157

CHAPTER 12

CARBON AND ITS COMPOUNDS

(A) CARBON

After studying this chapter you

-

CARBON - The Chemical Basis for Life

Life itself is based upon this remarkable chemistry of carbon.

Carbon

Chemistry.

158

What is Carbon?

6C12

ACTIVITY 12 A.1

1: Heat a little sugar taken in a spatula. You will observe a black residue.

This shows the presence of carbon in sugar.

2: You might have observed chapati or roti getting charred when over

heated, What might be the reason for this?

3: When a small quantity of milk is continuously boiled, it will get charred.

But when water is boiled it will not get charred, rather it just evaporates, Why?

4: Does salt get charred when heated like sugar? Try this activity and

draw your own inference.

5: When you heat sand, it does not get charred. Why?

6: Also many substances like calcium carbonate (CaCO3) which

contain carbon do not get charred when heating, why? Give reasons.

Allotropes of Carbon

Recall the differences between diamond and graphite.

Why are the physical properties of diamond and graphite so different?

The reason is the difference in the arrangement of carbon atoms in

diamond and graphite.

Diamond and Graphite are the two allotropes of carbon which are

chemically identical and differ markedly in their physical properties.

159

Do you know

A new allotrope of carbon that

was discovered in 1985, contains

60 carbon atoms C60

.This form has

been named Buckminsterfullerene

after the architect Buckminster

Fuller, who designed domed

structures that also resemble C60

molecule. (C60

molecules are often

called buckyballs)

Their discoverers – Robert Curl, Harold Kroto and Richard Smalley –

received the Nobel Prize in Chemistry in 1996.

Know this

The carbon can form alloys with iron, of which the most common is carbon

steel. Graphite is combined with clays to form the ‘lead’ used in pencils used

for writing and drawing. It is also used as a lubricant and a pigment, as a

moulding material in glass manufacture, in electrodes for dry batteries and

in electroplating and electroforming, in brushes for electric motors and as a

neutron moderator in nuclear reactors .

r

Carbon forms an exceptionally large number of compounds because

of its unique characteristics like catenation, tetravalency and

isomerism .

Catenation

C CC

C

C C

C

C

C C

C

CC

Do you know ?

Why aren’t there millions of compounds of B, Si, Ge, Sn, N, P, O,

S, Se and Te ?

Like carbon, the above elements also catenate and compound with B-B,

Si-Si, Ge-Ge, Sn-Sn, N-N, P-P, O-O, S-S, Se-Se and Te-Te bonds are known.

These compounds are unstable and very reactive and do not last long

whereas many compounds with C-C bonds exist for centuries under ordi-

nary conditions. The unusual stability of compounds with chains of carbon

atoms is a result of the great strength of the C-C bond . The C-C bond is the

second strongest single bond between like atoms after the H-H bond.

161

Tetravalent Character

Observe : the methane

molecule is three dimensional with H-C-H

bond angle 1090281 by convention the

methane molecule is represented in two

dimension with H-C-H bond angle 900

6

1s2 2x

1z

1s2 1x

1z1

Carbon is tetravalent

P=6P=6

H

H

HH H

H

H

H

C

162

Tetravalency of Carbon

ii

iii

C C

H H

H H

C C C

HHH

H

H

HH

H

H

H

C

H H

H

H

H

H

HH

H

H

H

HC

C C

C

CC

1. ISOMERISM

163

C C C

HHH

H

H

HH

H

H

H

C

Note

isomers why?

The simplest hydrocarbons methane (CH4), ethane (CH

3CH

3), and propane

(CH3CH

2CH

3) have no isomers, as there is no scope for branching of C-C chain

Try this

5H12

Historical Importance

Vital force theory

164

4 4 2 2

Friedrich Wohler -1800– 1882 :

Know this

2

2 3

165

Difference between organic and Inorganic Compounds

SL.

No.

Property Organic

compounds

Inorganic compounds

166

What is Organic Chemistry ?

Organic chemistry, is the study of carbon compounds.

“Let us learn to dream not of personal desire

But of Universal truth to be shared with others”

Know this

167

Exercise

I. Answer the following

II. Fill in the blanks

168

III. Choose the most appropriate answer from the four alternative

given

2 2 2

169

IV. Answer the following questions

V. Match the following

A B

(B) HYDROCARBONS

After studying this chapter you

Hydrocarbons

171

Do you know?

The orange colour of carrots, the yellow colour of butter and yolk of egg,

the red colour of tomatoes, the wax coating on apples which increases the

shelf life of apples and the cooking gas are all Hydrocarbons.

Activity 12 B.1

Make a list hydrocarbon products used in your daily life.

So what are these Hydrocarbons?

Hydrocarbons are the simplest binary organic compounds

containing carbon and hydrogen only.

functional group

172

Know this

Activity 12 B.2

Take a candle and observe the smell by holding it near your nose.

Lastly put out the candle and notice the smell.

You will wonder to know that the smell is found only when the

candle is put out not in the previous cases. It clearly indicates that

the wax of the candle which is hydrocarbon has no smell either in the

solid or in the liquid state but has characteristic odour only in vapour

state. Hydrocarbons usually do not have any characteristic

odour but some higher hydrocarbons in their vapour state have

characteristic smell.

173

Sources of Hydrocarbons

Aliphatic Hydrocarbons

Know this

174

Aliphatic hydrocarbons

Saturated Hydrocarbon Unsaturated Hydrocarbon

CnH

2n+2

An alkane An alkene An alkyne

CnH

2nC

nH

2n-2

C C C CC C

Saturated Hydrocarbons :

Know this

175

Know this

Name Methane Ethane Propane Butane pentane

1 2 3 4 5

4 6 8 12

CH4

C2H6

C3H8

C4H C

5H12

nH

C6H

14

CH4 2

Nomenclature of Alkanes

176

Number of Carbon atoms

1

2

3

4

5

6

7

8

9

Dec-

177

Activity 12 B.3

Follow the examples given above and write the structural formulae for the other six alkanes, containing carbon atoms 5 to 10. Use the formula C

nH

2n+2.

Using paper balls, clay balls and toothpicks, construct the structures of following hydrocarbons.

Take two methane molecules already prepared. Construct ethane molecule.

Tabulate the changes that you made.

Class of Compound General Name

C C

-ene

Methane (CH4) ‘Marsh gas’

Marsh gas

Methane

178

Preparation of Methane

By heating fused sodium acetate with soda lime:

CH3 2 3 4

Think

179

Physical Properties

Chemical Properties

Combustibility

1. Complete Combustion :

CH4 2

2. Incomplete Combustion :

2CH4 2 2

Do you know

What is carbon monoxide?

Carbon monoxide is a very poisonous gas. It can not be seen or smelt.

a room without anyone knowing. Every year, people die from carbon monoxide

poisoning.

Why is carbon monoxide poisonous?

Carbon monoxide acts as a poison by combining with haemoglobin in the

blood. Haemoglobin normally reacts with oxygen from the air and transports

the oxygen to the parts of the body which need it. Carbon monoxide is much

more reactive with haemoglobin than oxygen is. It combines to form carboxy

haemoglobin a stable compound with haemoglobin, preventing the transport

of oxygen around the body. The person dies of suffocation from inside.

Substitution Reaction:

CH4 2 3

181

CH4 2 3

CH3 2 2 2

CH2 2 2 3

3 2 4

Homologous Series

2

4 2H6 5

H12 6

H14

CH4

CH2

C2H6

C5H12

CH2

C6H14

182

Activity 12 B. 4

Complete the table below

1 4 4 CH4

2 6 7 C2H6

3

4

5

Unsaturated hydrocarbons

Alkenes :

nH2n

2H4ethene

Activity 12 B. 5

Take the ethane model you prepared. Re organize this molecule into ethene

and answer the following questions.

What is the chemical structure of this new compound?

Is this still an organic hydrocarbon?

What have you done to the ethane molecule?

If the chemical formula for the compound has changed, is it still ethane?

183

Naming Alkenes

Observe the following examples.

Name

No. C

atoms

(n)

No. H

atoms

(2 n)

Moleculer

FormulaStructural formula

2 C2H4

3 C3H6

CCC

H

HH

H

HH

4 C4H8 C

H

H

5 C5H CCC C C

HH H

HH

HH

H

H H

2

Compare the structure of ethene with that of ethane.

CC

H

H

H

H H

H

184

-

Alkynes

alkynes.

nH2n-2

Naming Alkynes :

2H2

Know this

185

Name

No. C

atoms

(n)

No. H

atoms

(2xn)-2

Molecular

FormulaStructural formula

2 C2H2

3 C3H4

4 C4H6

5 C5H8

2

Cycloalkanes

nH2n

C3 H

6

H H

H

HH

HC CC

C4 H

8

H

H

H H

H

H

H H

C

C C

C

C5 H

10

H H

H

H

H

H H

H

H

HC

C C

CC

C6 H

12

H H

H

H

H

H

HH

H

H

H

HC

C C

C

CC

186

Compare Alkanes, Alkenes, Alkynes, and Cycloalkanes

4

2H6 2

H4 2

H2

3H8 3

H6 3

H4 3

H6

4H

4H8 4

H6 4

H8

5H12 5

H5H8 5

H

Think

Aromatic hydrocarbons

C6H

6

Structure of Benzene:

Know this

187

Other Aromatic Hydrocarbons

Examples:

C6 H

5 CH

3

H

H

H

H

H

C

C C

C

C CH3

C CH3

H H

H

H

H

C

C

C

C

H

H

H

C

C C

C

CC

Note

The name AROMA is a misnomer in the case of Aromatic Hydrocarbons.

do not have any odour or some have nauseating odour.

Eg; Naphthalene - smell of moth ball. Benzene and Toluene - smell of

Kerosene and so on. Camphor - having good smell but does not contain

aromatic ring.

Uses of Aromatic Compounds

1. Benzene is used

188

2. Toluene is used

3. Napthalene is used

Know this

189

(C) FUNCTIONAL GROUPS

3

2H5

3H7

‘group of atoms –OH’

“Functional groups are the sites where reactions occur in

organic molecules” atoms

molecules

chemical reactions

R X]

R X

Alcohols

Carboxylic acids

Aldehydes

2

Amines2

Know this

1

IUPAC Nomenclature of class of Organic Compounds

Alcohols

-

3CH

2CH

2

191

Group of

organic

compoundsGeneral

Formula

Functional

Group

IUPAC

name of

family

(word root

olOH

H H

H

H H

C C

2H5

-C-Hal

H

H

H

H O

C C

3

oic

acid

OH

H

H

H O

C C

3

Hamine

H

H

N

H H

H

H H

C C

192

Activity 12 C.1

of above mentioned class of compounds

Poly functional compounds

2

H2N-CH

2-COOH

Organic compounds having more than one functional group are called polyfunctional compounds.

OH

COOH

Know this

193

Know this

Molecular formula of Sodium hydroxide is NaOH-(contains one

hydroxyl ion).

Molecular formula of Ammonium hydroxide is NH4OH --- one hydroxyl

ion.

Molecular formula of Calcium Hydroxide is Ca(OH)2 --- two hydroxyl

ions.

In all the above examples, hydroxyl ions (OH- ions) are common, number

may change but hydroxyl ions present in the above compounds give

the properties of a base to the compound in which they are present.

How many hydroxyl ions are there in Aluminium hydroxide? Al(OH)3.

You have come across alcohols like Methyl alcohol- molecular formula

CH3OH and Ethyl alcohol- molecular formula C

2H

5OH in your previous

classes.

Though these compounds contain hydroxyl group they are not called

hydroxides but called alcohols. Why?

CH3OH is not called methyl hydroxide but called methyl alcohol

On the other hand compounds containing hydroxide ions are not called

alcohols but called hydroxides.

NaOH is not called sodium alcohol but called Sodium hydroxide

So how are these hydroxyl ions and hydroxyl groups different from one

another?

In the case of organic compounds like alcohols hydroxyl group is just a

group of atoms -OH which is cavalently bonded to a carbon atom. The

-OH is a functional group occurs in several classes of organic compounds

including alcohols, phenols and carboxylic acids. You should not

confuse it with the hydroxide ion, -OH of inorganic hydroxides which

is a diatomic ion.

194

(D) HYDROGENATION OF OILS

Activity 12 D.1

Take 5 used medicine bottles and clean them thoroughly. Allow them to dry.

In each of the bottle take one spoon of molten Vanaspathi, coconut oil, palm oil,

water to each of the bottle. Keep the bottles exposed to air and sunlight for about

a week. Smell the bottles. In which of the bottle can you get the foul smell of

rancid Fat or Oil more?

C

H

H

H H H H H H H H H H H H H H H H H

H H H H H H H H H H H H H H H H H

C C C C C C C C C C C C C C C C C C

C

C

C

H

H

H

H

H

C17

H35

COOH

195

How are fats different from oils?

shelf life

hydrogenation

196

Think

Recall

acids present in the oils or fats by adding sodium or potassium

hydroxide.

2

(Unsaturated fatty acids)

hydroxide in ‘mg’ (milligrams) required to neutralize the fatty acid present

in one gram of oil or fat. In the manufacture of soaps it helps to prepare

soap which does not contain excess of potassium hydroxide.

Know this

197

Know this

fatty acids and various long chain alcohols . It is used in cosmetics, preparation

of dripless candles and skin ointments.

Everything that looks like oil is not really oil. Hydrocarbon oils are not oils

as they do not contain fatty acids. Glycerol which is used in medicines and

cosmetics is obtained by the hydrolysis of oils.

Awarness

Next time You enter the grocery shop observe the label ‘PUFA’ on cooking

oil packets.

PUFA : Poly unsaturated fatty acids

What are PUFA’s?

Poly unsaturated fatty acids contain unsaturated hydrocarbon chain.

Because of the presence of double bonds the PUFA reacts. This makes

them more reactive than saturated fatty acids and more susceptible to being

attacked and damaged by free radicals. Free radical damage can cause

accelerated aging, hormone imbalance, cancer, and immune disorders.

198

Exercise

Chapter 12 (B),(C) and (D)

I. Classify the following into saturated and unsaturated

hydrocarbons.

II. Give reasons for the following

III. Answer the following

199

2 2

3 3

IV. Choose the correct answer from the four alternatives given

below

is

5H

5H

5H

5H

2

nH2n n

H4n

nH

nH

V. Match the following.

A B