Chapter 4 Carbon and its Compounds Class 10 Notes

Carbon and its Compounds

Bonding in Carbon: The Covalent bond, Electron dot structure, Physical properties of organic compounds, Allotropes of Carbon.
Covalent Bond: The atomic number of carbon is 6. Its electronic configuration is 2, 4. It requires, 4 electrons to achieve the inert gas electronic configuration. But carbon cannot form an ionic bond
It could gain four electrons forming C4- cation. But it would be difficult for the nucleus with six protons to hold on to ten electrons.
It could lose four electrons forming C4+ cations. But it requires a large amount of energy to remove four electrons.

Thus, carbon overcomes this problem by sharing of its valence electrons with other carbon atoms or with atoms of other elements.
The bond formed by mutual sharing of electron pairs between two atoms in a molecule is known as Covalent Bond.
Types of Covalent Bond:
• Single Covalent Bond: When a single pair of electrons are shared between two atoms in a molecule. For example; F2, Cl2, H2 etc.
• Double Covalent Bond: When two pairs of electrons are shared between two atoms in a molecule. For example; O2, CO2 etc.
• Triple Covalent Bond: When three pairs of electrons are shared between two atoms in a molecule. For example; N2 etc.
Electron Dot Structure: The electron dot structures provides a picture of bonding in molecules in terms of the shared pairs of electrons and octet rule.
Formation of Hydrogen Molecule
Atomic number of Hydrogen = 1
Number of valence electrons = 1
Formation of CH4 Molecule
Atomic number of Carbon = 6 [2, 4]
Number of valence electrons = 4
Atomic number of Hydrogen = 1
Number of valence electrons = 1

Formation of CO2 Molecule
Atomic number of Carbon = 6 [2, 4]
Number of valence electrons = 4
Atomic number of Oxygen = 8 [2, 6]
Number of valence electrons = 6
Formation of H2S Molecule
Atomic number of Sulphur = 16 [2, 8, 6]
Number of valence electrons = 6
Physical Properties of Organic Compounds
Most of the organic compounds have low boiling and melting point, due to the weak force of attraction (i.e., the inter-molecular force of attraction) between these molecules.
Most carbon compounds are poor conductors of electricity, due to the absence of free electrons and free ions.
 Compounds M.P. (K) B.P. (K) Acetic acid (CH3COOH) 290 391 Chloroform (CHCl3) 209 334 Ethanol (CH3CH2OH) 156 351 Methane (CH4) 90 111
Allotropes of Carbon
Allotropy: The phenomenon in which the element exists in two or more different physical states with similar chemical properties are called Allotropy.
Carbon has Three Main Allotropes
• Diamond: In this, carbon, an atom is bonded to four other atoms of carbon forming three-dimensional structures. It is the hardest substance and an insulator. It is used for drilling rocks and cutting. It is also used for making jewellery.
• Graphite: In this, each carbon atom is bonded to three other carbon atoms. It is a good conductor of electricity and used as a lubricant.
• Buckminster Fullerene: It is an allotrope of the carbon-containing cluster of 60 carbon atoms joined together to form spherical molecules. It is dark solid at room temperature.
Versatile nature of Carbon, Hydrocarbons, Isomerism, Homologous series, Functional groups, Nomenclature of functional groups.
Versatile Nature of Carbon: The existence of such a large number of organic compounds is due to the following nature of carbon,
• Catenation
• Tetravalent nature.
(i) Catenation: The self linking property of an element mainly carbon atom through covalent bonds to form long straight, branched and rings of different sizes are called Catenation.
This property is due to
• The small size of the carbon atom.
• The great strength of the carbon-carbon bond.
Carbon can also form stable multiple bonds (double or triple) with itself and with the atoms of other elements.
Straight Chain

Branched Chain

Rings
(ii) Tetravalent Nature: Carbon has valency of four. It is capable of bonding with four other atoms of carbon or some other heteroatoms with single covalent bond as well as double or triple bond.
Hydrocarbons: Compounds of carbon and hydrogen are known as hydrocarbons.
For example; Methane (CH4), Ethane (C2H6), Ethene (C2H4), Ethyne (C2H2) etc.
Saturated Hydrocarbon (Alkanes): General formula is CnH2n+2.
n = number of carbon atoms.
In this, the carbon atoms are connected by only a single bond.
For example; Methane (CH4), Ethane (C2H6) etc.
Unsaturated Hydrocarbons
Alkenes: General formula is CnH2n, where n = number of carbon atoms.
In this, the two carbon atoms are connected by double bond.
Alkynes: General formula is CnH2n-2, where n = number of carbon atoms. In this, the two carbon atoms are connected by triple bond.
Electron Dot Structure of Hydrocarbons
Isomerism: Compounds having the same molecular formula but different structural formula and properties are known as Isomers and this phenomenon is known as Isomerism.
Structural Isomerism: Compounds having the same molecular formula but different structures are called Structural isomers. Example: Isomers of butane (C4H10)

Homologous Series: Series of organic compounds having the same functional group and chemical properties and successive members differ by a CH2 unit or 14 mass units are known as Homologous series.
Homologous series of Alkanes, Alkenes and Alkynes
Characteristic of Homologous Series
• The successive members in homologous series differ by CH2 unit or 14 mass unit.
• Members of given homologous series have the same functional group.
• All the members of homologous series shows similar chemical properties.
Functional Group: An atom or group of atoms present in a molecule which largely determines its chemical properties are called Functional Group.

Nomenclature of Organic Compounds: It is difficult to remember millions of compounds by their individual common name. Thus, to systematize the nomenclature of organic compounds IUPAC (International Union of Pure and Applied Chemistry) has given certain rule which is as follows:
1. Identify the Number of Carbon Atoms in the Compound
 S. No Number of Carbon Atoms Word Root (-) (Suffix) Single bond 1. One carbon atoms (1-C) Meth + ane 2. Two carbon atoms (2-C) Eth + ane 3. Three carbon atoms (3-C) Prop + ane 4. Four carbon atoms (4-C) But + ane 5. Five carbon atoms (5-C) Pent + ane 6. Six carbon atoms (6-C) Hex + ane
2. Identify the functional group
 S. No. Functional Group Prefix Suffix 1. Double bond (=) — ene 2. Triple bond (≡) — yne 3. Chlorine (—Cl) Chloro — 4. Bromine (—Br) Bromo — 5. Alcohol (-OH) — ol 6. Aldehyde (-CHO) — al 7. Ketone (-CO-) — one 8. Carboxylic acid (-COOH) — oic acid
3. Name the Compounds By Following Order
Prefix + Word Root + Suffix

Chemical Properties of Carbon Compounds: The important chemical properties are as follows:
1. Combustion: The complete combustion of carbon compounds in the air gives carbon dioxide water, heat and light.
CH3CH2OH(l) + O2(g) → CO2(g) + H2O(l) + Heat and light
Carbon burns in air or oxygen to give carbon dioxide and heat and light.
C(s) + O2(g) → CO2(g) + Heat and light
Saturated hydrocarbons burn with a blue flame in the presence of a sufficient supply of air or oxygen.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + Heat and light
In presence of limited supply of air, saturated hydrocarbon forms a sooty flame.
Unsaturated hydrocarbons burn with a yellow smoky flame.
The gas and kerosene stove used at home has inlet for air so that, burnt to given clean blue flame.
Due to presence of small amount of nitrogen and sulphur, coal and petroleum produces carbon dioxide with oxides of nitrogen and sulphur which are major pollutant.
2. Oxidation: Oxidation of ethanol in presence of oxidizing agents gives ethanoic acid.
Oxidizing Agent: Some substances are capable of adding oxygen to others, are known as Oxidising Agent.
Example: Alkaline KMnO4 (or KMnO4—KOH)
Acidified K2Cr2O7 (or K2Cr2O7—H2SO4)
KMnO4 – Potassium permanganate
K2Cr2O7 – Potassium dichromate
3. Addition Reaction: Addition of dihydrogen with unsaturated hydrocarbon in the presence of catalysts such as nickel or platinum or palladium are known as Hydrogenation (addition) reaction.
Catalyst: Substances that cause a reaction to occur or proceeds to different rate without consuming in it are called a catalyst. For example; Ni, Pt, Pd, etc.
Process of converting vegetable oil into solid fat (vegetable ghee) is called Hydrogenation of Oil.
Vegetable oil + H2 $\xrightarrow [ Ni\quad Catalyst ]{ \triangle }$  Vegetable ghee
Vegetable fats are saturated fats which are harmful for health.
Vegetable oil containing unsaturated fatty acids are good for health.
4. Substitution Reaction: Replacement of one or more hydrogen atom of an organic molecule by another atom or group of the atom is known as Substitution Reaction.
Some Important Carbon Compounds :
Ethanol (CH3CH2—OH): Commonly known as Ethyl Alcohol.
Physical Properties
• It is colourless, inflammable liquid.
• It is miscible with water in all proportions.
• It has no effect on the litmus paper.
Chemical Properties
• Reaction with sodium
• Reaction with concentrated H2SO4 (Dehydration Reaction)
Dehydrating agent: Substances which removes water from ethanol (alcohols) is known as Dehydrating agent. For example; Cone. H2SO4.
Uses: As solvent, as antiseptic (tincture iodine), as anti-freeze in automobiles.
Ethanoic Acid (CH3COOH): Commonly known as Acetic acid. 5-8% of ethanoic acid in water is called Vinegar. The melting point of pure ethanoic acid is 290 K and hence, it often freezes in cold climate so named as glacial acetic acid.
Physical Properties
• It is a colourless, pungent-smelling liquid.
• Miscible with water in all proportions.
• Turns blue litmus to red.
Chemical Properties
(i) Esterification Reaction: Reaction of ethanoic acid with an alcohol in the presence of a few drops of conc. H2SO4 as catalyst gives a sweet-smelling substance known as Esters, called Esterification reaction.

Esters are used in making perfumes and flavouring agents.
Saponification Reaction: Reaction of esters with sodium hydroxide, gives alcohol and sodium salt of carboxylic acid (soap). This reaction is known as Saponification Reaction.
(ii) Reaction with Carbonates and Hydrogen Carbonates: Ethanoic acid reacts with sodium carbonates and sodium hydrogen carbonates to give rise to a salt, carbon dioxide and water.
• Used as vinegar.
• Used as raw material for the preparation of acetyl chloride and esters.
Soap: Sodium or potassium salts of long chain fatty acids is called Soap.
General formula: RCOONa+
Detergent: Ammonium and sulphonate salts of long chain fatty acids are called Detergent.
Example: CH3—(CH2)11—C6H4—SO3Na.
Hard and Soft Water: Water that does not produce lather with soap readily is called Hard water and which produces lather with soap is called Soft Water.
Hardness of water is due to the presence of bicarbonates, chlorides and sulphate salt of calcium and magnesium.
Difference between soaps and detergents
 Soaps Detergents (i) These are sodium or potassium salts of long chain fatty acids. (i) These are ammonium and sulphonate salts of long chain fatty acids. (ii) Ionic part of the soap is —COO–Na+ (ii) Ionic part of detergent is —OSO3-Na+. (iii) Their efficiency decreases in hard water (iii) Their efficiency is unaffected in hard water. (iv) Soaps are biodegradable. (iv) Detergents are non-biodegradable.
Advantage of Detergents: The main advantage of detergent over soaps is that soaps cannot be used in hard water for washing because hard water reacts with soap to form curdy white precipitate called Scum.

Thus, in hard water, soap does not give lather while detergent does.
Cleansing Action of Soaps and Detergents: Both soaps and detergents cantains two parts. A long hydrocarbon part which is hydrophobic (water repelling) in nature and a short ionic part which is hydrophillic (water attracting) in nature.
The hydrocarbon part of the soap molecule links itself to the oily (dirt) drop and ionic end orients itself towards water and forms a spherical structure called micelles. The soap micelles helps in dissolving the dirt in water and wash our clothes.

Covalent Bond: A chemical bond formed between two atoms by sharing of valence electrons between two atoms so that each atom acquires the stable electronic configuration of the nearest noble gas.
Covalency: The number of electrons contributed by each atom for sharing.
Carbon always forms a covalent bond: Atomic no of carbon is 6. So, its configuration is K-2, L-4. Therefore, it should either lose or gain 4 electrons to achieve the noble gas configuration and become stable.
However, it is difficult for carbon to gain or lose four electrons because of the following reasons:
• It cannot gain 4 electrons to form C4- ion having Neon gas (2, 8) configuration because this anion would be highly unstable due to a large amount of energy required to overcome the forces of repulsion between the four electrons being added and the six electrons already present in the carbon atom.
• It cannot lose 4 electrons to form C4+ ion having Helium gas (2) configuration because this cation would be highly unstable due to a large amount of energy required to remove four electrons from the carbon atom.
Tetravalency of Carbon: A carbon atom has four electrons in the valence shell. Therefore, carbon forms four covalent bonds, i.e., carbon is tetravalent.
Allotropic forms of Carbon: The phenomenon of existence of an element in two or more forms which have different physical properties but identical chemical properties is called allotropy.
Three allotropic forms of carbon:
• Diamond
• Graphite
• Fullerenes
Hydrocarbon: Organic compounds of carbon and hydrogen are called hydrocarbons.
Saturated Compound: Compounds of carbon which have only single bonds between the carbon atoms are called saturated compounds e.g., Ethane, Propane, Butane etc.
Unsaturated Compound: Compounds of carbon which contain one or more double or triple bonds between carbon atoms are called unsaturated compounds
e.g., Ethene, Propene, Butyne, etc.
Alkanes
• General formula – CnH2n+2
• Saturated hydrocarbons
• Methane – CH4
• Ethane – C2H6
Alkenes
• General formula – CnH2n
• Unsaturated hydrocarbon.
• Ethene – C2H4
• Propene – C3H6
Homologous series: A family of organic compounds having the same functional group, similar chemical properties and the successive (adjacent) members differ by a CH2 unit or 14 mass unit.
Characteristics of a homologous series:
All the members of a homologous series can be represented by a general formula.
• Alkane – CnH2n+2
• Alkyne – CnH2n-2
• Alcohol – CnH2n+1OH
• Ketone – CnH2n+1COCnH2n+1
• Alkene – CnH2n
• Haloalkane – CnH2n+1X
• Aldehyde – CnH2n+1CHO
• Carboxylic acid – CnH2n+1COOH
The molecular formula of two successive (adjacent) members of a homologous series differs by a CH2 unit.
The molecular masses of any two successive members of a homologous series differ by 14 u.
All the members of a given homologous series have the same functional group.
All the members of a series show similar chemical properties.
The members of a homologous series show a gradation in physical properties.
Nomenclature of carbon compound: International Union of Pure and Applied Chemistry (IUPAC) decided some rules to name the carbon compounds. This was done to maintain uniformity throughout the world. Names which are given on this basis are popularly known as IUPAC name. The rules for nomenclature are as follows:
(i) Identify the number of carbon atoms in the carbon compound. Name the carbon compounds according to the number of carbon atoms.
Example, Saturated hydrocarbon having one carbon atom is named as Methane. Saturated hydrocarbon having two carbon atoms is named as Ethane.
• An unsaturated hydrocarbon with a double bond having two carbon atoms is named as Ethene.
• An unsaturated hydrocarbon with a triple bond between carbon atoms is named as Ethyne.
(ii) If the structure has a branched chain, identify the longest chain and then identify the number of carbon atoms.
(iii) In the case of a functional group present, write the prefix or suffix of the functional group as given below. Then write the name of the parent compound:
Chemical properties of Ethanol
• Ethanol (C2H5OH) compound is a colourless liquid at room temperature. It is the second member of the homologous series of alcohols. Its common name is ethyl alcohol. Its functional group is – OH.
• It has a very low melting point (156 K) and low boiling point (351 K or 78°C).
• Ethanol is highly soluble in water.
• Ethanol is one of the main components of alcoholic drinks.
• It is a good organic solvent.
• It is a neutral substance, so it does not have any effect on either blue litmus solution or red litmus solution.
• It bums with a blue flame in the presence of O2 of air. This combustion is an oxidation process.
• In the presence of alkaline KMnO4, it is oxidised to ethanoic acid.
• Ethanol alcohol reacts with sodium(Na) metal vigorously to form sodium ethoxide and evolves H2 gas.
2C2H5OH + 2Na → 2C2H5ONa (Sodium ethoxide) + H2 (g)
• Ethanol on dehydration in the presence of cone. H2SO4 acid at 443 K forms ethene gas. H2SOacid absorbs water molecules from the alcohol molecules and acts as a strong dehydrating agent.
Chemical properties of Ethanoic acid
• Ethanoic acid commonly called acetic acid (CH3COOH) is a colourless liquid. The functional group present in it is carboxylic acid – COOH.
• It’s melting point is 290 K and the boiling point is 391 K.
• Being an acid, it turns blue litmus red.
• It is sour in taste.
• Ethanoic acid reacts with alcohols in the presence of cone. H2SO4 acid to form sweet smelling compounds called esters.
• Ethanoic acid reacts with bases to form its salt and water.
• It reacts with carbonate and hydrogen-carbonate compounds of metals to form its salt (sodium ethanoate commonly called sodium acetate) and release CO2 gas.
Cleansing action of soap: The dirt is generally held to the surface of a dirty cloth by a thin film of oil or grease.
When a dirty cloth is treated with soap or detergent solution, the non- polar tail of the soap or the detergent dissolve in oil or grease while the polar heads are held by the surrounding water. Soap or detergent micelle is formed with the oily or greasy dirt lying at their Centre (Soap or detergent is attracted both by the greasy dirt and water.

When the surface of the cloth is mechanically scrubbed or beaten on a stone or with a wooden paddle or agitated in a washing machine, the loosened oily particle is removed from the dirty surface and the cloth is cleaned. Detergents lower the surface tension of water to a greater extent than soap, therefore the cleansing action of detergent is much higher than those of soaps.
1. The earth’s crust has only 0.02% carbon in the form of minerals (like carbonates^bicarbonates, coal, and petroleum).
2. The atmosphere has 0.03% of carbon dioxide.
3. In spite of its small amount available in nature, carbon is a versatile element as it forms the basis for all living organisms and many things which we use.
4. Bonding in carbon :
• The atomic number of carbon = 6
• An electronic configuration has 2 electrons in K shell and 4 electrons in L shell.
• In order to attain the noble gas configuration, carbon should either gain 4 electrons or lose 4 electrons or can share it’s 4 electrons with some other element.
• The gain of 4 electrons (to form an octet, i.e., 8 electrons in C4- anion) is difficult because then a nucleus with 6 protons will have to hold extra four electrons.
• Loss of 4 electrons (to attain duplet, i.e., 2 electrons like He atom in C4+ cation) is difficult as it requires a large amount of energy to remove four electrons.
• Carbon, hence, overcomes this difficulty by sharing it’s four valence electrons with other atoms of carbon or with atoms of other elements. These electrons contributed by the atoms for mutual sharing in order to acquire the stable noble gas configuration is called covalency of that atom. Hence, carbon shows TETRACOVALENCY.
• The simplest molecule formed by sharing of electrons (i.e., covalent bonds), can be represented by electron dot structure.
5. Allotropes of carbon: The phenomenon by means of which an element can exist in two or more forms, with similar chemical properties but different physical properties are called allotropy and the different forms are called allotropes. Carbon shows three allotropic forms :

Note:
• Diamond is the hardest substance whereas graphite is very soft.
• Diamond is used for grinding and polishing of ‘ hard materials and graphite is used as a lubricant.
• Diamond has a three-dimensional rigid structure but graphite has a hexagonal sheet layer structure.
• Diamond is a bad conductor of electricity but graphite is a very good conductor of electricity.
6. Fullerenes: A new category of carbon allotrope, fullerenes are spherical in shape or a soccer ball like. The first fullerene identified was C-60 with 60 carbon atoms arranged like the geodesic dome designed by US architect, Buckminster Fuller, hence these are also known as Buckminster Fullerenes or Bucky Ball structures.
7. Cause of versatile nature of carbon: Four main reasons for the versatile nature of carbon are:
(a) Catenation: It is the unique property of self-linkage of carbon atoms by means of covalent bonds to form straight chains, or branched chains, or the rings of different sizes (as shown below):

(b) Tetracovalency: Due to small size, and presence of four valence electrons, carbon can form strong bonds with other carbon atoms, hydrogen, oxygen, nitrogen, or sulphur, etc. For example, compounds of carbon with hydrogen are called hydrocarbons.
(c) Multiple Bond Formation : Small size of carbon also enables it to form multiple bonds, (i.e., double bonds or triple bonds) with other elements as well as with its own atoms. This increases the number of carbon compounds.
Note:
• Compounds of carbon with double bonds and triple bonds are called as unsaturated compounds while those with carbon-carbon single bonds are called saturated compounds.
• Alkenes (with —C = C —) and Alkynes (with —C = C—) are hence unsaturated, whereas Alkanes (with — C — C—) are saturated compounds.
(d) Isomerism: The phenomenon by means of which the carbon compounds with same molecular formula show different structures, and properties, e.g., A chain of 4 carbon atoms can be written in two ways :

Hence, the number of carbon compounds increases to a huge number.
8. Hydrocarbons: a Large number of hydrocarbons can be classified as:

Note: In an open chain, the name of parent chain is derived from the root word and suffix ane, ene or yne is added depending on the type of bond present in a chain :

Important: No alkene or alkyne is possible with single carbon atom because double or triple bond is not possible between carbon and hydrogen atom. It is only between two carbon atoms.
9. Functional Group:
• An atom or a group of atoms which when present in a compound gives specific properties to it, is called a functional group.
• A single line shown along with a functional group is called as its free valency by which it gets attached to a compound by replacing one hydrogen atom or atoms, e.g., -Cl.
• Functional group, replacing the hydrogen is also called as heteroatom because it is different from carbon, and can be nitrogen, sulphur, or halogen, etc.
Important: Replacement of hydrogen atom by a functional group is always in such a manner that valency of carbon remains satisfied.

Note : Cl is named as prefix Chloro; Br as Bromo; NH2 as Amino and N02 as Nitro.
Important Note: Symbol ‘R’ in a formula represents an Alkyl Group which is formed by the removal of one hydrogen atom from an alkane.
10. Homologous series: A series of organic compounds in which every succeeding member differs from the previous one by -CH2 group or 14 a.m.u.
Note : As the molecular mass increases in a series, : so physical properties of the compounds
show a variation, but chemical properties which are determined solely by a functional group, remains same within a series.
11. Nomenclature of Organic Compounds
• Trivial or common names: These names were given after the source from which the organic compounds were first isolated, e.g., If a compound has one carbon atom, then its common name will have root word form and so on (see table).
• IUPAC name: International Union of Pure and Applied Chemistry gave following rules for naming various compounds :
• Identify the number of carbon atoms and write the word root corresponding to it. e.g., If a number of carbon atoms is three, then the word root is a prop.
• Presence of a functional group is indicated by prefix or suffix as given in table 2, and table 3.
• If the name of the functional group is to be given as a suffix, the last letter ‘e’ in the name of the compound is deleted and the suffix is added. e.g., a ketone with three carbon atoms is named as :
Propane – e = Propan + ‘one’ = Propanone. Alcohol with three carbons is propanol. Carboxylic acid with three carbons is propanoic acid.
• Halogens, in IUPAC, are written as Prefixes, e.g., Compound With two carbons and one chloro group is named as chloroethane (CH3CH2CI).
12. Chemical properties of carbon compounds :
Main properties of carbon compounds are :
(a) Combustion Reaction
(b) Oxidation Reaction
(d) Substitution Reaction
(a) Combustion Reaction: A chemical reaction in which a substance burns in the presence of air or oxygen is called combustion reaction.
Note: Combustion is always an EXOTHERMIC reaction, e.g.,

Remember:
• Saturated hydrocarbons generally give clean flame whereas unsaturated hydrocarbons give sooty flame (because carbon content is more than hydrogen content in these, and hence carbon shows incomplete combustion and appears as soot).
• Saturated hydrocarbons can give sooty flame in a limited supply of oxygen.
(b) Oxidation Reaction: The addition of oxygen in a compound upon combustion is called oxidation.
In addition to combustion, oxidation can also be : brought about by some substances which are
capable of giving oxygen to others, i.e., Oxidising agents, e.g., Acidified K2Cr207 (Potassium dichromate) and alkaline KMn04 (Potassium permanganate).
Note:
(c) Addition Reaction: Addition of a molecule in unsaturated compounds in the presence of a catalyst, to give saturated compound is called an addition reaction, e.g.,
Hydrogenation of vegetable oils as shown in the reaction below :
(d) Substitution Reaction: The reactions which involve the replacement of an atom or group of atoms from a molecule by another atom without any change in structure in the remaining part of the molecule.
13. Ethanol: (or alcohol)
Colourless liquid, soluble in water, and has a distinct smell and burning taste. Its consumption in small quantities causes drunkenness and can be lethal.
14. Ethanoic Acid: CH3COOH
Common Name: Acetic Acid.
5-8% solution of acetic acid in water is called Vinegar. And 100% pure acetic acid is called Glacial acetic acid because it has m.pt. 290 K and freezes forming glacier like crystals.
Reactions of ethanoic acid :

Saponification : Esters in the presence of acid or base react to give back alcohol and carboxylic acid is called saponification.
15. Soaps and Detergents :
Soaps and Synthetic Detergents: Soaps and detergents are substances used for cleaning.
Soap: Soaps are sodium or potassium salts of higher fatty acids, such as Oleic acid (C17H33COOH), Stearic acid (C17H35COOH), Palmitic acid (C15H31COOH), etc. These acids are present in the form of their esters along with glycerol (alcohol containing three hydroxyl groups). These esters, called ‘glycerides’ are present in fats and oils of animal and vegetable origin.
Preparation of Soap: When an oil or fat (glyceride) is treated with sodium hydroxide solution, it gets converted to sodium salt of the acid (soap) and glycerol. The reaction is known as saponification.

Detergents: Chemically, detergents are sodium salts of sulphonic acids, i.e., detergents contain a sulphonic acid group (—S03H), instead^of a carboxylic acid group (—COOH), on one end of the hydrocarbon.

The cleansing action of detergent is considered to be more effective than a soap.
Cleansing Action of Soaps and Detergents: The cleansing action of soaps and detergents follows the same principle.

When soap or detergent is dissolved in water, the molecules gather together as clusters, called micelles. The tails stick inwards and the heads outwards.
In cleansing, the hydrocarbon tail attaches.itself to oily dirt. When water is agitated, the oily dirt tends to lift off from the dirty surface and dissociates into fragments. This gives an opportunity to other tails to stick to oil. The solution now contains small globules of oil surrounded by detergent molecules. The negatively charged heads present in water prevent the small globules from coming together and form aggregates. Thus, the oily dirt is removed from the object.
16. Scum: The insoluble precipitates formed by soap molecule when they react with calcium and magnesium ions present in hard water. Due to this, a lot of soap gets wasted and cleansing action gets reduced to a larger extent.

Question 1
What would be the electron dot structure of carbon dioxide which has the formula CO2 ?
Question 2
What would be electron dot structure of sulphur which is made up of eight atoms of sulphur.
Page Number: 68 – 69
Question 1
How many structural isomers can you draw for pentane ?
Three, these are n-pentane, iso-pentane and neo-pentane.
Question 2
What are the two properties of carbon which lead to the huge number of carbon compounds we see around us ?
(i) Tetravalency
(ii) Catenation.

Question 3
What will be the formula and electron dot structure of cyclopentane ?
The molecular formula of cyclopentane is C5 H10 .
The electron dot structure of cyclopentane is given on the next page.
Question 4
Draw the structures for the following compounds :
(i) Ethanoic acid
(ii) Bromopentane
(iii) Butanone
(iv) Hexanal
(i) Ethanoic acid (CH3COOH)

(ii) Bromopentane (C5H11Br)

(iii) Butanone (CH3 — CH2 — COCH3)

(iv) Hexanal (C5H11CHO)
Structural isomers for bromopentane: There are three structural isomers for bromopentane depending on the position of Br at carbon 1, 2, 3.

Positions 4 and 5 are same as 1, 2.
Question 5
How would you name the following compounds ?

(i) Bromoethane
(ii) Methanal
(iii) 1 – Hexyne
Page Number: 71
Question 1
Why is the conversion of ethanol to ethanoic acid an oxidation reaction ?
Conversion of ethanol into ethanoic acid is an oxidation reaction because addition of oxygen to a substance is called oxidation. Here, oxygen is added to ethanol by oxidising agent like alkaline potassium permanganate or acidified potassium dichromate and it is converted into acid.
Question 2
A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used ?
A mixture of 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 enough to melt metals for welding.
Page Number: 74
Question 1
How would you distinguish experimentally between an alcohol and a carboxylic acid ?
Differences between alcohol and carboxylic acid
 Test Alcohol Carboxylic acid (i) Litmus test No change in colour. Blue litmus solution turns red. (ii) Sodium hydrogen carbonate test C2H5OH + NaHCO3 → No reaction No brisk effervescence. CH3COOH + NaHCO3 → CH3COONa + H2O + CO2 Brisk effervescence due to evolution of CO2. (iii) Alkaline potassium permanganate On heating, pink colour disappears. Does not happen so.
Question 2
What are oxidising agents ?
Oxidising agents are the substances which give oxygen to another substances or which remove hydrogen from a substance.
For example, acidic K2Cr2O7 is an oxidising agent, that converts (oxidises) ethanol into ethanoic acid.
Page Number: 76
Question 1
Would you be able to check if water is hard by using a detergent ?
No, because detergents can lather well even in hard water. They do not form insoluble calcium or magnesium salts (scum). On reacting with the calcium ions and magnesium ions present in the hard water.
Question 2
People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes ?
It is necessary to agitate to get clean clothes because the soap micelles which entrap oily or greasy particles on the surface of dirty cloth have to be removed from its surface. When the cloth wetted in soap solution is agitated or beaten, the micelles containing oily or greasy dirt get removed from the surface of dirty cloth and go into water and the dirty cloth gets cleaned.

NCERT Solutions for Class 10 Science Chapter 4 Textbook Chapter End Questions

Question 1
Ethane, with the molecular formula C2Hhas
(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds
(b) 7 covalent bonds.
Question 2
Butanone is a four-carbon compound with the functional group
(a) carboxylic acid
(b) aldehyde
(c) ketone
(d) alcohol
(c) Ketone.
Question 3
While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
(a) the food is not cooked completely.
(b) the fuel is not burning completely.
(c) the fuel is wet.
(d) the fuel is burning completely.
(b) The fuel is not burning completely.
Question 4
Explain the nature of the covalent bond using the bond formation in CH3Cl.
Covalent bond is formed by sharing of electrons so that the combining atoms complete their outermost shell.
In CH3Cl : C = 6, H = 1 and Cl = 17 And their electronic configuration is C – 2,4, H – 1 and Cl – 2, 8, 7

Three hydrogen atoms complete their shells by sharing three electrons (one electron each) of carbon atom.
Chlorine completes its outer shell by sharing its one out of seven electrons with one electron of carbon atom.
Thus carbon atom shares all its four electrons with three hydrogen atoms and one of chlorine atom and completes its outermost shell and single covalent bonds are formed in CH3Cl.
Question 5
Draw the electron dot structures for
(a) ethanoic acid
(b) propanone
(c) H2S
(d) F2.
Question 6
What is a homologous series ? Explain with an example.
Homologous series : 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.
Characteristics of homologous series :
(i) All members of a homologous series can be represented by the same general formula. For example, the general formula of the homologous series of alkanes is CnH2n+2, in which ‘n’ denotes number of carbon and hydrogen atoms in one molecule of alkane.
(ii) Any two adjacent homologues differ by one carbon atom and two hydrogen atoms in their molecular formulae.
(iii) The difference in the molecular masses of any two adjacent homologues is 14u.
(iv) All the compounds of a homologous series show similar chemical properties.
(v) The members of a homologous series show a gradual change in their physical properties with increase in molecular mass.
For example, general formula of the homologous series of alkanes is CnH2n+2, in which ‘n’ denotes number of carbon atoms in one molecule of alkane. Following are the first five members of the homologous series of alkanes (general formula CnH2n+2).
 Value of n Molecular formula Name of compound 1 CH4 Methane 2 C2H6 Ethane 3 C3H8 Propane 4 C4H10 Butane 5 C5H12 Pentane
Question 7
How can ethanol and ethanoic acid he differentiated on the basis of their physical and chemical properties ?
Difference on the basis of physical properties
 Property Ethanol Ethanoic acid (i) State Liquid Liquid (ii) Odour Sweet smell Pungent vinegar-like smell (iii) Melting point 156 K 290 K (iv) Boiling point 351 K 391 K
Difference on the basis of chemical properties
 Test Ethanol Ethanoic acid (i) Litmus test No change in the colour of litmus solution. Blue litmus solution turns red. (ii) Sodium hydrogen carbonate test C2H5OH + NaHCO3 → No reaction No brisk effervescence. CH3COOH + NaHCO3 → CH3COONa + H2O + CO2 Brisk effervescence due to evolution of CO2. (iii) Alkaline potassium permanganate On heating, pink colour disappears. Does not happen so.
Question 8
Why does micelle formation take place when soap is added to water ? Will a micell be formed in other solvents such as ethanol also ?
Micelle formation takes place when soap is added to water because the hydrocarbon chains of soap molecules are hydrophobic (water repelling) which are insoluble in water, but the ionic ends of soap molecules are hydrophilic (water attracting) and hence soluble in water.
Such micelle formation will not be possible in other solvents like ethanol in which sodium salt of fatty acids do not dissolve.
Question 9
Why are carbon and its compounds used as fuels for most applications ?
Carbon and its compounds give a large amount of heat per unit weight and are therefore, used as fuels for most applications.
Question 10
Explain the formation of scum when hard water is treated with soap.
Hard water contains salts of calcium and magnesium. Calcium and magnesium on reacting with soap form insoluble precipitate called scum. The scum formation lessens the cleansing property of soaps in hard water.
Question 11
What change will you observe if you test soap with litmus paper (red and blue)?
Red litmus will turn blue because soap is alkaline in nature. Blue litmus remains blue in soap solution.
Question 12
What is hydrogenation ? What is its industrial application ?
The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydro-carbon is called hydrogenation. The process of hydrogenation takes place in the presence of nickel (Ni) or palladium (Pd) metals as catalyst.

Application : The process of hydrogenation has an important industrial application. It is used to prepare vegetable ghee (or vanaspati ghee) from vegetable oils.
Question 13
Which of the following hydrocarbons undergo addition reactions :
C2H6, C3H8, C3H6, C2H2 and CH4
Addition reactions take place only in unsaturated hydrocarbons. So addition reaction take place only in C3H6 and C2H2.
Question 14
Give a test that can be used to differentiate chemically between butter and cooking oil.
Butter is a saturated carbon compound while cooking oil is an unsaturated carbon compound. An unsaturated compound decolourises bromine water, while a saturated compound cannot decolourise it. So we can distinguish chemically between a cooking oil and butter by the bromine water. Add bromine water to a little of cooking oil and butter taken in separate test-tubes.
• Cooking oil decolourises bromine water showing that it is an unsaturated compound.
• Butter does not decolourise bromine water showing that it is a saturated compound.
Question 15
Explain the mechanism of the cleaning action of soaps.
OR
Explain the cleansing action of soaps. [CBSE 2015 (Delhi)]
When a dirty cloth is put in water containing dissolved soap, then the hydrocarbon end of the soap molecules in micelle attach to the oil or grease particles present on the surface of dirty cloth. In this way the soap micelle entraps the oily or greasy particles by using its hydrocarbon ends. The ionic ends of the soap molecules in the micelles, however, remain attached to water. When the dirty cloth is agitated in soap solution, the oily and greasy particles present on its surface and entrapped by soap micelles get dispersed in water due to which the soap water becomes dirty but the cloth gets cleaned. The cloth is cleaned thoroughly by rinsing in clean water a number of times.

Question 1
What would be the electron dot structure of carbon dioxide which has the formula CO2?
Solution:
Question 2
What would be the electron dot structure of a molecule of sulphur, which is made up of eight atoms of sulphur? (Hint – The eight atoms of sulphur are joined together in the form of a ring.)
Solution:

Question 3
How many structural isomers can you draw for pentane?
Solution:
We can draw 3 structural isomers for pentane.
Question 4
What are the two properties of carbon that lead to the huge number of carbon compounds we see around us?
Solution:
Due to its large valency, carbon atoms can form covalent bonds with a number of carbon atoms as well as with a large number of other atoms such as hydrogen, oxygen, nitrogen, sulphur, chlorine and many more atoms. This leads to the formation of a large number of organic compounds.

Question 5
What will be the formula and electron dot structure of Cyclopentane?
Solution:
Question 6
Draw the structures for the following compounds.
i. Ethanoic acid
ii. Bromopentane
iii. Butanone
iv. Hexanal
Solution:
Question 7
How would you name the following compounds?
Solution:
i. Ethyl bromide
ii. Formaldehyde
iii. Hexyne
Question 8
Why is the conversion of ethanol to Ethanoic acid an oxidation reaction?
Solution:
The conversion of ethanol into ethanoic acid is called an oxidation reaction because oxygen is added to it during this conversion.
Question 9
A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Solution:
When a mixture of oxygen and ethyne is burnt, it burns completely producing a blue flame. This blue flame is extremely hot which produced a very high temperature which is used for welding metals. But the mixture of ethyne and air is not used for welding purposes because burning of ethyne in air produces a sooty flame, which is not enough to melt metals for welding.
Question 10
What are oxidizing agents?
Solution:
Oxidizing agents are the substances that gain electrons in an redox reaction and whose oxidation number is reduced.
Question 11
Explain the nature of the covalent bond using the bond formation of CH3Cl.
Solution:
CH3Cl(methyl chloride) is made up of one carbon atom, three hydrogen atoms and one chlorine atom. Carbon atom has 4 valence electrons, each hydrogen atom has one valence electron, and a chlorine atom has 7 valence electrons. Carbon atom shares its four valence electrons with three hydrogen atoms and 1 chlorine atom to form methyl chloride as follows:

From the above reaction, in the dot structure of methyl chloride (CH3Cl) there are four pairs of shared electrons between carbon and other atoms. Each pair of shared electrons constitutes one single covalent bond. So, methyl chloride has four single covalent bonds.
Question 12
Draw the electron dot structures for-
Solution:
Question 13
What is a homologous series? Explain with an example.
Solution:
Homologous series is a series of compounds with a similar general formula, possessing similar chemical properties due to the presence of the same functional group, and shows a gradation in physical properties as a result of increase in molecular size and mass. For example, methane has a lower boiling point than ethane since it has more intermolecular forces with neighbouring molecules. This is because of the increase in the number of atoms making up the molecule.
Question 14
How can ethanol and Ethanoic acid be differentiated on the basis of their physical and chemical properties?
Solution:
(i) Ethanol has a pleasant smell whereas ethanoic acid has the smell of vinegar.
(ii) Ethanol has a burning taste whereas ethanoic acid has a sour taste.
(iii) Ethanol has no action on litmus paper whereas ethanoic acid turns blue litmus paper red.
(iv) Ethanol has no reaction with sodium hydrogencarbonate but Ethanoic acid gives brisk effervescence with sodium hydrogencarbonate.
Question 15
Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Solution:
Micelle formation takes place when soap is added to water. This is because when soap is added to water in which dirty clothes are soaked, the two parts of the soap molecule dissolves in two different mediums. The organic tail dissolves in the dirt, grime or grease and the ionic head dissolves in water. When the clothes are rinsed or agitated, the dirt gets pulled out of the clothes in the water by the soap molecule. In this way the soap does its cleaning work on dirty and grimy clothes or hands.
The soap molecules actually form a closed structure because of mutual repulsion of the positively charged heads. This structure is called a micelle.
Question 16
Why are carbon and its compounds used as fuels for most applications?
Solution:
Carbon and its compounds are used as fuels for most of the applications because they burn in air releasing a lot of heat energy.
Question 17
Explain the formation of scum when hard water is treated with soap.
Solution:
The precipitate form of scum is formed when soap is used for washing clothes. With hard water, a large amount of soap is wasted in reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate. The precipitate form formed by the action of hard water on soap, sticks to the clothes being washed and interferes with the cleaning ability of the additional soap. This makes the cleaning of clothes difficult.
Question 18
What change will you observe if you test soap with litmus paper (red and blue)?
Solution:
Soap is the salt of a strong base (NaOH) and a weak acid (carboxylic acid), so a solution of soap in water is basic in nature. Being basic, a soap solution turns red litmus paper blue.
Question 19
What is hydrogenation? What is its industrial application?
Solution:
It is a class of chemical reactions in which the net result is addition of hydrogen (H2) to unsaturated organic compounds such as alkenes, alkynes, etc. Hydrogenation is widely applied to the processing of vegetable oils and fats. Complete hydrogenation converts unsaturated fatty acids to saturated ones.
Question 20
C2H5, C3H8, C3H6, C2H2 and CH4
Solution:
Alkenes and alkynes (unsaturated hydrocarbons) undergo addition reactions. From the above hydrocarbons C2H2 is an alkyne, whereas C3H6 is an alkene. So, C3H6 and C2H2 will undergo addition reactions.
Question 21
Give a test that can be used to differentiate chemically between butter and cooking oil.
Solution:
Bromine water test can be used to differentiate chemically between butter and cooking oil. Add bromine water to a little of cooking oil and butter taken in separate test tubes. <font
a. Decolourising of bromine water by cooking oil (unsaturated compound)
b. Butter (saturated compound) does not decolourise bromine water
Question 22
Explain the mechanism of the cleaning action of soaps.
Solution:
We all know that soap is used to remove dirt and and grime from substances. Generally dirt and grime get stuck because they have an oily component, which is difficult to remove, by plain brushing or washing by water. A soap molecule has two parts, a head and a tail i.e. the long chain organic part and the functional group –COO Na+.
A soap molecule has a tadpole like structure shown below.
The organic part is water insoluble but is soluble in organic solvents or in oil or grease. The ionic part is soluble in water, as water is a polar solvent. When soap is added to water in which dirty clothes are soaked, the two parts of the soap molecule dissolve in two different mediums. The organic tail dissolves in the dirt, grime or grease and the ionic head dissolves in water. When the clothes are rinsed or agitated, the dirt gets pulled out of the clothes, by the soap molecule. In this way soap does its cleaning work on dirty and grimy clothes or hands.

The soap molecules actually form a closed structure because of mutual repulsion of the positively charged heads. This structure is called a micelle. The micelle pulls out the dirt and grime more efficiently.
Question 23
Would you be able to check if water is hard by using a detergent?
Solution:
We would not be able to check whether a sample of water is hard by using a detergent, this is because a detergent forms lather easily even with hard water.
Question 24
People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat ii with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
Solution:
It is necessary to shake to get clean clothes because the soap micelles, which entrap oily or greasy particles on the surface of dirty clothes, have to be removed from their surface. When the clothes which are wet by soap solution are beaten, the micelles containing oil or greasy dirt particles get removed from the surface of dirty clothes and go into water and the dirty cloth gets cleaned.
Multiple Choice Questions (MCQs) [1 Mark each]
Question 1.
Buckminster fullerene is an allotropic form of [NCERT Exemplar]
(a) phosphorus
(b) sulphur
(c) carbon
(d) tin
(c) Buckminster fullerene is an allotrope of carbon containing clusters of 60 carbon atoms joined together to form spherical molecules. Its formula isC60 (C-sixty). It is a dark solid at room temperature and as compared to another allotropic form of carbon (diamond and graphite), it is neither very hard nor soft.
Question 2.
The hetero atoms present in
CH3 – CH2 – O – CH2 – CH2Cl are [NCERT Exemplar]
(i) oxygen
(ii) carbon
(iii) hydrogen
(iv) chlorine
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
(d) Atoms other than C and H, if present in organic compound, are called heteroatoms.
Question 3.
In which of the following .compounds -OH is the functional group? [NCERT Exemplar]
(a) Butanone
(b) Butanol
(c) Butanoic
(d) Butanal
(b) Butanol, CH3—CH2—CH2—CH2—OH
The general formula of alcohols is CnH2n+1— OH.
For butanol, n = 4. So, formula is
C4H9—OH or CH3—CH2—CH2—CH2—OH
Question 4.
The soap molecule has a [NCERT Exemplar]
(a) hydrophilic head and a hydrophobic tail
(b) hydrophobic head and a hydrophilic tail
(c) hydrophobic head and a hydrophobic tail
(d) hydrophilic head and a hydrophilic tail
(a) A soap molecule is made up of two parts- a long hydrocarbon part and a short ionic part —COONa group. The long hydrocarbon chain is hydrophobic (water repelling) and ionic portion is hydrophilic (water attracting).
Question 5.
Structural formula of benzene is [NCERT Exemplar]

(c) Benzene molecule contains alternate single and . double bonds. Its formula is C6H6. In structure (b) formula is C6H12. In structure (a) double bond is not at alternate position. In (d) formula is C6H8.
Question 6.
Which of the following is not a straight chain hydrocarbon? [NCERT Exemplar]

chain hydrocarbon not straight chain hydrocarbon. Rest three are straight chain hydrocarbons.
Question 7.
Which among the following are unsaturated hydrocarbons? [NCERT Exemplar]

(a) (i) and (iii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
(c) Unsaturated hydrocarbons have double or triple bond in the structure. Both (ii) and (iv) structures have triple and double carbon-carbon bonds respectively.
Question 8.
Chlorine reacts with saturated hydrocarbons at room temperature in the [NCERT Exemplar]
(a) absence of sunlight
(b) presence of sunlight
(c) presence of water
(d) presence of hydrochloric acid
(b) Chlorine reacts with saturated hydrocarbon at room temperature in the presence of sunlight.
Question 9.

In the above given reaction, alk.KMnO4 acts as [NCERT Exemplar]
(a) reducing agent
(b) oxidising agent
(c) catalyst agent
(d) dehydrating
(b) KMnO4 acts as oxidising agent, because it removes hydrogen from CH3CH2OH and adds one oxygen to it.
Question 10.
Butanone is a four carbon compound with functional group [NCERT Exemplar]
(a) carboxylic acid
(b) aldehyde
(c) ketone
(d) alcohol
(c) In butanone, the functional group is
Question 11.
Identify the unsaturated compounds from the following [NCERT Exemplar]
(i) Propane
(ii) Propene
(iii) Propyne
(iv) Chloropropane
(a) (i) and (ii)
(b) (ii) and (iv)
(c) (iii) and (iv)
(d) (ii) and (iii)
(d) Propene, CH3CH=CH2 (ii) and propyne, CH3— C = CH (iii) both have double and triple bonds, respectively, hence are unsaturated compounds.
Question 12.
Which of the following does not belong to the same homologous series? [NCERT Exemplar]
(a) CH4
(b) C2H6
(c) C3H8
(d) C4H8
(d) Because succesive members of a homologous series differ by —CH2 unit.

Thus, C4H10 is the next member of this series. So, homologous series of alkanes is:
methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10).
So, C4H8 does not belong to the homologous series.
Question 13.
Ethane with molecular formula C2H6 has [NCERT Exemplar]
(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds
(b) Structure formula of ethane (C2H6) is

It is clear that it has 7 covalent bonds.
Question 14.
Which of the following are correct structural isomers of butane? [NCERT Exemplar]

(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (ii)
(d) (iii) and (iv)
(a) Structure (i) is n-butane and structure (iii) is iso-butane. Since, molecular formula is same, only structures are different. So, (i) and (iii) are isomers while structures (ii) and (iv) have molecular formulaC4H8.
Question 15.
In the soap micelles, [NCERT Exemplar]
(a) the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster
(b) ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster
(c) Both ionic end and carbon chain are in the interior of the cluster
(d) Both ionic end and carbon chain are on the exterior of the cluster
(a) A ‘spherical aggregate of soap molecules’ in the soap solution in water is called a ‘micelle’. In a soap micelle, the soap molecules are arranged readily with hydrocarbon ends directed towards the centre and ionic ends directed outwards.
Question 16.
Vinegar is a solution of [NCERT Exemplar]
(a) 50% – 60% acetic acid in alcohol
(b) 5% – 8% acetic acid in alcohol
(c) 5% – 8% acetic acid in water
(d) 50% – 60% acetic acid in water
(c) A 5%-8% solution of acetic acid in water is called vinegar.
Question 17.
Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of [NCERT Exemplar]
(b) substitution reaction
(c) displacement reaction
(d) oxidation reaction
(a) Oils are unsaturated compounds containing double bonds. Addition reactions are characteristic property of unsaturated hydrocarbons. The given reaction is an example of addition reaction.
Question 18.
Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of [NCERT Exemplar]
(a) helium
(b) neon
(c) argon
(d) krypton
(b) Electronic configuration of carbon (C) = 2, 4 when it forms four covalent bonds by sharing its four valence electrons with hydrogen, it forms CH4 molecule like this

Now, electronic configuration of C in CH
4 = 2, 8.
Atomic number of Ne is 10. Its electronic K L configuration is 2,8. Therefore, after the formation of four bonds, carbon attains the electronic configuration of neon.
Question 19.
Mineral acids are stronger acids than carboxylic acids because
(i) mineral acids are completely ionised.
(ii) carboxylic acids are completely ionised.
(iii) mineral acids are partially ionised.
(iv) carboxylic acids are partially ionised.
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)
(a) Mineral acids are strong acids which ionise almost completely and carboxylic acids are weak acids which ionise only pardally.
Question 20.
While cooking, if the bottom of the vessel is getting blackened on the outside, it means that [NCERT Exemplar]
(a) food is not cooked completely
(b) the fuel is not burning completely
(c) fuel is wet
(d) fuel is burning completely
(b) The unburnt particles of the fuel present in smoke blacken the vessel from outside.
Question 21.
The reaction in which a reagent (partially or completely) replaces atom or group of atoms from saturated compounds or A are called B reaction.
Here, A and B respectively refers to
(b) unsaturated compounds, substitution
(c) benzene, substitution
(c) Substitution reaction is usually given by saturated compounds and benzene. Unsaturated compounds usually give addition reactions.
Question 22.
The table gives information about some esters and the fragrance they produce.
 Ester Fragrance Ethyl methanoate Rum Methyl butanoate Apple Ethyl butanoate Pineapple Propyl ethanoate Pear
Which structure do the ester compounds in the table have in common?

(d) All esters have the common structure of carboxylic group represented by the suffix date.