CBSE Class 10 Science Carbon And Its Compounds Notes Set 03

CARBON & ITS COMPOUNDS

Carbon in nutshell

• Sixth most abundant element in the universe.
• Forms the largest number of compounds and is studied as a separate branch of chemistry known as organic chemistry.
• Atomic No = 6 ; Mass No. = 12
• Earth’s crust has only 0.02% carbon in the form of minerals and atmosphere has 0.03% of carbon dioxide.

Bonding in carbon

The covalent bond

We know that the reactivity of elements is explained as their tendency to attain a completely filled outer shell, that is, attain noble gas configuration. Elements forming ionic compounds achieve this by either gaining or losing electrons from the outermost shell. In the case of carbon,it has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration. If it were to gain or lose electrons –

• It could gain four electrons forming \( C^{4-} \) anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.
• It could lose four electrons forming \( C^{4+} \) cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.

Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. Not just carbon, but many other elements form molecules by sharing electrons in this manner. The shared electrons ‘belong’ to the outer shells of both the atoms and lead to both atoms attaining the noble gas configuration. This type of bonding is called covalent bonding.

Thus the bonds which are formed by the sharing of an electron pair between two same or different atoms are known as covalent bonds.

The no. of electrons shared show the covalency of that atom.

Properties of covalent compounds

• Covalently bonded molecules are seen to have strong bonds within the molecule, but intermolecular forces are small. This gives rise to the low melting and boiling points of these compounds. Exceptions : diamond & graphite.
• Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.
• These compounds are generally insoluble in water but some which are capable to form H-bond are soluble in water.

Allotropes of carbon

Diamond

• Each carbon in a diamond crystal is bonded to four other carbon atoms making a giant macromolecular array (lattice).
• It is the hardest naturally occuring substance.
• It is brittle (not malleable).
• Diamond is an insulator (non-conductor of electricity) but good thermal conductor (heat).
• It is insoluble in water due to its non polar nature.
• It has very high melting point of about \( 3500 \text{ } ^{\circ}C \) due to strong covalent bonds.

Uses of Diamond

• They are used in jewellery because of their ability to reflect and refract light.
• Black diamonds called carbonado are used in cutting glass and drilling rocks.
• Diamond has extraordinary sensitivity to heat rays and due to this reason, it is used for making high precision thermometers.
• Diamond has the ability to cut out harmful radiations and due to this reason, it is used for making protective windows for space probes.
• Diamond dies are used for drawing thin wires. Very thin tungsten wires of diameter of less than one sixth of the diameter of human hair have been drawn using diamond dies.

Graphite

• In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array.
• There are strong covalent bonds between carbon atoms in each layer. But, only weak forces exist between layers. This allows layers of carbon to slide over each other in graphite. That makes it slippery in nature.
• It is a dark grey solid having a metallic lustre.
• It has a soft greasy touch. It makes the paper grey.
• It density ranges from 1.5 to 2.3 \( g/cm^3 \).
• It is good conductor of heat and electricity.
• It is insoluble in ordinary solvents.
• Graphite when heated in the absence of air, melts at about \( 3730 \text{ } ^{\circ}C \)
• Graphite catches fire at \( 700 \text{ } ^{\circ}C \) in the presence of oxygen and forms carbon dioxide gas.
  \( C + O_2 \xrightarrow{700 \text{ } ^{\circ}C} CO_2 \)

Uses of Graphite

• As pencil lead : Graphite is mixed with clay or finely powdered sand. It is then moulded to form thin rods, which are called pencil lead. The hardness of pencil lead depends upon the amount of clay in it, i.e, more the clay, the harder is the pencil lead.
• As electrodes : Graphite is a good conductor of electricity. Moreover, it does not react with acids or alkalis. Thus, it is used for making electrodes for electrolytic cells, which are not affected by acids and alkalis.
• As a dry lubricant : Graphite powder suspended in oil is used as a lubricant in those part of machinery, where oil cannot be applied easily.
• As heat resistant crucibles : When graphite mixed with clay is moulded and baked, it forms heat resistant crucibles. The crucibles can withstand high temperatures on account of clay and are good conductors on account of graphite.
• In making light weight composite material : The graphite fibres are very strong. These fibres are used to reinforce plastic. The reinforced plastic with carbon fibres form a composite material. It is used for making (i) tennis rackets, (ii) fishing rods, (iii) bicycle frame, (iv) aircraft frames (v) parts of the spacecraft, and (vi) dish antennas.
• In making artificial diamonds : Graphite is heated to a temperature of \( 2000 \text{ } ^{\circ}C \) in the presence of some noble gas at a pressure of 100,000 times the atmospheric pressure. The high pressure and temperature breaks the carbon atoms in graphite, which rearrange themselves into diamond structure. Roughly 90% of the diamonds required for making tools are made artificially from graphite.

Fullerenes

• These are small molecules of carbon in which the giant structure is closed over into spheres of atoms (bucky balls) or tubes (sometimes called nano-tubes).
• The smallest fullerene has 60 carbon atoms arranged in pentagons and hexagons like a football. This is called Buckminster fullerene.
• The name ‘buckminster fullerene’ comes from the inventor of the geodesic dome (Richard Buckminster Fuller) which has a similiar structure to a fullerene.
• Fullerenes were first isolated from the soot of chimneys and extracted from solvents as red crystals.
• Fullerenes are insoluble in water but soluble in methyl benzene. They are non-conductors as the individual molecules are only held to each other by weak Vander Waal’s forces.
• They are not very reactive due to the stability of the graphite-like bonds, and are also fairly insoluble in many solvents.

Uses of fullerenes

• Fullerenes and their compounds may prove to be of great use as semiconductors, superconductors, lubricants, catalysts, electric wires and as fibres to reinforce plastic (to make plastic strong).
• Some of the compounds of fullerenes appear to be active against diseases like cancer and AIDS. This can lead to finding cure for cancer and AIDS.

Versatile nature of carbon

Catenation

Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. These compounds may have long chains of carbon, branched chains of carbon or even carbon atoms arranged in rings.

Tetravalency

Carbon atoms may be linked by single, double or triple bonds. Compounds of carbon, which are linked by only single bonds between the carbon atoms are called saturated compounds. Compounds of carbon having double or triple bonds between their carbon atoms are called unsaturated compounds. Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.

Stability of C–C bonds

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.

Small size of carbon

The bonds that carbon forms with most other elements are very strong making these compounds exceptionally stable. One reason for the formation of strong bonds by carbon is its small size. This enables the nucleus to hold on to the shared pairs of electrons strongly. The bonds formed by elements having larger atoms are much weaker.

Important note

Remember that the strength of bond decreases with increase in the size of atoms.

Vital force theory

Because of versatile nature of carbon, it forms many compounds. In eighteenth century all known compounds were divided into two categories.

Compound

• Organic compounds: Like urea, sugar, oils, fats dyes etc. which were isolated directly or indirectly from living organisms such as animals and plants.
• Inorganic compounds: Like marble, common salt, alum, \( CuSO_4 \) etc which were isolated from non-living sources such as rocks and minerals.

Vital force theory

This theory was given by Berzelius in 1815. According to him, organic compounds are 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

Berzilius's theory was disapproved by Friedrich Wohler in 1828 by preparing urea from ammonium cyanate (\( NH_4CNO \)) in laboratory.

Structure of urea: \( H_2N - \overset{||}{C} - NH_2 \)

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.

Classification of organic compounds

• Hydrocarbon
  • Aliphatic compound
    • Straight chain compounds e.g. \( CH_3–CH_2–CH_2–CH_3 \)
    • Branched chain compound e.g. \( \text{isobutane} \)
    • Saturated (Alkanes)
    • Unsaturated (Alkenes, Alkyne)
  • Cyclic
    • Heterocyclic [Contain an atom other than C in the ring] e.g. Furan
    • Carbocyclic [Only C atoms are present in the ring] e.g. cyclopropane
      • Saturated
      • Unsaturated
  • Aromatic compound
    • Unsaturated compound
    • Always cyclic
    • Planar and follow Huckel's rule
    • Conjugation is present
    • Delocalisation of electron is present

Saturated and unsaturated hydrocarbon

On the basis of bonding carbon compounds can be classified in two categories.

• Saturated hydrocarbons
• Unsaturated hydrocarbons

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 \( C_nH_{2n+2} \) where 'n' is the number of carbon atoms.

General formula of saturated hydrocarbon (\( C_nH_{2n+2} \))

Nomenclature of carbon compounds

There are two ways to name carbon compounds :

• 1. Trivial system
• 2. IUPAC system

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.

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

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.

C-1 : Meth
C-2 : Eth
C-3 : Prop
C-4 : But
C-5 : Pent
C-6 : Hex
C-7 : Hept
C-8 : Oct
C-9 : Non
C-10 : Dec

Suffix
The word root is linked to the suffix which may be primary or secondary or both.

Primary suffix : It indicates the nature of linkage in the carbon atoms. For example if the carbon atom is linked by single covalent bond (C–C), the primary suffix - ane is used. Similarly for a double bond between two carbon atoms (C=C), –ene is used, the suffix –yne is used for a triple bond between two carbon atoms (\( C \equiv C \)).

Secondary suffix : It indicates the presence of functional group in the organic compound. A few important secondary suffixes are listed below,

• Alcohols (– OH) : –ol
• Aldehydes (– CHO) : –al
• Ketones (>C=O) : –one
• Carboxylic acids (–COOH) : –oic acid

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:

• –F : Fluoro
• –Cl : Chloro
• –Br : Bromo
• –I : Iodo
• –R : Alkyl

Thus a complete IUPAC name of an organic compound may be represented as
\[ \text{Prefix} + \text{Word root} + \text{Primary suffix} + \text{Secondary suffix} \]

Isomerism

The existence of an organic compound with the same molecular formula and different structural formulae is called isomerism. The isomerism can be of various types depending on the type of variation in the structures of the molecules.

(i) Chain isomerism: The phenomenon in which two or more organic compounds have the same molecular formula but differ in the arrangement of carbon atoms in the longest chain. All types of hydrocarbons (alkanes, alkenes and alkynes) with more than 3 carbon atoms exhibit this type of isomerism. The molecule in which all carbon atoms are arranged in a straight chain is called n-isomer. The molecule in which there is a branched chain arrangement in the molecule a prefix iso or neo is used depending on the type of branching.

Ex. 1. Pentane
\( H_3C – CH_2 – CH_2 – CH_2 – CH_3 \) (n–Pentane)
\( H_3C – CH_2 – CH(CH_3) – CH_3 \) (Isopentane)
\( (CH_3)_4C \) (Neopentane)

2. Pentene
\( H_2C = CH – CH_2 – CH_2 – CH_3 \) (n – Pentene)
\( H_2C = CH – CH(CH_3) – CH_3 \) (Isopentene)

3. Pentyne
\( HC \equiv C – CH_2 – CH_2 – CH_3 \) (n – Pentyne)
\( HC \equiv C – CH(CH_3) – CH_3 \) (Isopentyne)

(ii) Position isomerism: The phenomenon in which the hydrocarbon has the same chain but differs in the position of multiple bonds or constituents on the parent chain is called position isomerism. This is exhibited by unsaturated hydrocarbons (alkenes and alkynes) with more than 3 carbon atoms (or) saturated hydrocarbons with substituents as side chain.

Ex. (i) Butene (Molecular formula - \( C_4H_8 \))
\( H_3C – CH_2 – CH = CH_2 \) (1 -Butene)
\( H_3C – CH = CH – CH_3 \) (2 -Butene)

(ii) Pentyne (Molecular formula - \( C_5H_8 \))
\( CH_3 – CH_2 – CH_2 – C \equiv CH \) (1- Pentyne)
\( H_3C – CH_2 – C \equiv C – CH_3 \) (2 -Pentyne)

(iii) 5-carbon chain with methyl substituent.
\( H_3C – CH_2 – CH(CH_3) – CH_2 – CH_3 \) (3 -Methylpentane)
\( H_3C – CH(CH_3) – CH_2 – CH_2 – CH_3 \) (2 -Methylpentane)

(iii) Functional isomerism: Compounds with the same molecular formula but different functional groups are called functional isomers and this phenomenon is called functional isomerism.

Ex. Two functional isomers are possible with the molecular formulae \( C_2H_6O \). One isomer with an alcoholic functional group (R—OH) and the other with an ether linkage or functional group (R—O—R)

(a) Molecular formulae: \( C_2H_6O \)
\( CH_3 – CH_2 – OH \) (Ethyl alcohol, IUPAC : Ethanol)
\( CH_3 – O – CH_3 \) (Dimethyl ether, IUPAC : Methoxy methane)

(b) Molecular formulae: \( C_3H_6O \)
\( H_3C — CH_2 — CHO \) (Propanaldehyde, IUPAC : Propanal)
\( H_3C — CO — CH_3 \) (Acetone, IUPAC : Propanone)

Two functional isomers namely propionaldehyde and acetone are possible for the molecular formulae \( C_3H_6O \), one with aldehydic functional group (R — C — H) and the other with ketone functional group (R — C — R).

(iv) Metamerism: The isomers in which there is unequal distribution of carbon chain or atoms on either side of the functional group are called metamers and this phenomenon is termed 'metamerism'. Thus metamers differ in the size of an alkyl group or chain on either side of the functional group. This is exhibited by compounds having divalent functional groups.

Example: Molecular formula: \( C_4H_{10}O \)
\( H_3C — CH_2 — O — CH_2 — CH_3 \) (Diethyl ether, IUPAC : Ethoxyethane)
\( H_3C — O — CH_2 — CH_2 — CH_3 \) (Methyl propyl ether, IUPAC : Methoxypropane)

Chemical properties of carbon compounds

Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the release of heat and light. Most carbon compounds also release a large amount of heat and light on burning.

(i) \( C + O_2 \to CO_2 + \text{heat and light} \)

(ii) \( CH_4 + O_2 \to CO_2 + H_2O + \text{heat and light} \)

(iii) \( CH_3CH_2OH + O_2 \to CO_2 + H_2O + \text{heat and light} \)

Saturated hydrocarbons will generally give a clean flame while unsaturated carbon compounds will give a yellow flame with lots of black smoke. However, limiting the supply of air results in incomplete combustion of even saturated hydrocarbons giving a sooty 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 observe the bottoms of cooking vessels getting blackened, it means that the air holes are blocked and fuel is getting wasted. Fuels such as coal and petroleum have some amount of nitrogen and sulphur in them. Their combustion results in the formation of oxides of sulphur and nitrogen which are major pollutants in the environment. This is because a flame is only produced when gaseous substances burn. When wood or charcoal is ignited, the volatile substances present vapourise and burn with a flame in the beginning. A luminous flame is seen when the atoms of the gaseous substance are heated and start to glow. The colour produced by each element is a characteristic property of that element. Carbon compounds can be easily oxidised on combustion. In addition to this complete oxidation, we have reactions in which alcohols are converted to carboxylic acids.

Types of fuels

• Solid fuels- wood, coal, coke, charcoal etc.
• Liquid fuels-kerosene, petrol, diesel etc.
• Gaseous fuels- LPG, CNG, coal gas, water gas etc.

Combustion

• A chemical process in which a substance reacts with oxygen to give heat is called combustion.
• The substance that undergoes combustion is called to be a combustible. It is also called fuel. E.g. petrol, kerosene.
• The fuel may be solid, liquid or gas. For combustion air is necessary.
• The lowest temperature at which a substance catches fire is called ignition temperature.
• A combustible substance cannot catch fire or burn as long as its temperature is lower than its ignition temperature.
• The substances which have very low ignition temperature and can easily catch fire with a flame are inflammable substances. E.g. petrol, alcohol, LPG (Liquified petroleum gas) etc.

Types of combustion

• Combustion in which gas burns rapidly and produces light and heat is known as rapid combustion. E.g. burning of gas stove in kitchen.
• The type of combustion in which a material suddenly bursts in the flame without application of any external source is called spontaneous combustion. E.g. spontaneous combustion of coal dust.
• Combustion in which a sudden reaction takes place with the evolution of heat, light and sound is known as explosion e.g. ignition of fire crackers.

Flame

A flame (from Latin flamma) is the visible (light-emitting), gaseous part of a fire. It is caused by a highly exothermic reaction (for example, combustion, a self-sustaining oxidation reaction) taking place in a thin zone. If a fire is hot enough to ionize the gaseous components, it can become a plasma. Colour and temperature of a flame are dependent on the type of fuel involved in the combustion, as, for example, when a lighter is held to a candle. The applied heat causes the fuel molecules in the candle wax to vaporize. In this state they can then readily react with oxygen in the air, which gives off enough heat in the subsequent exothermic reaction to vaporize yet more fuel, thus sustaining a consistent flame.

Flame zones

• Inner most zone : It is cooler than outer zone and it is dark.
• Middle zone : It is the largest zone of candle flame. This zone gives soot and smoke.
• Outer most zone : This zone of the flame is thin and blue in colour. This is the hottest zone of the flame. The temperature of this zone is maximum around 1800°C.

Some important carbon compounds

Ethanol
Ethanol is a liquid at room temperature. It is commonly called alcohol and is the active ingredient of all alcoholic drinks. In addition, because it is a good solvent, it is also used in medicines such as tincture iodine, cough syrups, and many tonics. Ethanol is also soluble in water in all proportions. Consumption of small quantities of dilute ethanol causes drunkenness. Even though this practice is condemned, it is a socially widespread practice. However, intake of even a small quantity of pure ethanol (called absolute alcohol) can be lethal. Also, long-term consumption of alcohol leads to many health problems.

Reaction of Ethanol

(i) Reaction with sodium -
\( 2Na + 2CH_3CH_2OH \)
\( \implies \) \( 2CH_3CH_2O–Na^+ + H_2 \) (Sodium ethoxide)
Alcohols react with sodium leading to the evolution of hydrogen. With ethanol, the other product is sodium ethoxide.

(ii) Reaction to give unsaturated hydrocarbon: Heating ethanol at 443 K with excess concentrated sulphuric acid results in the dehydration of ethanol to give ethene. The concentrated sulphuric acid can be regarded as a dehydrating agent which removes water from ethanol.
\( CH_3 – CH_2OH \xrightarrow[\text{Hot conc. } H_2SO_4]{} CH_2 = CH_2 + H_2O \)

Effect of alcohol on living beings
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 the normal inhibitions, and finally stupour. The individual may feel relaxed but does not realise that his sense of judgement, sense of timing, and muscular coordination have been seriously impaired. Unlike ethanol, intake of methanol in very small quantities can cause death. Methanol is oxidised to methanal in the liver. Methanal reacts rapidly with the components of cells. It causes the protoplasm to get coagulated, in much the same way an egg is coagulated by cooking. Methanol also affects the optic nerve, causing blindness. Ethanol is an important industrial solvent. To prevent the misuse of ethanol produced for industrial use, it is made unfit for drinking by adding poisonous substances like methanol to it. Dyes are also added to colour the alcohol blue so that it can be identified easily. This is called denatured alcohol.

Ethanoic acid
Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids. 5-8% solution of acetic acid in water is called vinegar and is used widely as a preservative in pickles. The melting point of pure ethanoic acid is 290 K and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid. The group of organic compounds called carboxylic acids are obviously characterised by a special acidity. However, unlike mineral acids like HCl, which are completely ionised, carboxylic acids are weak acids.

Reactions of ethanoic acid

Esterification reaction: Esters are most commonly formed by reaction of an acid and an alcohol. Ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst to give an ester.
\( CH_3-COOH + CH_3-CH_2-OH \xrightarrow{\text{Acid}} CH_3-C(=O)-O-CH_2-CH_3 \) (Ester)
Esters are sweet-smelling substances. These are used in making perfumes and as flavouring agents. Esters react in the presence of an acid or a base to give back the alcohol and carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.
\( CH_3COOC_2H_5 \xrightarrow{NaOH} C_2H_5OH + CH_3COOH \)

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:
\( NaOH + CH_3COOH \)
\( \implies \) \( CH_3COONa + H_2O \)

Reaction with carbonates and hydrogencarbonates: Ethanoic acid reacts with carbonates and hydrogencarbonates to give rise to a salt, carbon dioxide and water. The salt produced is commonly called sodium acetate.
\( 2CH_3COOH + Na_2CO_3 \)
\( \implies \) \( 2CH_3COONa + H_2O + CO_2 \)
\( CH_3COOH + NaHCO_3 \)
\( \implies \) \( CH_3COONa + H_2O + CO_2 \)

Soaps and detergents

Commercially used soaps are sodium salts of fatty acid, such as oleic acid (\( C_{17}H_{33}COOH \)), stearic acid and palmitic acid (\( C_{15}H_{31}COOH \)) which are plant or animal origin. Soap is made from oil or fat which are esters of fatty acids or glycerols as shown in the following equation.
\( C_{15}H_{31}-COOCH_2 \)
\( C_{15}H_{31}-COOCH + 3NaOH \)
\( \implies \) \( CH_2OH – CHOH – CH_2OH + 3C_{15}H_{31}COONa \) (Soap)

The above reaction is known as saponification. The soap from the solution is separated by the addition of common salt.

The washing action of soap

Synthetic detergents have a structure similar to that of soap. The water attracting part in detergents is sulphonate (\( –SO_3Na \)) group. Synthetic detergents can lather well even with hard water as unlike soaps, they do not from insoluble calcium or magnesium salts with hard water. The essential constituents of washing powders are as follows.

• Sodium sulphate and sodium silicate -to keep the washing powder dry.
• Sodium tripolyphosphate or sodium carbonate - to maintain alkalnity which helps in removing dirt.
• Carboxymethyl cellulose (CMC) to keep the dirt suspend in water.
• Detergents - about 15-30% by mass.
• Mild bleaching agent such as sodium perborate -to produce whiteness.

Vegetable oils generally have long unsaturated ‘C’ chains while animal fats have saturated ‘C’ chains. Synthetic detergents containing branched hydrocarbons are not biodegradable, i.e. they are not decomposed by bacteria present in water. So these are pollutants for riverwater.

Important points to ponder

• Catalytic hydrogenation is not shown by saturated hydrocarbon.
• Hydrogenation reduces the number of unsaturated ‘C’ chains which produce rancidity in foods (due to the production of carboxylic acids & aldehydes) and hence slows down the development of rancidity.
• Unsaturated carbon compounds disappears orange colour of bromine water.
• Saturated hydrocarbons are less reactive than unsaturated hydrocarbons.