows:
(i) All the members of a homologous series can be represented by the same general formula.
For example, all the members of the alkene series are represented by the same formula CnH2n.
(ii) The members of a homologous series show a gradual change in their physical properties like melting point, boiling point and density with the increase in their molecular masses.
(c) The organic compound C18H36 is a member of the homologous series of alkenes having the general formula CnH2n..

Name of the series Alkanes Alkanes Alkynes
Molecular formula of hydrocarbons CH4, C2H6, C4H10 C2H4, C3H6 C2H2 , C3H4

(e) Heteroatom is any atom other than carbon and hydrogen. Examples: Nitrogen, sulphur, chlorine and bromine are heteroatoms. The name and formula of two organic compounds containing different heteroatoms are (i) chloromethane, CH3Cl, and (ii) formaldehyde HCHO.


Exercise : Solution of Questions on page Number : 242


Answer 39:
(a) Functional group: An atom or a group of atoms which determine the properties of an organic compound is called a functional group.
For example: The alcohol group -OH is also known as an alcoholic group or hydroxyl group. The compounds in which the alcohol group is present are termed as alcohols. The general formula of an alcohol is R-OH (R is an alkyl group) like ethanol which has the molecular formula C2H5OH. All the compounds having this functional group will have similar properties.
(b) The three common functional groups present in the organic compounds are as follows:

Functional groups  Aldehyde group  Halo group  Ketone group
Symbol  -CHO  (-X)  -CO-
Formula R -CHO  R-X R-CO-R’

(c) (i) The functional group present in CH3COOH is carboxylic acid group (-COOH).
(ii) The functional group present in CH3CH2CHO is the aldehyde group (-CHO).
(iii) The functional group present in C2H5OH is the alcohol group (OH).
(iv) The functional group present in CH3COCH2CH3 is the ketone group (-CO-).
(d) The functional group which always occurs in the middle of the carbon chain is the ketone group (-CO-). In a ketone, a carbon atom is bonded to one oxygen through a double bond. The two remaining free electrons in the carbon atom are shared with two different alkyl groups. This is why the -CO group always occurs in the middle of the carbon chain.
(e) Molecular structures of the compounds are as follows:
(i)

(ii)

(iii)

(iv)


Answer 40:
(a) When carbon is burned in air, carbon dioxide is evolved along with a large amount of heat and light energy.
The chemical equation of the above reaction is as follows:
C + O2 → CO2 + Heat + Light
(b) Coal and petroleum are called fossil fuels because they are produced through the decomposition of the pre-historic organisms (plants and animals) buried deep in the soil since millions of years ago.
(c) Coal evolved in the Earth millions of years ago by the decomposition of trees and plants that got buried deep into the soil. Natural phenomena like volcanoes and earthquakes caused the forests to get buried deep under the surface of the Earth. The extreme temperature and pressure inside the soil converted the wood into coal in the absence of air.
(d) Petroleum evolved, millions of years ago, through the decomposition of the microscopic remains of the plants and animals buried deep under the sea. When the marine plants and animals died, millions of years back, their bodies sank to the bottom of the sea, thereby getting buried into the sand and mud. The high pressure, heat and bacteria caused the chemical reactions in the absence of air and converted the microscopic remains into petroleum. This is the reason why petroleum is found trapped between two layers of non-porous rocks.
(e) Other than coal and petroleum, natural gas is a fossil fuel.


Answer 41:
(d) C3H8
C3H8 is the molecular formula of a homologue of butane as it satisfies the general formula CnH2n+2 of the alkane series.


Answer 42:
(b) C5H10O
C5H10O represents two organic compounds ketones (C2H5-CO-C2H5) and aldehydes (C2H5-CH2-CH2-CHO) which have different functional groups.


Answer 43:
(c) six
The number of carbon atoms present in the molecule of the fifth member of the homologous series of alkynes is 6, as the first compound of this series has minimum two carbon atoms.


Answer 44:
(b) Charcoal
Charcoal glows red and burns without a flame.


Answer 45:
(d) ketone group
The ketone group (-CO-), with the general formula R-CO-R, is always present in the middle of a carbon chain.


Answer 46:
(c) C3H6O
C3H6O contains an aldehyde group, as the compound satisfies the general formula of the aldehydes CnH2nO.


Answer 47:
(c) ketones and aldehydes
Ketones and aldehydes are the organic compounds which are isomeric to one another.


Answer 48:
(b) LPG
LPG is the fuel which usually burns with a blue flame, as the burner of a stove has many holes to allow enough oxygen for complete combustion.


Answer 49:
(c) Wax
Due to incomplete combustion, wax burns by producing a yellow, luminous flame.


Answer 50:
(c) alkynes
The compound C48H94 belongs to the homologous series of alkynes, as it satisfies the general formula CnH2n-2.


Answer 51:
(d) C6H12O
C6H12O (hexanone or C2H5-CO-C3H7) represents a ketone.


Answer 52:
(c) charcoal
Charcoal is not a fossil fuel. It is formed from wood and coal.


Answer 53:
(c) -CO-
Butanone (C2H5-CO-CH3) is a four-carbon compound having the functional group -CO- (ketones).


Answer 54:
(c) C5H10O
The molecular formula of the third member from the homologous series of ketones is C5H10O (Pentanone or C2H5-CO-C2H5).


Answer 55:
(d) -CHO
The functional group present in propanal (C2H5CHO) is -CHO (aldehyde group).


Exercise : Solution of Questions on page Number : 243


Answer 56:
(a) The isomer A is propanone (acetone).
(b) The electron-dot structure of propanone is:

(c) The isomer B is propanal.
(d)The electron-dot structure of propanal is:

(e) Methanal or formaldehyde is the lower homologue of compound B, which is used to preserve biological specimens.


Answer 57:
(a) The hard material, X, mined from the Earth and used in the generation of electricity is coal. The soft material, Y, used as a fuel in the form of candles is wax. The gaseous material, Z, occurring along with petroleum and increasingly used as a vehicular fuel in its compressed form is natural gas.
(b) (i) Wax burns by producing a yellow, luminous flame due to incomplete combustion. This is because oxygen doesn’t get a proper way to get into the wax vapour to burn it completely.
(ii) Coal ultimately burns without producing a flame. It comprises some volatile substances that burn with a flame, and once the those substances have completely burned out, the coal starts glowing red.
(iii) Natural gas can burn in a gas stove by producing a blue flame. This is because a stove has holes in its burner that allows proper amount of oxygen needed for the complete combustion of the natural gas.


Answer 58:
a) The organic compound ‘B’ comprises an alcohol group. Butanol is the name of the compound, and its formula is C4H9OH.
Its structural formula is as follows:

(b) The organic compound ‘A’ contains a carboxyl group. The name of the acid is butanoic acid, and its formula is C3H7COOH. Its structural formula is as follows:

(c) Compound ‘C’ (C4H8O), represents the molecular formula of an aldehyde as well as a ketone. The aldehyde represented by this formula is butanal (C3H7CHO).
The ketone represented by this formula is butanone (CH3COCH2CH3).
Their structural formulae are as follows:


Answer 59:
(a) The liquid ‘X’ is ethanoic acid which turns the blue litmus red. It belongs to the homologous series of carboxylic acid. Methanoic acid is the other member of this homologous series.
(b) The liquid ‘Y’ is propanone which is colourless, and is widely used as a nail polish remover. It belongs to the homologous series of ketones. Butanone is the name of the other member of this homologous series.
(c) Propanal is an organic compound having the same molecular formula as of the liquid ‘Y’ (Propanone), but the former belongs to the homologous series of aldehydes.
(d) The liquid ‘Z’ is ethanol which has no action on the litmus, and is used in the tincture of iodine. It belongs to the homologous series of alcohols. Methanol is the other member of this homologous series.


Answer 60:
(a) When one H atom of C3H8 is replaced by a Cl atom, chloropropane is formed. It has the molecular formula CH3-CH2-CH2-Cl.
(b) When one H atom of C3H8 is replaced by a OH group, propanol is formed. It has the molecular formula CH3-CH2-CH2-OH.
(c) When one H atom of C3H8 is replaced by a CHO group, butanal is formed. It has the molecular formula CH3-CH2-CH2-CHO.
(d) When one H atom of C3H8 is replaced by a COOH group, butanoic acid is formed. It has the molecular formula CH3-CH2-CH2-COOH.
(e) When two H atoms, joined to the middle carbon atom of C3H8, are replaced by one O atom, propanone is formed. It has the molecular formula CH3-CO-CH3.


Exercise : Solution of Questions on page Number : 262


Answer 1:
Carbon dioxide evolves when ethanoic acid is added to sodium carbonate.
2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
When the gas evolved during this reaction, is passed through the lime water in a test tube, the latter turns milky. This indicates that the gas evolved is carbon dioxide.


Answer 2:
CH3COOH (ethanoic acid) gives brisk effervescence with sodium hydrogencarbonate. It reacts with sodium hydrogencarbonate to give sodium ethanoate, carbon dioxide and water. Effervescence is due to carbon dioxide evolved.


Answer 3:
Carboxylic acid group (-COOH) is the functional group which gives brisk effervescence with NaHCO3.


Answer 4:
Ethene (C2H4)is formed when ethanol is heated with concentrated sulphuric acid (H2SO4) at 170oC. This reaction is known as dehydration as it involves the removal of water molecule from ethanol.


Answer 5:
Unsaturated hydrocarbons, such as acetylene have high percentage of carbon. They have a higher percentage of carbon as compared to corresponding alkanes and alkenes. When ethyne is burned in air, it does not get completely oxidised, thereby producing a sooty flame.


Answer 6:
When hydrogen is added to ethene, ethane is formed. When hydrogen is added to unsaturated hydrocarbons in presence of Ni catalyst, it saturates them and forms alkanes.
C2H4 →H2Ni C2H6.


Answer 7:
Ethene is an unsaturated hydrocarbon, it combines with bromine in the bromine water thereby discharging its reddish-brown colour. However, ethane is a saturated compound and it does not react with bromine in the bromine water and can have no effect on the colour of bromine water.


Answer 8:
Nickel and palladium are the two catalysts which can be used in the hydrogenation of unsaturated compounds.


Answer 9:
Disadvantages of incomplete combustion are as follows:
(i) Due to incomplete combustion, greater amount of fuel is wasted and less heat is released as compared to that in complete combustion.
(ii) Incomplete combustion leads to the production of a gas called carbon monoxide which is extremely poisonous.


Answer 10:
Ethanol reacts with sodium to form sodium ethoxide along with the rapid effervescence of hydrogen gas.
The chemical equation of this reaction is as follows:
2C2H5OH + 2Na → 2C2H5O– Na+ + H2.


Answer 11:
Ethanol gets oxidised to ethanoic acid in the presence of potassium permanganate solution (alkaline) which acts as an oxidising agent.
The chemical reaction is as follows:
CH3CH2OH + 2[O] → CH3COOH + H2O.


Answer 12:
Ethanol is the liquid carbon compound which is used as an additive in petrol by some countries.


Answer 13:
The raw materials required for making soap in a laboratory or at home are as follows:
1. Vegetable oil (Castor oil)
2. Sodium hydroxide (Caustic soda), and
3. Sodium chloride (Common salt)


Answer 14:
Detergents cannot be used to check the hardness of water, as they lather easily in both soft and hard water. However, the hardness of water can be detected using soaps, as soaps don’t lather easily in hard water.


Answer 15:
Carboxylic acids react with sodium bicarbonate to form Sodium ethanoate and water along with carbon dioxide, which produces effervescence in the reaction mixture. This reaction is used as a test for the presence of carboxylic acids.
CH3COOH + NaHCO3 →CH3COONa + CO2 + H2O.


Answer 16:
Ethanol gets converted into ethanoic acid by taking up oxygen released by potassium permanganet in the reaction mixture. Since, this reaction involves addition of oxygen to ethanol, it is an oxidation reaction.
The chemical equation for the above reaction is as follows:
CH3CH2OH + 2[O] → CH3COOH + H2O.


Answer 17:
Alkanes are saturated hydrocarbons, and they burn readily in the air with a blue non-sooty flame to release a lot of heat and light energy. This heat energy can be used for heating water, cooking food and operating machines in factories and generators in thermal power stations. That is why they are excellent fuels.


Answer 18:
Sodium hydrogencarbonate is the compound which can be used to distinguish between ethanol and ethanoic acid. It gives effervescence of carbon dioxide, with ethanoic acid.


Answer 19:
(a) CH3CH2OH →170°conc H2SO4 CH2=CH2
(b) CH3COOH + C2H5OH →conc H2SO4 CH3COOC2H5 + H2O


Exercise : Solution of Questions on page Number : 263


Answer 20:
(a) CH4 + 2O2 → CO2 + 2H2O + Heat + Light
(b) CH4 + Cl2 → CH3Cl + HCl


Answer 21:
(a) The process of burning of a hydrocarbon in the presence of air to give CO2, H2O, heat and light is known as combustion.
(b) The sodium salt of a long chain fatty acid is called soap.
(c) Detergent is better than soap for washing clothes when the water is hard.
(d) The organic acid present in vinegar is ethanoic acid.


Answer 22:
CH4, C3H8 and C5H12 are the hydrocarbons which have substitution reactions. This happens because CH4 (Methane), C3H8 (Propane) and C5H12(Pentane) are all saturated hydrocarbons (alkanes). Substitution reaction, which is a characteristic of saturated hydrocarbons, is the reaction in which one or more hydrogen atoms of a hydrocarbon are replaced by some other atoms (such as chlorine).


Answer 23:
C2H4 and C3H4 are the compounds supporting addition reactions. This is because the compounds C2H4(Ethene) and C3H4 (Propyne) are unsaturated hydrocarbons.


Answer 24:
(a) Ethanol, a highly inflammable liquid, burns readily in the air to release carbon dioxide and water vapour along with a lot of heat and light.
The chemical equation of the above reaction is:
C2H5OH + 3O2 → 2CO2 + 3H2O + Heat + Light
(b) Ethanol, a highly inflammable liquid, readily burns in the air with a clear flame to give heat and light. Therefore, ethanol is used as a fuel.
(c) Uses of ethanol:
1. Ethanol is used in the manufacture of several products like dyes, perfumes and synthetic rubber.
2. Ethanol is used as a solvent in many organic compounds. Since it is a good solvent, it is also used in medicines like cough syrups and tincture iodine.


Answer 25:
(a) When propanoic acid is warmed with methanol in the presence of a few drops of concentrated sulphuric acid in it, esterification takes place and an ester named methyl propanoate is formed along with water.
The chemical equation for the above reaction is:
C2H5COOH + CH3OH → C2H5COOCH3 + H2O.
(b) Soap is the salt of a strong base (sodium hydroxide) and a weak acid (carboxylic acid); therefore, it’s solution with water will be also basic in nature. Hence, it will turn a red litmus paper blue.
(c) Denatured alcohol is ethyl alcohol in which small amounts of poisonous substances like methanol and copper sulphate are added to make it unfit for consumption.
Ethyl alcohol is used for manufacturing various products in different industries. Therefore, government supplies ethyl alcohol to the industries without charging production tax. In order to prevent the misuse of ethyl alcohol for drinking purposes, it is denatured by adding poisonous substances such as methanol, pyridine or copper. This makes the alcohol unfit for consumption.


Answer 26:
(a) Alcohols are slightly acidic in nature and can be detected by their reaction with sodium. When sodium is added to alcohol, sodium alkoxide is formed along with the release of hydrogen gas that burns with a pop sound. This confirms that the compound is an alcohol. Alcohols do not change the colour of the litmus paper.
(b) Following are the harmful effects of drinking alcohol:
(i) Alcohol has a severe impact on our nervous system and brain. The reflex to judging any situation slows down and a person fails to react quickly. Therefore, chances of accidents increases when a person is driving a vehicle under the influence of alcohol.
(ii) The consumption of alcohol brings about a drastic decline in the mental restrain, and this makes a drunken man quarrelsome. Due to this, violence and crimes have increased in the society.
(iii) Excess consumption of alcohol over the time can damage stomach, liver, heart and brain. Cirrhosis, which is a liver disease, can even cause death.
(c) Methanol is a poison when taken internally. Though both methanol and ethanol are metabolised by the liver, the rate of metabolism differs. Methanol gets oxidised to methanal in the liver, which rapidly reacts with the cell components and causes coagulation of protoplasm. As a result, the cells stop functioning causing death of the person who consumes methanol.


Answer 27:
(a) Ethanol can be converted into ethene by the dehydration reaction.
The chemical equation for the above reaction is as follows:
CH3-CH2OH → CH2=CH2 + H2O
When ethanol is heated with concentrated sulphuric acid at 170oC, ethanol gets dehydrated to form ethene, an unsaturated hydrocarbon. Concentrated sulphuric acid acts as the dehydrating agent in this reaction.
(b) Propanol is converted into propanoic acid by the oxidation reaction.
The chemical equation for the above reaction is as follows:
CH3-CH2-CH2-OH → CH3CH2COOH
Propanol is oxidised to propanoic acid in the presence of alkaline potassium permanganate solution (alkaline KMnO4). Alkaline potassium permanganate solution acts as an oxidising agent as it adds oxygen to convert propanol to propanoic acid.


Answer 28:
(a) The gas stove used in our homes comprises burners with tiny holes in them so as to let in sufficient oxygen required for the fuel to burn. When there is sufficient oxygen, the fuel will burn completely with a blue flame. If the fuel fails to burn completely, a sooty flame will be produced (due to the incomplete combustion) which will blacken the bottom of the vessel. Therefore, the air holes in the gas burner need to be adjusted so that the burner gets enough oxygen to burn the fuel completely.
(b) Synthetic detergents are not biodegradable, as they can not be decomposed by microorganisms such as bacteria. Since, they don’t decompose, they pollute water bodies like rivers and lakes.


Answer 29:
(a) When 5% alkaline potassium permanganate solution is added drop by drop to warm ethanol in a test tube, an oxidation reaction would be observed by us. Ethanol is oxidised to ethanoic acid in the presence of the strong oxidising agent alkaline potassium permanganate.
The chemical equation for the above reaction is as follows:
CH3CH2OH + 2[O] → CH3COOH + H2O
(b) Experimentally, we can distinguish between an alcohol and carboxylic acid by conducting a litmus test. Take two test tubes and pour about 2 ml of carboxylic acid in one, and 2 ml of alcohol in the other. Add one drop of blue litmus solution in each of the test tubes.
The solution which shows no effect is alcohol, and the solution that turns the blue litmus red is carboxylic acid.


Answer 30:
The functional group of organic compounds that can be hydrogenated are double bonds in alkenes and triple bonds in alkynes.
Hydrogenation is the process of addition of hydrogen to an unsaturated hydrocarbon, in the presence of a catalyst, in order toconvert it into a saturated hydrocarbon.
For example, alkene (double bond) can be converted to an alkane (single bond) by adding hydrogen in the presence of a catalyst.
Vegetable oil (unsaturated compound) is heated with hydrogen in the presence of the catalyst nickel to form saturated fat (vegetable ghee).
The chemical equation for the above reaction is as follows:
R2C=CR2 + H2 → R2CH-CHR2  (R is the alkyl group)
Vegetable oils, at room temperature, are in the liquid state. On hydrogenation, they convert to a solid or semi-solid state. Their physical properties such as melting point and boiling point changes.
Vegetable oils are the natural organic compounds that can be hydrogenated.


Answer 31:
(a) When ethanol reacts with sodium, a rapid effervescence of hydrogen gas is observed.
(b) Esters are formed when carboxylic acid reacts with alcohol in the presence of concentrated sulphuric acid.
(c) When dilute ethanoic acid is put on a universal indicator paper, it turns the paper orange, marking the pH level to be 4. This shows that dilute ethanoic acid is a weak acid. On the other hand, when dilute hydrochloric acid is dropped on the universal indicator paper, it turns the paper red, marking its pH level to be about -1. This shows that hydrochloric acid is a strong acid.


Answer 32:
(a) The organic compound CH3COOH is a carboxylic acid, and its name is ethanoic acid.
(b) Ethanol (CH3CH2OH) should be oxidised to prepare ethanoic acid (CH3COOH).
(c) CH3COOH is physically found in its liquid state.
(d)Advantage of soaps over detergents:
Soaps are biodegradable; therefore, they don’t cause water pollution, while a few detergents are not biodegradable, thereby pollute water bodies like rivers and lakes.


Exercise : Solution of Questions on page Number : 264


Answer 33:
(a) When ethanol reacts with ethanoic acid in the presence of a few drops of concentrated sulphuric aciddiv, a sweet smelling ester named ethyl ethanoate is formed.
The chemical equation for the above reaction is:
CH3COOH+2H5OH→Conc. H2SO4CH3COOC2H5+ H2O
(b) When ethanol is heated with concentrated sulphuric acid at 170oC, it gets dehydrated to form ethene (unsaturated hydrocarbon). This reaction is termed as dehydration reaction as it involves the removal of water molecules from the alcohol (ethanol). In this reaction, the concentrated sulphuric acid acts as a dehydrating agent.
The chemical equation for the above reaction is:
CH3CH2OH → CH2 =CH2  + H2O


Answer 34:
(a) When ethanol is oxidised with alkaline potassium permanganate (alkaline KMnO4) or acidified potassium dichromate (acidified K2Cr2O7), ethanoic acid is formed. Alkaline potassium permanganate and acidified potassium dichromate are strong oxidising agents, as they provide oxygen for oxidising other substances in the reaction. This reaction is known as the oxidation reaction.
The chemical equation for the above reaction is as follows:
CH3CH2OH + 2[O] → CH3COOH + H2O
(b) CH3COOH (ethanoic acid) and HCOOH (formic acid) are the compounds which can turn blue litmus solution red. This happens because ethanoic acid and formic acid are the organic compounds which are acidic in nature.


Answer 35:
(a) Following is the process of preparing soap in the laboratory:
Raw materials required are:
(i) Vegetable oil like castor oil
(ii) Sodium hydroxide (caustic soda), and
(iii) Sodium chloride (common salt)
Steps involved in the preparation of soap are:
1. Take a beaker with about 20 ml of castor oil in it.
2. Also, add 30 ml of 20% sodium hydroxide to the beaker.
3. Heat the mixture and stir it constantly until a soap is formed.
4. Add 5-10 grams of common salt to it and stir the mixture. On cooling the solution, we will see the solid soap getting separated.
5. The solid soap, once separated, is made to set, and then it is cut into pieces called soap bars.
(b) Common salt (sodium hydroxide) is added during the preparation of soap to separate the soap from the aqueous solution. On adding common salt, solubility of the soap, present in the solution, decreases. This allows the soap to be taken out from the solution in its solid form.
(c) (i) Hard water contains calcium and magnesium salts; and, when a soap is used for washing clothes with hard water, a good amount of it gets utilised in reacting with the calcium and magnesium ions to form an insoluble scum. So, a large amount of soap gets wasted in this process.
(ii) The curdy precipitate called scum, produced by the reaction of hard water on soap, sticks to the clothes making them difficult to be cleaned. Therefore, soaps are not suitable for washing clothes in hard water.


Answer 36:
a) When methane (natural gas) burns in air, carbon dioxide and water vapour are formed along with the release of a large amount of heat. This process is known as combustion.
The chemical equation of the combustion reaction is as follows:
CH4 + 2O2  → CO2 + 2H2O + Heat + Light
(b) When ethanoic acid reacts with sodium carbonate, a brisk effervescence of carbon dioxide gas is observed. The salt formed due to this reaction is sodium ethanoate.
The chemical equation for the above reaction is as follows:
2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
(c) Bromine water test can be used to chemically differentiate between a butter and cooking oil.
Take two test tubes, one with a small amount of butter in it and the other with some cooking oil.
Add bromine water to both the test tubes.
Observation:
(i) Cooking oil decolourises bromine water indicating that it is an unsaturated compound.
(ii) Butter does not decolourise bromine water indicating that it is a saturated compound.


Answer 37:
(a) Substitution reaction is a characteristic of saturated hydrocarbons (alkanes). It is the reaction in which one or more hydrogen atoms of a hydrocarbon are replaced by other atoms.
Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride. In this reaction, the hydrogen atom from methane is replaced by the chlorine atom.
The chemical equation for the above reaction is as follows:
CH4 + Cl2 →  CH3Cl + HCl
(b) An oxidising agent is a reactant which readily transfers oxygen atoms to another substance by reducing itself in the process. Two oxidising agents which can oxidise ethanol to ethanoic acid are alkaline potassium permanganate (KMnO4) and acidified potassium dichromate (K2Cr2O7).
(c) Ethanoic acid is a carboxylic acid which when reacts with ethanol (alcohol) produces sweet smelling ester. The process in which the carboxylic acid reacts with alcohol, in the presence of a catalyst, to form an ester is called esterification.The chemical equation for the above reaction is as follows:
CH3COOH+2H5OH →Conc. H2SO4 CH3COOC2H5+H2O


Answer 38:
(a) Methane is a hydrocarbon which has a single bond. Its formula is CH4.
The characteristic chemical property of methane is the substitution reaction. It is a reaction in which one or more hydrogen atoms are replaced by some other atoms.
Chemical equation:
CH4 + Cl2 →sunlight CH3Cl + HCl
Ethene is a hydrocarbon containing a double bond. Its formula is C2H4.
The characteristic chemical property of ethene is the addition reaction. It is a reaction in which unsaturated compound (ethene) is combined with another substance to form a single product (saturated compound).
Chemical equation:
CH= CH2 + H2  →HeatNi catalyst CH3 – CH3
(b) Detergent, a sodium salt of a long chain benzene sulphonic acid, is a cleansing agent. It has cleansing properties in water. A detergent has two parts, a large non-ionic hydrocarbon group and an ionic group such as sulphonate group SO3Na+. Name of a detergent is sodium n-dodecyl benzene sulphonate.
(c) Detergents have replaced soap as a washing agent because they do not form insoluble calcium and magnesium salts (scum) in hard water. Solubility of detergents, even in hard water, is better than a soap. Detergents also froth well.


Answer 39:
(a) Ethanoic acid reacts with sodium hydrogen carbonate to produce a brisk effervescence of carbon dioxide gas. The salt formed in this reaction is sodium ethanoate.
The chemical equation of the above reaction is:
CH3COOH + NaHCO3 → CH3COONa + CO2+ H2O
(b) Carbon and its compounds are used as fuels for numerous applications, as they release a lot of heat energy when burned in air.
(c) Detergent is better for washing clothes in hard water because it does not form insoluble magnesium or calcium salts (scum) on combining with the calcium or magnesium ions present in the hard water. Soap on the other hand reacts with these calcium and magnesium ions present in the hard water to form insoluble calcium and magnesium salts of fatty acids. Therefore, soaps don’t lather easily in hard water, while detergents do.


Answer 40:
(a) Substitution reaction is a reaction in which hydrogen atoms of a hydrocarbon are replaced by other atoms. It is a characteristic of saturated hydrocarbons (alkanes).
For example:
Methane (alkane) reacts with chlorine, in the presence of sunlight, to form chloromethane and hydrochloric acid.
The chemical equation of this reaction is as follows:
CH4 + Cl2 → CH3Cl + HCl
(b) Soap is prepared by heating animal fat or vegetable oil (esters) with concentrated sodium hydroxide solution. Esters react with sodium hydroxide to give soap and glycerol. Saponification is the process of preparing soap by the hydrolysis of fats with alkalis.
Equation involved in soap making :
Fat or oil (Ester) + Sodium Hydroxide → Soap (Sodium salt of fatty acid) + Glycerol (alcohol)


Answer 41:
(a) When ethanol (ethyl alcohol) is heated in the presence of alkaline potassium permanganate solution or acidified potassium dichromate solution, it gets oxidised to ethanoic acid. This reaction is known as oxidation reaction.
The chemical equation for the above reaction is:
CH3CH2OH+2[O]→or acidified K2Cr2O7alkaline 
KMnO4,Heat CH3COOH+H2O
(b) Ethanoic acid releases carbon dioxide gas on reacting with sodium bicarbonate. It is represented by the following equation:
CH3COOH+NaHCO3→CH3COONa+CO2+H2O
On the other hand, ethanol does not give out a brisk effervescence (carbon dioxide) with sodium bicarbonate.
(c) Scum is formed when a soap is used in hard water. This happens because a large amount of soap is utilised in reacting with the magnesium and calcium ions of hard water. An insoluble curdy precipitate, scum, sticks to the clothes making them difficult to be cleaned.


Answer 42:
(a) When methane reacts with chlorine, substitution reaction takes place. Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride. In this reaction, chlorine substitutes hydrogen; therefore, this reaction is also known as chlorination.
The chemical equation for this reaction is: CH4 + Cl2 →CH3Cl + HCl
(b) Hydrogenation is the process of adding hydrogen to an unsaturated hydrocarbon for obtaining a saturated hydrocarbon in the presence of a catalyst.
Chemical reaction:  CR2 = CR+ H2 →Heat Ni catalyst HCR2 – HCR2
Industrial application: The hydrogenation process is used to make ghee (saturated fat) from vegetable oils (unsaturated fat).
(c)

Sl.No Soaps Detergents
1. Soaps are salts of sodium or potassium of the long chain carboxylic acids. The ionic group present in a soap is COONa+.​ Detergents are salts of sodium of long chain benzene, sulphonic acids or long chain alkyl hydrogensulphates. The ionic group present in a detergent is SO3– Na+.​
2. Soaps have weak cleansing action compared to detergents. The cleansing action of detergents is stronger to that of soaps.

Answer 43:
(a) When ethanoic acid reacts with sodium hydroxide, a salt called sodium ethanoate along with water is formed.
The chemical equation of the reaction is as follows:
CH3COOH + NaOH →CH3COONa + H2O
(b) When an unsaturated compound like vegetable oil is hydrogenated at room temperature, saturated product like ghee is formed (semi solid). The catalyst used in this process of hydrogenation is nickel.
(c) Advantages of detergents over soaps:
(i) Detergents can be used with hard water, while soaps cannot be used with hard water.
(ii) The cleansing action of detergents is stronger than soaps.
(iii) Detergents have a greater solubility in water as compared to soaps.
Disadvantage of detergents:
(i) Some detergents are not bio-degradable; therefore, they pollute water bodies like lakes and rivers. Soaps, on the other hand, are bio-degradable and don’t cause water pollution.


Answer 44:
(a) The organic compound ‘X’ with molecular formula C2H4O2 is ethanoic acid. Formula of X (ethanoic acid) is CH3COOH.
(b) Ethyne (acetylene) is an unsaturated hydrocarbon. When ethyne is burned in air, it produces an extremely sooty flame due to incomplete combustion. The temperature of the flame is not high enough to melt metals for welding; therefore, a mixture of ethyne and air is used for welding.

(c) Addition reaction is a characteristic of unsaturated hydrocarbons like alkenes and alkynes. An unsaturated hydrocarbon combines with another substance to produce a single product (saturated hydrocarbon), in the presence of a catalyst.


Answer 45:
(a) When an unsaturated hydrocarbon combines with another substance to form a single product, the reaction is termed as an addition reaction. Addition reactions are undergone by all alkenes and alkynes containing either a double bond or a triple bond.
Example: When ethene (C2H4) reacts with hydrogen in the presence of a nickel catalyst, ethane is formed. Addition of hydrogen converts the unsaturated hydrocarbon having a double bond to a saturated hydrocarbon comprising a single bond.
Let us look at the chemical equation of the addition reaction:
CH2=CH2 + H2 → CH3-CH3
(b) Hydrogen is added to groundnut oil when the latter is to be converted to vanaspati ghee. The process of adding hydrogen to an unsaturated hydrocarbon, to produce a saturated hydrocarbon in the presence of a catalyst, is called hydrogenation.
(c) Vegetable oil is good for our health as it contains unsaturated fatty acids (liquid form). Butter is not good for our health as it comprises saturated fatty acids (solid fat).


Exercise : Solution of Questions on page Number : 265


Answer 46:
(a) When ethanoic acid reacts with sodium hydrogen carbonate, a brisk effervescence of carbon dioxide gas (Y) is evolved. The salt (X) formed as a result of this reaction is sodium ethanoate.
Let’s react ethanoic acid with sodium hydrogen carbonate.
(i) Take a boiling tube and add 0.5gm of sodium hydrogen carbonate to it. To this, add 2 ml of dilute ethanoic acid through a thistle funnel.
(ii) You will notice a brisk effervescence of carbon dioxide gas.
(iii) Take a test tube containing lime water and pass the carbon dioxide gas through it.
(iv) You will observe the lime water turning milky. Carbon dioxide is the only gas which turns lime water milky.
This activity proves that carbon dioxide gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate.
The diagram of the entire experiment is shown below:

The chemical equation of the above reaction is as follows:
CH3COOH+NaHCO3→CH3COONa+CO2+H2O
(b) Uses of ethanoic acid:
(i) Ethanoic acid is used in the preparation of plastics, dyes and pharmaceuticals.
(ii) Dilute ethanoic acid (vinegar) is used as a food preservative, and as an appetiser in dressing food dishes.


Answer 47:
(a) Esters are sweet-smelling substances which are used to make perfumes. The process in which a carboxylic acid reacts with an alcohol to form an ester is called esterification.
An ester is formed when ethanol (alcohol) reacts with ethanoic acid, on heating, in the presence of a few drops of concentrated sulphuric acid. The name of the ester formed is ethyl ethanoate.
Let’s prepare an ester.
(i) In a test tube, take 1 ml of ethanoic acid and add some ethanol to it along with a few drops of concentrated sulphuric acid.
(ii) Warm the test tube in a beaker, containing hot water, for 5 minutes.
(iii) Take about 50 ml of water in another beaker and pour the contents of the test tube into it. When you smell it, a sweet fragrance is obtained indicating the formation of an ester.
The diagrammatic representation of the above process is as follows:

The chemical equation involved in the formation of ester is as follows:
CH3COOH + C2H5OH →Conc. H2SO4 CH3COOC2H5 + H2O
(b) Uses of esters:
(i) Esters are used in making artificial perfumes because of their sweet fragrance.
(ii) Esters are used as flavouring agents in ice-creams, sweets and cold drinks.


Answer 48:
(a) Catalytic hydrogenation is the reaction usually used to convert vegetable oils to fats. Hydrogenation is a process in which hydrogen molecules are added to an unsaturated hydrocarbon in the presence of a catalyst to obtain a saturated hydrocarbon. In this process, the double bonds are removed from the unsaturated compounds (oils).
For example: When hydrogen is added to vegetable oils (unsaturated), a saturated product called ghee (semi-solid) is obtained.
The chemical equation of this hydrogenation reaction in the presence of catalyst nickel is shown below:
R2C=CR2 + H2 →R2HC-CHR2
(b) Saponification is a process of preparing soap by the hydrolysis of fats or oils with alkalis.
When animal fat or vegetable oil (ester) is heated with concentrated sodium hydroxide solution, soap and glycerol (alcohol) are formed.
Equation: Fat or oil (Ester) + Sodium Hydroxide → Soap + Glycerol (an alcohol)
The chemical equation is as follows:

(c) Micelles are formed when soap is added to water. This is because the hydrocarbon chains of a soap molecule are hydrophobic and insoluble in water, but the ionic ends are hydrophilic and soluble in water. Micelles are an aggregate of soap molecules that arrange themselves in a spherical shape in the soap solution.
Micelles will not form in a solvent like ethanol, as the hydrocarbon chain of soap molecules is hydrophobic; hence, not be soluble in organic solvent like ethanol.


Answer 49:
(a) Soap is a mixture of sodium or potassium salts of various natural fatty acids and oils, which when used with water show cleansing properties. A soap contains a large, non-ionic hydrocarbon group and an ionic group COO-Na+.
An example for a soap is sodium stearate (C17H35COO-Na+). It is a salt of sodium of fatty acid called stearic acid with a non-ionic hydrocarbon group C17H35, and an ionic carboxylate group COO- Na+.
(b) A molecule of soap has a tadpole like structure and is made up of two parts, a long hydrocarbon part and a short ionic part. The hydrocarbon part of the soap molecule is soluble in grease and oil but remains insoluble in water (hydrophobic), whereas the short ionic group is soluble in water (hydrophilic) because of the polar nature of the water molecules.
The structure of a soap molecule is as follows:

(c) Cleansing action of soap: Soap forms a colloidal suspension when dissolved in water. The soap molecules group together to form spherical micelles. When a soiled cloth is immersed in soap water, the hydrocarbon ends of the soap molecules in the micelles entrap the oil and grease on cloth’s surface. The ionic ends of the soap molecules in the micelles (having negative charges) are attached to the water. As the soiled cloth gets agitated in the soap solution, the oil and grease entrapped by the soap micelles get dispersed into the water and the soap water becomes dirty while the cloth gets rid of the dirt and becomes clean. Cleansing of the cloth is then done by thoroughly rinsing it in clean water.
The following diagram illustrates the cleansing action of soap:


Answer 50:
(b) the fuel is not burning completely
While cooking, if the bottom of the utensil is getting blackened on its outer side, it means that the fuel is not burning properly, thereby leading to soot formation.


Answer 51:
(b) oxidising agent
Alkaline potassium permanganate solution is an aqueous solution of potassium permanganate. It acts as an oxidising agent by providing oxygen, and converts ethanol to ethanoic acid.


Answer 52:
(c) dehydrating agent
Sulphuric acid acts as a dehydrating agent as it removes water molecules from the alcohol (ethanol), and converts it to ethene.


Answer 53:
(d) addition reaction
When a vegetable oil is treated with hydrogen in the presence of nickel or palladium catalyst, an addition reaction takes place and a saturated fat is formed.


Answer 54:
(a) hydrophilic head and a hydrophobic tail
The soap molecule has a hydrophilic head and a hydrophobic tail.


Answer 55:
(b) presence of sunlight
When chlorine reacts with saturated hydrocarbons at room temperature and in the presence of sunlight, substitution reaction takes place.


Answer 56:
(b) hydrocarbon ends directed towards the centre and ionic ends directed outwards
In a soap micelle, the soap molecules are arranged radially with the hydrocarbon ends, i.e. hydrophobic, directed towards the centre; and, ionic ends, i.e. hydrophilic, directed outwards.


Answer 57:
(d) sodium ethoxide and hydrogen
When ethanol reacts with sodium, sodium ethoxide is formed and hydrogen gas is evolved.


Answer 58:
(b) 5 to 8 percent ethanoic acid in water
Vinegar is a solution comprising 5 to 8 percent ethanoic acid mixed with water.


Exercise : Solution of Questions on page Number : 266


Answer 59:
(c) chloroform
Chloroform is not an ingredient for manufacturing denatured alcohol. For denaturation of alcohol, methyl alcohol, copper sulphate and pyridine are used.


Answer 60:
(c) C​6H14
C6H14 is an alkane as its formula can be expressed as CnH2n+2. Alkanes are stable and cannot decolourize reddish-brown bromine water in the absence of a catalyst.


Answer 61:
(c) vinegar
Vinegar can produce brisk effervescence with the baking soda solution.


Answer 62:
(b) baking soda
Baking soda is not required for the preparation of soap in the laboratory. For the preparation of soap, vegetable oil, caustic soda and common salt are needed.


Answer 63:
(d) CH3OH
CH3OH (methanol), when consumed, oxidises into methanal into the liver. This causes coagulation of protoplasm in the cells, as methanal reacts rapidly with the components of the cells. Due to this, the cells stop functioning and damage the optic nerve leading to blindness.


Answer 64:
(c) cirrhosis
Cirrhosis is the liver disease caused by the excessive consumption of alcohol over a prolonged period.


Answer 65:
(b) C6H12O2
Ethylbutanoate ester has the molecular formula C6H12O2 (C2H5COOC3H7).


Answer 66:
The neutral organic compound ‘X’ having the molecular formula C2H5OH is ethanol (alcohol with functional group -OH).
When ethanol undergoes oxidation reaction (controlled combustion) with acidified potassium dichromate, it gets oxidised to form an acidic compound, Y, called ethanoic acid (CH3COOH).
Ethanol reacts with ethanoic acid in the presence of concentrated sulphuric acid to release a sweet smelling ester, Z, called ethyl ethanoate (CH3-COO-CH2-CH3).
The chemical equations involving the compounds are as follows:
CH3CH2OH + 2[O] → CH3COOH + H2O.
CH3COOH + CH3CH2OH→ CH3COOC2H5 + H2O


Answer 67:
C2H5OH (ethanol) and CH3COOH (ethanoic acid) are the compounds which can react with each other, in the presence of concentrated sulphuric acid, to form a sweet smelling ester called ethylethanoate. Its formula is CH3 -COO-CH2-CH3.
The chemical equation for the above reaction is as follows:
C2H5OH+CH3COOH→Conc.H2SO4CH3COOC2H5+ H2.


Answer 68:
The functional group present in this organic compound is the alcohol (hydroxyl) group (-OH). When a neutral organic compound of alcohol group such as ethanol (C2H5OH) is warmed with some ethanoic acid, in the presence of a small quantity of concentrated sulphuric acid, a sweet smelling ester is produced.


Answer 69:
The structural formula of the ester corresponds to the compound ethylethanoate (CH3COOC2H5). Esters are sweet smelling substances which are formed when an alcohol reacts with carboxylic acid in the presence of concentrated sulphuric acid.
(a) The formula of the ethanoic acid is CH3COOH.
(b) The formula of the alcohol (ethanol) is CH3-CH2-OH.
The chemical equation showing the reactants and the products is as follows:
CH3COOH+CH3CH2OH →Conc. H2SO4 CH3COOCH2CH3+H2O.


Answer 70:
(a) The compound C4H9COOC2H5 is a sweet-smelling ester.
(b) C2H5OH is the formula of ethanol which when treated with concentrated sulphuric acid at 170 C to form an alkene called ethene. It has the molecular formula C2H4.
(c) CH4 (methane) is the compound which on repeated chlorination forms chloroform.
(d) CH3OH (methanol or methyl alcohol) is added to alcohol to denature it.
(e) CH3COOH (ethanoic acid) is a constituent of vinegar.
(f) C2H5OH (ethanol) is the compound which is used to sterilise wounds and syringes.


Answer 71:
(a) The organic acid, X, which often freezes in the winters in cold countries, is ethanoic acid. It has the molecular formula CH3COOH.
The formula with its functional group is represented as:

When ethanoic acid is warmed with methanol in the presence of a few drops of concentrated sulphuric acid, the compound ‘Y’ with sweet fragrance is formed. This compound is called methyl ethanoate, and its molecular formula is CH3COOCH3.
The formula with its functional group is represented as:

(b) The chemical equation of the above stated reaction is as follows:
CH3COOH + C2H5OH →conc H2SO4 CH3COOC2H5 + H2O


Answer 72:
(a) The organic compound, A, is propanol (CH3-CH2-CH2OH) which is a liquid (alcohol) at room temperature. Propanol reacts with sodium to evolve hydrogen with a pop sound.
(b) When propanol is heated with concentrated sulphuric acid at 170oC, a compound ‘B’ called propene is formed. Propene is an unsaturated hydrocarbon; therefore, it decolourizes bromine water.
(c) Propanol is converted to propene through dehydration. Dehydration is a chemical reaction which involves the loss of water molecule from the reacting molecules. When an alcohol (propanol) is converted to alkene (propene), loss of water molecule or dehydration reaction takes place.
The chemical equation for conversion of propanol to propene is as follows:
CH3-CH2-CH2-OH → CH3-CH=CH2 + H2O
(d) The compound, C, is propane (CH3-CH2 -CH3). When alkenes (unsaturated hydrocarbons) add one molecule of hydrogen, in the presence of nickel as a catalyst, alkanes are formed (saturated hydrocarbons). Therefore, propene (alkene) adds one hydrogen to form propane.
(e) As the conversion of propane to propene involves addition of hydrogen, the reaction is known as hydrogenation or addition reaction.
The conversion of propene to propane by the addition of hydrogen is as follows:
CH3-CH=CH2 + H2 → CH3-CH2-CH3.


Answer 73:
The organic compound, A, with the molecular formula C2H4O2 is ethanoic acid (CH3COOH), as it evolves hydrogen with a pop sound on reacting with sodium.
When ethanoic acid reacts with sodium, a compound B called the sodium ethanoate (CH3COONa) is formed.
The alcohol, C, is methanol (CH3OH) which is treated with ethanoic acid in the presence of concentrated sulphuric acid to form a compound D.
The sweet-smelling compound D is methyl ethanoate (CH3COOCH3).
The chemical equation for the above stated reaction is as follows:
CH3OH + CH3COOH → CH3COOCH3 + H2O
When ethanoic acid reacts with alcohol in the presence of concentrated sulphuric acid, a sweet-smelling cmpound, ester is formed. Methyl ethanoate is a carboxylate ester, which on reaction with sodium hydroxide gives back methanol and Sodium ethanoate.
The chemical equation is as follows:
CH3COOCH3 + NaOH → CH3COONa + CH3OH


Answer 74:
C6H12 (Hexene) and C6H10 (Hexyne or Cyclohexene ) are the hydrocarbons which can decolourize bromine water, as they are unsaturated. Bromine undergo addition reactions with unsaturated compounds like alkenes and alkynes containing a double or a triple bond. When bromine water is added to an unsaturated compound, the former gets added to the latter, thereby turning colourless from its reddish brown colour.
C6H14 (Hexane) is a hydrocarbon which cannot decolourize bromine water because it is a saturated compound (alkane). Saturated compounds don’t undergo addition reactions; therefore, they don’t decolourize bromine water.


Answer 75:
(a) The compound X is butanol, and its formula is C4H9OH.
(b) The compound Y is butanoic acid, and its formula is C3H7COOH.
(c) The compound Z is butyl butanoate, and its formula is C3H7COOC4H9.
(d) The type of smell produced by the compound is a sweet, fruity fragrance.
(e) Ester is the general name given to the compound formed by the reaction of X and Y.
(f) Esterification is the general name of the reaction which takes place between butanol and butanoic acid to produce butyl butanoate.


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