Carbon and its Compounds

"Carbon is the fourth most abundant element in the Universe after hydrogen, helium and oxygen and is the second most abundant element in the human body and is present in all known life forms."

In earlier standards, we have studied about carbon is a versatile non-metallic element.

1.0Introduction

The compounds obtained from 'Carbon' are widely used as clothes, medicines, books, food, fertilizer, fuel, etc. All living structures are carbon based.

Carbon is a non-metal with symbol "C". The amount of carbon present in the earth's crust and in the atmosphere is quite meagre. The earth's crust has only $0.02\%$ carbon in the form of mineral (like carbonates, hydrogen carbonates, coal and petroleum) and the atmosphere has $0.03\%$ of carbon dioxide. Inspite of this small amount of carbon available in nature, the importance of carbon seems to be immense.Carbon forms a large number of compounds with hydrogen which are known as hydrocarbons. In addition to hydrogen, carbon compounds may also contain some other elements such as oxygen, halogen, nitrogen, phosphorus, sulphur, etc.

2.0Active Chemistry 1

is most stable and comprises nearly $99\%$ of all carbon on earth.

Aim To illustrate that most of the things we use or consume in our day-to-day life are made up of compounds of carbon. Materials required: Ten things you used or consumed.

Method Make a list of ten things you have used or consumed since morning. Compare this list with the lists made by your classmates and then sort the items into the following table. If there are items which are made up of more than one material, put them into both the relevant columns.

Discussion Except water and cooking utensils (made up of metals, glass/clay or ceramics), a large number of things such as soaps, detergents, newspaper, books, furniture (made up of wood and plastic) and various food items are made up of only compounds of carbon. However, some of the things such as mugs, cups/plates are usually made up of glass or ceramics while buckets are made up of metals or plastics.

Conclusion Most of the things we use or consume in our day to day life are made up of compounds of carbon.

3.0Bonding in carbon compounds

Carbon forms covalent bonds in its compounds with similar kind of atoms or different kind of atoms. In each compound the valency of carbon is four. That is, carbon has tetravalent character.

Covalent Bond

A chemical bond formed between two atoms of the same element or two atoms of different elements by sharing of electrons is called a covalent bond.

Necessary conditions for the formation of covalent bond

• The combining atoms should have non-metallic character.
• The combining atoms should contain 4 to 7 electrons in their respective valence shell.
• In hydrogen, there is only 1 valence electron, but it also forms covalent bond.
• The combining atoms need $1,2,3$ or 4 electrons to complete their octet (hydrogen completes its duplet).
• The combining atoms should contribute equal number of electrons to form pair of electrons to be shared.
• After sharing, the pair of electrons of each combining atom should attain stable electronic configuration like its nearest noble gas.

Why does carbon form only covalent bond?

• Explanation Reactivity of an element is explained as its tendency to attain a completely filled outer shell configuration that is to attain its nearest noble gas configuration. Carbon has 4 electrons in its outer most shell. In order to complete the shell, it should either gain or loss electrons. (i) It could gain four electrons forming C4- anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons. (ii) It would lose four electrons forming ${\mathrm{C}}^{4+}$ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in it nucleus holding on to just two electrons. Thus, carbon can neither gain nor lose 4 electrons but can share with other atoms to attain nearest noble gas configuration.

Melting and boiling points of compounds of carbon are low as compared to those of ionic compounds because the force of attraction between the molecules of these compounds are not very strong.

Covalent compounds have low melting and low boiling points because intermolecular forces (cohesive forces) in covalent compounds are weaker than those in ionic compounds. Some exception like diamond and graphite are covalent solids which have very high M.P. & B.P.

Melting and Boiling points of some compounds of carbon

Classification of covalent bond On the basis of the number of electrons shared by two combining atoms, the covalent bond are of three types

(i) Single covalent bond: A single covalent bond is formed by the sharing of one pair of electrons between the two atoms. It is represented by one short line ( - ) between the two atoms. Examples: $\mathrm{H}-\mathrm{H}$ or ${\mathrm{H}}_2,\mathrm{Cl}-\mathrm{Cl}$ or ${\mathrm{Cl}}_2,\mathrm{H}-\mathrm{Cl}$ or $\mathrm{HCl},{\mathrm{CH}}_3-{\mathrm{CH}}_3$ or ${\mathrm{C}}_2{\mathrm{H}}_6$.

(ii) Double covalent bond: A double covalent bond is formed by the sharing of two pairs of electrons between the two combining atoms. It is represented by putting two short lines (=) between the two bonded atoms. Examples: $\mathrm{O}=\mathrm{O}$ or ${\mathrm{O}}_2,\mathrm{O}=\mathrm{C}=\mathrm{O}$ or ${\mathrm{CO}}_2,{\mathrm{H}}_2\mathrm{C}={\mathrm{CH}}_2$ or ${\mathrm{C}}_2{\mathrm{H}}_4$.

(iii) Triple covalent bond: A triple bond is formed by the sharing of three pairs of electrons between the two combining atoms. It is represented by putting three short lines ( $\equiv$ ) between two bonded atoms. Examples: $\mathrm{N}\equiv \mathrm{N}$ or ${\mathrm{N}}_2,\mathrm{CH}\equiv \mathrm{CH}$ or ${\mathrm{C}}_2{\mathrm{H}}_2$.

4.0Formation of some covalent compounds

Lets discuss formation of some covalent compounds by Lewis dot structure/Electron dot structure.

Formation of hydrogen \left(\mathrm{H}_{2}\right)

Atomic number of hydrogen is 1 . Hence it has one electron in its K -shell and thus require one more electron to complete the K -shell and attain electronic configuration of nearest noble gas i.e. He.

Hydrogen Atomic number - 1 $\begin{array}{ll}\text{ Shell }& -\mathrm{K}\\ \text{ Electron }& -1\end{array}\}$ Incomplete duplet (unstable)

Helium $\begin{array}{lr}\text{ Atomic number }-2& \\ \text{ Shell }& -\mathrm{K}\\ \text{ Electron }& -2\end{array}\}$ Complete duplet (stable)

Formation of ${\mathrm{Cl}}_2$ Molecule

The atomic number of chlorine is 17 , thus there are 17 electrons in an atom of chlorine.

Electronic configuration of Cl atom Shells $\begin{array}{rcc}\mathrm{K}& \mathrm{L}& \mathrm{M}\\ 2& 8& 7\end{array}\}$ Incomplete octet

Electronic configuration of Ar atom $\begin{array}{lccc}\text{ Shells }& \mathrm{K}& \mathrm{L}& \mathrm{M}\\ \text{ Electrons }& 2& 8& 8\end{array}\}$ complete octet

Chlorine atom needs one more electron to complete its octet

Formation of oxygen $\left({\mathrm{O}}_2\right)$

The atomic number of 0 atom is 8 . There are 6 electrons in the valence shell of oxygen atom, it needs 2 more electrons to attain the nearest stable inert gas [Neon $(2,8)]$ configuration.

Formation of nitrogen molecule ${\mathrm{N}}_2$

The atomic number of nitrogen is 7 and its electronic configuration is $\mathrm{K}(2)$, L(5). It needs 3 electrons more to complete its octet like noble gas neon $(2,8)$.

Formation of ammonia molecule $\left({\mathrm{NH}}_3\right)$

The atomic number of N is 7 . Its electronic configuration is 2,5 . There are 5 electrons in its valence shell. It needs 3 electrons more to complete its octet like noble gas, neon $(2,8)$.

Formation of ${\mathrm{H}}_2\mathrm{O}$ molecule

The electronic configuration of hydrogen is $\mathrm{K}(1)$ and that of oxygen is $\mathrm{K}(2),\mathrm{L}(6)$. Thus, each hydrogen require one electron and oxygen require two electrons to achieve the stable electronic configuration.

Formation of ${\mathrm{CH}}_4$ molecule

Methane is a covalent compound containing four covalent bonds. It contains one carbon atom and four hydrogen atoms covalently bonded to central carbon atom.

5.0Allotropes of carbon

Allotropy: It is the phenomenon of existence of an element in two or more forms which have different physical properties but identical chemical properties. The different forms are called allotropes. Carbon forms three crystalline allotropes, (i) Diamond (ii) Graphite (iii) Fullerene

(i) Diamond Diamond is a crystalline allotrope of carbon. Its atomic symbol and empirical formula is ' C '.

• Structure In diamond, each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. This tetrahedral arrangement of carbon atoms gives a rigid, threedimensional structure to diamond.
• Properties

• Pure diamond is a transparent and colourless solid.
• Polished diamond sparkles brightly because it reflects most of the light.

• Preparation of synthetic diamond Diamond can be synthesized by subjecting pure carbon to very high pressure and temperature. These synthetic diamonds are smaller than natural diamonds.

(ii) Graphite Graphite is also known as black lead as it marks paper black. The name graphite has been taken from the Greek word "graphein" (which means to write) in reference to its uses as 'lead' in lead pencils.

• Structure Graphite is an opaque and dark grey solid. In a crystal of graphite the carbon atoms are arranged in a hexagonal pattern in parallel planes. In a layer of graphite each carbon atom is strongly bonded to three other carbon atoms by covalent bonds. Thus, one valence electron of each carbon atom is free in every layer of graphite crystal. The free electron makes graphite a good conductor of electricity. Each layer is bonded to the adjacent layers by weak forces. As a result, each layer can easily slide over the other. This makes graphite slippery in nature.
  
  Structure of graphite

(iii) Fullerene Fullerenes are recently discovered, spherical or tube-like allotropes of carbon. The molecule containing sixty atoms of carbon has been named as Buckminster fullerene. Fullerenes has been named after American architect and engineer R. Buckminster-fuller whose geodesic domes follow similar building principles.

Fullerene was discovered in 1985 by Robert F. Curl Jr. Harold Kroto and Richard E. Smally.

• Types of fullerene ${\mathrm{C}}_{60},{\mathrm{C}}_{70},{\mathrm{C}}_{74}$ and ${\mathrm{C}}_{78}$ are the members of fullerene family. But ${\mathrm{C}}_{60}$ is the most stable and most studied form of fullerenes. ${\mathrm{C}}_{60}$ molecule has marvelously symmetrical structure. It is a fused ring of aromatic system containing 20 hexagons and 12 pentagons of C -atoms.

6.0Versatile nature of carbon

About three million (or thirty lakh) compounds of carbon are known. The existence of such a large number of organic compounds is due to the following characteristic features of carbon. (i) Catenation: tendency to form carbon-carbon bond "The property of forming bonds with atoms of the same element is called catenation". Carbon has the maximum tendency of catenation in the periodic table. This is because of strong carboncarbon bonds as compared to other atoms.

No other element exhibits the property of catenation to the extent seen in carbon compounds. Silicon forms compounds with hydrogen which have chains of upto seven or eight atoms, but these compounds are very reactive. The carbon-carbon bond is very strong and hence stable. This gives us the large number of compounds with many carbon atoms linked to each other.

When two or more carbon atoms combine with one another, they form different types of chains such as, (i) Straight chains (ii) Branched chains (iii) Closed chain or ring chains

Why carbon shows maximum catenation among all elements?

• Explanation: Causes of maximum catenation in carbon are: (i) Small size. (ii) Unique electronic configuration $(2,4)$. (iii) Great strength of carbon-carbon bonds ( $355\mathrm{kJ}/\mathrm{mol}$ ).

(ii) Tetravalency of carbon The atomic number of carbons is $6$ and hence its electronic configuration of carbon atom is $2,4$. It has four electrons in the outermost shell, therefore its valency is four (tetravalency). Thus, carbon forms four covalent bonds in its compounds. Compounds of carbon are formed with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements giving rise to compounds with specific properties, which depends upon the elements other than carbon present in the molecule.

(iii) Tendency to form multiple bonds Due to small size, carbon can easily form double or triple bonds (called multiple bonds) with itself and with the atoms of other elements as nitrogen, oxygen, sulphur etc.

Is it possible for two carbon atoms to share four electron pairs to complete the octet and form \mathrm{C}_{2} molecule?

• Explanation: No, two carbon atoms cannot mutually share more than 3 electron pairs. Actually, as a result of electron sharing, the nuclei of the participating atoms are also drawn closer. After sharing three pairs, the nuclei are so close that the force of repulsion in the positively charged nuclei will push them apart. The atoms are no longer in a position to share one more pair and form four bonds.

(iv) Isomerism

Compounds having same molecular formula but different structural formulae are known as isomers and the phenomenon of existence of isomers is termed as isomerism.

As the number of carbon increases in the compound, number of isomers also increases.

7.0Organic compounds

Because of versatile nature of carbon, it forms many compounds. Organic chemistry: Branch of chemistry which deals with the study of organic compounds. Hydrocarbons: Organic compounds of carbon and hydrogen. In eighteenth century all known compounds were divided into two categories.

Vital force theory

This theory was given by Berzelius in 1815. According to him, organic compounds were produced only under the influence of some mysterious force existing in the living organism. This mysterious force was called the vital force. So, it was believed that no organic compound can be prepared in the laboratory. Wohler's synthesis Berzelius's theory was disapproved by Friedrich Wohler in 1828 by preparing urea from ammonium cyanate $\left({\mathrm{NH}}_4\mathrm{CNO}\right)$ in laboratory.

Modern definition of organic compounds

Compounds of carbon, containing usually hydrogen and one and more other element such as oxygen, nitrogen, sulphur, halogens, phosphorus, etc. are called organic compounds.

8.0Saturated and unsaturated hydrocarbon

On the basis of bonding, carbon compounds can be classified in two categories: (i) Saturated hydrocarbons (ii) Unsaturated hydrocarbons

(i) Saturated Hydrocarbon The hydrocarbons which contain only single carbon-carbon covalent bonds are called saturated hydrocarbons. They are also called alkanes. General formula for alkanes is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$ where ' n ' is the number of carbon atoms. General formula of saturated hydrocarbon ( ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$ )

H Hydrocarbons C

(a) Structure of methane $\left[{\mathrm{CH}}_4\right]$

Methane consists of one carbon and four hydrogen atoms, which are covalently bonded to each other's, forming following structure.

(b) Structure of ethane $[{\mathrm{C}}_2{\mathrm{H}}_6]$ To derive the structure of ethane, the following steps are followed. Step-I: Link the two carbon atoms. C-C Carbon atoms are linked together with a single bond. Step-II: Three valencies of each carbon atom remain unsatisfied, so each is bonded to three hydrogen atoms giving the following structure.

CC

Each carbon atom is bonded to three hydrogen atoms.

(c) Structure of propane$\left[{\mathrm{C}}_3{\mathrm{H}}_8\right]$

In a similar manner we can derive the structure of propane.

(ii) Unsaturated hydrocarbons The hydrocarbons in which two carbon atoms are bonded to each other by a double (=) or a triple ( $\equiv$ ) bond is called an unsaturated hydrocarbon. Unsaturated hydrocarbons are of two types viz. alkenes and alkynes. (a) Alkenes $(-\stackrel{\text{ l }}{\mathrm{C}}=\stackrel{\mathrm{l}}{\mathrm{C}}-$ )

The hydrocarbons in which the two carbon atoms are bonded by a double bond are called alkenes.

Their general formula is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$ where " n " is the number of carbon atoms. Alkenes are also known as olefins. In greek 'ole' means oil and fins means production because lower members of alkenes form oily product with chlorine.

General formula of alkenes: ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2n}$

We cannot form methene because it has only one carbon.

Formation of ethene molecule $[{\mathrm{C}}_2{\mathrm{H}}_4]$ The electronic configuration of carbon atom is 2, 4. There are four valence electrons in one C atom. Each H atom contains one valence electron.

(b) Alkyne $(-C=\mathrm{C}-)$

The hydrocarbons in which two carbon atoms are bonded by a triple bond are called alkynes. Their general formula is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}-2}$ where ' n ' is the number of carbon atoms. Unsaturated hydrocarbons are more reactive than saturated hydrocarbons. General formula of alkynes: ${\mathrm{C}}_{\mathbf{n}}{\mathbf{H}}_{2n-2}$

Formation of ethyne molecule $\left({\mathrm{C}}_2{\mathrm{H}}_2\right)$

Alkanes general formula of alkane is ${\mathbf{CnH}}_{2n+2}$ Alkenes general formula of alkane is ${\mathbf{C}}_n{\mathbf{H}}_{2n}$ Alkynes general formula of alkane is ${\mathbf{CnH}}_{\mathbf{n}}\mathbf{n}-2$

9.0Chains, branches and rings

On the basis of structure carbon compounds can be divided into 3 categories: (a) Straight chain compounds (b) Branched chain compounds (c) Closed chain / cyclic / ringed compounds

(a) Straight chain compounds If a carbon compound has carbon-carbon link in chain structure, we get a straight chain compound. Open chain compounds, whether straight chain or branched chain are known as aliphatic compounds. In these, a carbon can form bond with a maximum of 2 carbon atoms e.g.

(i) Straight chain alkanes

(ii) Straight chain alkenes ${\mathrm{H}}_2\mathrm{C}={\mathrm{CH}}_2{\mathrm{CH}}_3-\mathrm{CH}={\mathrm{CH}}_2$ ${\mathrm{CH}}_3-\mathrm{CH}=\mathrm{CH}-{\mathrm{CH}}_3$ or ${\mathrm{CH}}_2=\mathrm{CH}-{\mathrm{CH}}_2-{\mathrm{CH}}_3$ Ethene Propene Butene

(iii) Straight chain alkynes $\mathrm{HC}\equiv \mathrm{CH}{\mathrm{H}}_3\mathrm{C}-\mathrm{C}\equiv \mathrm{CH}{\mathrm{H}}_3\mathrm{C}-\mathrm{C}\equiv \mathrm{C}-{\mathrm{CH}}_3$ or $\mathrm{HC}\equiv \mathrm{C}-{\mathrm{CH}}_2-{\mathrm{CH}}_3$ Ethyne Propyne Butyne

(b) Branched structure

The alkanes containing three or less carbon atoms do not form branches. ${\mathrm{CH}}_4$ ${\mathrm{CH}}_3-{\mathrm{CH}}_3$ ${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_3$ Methane Ethane Propane The alkane containing four carbon atoms $\left({\mathrm{C}}_4{\mathrm{H}}_{10}\right)$ has two types of arrangement of carbon atoms.

Thus, carbon compounds in which at least one carbon of the chain is linked to three or four other carbon atoms are called branched chain compounds. Like saturated compounds, unsaturated compounds can also have branched chain structure. For example, ${\mathrm{C}}_4{\mathrm{H}}_8$, butene may have following structure.

Boiling point (i) Butane has a straight chain structure whereas iso-butane has a branched chain structure. A branched exhibits weaker Vander Waals forces as compared to straight chains. Strong intermolecular forces in butane results in a higher boiling point as larger energy is required to separate them. (ii) ${\mathrm{C}}_4{\mathrm{H}}_{10}\to$ (Butane) Butane have 2-isomers.

(c) Closed chains or cyclic hydrocarbons or ring hydrocarbons

These hydrocarbons contain closed chain or ring of atoms in their molecules. These further can be of two types: (i) Alicyclic hydrocarbon or saturated cyclic carbon compounds or cycloalkanes

These hydrocarbons contain a ring chain of three or more carbon atoms. These cyclic compounds are named by writing prefix 'cyclo' before the name of corresponding straight chain hydrocarbon.

10.0(ii) Aromatic hydrocarbon or unsaturated cyclic carbon compound

These have at least one benzene ring in their molecules. It is a special type of ring of six carbon atoms with three double bonds in alternate positions. or

11.0Functional group

Carbon forms most of the compounds with hydrogen. But carbon also forms bonds with other atoms such as halogen, oxygen, nitrogen and sulphur. Therefore, carbon is said to be a very friendly element. These compounds are obtained by replacing one or more hydrogen atoms by other atoms such that the valency of carbon remains satisfied. The atom or a group of atoms replacing the hydrogen atom are called heteroatom or functional group respectively. Different organic compounds having same functional group have almost same properties. These are called families. To understand the meaning of a functional group, let us consider ethane ( ${\mathrm{C}}_2{\mathrm{H}}_6$ ) and ethanol $\left({\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\right)$. Here, ethanol is obtained by replacing one hydrogen atom of ethane by the hydroxyl group as shown below:

• Ethane is a gas while ethanol is a liquid at room temperature.
• Ethanol is an antiseptic and hypnotic (induces sleep) but ethane does not have these properties.
• Ethanol reacts with sodium to form sodium ethoxide with the evolution of hydrogen gas but ethane does not give this reaction.

Example of different compounds with same functional group

Properties of ${\mathrm{CH}}_3-\mathrm{OH}$ and ${\mathrm{CH}}_3-{\mathrm{CH}}_2\mathrm{OH}$ are similar and it is due to the presence of -OH (hydroxyl) group. This group is known as alcoholic group. Family of compounds having -OH group is called alcohol.

Halo group is a functional group as it imparts special property to the parent hydrocarbon, but according to IUPAC nomenclature, it is not considered as a functional group and thus its prefix is used for naming

Some Functional Groups in Carbon compounds

Hetero atom	Functional Group	Formula of Functional Group
Halogen atom ( $\mathrm{F},\mathrm{Cl},\mathrm{Br},\mathrm{I}$ )	Halo (Fluoro, Chloro, Bromo, Iodo)	$$\begin{gathered} -\mathrm{X} \\ (-\mathrm{F},-\mathrm{Cl},-\mathrm{Br},-\mathrm{I}) \end{gathered}$$
Oxygen (0)	1. Alcohol	-OH
	2. Aldehydes
	3. Ketones	$\begin{array}{lll}& & \\ \mathrm{C}=\mathrm{O}& \text{ or }& \text{ - }\mathrm{CO}\end{array}$
	4. Carboxylic acid	O=C(O)C(=O)O
	5. Ester	[R]OC([R])=O or RCOOR

12.0Homologous Series

"A series of organic compounds having similar structures and similar chemical properties in which the successive members differ in their molecular formula by - ${\mathrm{CH}}_2$ group". The different members of the series are called as homologous.

Characteristics of homologous series

(i) All the members of a homologous series can be described by a common general formula. Example: All alkanes can be described by the general formula ${\mathbf{C}}_{\mathbf{n}}{\mathbf{H}}_{2\mathrm{n}+2}$. (ii) Each member of a homologous series differs from its higher and lower neighbouring member by a common difference of $-{\mathrm{CH}}_2$ group. (iii) Molecular masses of the two adjacent homologous differ by 14 mass units, because molecular mass of $-{\mathrm{CH}}_2$ group is $12+$ $2=14$. (iv) All the members of a homologous series show similar chemical properties. for example, substitution reaction is shown by all alkanes. (v) All the members of a homologous series show a gradation in physical properties as molecular mass increases. For example, M.P. and B.P. increases with increase in molecular mass. (vi) All the members of the series can be prepared by similar methods known as the general method of preparation.

• Some members of alkane, alkene and alkyne homologous series.

13.0Nomenclature of carbon compounds

There are two ways to name carbon compounds:

• Trivial system: In earlier days, organic compounds were named after the source from which they were obtained. For example, urea got its name because the substance was obtained from the urine of mammals. These names are without any systematic basis and are known as common names or trivial names. Common name of methanol is wood spirit because it is obtained by destructive distillation of wood. Common name of methanoic acid is formic acid because it is extracted from red ants (formicus)
• IUPAC system: It is the system for naming organic compound given by International Union of Pure and Applied Chemistry. This system is very useful in the study of organic compounds. In IUPAC system of nomenclature, the name of organic compounds consists of three parts. (i) Word root (ii) Suffix (iii) Prefix

(i) Word root: The word root denotes the number of carbon atoms present in the chain. For chains containing upto four carbon atoms, special word roots (meth-C1, eth-C2, prop-C3, but-C4) have been used while those containing more than four carbon atoms, Greek numerals have been used to represent the word root. For example,

(ii) Suffix: It indicates the nature of linkage in the carbon atoms.

It indicates the presence of functional group in the organic compound. While adding secondary suffix the final 'e' from the name of the carbon chain is deleted. A few important suffixes are listed below

(iii) Prefix: There are few groups which are not regarded as functional groups in IUPAC name of a compound. These are regarded as substituent and are represented as prefixes and are put before the word root while naming a particular compound. A few important prefixes are given:

Thus a complete IUPAC name of an organic compound may be represented as Prefix + Word root + suffix

Rules

• Find and name the longest continuous carbon chain.
• Identify and name groups attached to this chain.
• Number the chain consequently, starting at the end nearest to a substituent group.
• Designate the location of each substituent group by an appropriate number and name.
• Assemble the name, listing groups in an alphabetical order.

The prefixes di, tri, tetra, etc. are used to designate several groups of the same kind.

Some examples,

For example, $-{\mathrm{CH}}_3$ (methyl), $-{\mathrm{C}}_2{\mathrm{H}}_5$ (ethyl) etc.

14.0Chemical properties of carbon compounds

Carbon compounds generally show following four chemical reactions.

Combustion reaction

Definition: Combustion is the process of complete burning of a substance in presence of oxygen along with the liberation of large amount of heat and light. It can be considered as rapid and complete oxidation. Any substance, which contain carbon and hydrogen, on proper combustion will produce carbon dioxide and water along with energy. Combustion of acetylene with oxygen produces a flame of over 3600K. Due to the high temperature of flame, oxyacetylene gas is used in welding and cutting.

Combustion of some common substance

(i) Combustion of carbon: Carbon (or charcoal) burn in air or oxygen to give ${\mathrm{CO}}_2$ producing heat and light. $$\begin{gathered} \mathrm{C}(\mathrm{s})+ \\ \text{ Carbon }{\mathrm{O}}_2(\mathrm{g}) \\ \text{ Oxygen }\stackrel{\text{ Combustion }}{\to }{\mathrm{CO}}_2(\mathrm{g}) \\ \text{ Carbon dioxide }+ \end{gathered}$$ Heat + Light

(ii) Combustion of hydrocarbon: Hydrocarbons burn to produce carbon dioxide $\left({\mathrm{CO}}_2\right)$, water ( ${\mathrm{H}}_2\mathrm{O}$ ) and heat and light.

Note: Natural gas and biogas contain methane. So, burning of natural gas and biogas are also combustion reactions. (iii) Burning of LPG (Butane) produces ${\mathrm{CO}}_2,{\mathrm{H}}_2\mathrm{O}$, heat and light.

${\mathrm{C}}_4{\mathrm{H}}_{10}(\mathrm{g})+\frac{13}{2}{\mathrm{O}}_2(\mathrm{g})\stackrel{\text{ Combustion }}{\to }4{\mathrm{CO}}_2(\mathrm{g})+5{\mathrm{H}}_2\mathrm{O}(\mathrm{g})+\text{ Heat }+\text{ Light }$ Butane/LPG

(iv) Combustion of alcohol $$\begin{gathered} {\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{aq})+3{\mathrm{O}}_2(\mathrm{g})\underset{\text{ Oxygen (from air) }}{\overset{\text{ Combustion }}{\to }}2{\mathrm{CO}}_2(\mathrm{g})+3{\mathrm{H}}_2\mathrm{O}(\mathrm{g})+\text{ Heat + light } \\ \text{ Ethanol } \end{gathered}$$

Active Chemistry

Aim: To illustrate that saturated hydrocarbons burn with a blue non-luminous flame, while unsaturated hydrocarbons give luminous yellow sooty flame. Materials required: Some carbon compounds (naphthalene, camphor, alcohol), burner, metal plate.

Method Take some carbon compounds (naphthalene, camphor, alcohol) one by one on a spatula and burn them. Observe the nature of the flame and note whether smoke is produced. Place the metal plate above the flame. Is there a deposition on the plate in case of any of the compounds?

Observation and Discussion:

Naphthalene, burns with a smoky flame and carbon particles get deposited as it undergoes incomplete combustion due to excess of carbon content. Alcohol and camphor burns with blue non-luminous flame and no carbon gets deposited. They undergo complete combustion, therefore produce more heat.

Conclusion Saturated compounds burn with a non-luminous blue flame while unsaturated compounds burn with a yellow sooty flame.

Active Chemistry

Aim: To illustrate that complete combustion of a fuel gives a blue flame while incomplete combustion gives a yellow sooty flame. Materials required: Burner, metal plate.

Method (i) Light the Bunsen burner. (ii) Close the air hole and observe the colour of the flame. (iii) Put a metal plate over it and observe the nature of deposit. (iv) Open the air regulator to allow the flow of air.

Observation

Conclusion In the presence of sufficient oxygen, fuel burns completely and hence does not give a yellow sooty flame, but a blue, non-sooty flame is produced.

Why do substances burn with or without the flame? Explanation (i) When a candle or the LPG gas burns, it always burns with a flame. Reason: A flame is produced only when gaseous substances burn. In candle wax melts and forms a gaseous substance and LPG is a gaseous fuel. (ii) When coal, wood or charcoal is ignited, it burns with a flame in the beginning and then glows red and gives lots of heat without producing a flame. Reason: When wood or charcoal is ignited, the volatile substances present in them, vaporizes and burns with a flame in the beginning and after that glows red. A luminous flame is produced when the atoms of a gaseous substances are heated and begin to glow for example, different elements produce different colour, like copper gives greenish blue colour in the flame. The gas/kerosene stove used at home has inlets for air so that a sufficiently oxygen rich mixture is burnt to give a clean blue flame. If you carefully observe the bottoms of vessels getting blackened, it is clear indication that the air holes are blocked and the fuel is getting wasted.

How formation of coal and petroleum takes place? Explanation Coal and petroleum have been formed from biomass which has been subjected to various biological and geological processes. Coal is the remain of tree ferns and other plants that lived millions of years ago and buried inside the earth during earthquakes and volcanoes. Due to huge pressure and temperature inside the earth and in the absence of air, the fossil fuels (vegetable matter or wood, etc.) were converted into coal. Petroleum and natural gas are the remains of tiny plants and animals that lived in the sea. It is a dark coloured, viscous and foul-smelling crude oil. The name petroleum is derived from Latin words. "petra"

Oxidation reaction

Definition: Addition of oxygen or removal of hydrogen is called oxidation and the substances which are capable of adding oxygen to other substances are called oxidising agents. Combustion is uncontrolled oxidation in which organic compounds are completely burnt and get oxidized to ${\mathrm{CO}}_2$ and water. However, in oxidation, oxygen is added to the compound, in a controlled manner. Carbon gives carbon monoxide or carbon dioxide depending upon the oxygen available.

Hydrocarbon when oxidised give different product as follows:

Alcohols also give different products on oxidation depending upon the reaction conditions. Example: (i) Alcohols on oxidation with certain oxidising agents such as chromic anhydride in acetic acid, yield corresponding aldehydes.

(ii) On oxidation with alkaline potassium permanganate (or acidified potassium dichromate), corresponding carboxylic acid is formed.

$$\begin{gathered} {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}(\mathrm{aq})+\underset{2[0]}{\text{ Alkaline }{\mathrm{KMnO}}_4}\text{ Heat }{\mathrm{CH}}_3\mathrm{COOH}(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\ell ) \\ \text{ Nascent oxygen }\text{ Ethanoic acid } \end{gathered}$$

Aim: To study the reaction of ethanol with alkaline potassium permanganate. Materials required: Ethanol, test tubes, water, alkaline ${\mathrm{KMnO}}_4$.

Method (i) Take about 3 ml of ethanol in a test tube and warm it gently in a water bath. (ii) Add $5\%$ solution of alkaline ${\mathrm{KMnO}}_4$ drop by drop into this solution. (iii) Observe the colour of alkaline ${\mathrm{KMnO}}_4$ after adding initially as well as finally.

Now answer Does the colour of potassium permanganate persists when it is added initially? Why does the colour of potassium permanganate not disappear when excess is added?

Discussion When a $5\%$ solution of alkaline ${\mathrm{KMnO}}_4$ is added to warm alcohol drop by drop, the colour of ${\mathrm{KMnO}}_4$ disappears initially because it oxidises ethanol to ethanoic acid and is itself reduced to manganese dioxide $\left({\mathrm{MnO}}_2\right)$. However, if the ${\mathrm{KMnO}}_4$ solution added is more than what is required to oxidise ethanol to ethanoic acid, then some of the ${\mathrm{KMnO}}_4$ solution remains unused and hence its colour will not disappear.

Conclusion Alkaline ${\mathrm{KMnO}}_4$ solution oxidises ethanol to ethanoic acid while it itself is reduced to ${\mathrm{MnO}}_2$. ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}(\mathrm{aq})\underset{\text{ ork }}{\overset{\text{ AlkalineKMno }{\mathrm{K}}_4\text{,Heat }}{\to }}{\mathrm{Cr}}_7{\mathrm{H}}_2{\mathrm{OO}}_4$ Heat ${\mathrm{CH}}_3\mathrm{COOH}(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\ell )$

Addition reaction

Definition: Reactions in which unsaturated hydrocarbons (unsaturated carbon compounds) react with a molecule like ${\mathrm{H}}_2,{\mathrm{X}}_2,{\mathrm{H}}_2\mathrm{O}$, etc. to form saturated compounds are called addition reactions. Hydrogenation reaction : Addition of hydrogen to an unsaturated carbon compound is called hydrogenation reaction. For example, Unsaturated hydrocarbons add hydrogen, in the presence of catalysts, such as nickel or palladium to give saturated hydrocarbons.

(i) Addition of hydrogen to ethene

Industrial importance of hydrogenation reactions

Hydrogenation of vegetable oils is essential because they contain unsaturated compounds which are very reactive and undergo oxidation easily on exposure to air and may turn rancid. Certain vegetable oils such as ground nut oil, cotton seed oil and mustard oil, contain double bonds ( $\mathrm{C}=\mathrm{C}$ ) and are liquids at room temperature. Because of the unsaturation, the vegetable oils undergo hydrogenation, like alkenes, to form saturated products called vanaspati ghee, which is

Substitution reactions

Definition: The reactions in which one or more hydrogen atoms of a hydrocarbon are replaced by some other atoms or groups are called substitution reaction. Example: Methane reacts with chlorine (or bromine) in the presence of sunlight and undergoes substitution reaction. It is called photochemical reaction because it takes place in the presence of sunlight.

15.0Some Important Carbon Compounds

Many carbon compounds are invaluable to us. But here we shall study the properties of two commercially important compounds - ethanol and ethanoic acid.

Ethanol (Ethyl Alcohol, \mathrm{C}_{2} \mathrm{H}_{5} \mathbf{O H} )

Ethanol is the second member of the homologous series of alcohols.

Physical properties (i) Physical state / colour and odour: Pure ethanol is a colourless liquid having a pleasant smell and a burning taste. (ii) Boiling and freezing points: It is a volatile liquid with a boiling point of $78.1^{\circ }\mathrm{C}$, and freezing point is $-118^{\circ }\mathrm{C}$. (iii) Solubility: Ethanol is miscible with water in all proportions, due to the formation of hydrogen bonds with water molecules. Consumption of ethanol causes drunkenness.

Chemical properties

(i) Combustion (or burning): Ethanol is highly inflammable liquid and readily burns in air with a blue flame to form water vapour, carbon dioxide and evolves heat. Thus, combustion of ethanol is an exothermic reaction. ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{aq})+3{\mathrm{O}}_2(\mathrm{g})\stackrel{\text{ Combustion }}{\to }2{\mathrm{CO}}_2(\mathrm{g})+3{\mathrm{H}}_2\mathrm{O}(\mathrm{g})+\text{ Heat }$

(ii) Reaction with sodium metal: Ethanol reacts with sodium metal to produce sodium ethoxide and hydrogen gas is evolved. $2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{aq})+2\mathrm{Na}(\mathrm{s})⟶2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{ONa}(\mathrm{aq})+{\mathrm{H}}_2(\mathrm{g})$ Ethanol Sodium metal Sodium ethoxide Hydrogen

Active Chemistry

Aim: To identify the gas evolved when sodium reacts with ethanol. Materials required: Sodium, ethanol.

Method Drop a small piece of sodium, about the size of a couple of grains of rice, into ethanol (absolute alcohol).

Now Answer (i) What do you observe? (ii) How will you test the gas evolved?

Discussion and conclusion When a small piece of sodium is added to absolute alcohol ( $100\%$ alcohol), a brisk effervescence due to the evolution of ${\mathrm{H}}_2$ gas takes place. Hydrogen is a combustible gas, therefore, when a burning splinter is brought near it, it burns with a 'pop' sound.

(iii) Reaction with conc. sulphuric acid (Dehydration): Ethanol when heated with excess of concentrated sulphuric acid at 443 K , gets dehydrated to give ethene. ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{aq})\underset{\text{ Excess }}{\overset{{\mathrm{H}}_2{\mathrm{SO}}_4\text{ (conc.), }443\mathrm{K}}{\to }}{\mathrm{H}}_2\mathrm{C}={\mathrm{CH}}_2(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\ell )$ Ethanol Ethene Note: The concentrated sulphuric acid can be regarded as a dehydrating agent which removes water from ethanol.

Uses of ethanol

(i) Ethanol is present in alcoholic beverages such as beer, wine, whisky. (ii) As a solvent for paints, varnishes, dyes, cosmetics, perfumes, soaps and synthetic rubber, etc. (iii) Ethanol is used in cough syrups, digestive syrups and tonics. (iv) A mixture of $80\%$ petrol and $20\%$ alcohol is called power alcohol. It is used as fuel in cars and aeroplanes. (v) A mixture of ethanol and water has lower freezing point than water this mixture is known as antifreeze and is used in radiators of vehicles in cold countries and at hill stations. (vi) As an antiseptic to sterilize wounds and syringes in hospitals. (vii) For the manufacture of terylene and polythene. (viii) As a preservative for biological specimens. (ix) Ethyl alcohol is used as hypnotic (induces-sleep). (x) Sugarcane plants are the most efficient converter of sunlight energy into chemical energy. Molasses (dark coloured thick syrup left after the crystallization of sugar from sugarcane juice) gives alcohol by fermentation in presence of yeast (which contains the enzymes invertase and zymase)

How alcohol affects human health? Explanation: Intake of even a small quantity of pure ethanol (called absolute alcohol) can be lethal. Also longterm consumption of alcohol leads to many health problems. When large quantities of ethanol are consumed, it tends to slow metabolic processes and to depress the central nervous system. This results in lack of coordination, mental confusion, drowsiness, lowering of normal inhibitions and finally stupor (unconscious state of mind). Drinking of alcohol over a long period of time damages liver.

How misuse of ethanol is avoided in industries? Explanation: Denatured alcohol: Ethanol to which certain poisonous and nauseating substances like methyl alcohol, pyridine, etc. have been added is termed as denatured alcohol. To prevent the misuse of ethanol (Alcohol), industrial alcohol is coloured blue so that it can be recognised easily. Methanol is highly poisonous compound for human beings. Methanol when taken, even in small amount, can cause death. Methanol gets oxidised to methanal in the liver, which causes coagulation of protoplasm. Methanol also effects the optic nerve and causes blindness.

Ethanoic acid (acetic acid) ${\mathbf{CH}}_3\mathbf{COOH}$

Ethanoic acid is commonly called acetic acid and belongs to the homologous series of carboxylic acid. Its chemical formula is ${\mathrm{CH}}_3\mathrm{COOH}$. $5-8\%$ solution of acetic acid in water is called vinegar and is used for preservating foods like sausages, pickles, etc.

Physical properties (i) At ordinary temperature, ethanoic acid is a colourless liquid with a strong pungent smell and sour taste. (ii) Its boiling point is 391 K and its density at 273 K is 1.08 (heavier than water). (iii) It is miscible with water due to the formation of hydrogen bonds with water molecules. (iv) On cooling at 289.6 K , it turns in ice-like crystals, hence named as glacial acetic acid. (v) It dissolves sulphur, iodine and many other organic compounds. (vi) It dimerises when dissolved in benzene. Active

Aim: To compare the strength of dilute acetic acid and dilute hydrochloric acid. Materials required: Dilute acetic acid, dilute hydrochloric acid, litmus paper, universal indicator. Method Compare the pH of dilute acetic acid and dilute hydrochloric acid using both litmus paper and universal indicator.

Now answer Are both acids indicated by the litmus test? Does the universal indicator show them as equally strong acids?

Discussion Both dilute hydrochloric acid and dilute acetic acid turn blue litmus red but this action does not tell whether hydrochloric acid is a stronger acid than acetic acid.

But when we compare the pH of the aqueous solution of these two acids using universal indicator, we find that the pH of dilute acetic acid is around 4 (yellowish pink colour) while that of hydrochloric acid is around 2 (light pink colour). Therefore, acetic acid is a weaker acid than hydrochloric acid.

Conclusion Since HCl is completely ionized while acetic acid is only partly ionized, therefore, hydrochloric acid is a stronger acid than acetic acid.

Chemical properties

(i) Reaction with alcohols (Esterification reaction) Esters are sweet-smelling substances. These are used in making perfumes and as flavouring agents. Ethanoic acid reacts with ethanol in the presence of conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$ to form ethyl ethanoate which is an ester. $$\begin{gathered} {\mathrm{CH}}_3\mathrm{COOH}(\mathrm{aq})+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{aq})\stackrel{\text{ Conc. }{\mathrm{H}}_2{\mathrm{SO}}_4\text{.heat }}{\to }{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\ell ) \\ \text{ Ethanoic acid Ethanol }\text{ Ethyl ethanoate } \\ \text{ (Ester) } \end{gathered}$$

The reaction of carboxylic acid with an alcohol to form an ester is called "esterification reaction".

Note: Ester can be hydrolysed in the presence of an acid or a base to give back the parent carboxylic acid and the alcohol.

Example (a) Ethyl ethanoate on acid hydrolysis gives ethanoic acid and ethanol. ${\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\ell )⟶{\mathrm{CH}}_3\mathrm{COOH}(\mathrm{aq}.)+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{aq})$ (b) Hydrolysis of ester in the presence of base (alkali) is called "Saponification reactions". ${\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5(\mathrm{aq})+\mathrm{NaOH}(\mathrm{aq})⟶{\mathrm{CH}}_3\mathrm{COONa}(\mathrm{aq})+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{aq})$ Ethyl ethanoate Sodium Hydroxide Sodium ethanoate Ethanol Note: Alkaline hydrolysis of higher esters is used in the manufacture of soaps.

Active Chemistry

Aim: To study the esterification process using ethanol and acetic acid. Materials required: Ethanol, ethanoic acid, conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$, beaker, water.

Method (i) Take 2 ml of ethanol in a test tube. (ii) Add 2 ml of ethanoic acid (acetic acid) into it. (iii) Add few drops of conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$. (iv) Warm it in a beaker containing water.

Observation Pleasant fruity smelling compound (called ester) is formed.

Conclusion Acetic acid reacts with alcohol in presence of conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$ which act as a dehydrating agent to form ester.

(ii) Reaction with a base Like mineral acids, ethanoic acid reacts with a base such as sodium hydroxide to give a salt (sodium ethanoate or commonly called sodium acetate) and water (neutralisation reaction). $\mathrm{NaOH}(\mathrm{aq})+{\mathrm{CH}}_3\mathrm{COOH}(\mathrm{aq})⟶{\mathrm{CH}}_3\mathrm{COONa}(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\ell )$

(iii) Reaction with sodium carbonate and sodium hydrogen carbonate Ethanoic acid decomposes sodium hydrogen carbonate and sodium carbonate with a rapid evolution of carbon dioxide gas.

${\mathrm{Na}}_2{\mathrm{CO}}_3(\mathrm{aq})+2{\mathrm{CH}}_3\mathrm{COOH}(\mathrm{aq})⟶2{\mathrm{CH}}_3\mathrm{COONa}(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\ell )+{\mathrm{CO}}_2(\mathrm{g})$ Sodium carbonate Ethanoic acid Sodium ethanoate Note: Reactions of ethanoic acid with $\mathrm{NaOH},{\mathrm{NaHCO}}_3,{\mathrm{Na}}_2{\mathrm{CO}}_3$ and active metals show that the hydrogen present in the carboxyl $(-\mathrm{COOH})$ group is acidic in nature.

Active Chemistry

Aim: To study the reaction of carboxylic acid with sodium carbonate and sodium hydrogen carbonate. Materials required: ${\mathrm{Na}}_2{\mathrm{CO}}_3$, ethanoic acid, sodium hydrogen carbonate.

Method (i) Take 1 g of ${\mathrm{Na}}_2{\mathrm{CO}}_3$ and add 2 ml of ethanoic acid into it. (ii) A gas is formed. (iii) Pass the gas formed through lime water and note down the observation. (iv) Repeat the same procedure with sodium hydrogen carbonate and record observation.

Observation Brisk effervescence due to carbon dioxide gas formed which turns lime water milky.

Conclusion Acetic acid reacts with ${\mathrm{Na}}_2{\mathrm{CO}}_3$ and ${\mathrm{NaHCO}}_3$ to liberate ${\mathrm{CO}}_2$ gas.

Uses of ethanoic acid

• Ethanoic acid is used in the manufacture of various dyes, perfumes and rayon.
• It is used for making vinegar.
• Its $5\%$ solution is bactericidal (destroys bacteria).
• It is used for coagulation of the latex.

16.0Soaps and detergents

Detergent

A substance capable of removing dirt and grease from any fabric or body is called detergent. They can be of two types, soaps and synthetic detergents. The term detergent is usually used for synthetic detergent.

(i) Soap

A soap is the sodium or potassium salt of a long-chain fatty acids (carboxylic acid). Soap is basic in nature so, soap solution turns red litmus to blue

Active Chemistry

Aim: To demonstrate that oil dissolves in soap solution. Materials required: Water, test tubes, oil, soap solution.

Method (i) Take about 10 mL of water each in two test tubes. Add a drop of oil (cooking oil) to both the test tubes and label them as A and B. (ii) To test tube B, add a few drops of soap solution. (iii) Now shake both the test tubes vigorously for the same period of time. (iv) Leave the test tubes undisturbed for some time and observe. Does the oil layer separate out? In which test tube does this happen first?

Observation (i) Oil and water layers separate out immediately in test tube A to which soap was not added. (ii) Only one layer of emulsion of oil in water can be observed in test tube B to which soap was added, if left undisturbed.

Conclusion Soap dissolves in dirt (oily in nature) and helps in cleaning clothes.

Examples of soap are: (i) Sodium stearate $\left({\mathrm{C}}_{17}{\mathrm{H}}_{35}\mathrm{COONa}\right)$ (ii) Sodium palmitate $\left({\mathrm{C}}_{15}{\mathrm{H}}_{31}\mathrm{COONa}\right)$

Preparation of soap

The soap is prepared by heating animal fats or vegetable oils (olive oil, castor oil or palm oil) with sodium hydroxide or potassium hydroxide. The process of formation of soap by the hydrolysis of fat or oil with alkali is called saponification. Oil or Fat + Sodium hydroxide $\to$ Soap + Glycerol

Structure

A soap molecule contains two parts that interact differently with water, (i) one part is a long hydrocarbon chain which is non-polar in nature and thus does not dissolve in water. It is also called hydrophobic part, (ii) other part belongs to the -COONa group. It is polar and hydrophilic in nature. A soap molecule may be represented as

Soap molecule

(ii) Synthetic detergents

Synthetic detergent differ from soaps in chemical composition. Synthetic detergents are sodium salts of long chain sulphonic acid. They are more efficient than soaps. They are usually used to make shampoos and products for cleaning clothes.

Cleansing action of soaps and detergents

The molecules of soap are sodium or potassium salts of long chain carboxylic acids. The ionic end of soap dissolves in water while the carbon chain dissolves in oil. The soap molecules, thus form structures called micelles where one end of the molecules is towards the oil droplet while the ionic end faces outside. This forms an emulsion in water. The soap micelle thus helps in dissolving the dirt in water and we can wash out clothes clean.

Active Chemistry

Aim: To demonstrate that soaps produce foam with soft water but curdy white precipitate with hard water. Materials required: Distilled water, hard water, soap solution, test tubes.

Method

(i) Take about 10 mL of distilled water (or rainwater) and 10 mL of hard water (from a tube well or hand-pump) in separate test tubes. (ii) Add a couple of drops of soap solution to both. (iii) Shake the test tubes vigorously for an equal period of time and observe the amount of foam formed.

Now answer (i) In which test tube do you get more foam? (ii) In which test tube do you observe a white curdy precipitate?

Observation (i) Test tube containing distilled water has more foam. (ii) Test tube containing hard water has curdy white precipitate.

Discussion and conclusion(i) Soap easily forms lather with soft water. (ii) Hard water prevents lathering of soap by forming curdy precipitate called scum. $\mathrm{Na}-$ Soap $+{\mathrm{Ca}}^{2+}/{\mathrm{Mg}}^{2+}⟶[$ Soap-Ca/Mg] $+{\mathrm{Na}}^{+}$ white ppt. When soaps 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 called scum, before it can be used for the real purpose of washing soap. A large amount of soap is needed for washing clothes when the water is hard.

Active Chemistry

Aim: To demonstrate that hard water produces foam with detergent but only curdy white precipitate with soap. Materials required: Test tubes, hard water, soap solution, detergent solution.

Method (i) Take two test tubes with about 10 mL of hard water in each. (ii) Add five drops of soap solution to one and five drops of detergent solution to the other. (iii) Shake both the test tubes for the same period.

Now answer (i) Do both the test tubes have the same amount of foam? (ii) In which test tube is a curdy solid formed?

Observation Test tube in which detergent is present contain more amount of foam. Curdy solid is formed in the test tube containing soap.

Conclusion Detergents have better cleansing action than soap. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water.

Differences between soaps and synthetic detergents

17.0Basic terminology

• Catenation - The self-linking of atoms of an element to create chains and rings
• Isomer - Compounds that have the same molecular formula but are structurally different.
• Saturated hydrocarbon - Compounds containing carbon to carbon single bonds only.
• Unsaturated hydrogen - Compounds containing carbon to carbon double/triple bonds only.
• Homologous series - A collection of compounds with the same general formula that differ only in the carbon chain length.
• Aliphatic compounds - Open chain compounds, whether straight chain or branched chain.
• Oxidising agent - The substances which are capable of adding oxygen to other substances.
• Hydrophilic end - A water-attracting molecule.
• Hydrophobic end - Water-hating or repelling
• Micelle - Micelles are molecule made up of a hydrophobic tail & a hydrophilic head mainly used to remove dirt.

18.0Memory Map