Carbon and its Compounds
CHEMICAL PROPERTIES OF CARBON COMPOUNDS
CHEMICAL PROPERTIES OF CARBON COMPOUNDS
Combustion
Carbon, in all its allotropic forms, burns in oxygen to give
carbon dioxide along with the release of 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
Why do substances burn with or without
a flame?
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.
Oxidation
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 –
Addition Reactions:
Unsaturated hydrocarbons add hydrogen in the
presence of catalysts such as palladium or nickel to
give saturated hydrocarbons. This reaction is called
hydrogenation.
This reaction is commonly used in the
hydrogenation of vegetable oils using a nickel
catalyst.
Catalysts
Catalysts are substances that
cause a reaction to occur or
proceed at a different rate
without the reaction itself being
affected.
e.g. Pt, Pd, Ni, Fe, Cu are most
commonly used catalyst.
Substitution Reactions:
In a substitution reaction one type of atom or a
group of atoms takes the place of another.
Saturated
hydrocarbons
generally
undergo
substitution reactions.
e.g. Chlorine can replace the hydrogen atoms one by
one in the presence of sunlight
CH4 + Cl2 → CH3Cl + HCl (in the presence of sunlight)
QUESTIONS FOR PRACTICE:
1.What do you mean by hydrogenation ? Explain with
suitable example.
2.Why is the conversion of ethanol to ethanoic acid an
oxidation reaction?
3. What is the role of a catalyst in a chemical reaction ?
4. A mixture of oxygen and ethyne is burnt for welding. Can
you tell why a mixture of ethyne and air is not used?
SOME IMPORTANT CARBON COMPOUNDS
ETHANOL
ETHANOIC ACID
ETHANOL
Production:
1.Ethanol can be produced by the
fermentation of sugars and starches from
many different sources
2. It can be synthesized by hydration of
alkene (ethene) in the presence of suitable
catalyst (conc. H2SO4 /P2O5/Al2O3).
Properties of Ethanol
1.Ethanol is a liquid at room temperature .
2.Ethanol is commonly called alcohol and
is the active ingredient of all alcoholic
drinks.
3.Ethanol is also soluble in water in all
proportions.
4. In addition, because it is a good solvent, it
is also used in medicines such as tincture
iodine, cough syrups, and many tonics.
Reactions of Ethanol
(i) Reaction with sodium –
This reaction shows the acidic nature of ethanol
(ii) Reaction to give unsaturated hydrocarbon:
Dehydration
The concentrated sulphuric acid can be regarded as a
dehydrating agent which removes water from
ethanol.
How do alcohols affect living beings?
Ethanol:
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.
Methanol:
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.
Denatured alcohol:
To prevent the misuse of ethanol
produced for industrial use, it is made
unfit for drinking by adding poisonous
substances like methanol to it. This is
called denatured alcohol. Dyes are also
added to colour the alcohol blue so that
it can be identified easily.
Ethanoic Acid
CH3COOH
→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.
Reactions of ethanoic acid:
1. Reaction with a base
It react with a base to give salt and water
NaOH + CH3COOH → CH3COONa + H2O
2.Reaction with carbonates and
hydrogen carbonates:
Ethanoic acid reacts with carbonates and
hydrogen carbonates to give rise to a salt,
carbon dioxide and water.
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2
3. Esterification reaction:
Ethanoic acid reacts with absolute ethanol in
the presence of an acid catalyst to give an
ester,it is called as esterification reaction.
Esters are sweet-smelling substances. These are used
in making perfumes and as flavouring agents.
Saponification
Esters react in the presence of an acid or a
base to give back the alcohol and carboxylic
acid or its salt. This reaction is known as
saponification because it is used in the
preparation of soap.
CH3COOC2H5 + NaOH → CH3COONa + C2H5OH
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
our clothes clean.
• Natural soaps are prepared by boiling lard or
other animal fat with NaOH, in a reaction
called saponification (Latin, sapo, soap).
O
O CH2 OCR
saponification
+ 3 N aOH
RCOCH
O
CH2 OCR
CH2 OH
A triglyceride
(a triester of glycerol)
CHOH
+
CH2 OH
1,2,3-Propanetriol
(Glycerol; Glycerin)
O
+
3 RCO N a
Sodium soaps
-
+
COO Na
Mechanism Of The Cleaning Action Of Soaps.
• Their long hydrophobic hydrocarbon chains are
insoluble in water and tend to cluster in such a
way as to minimize their contact with water.
• Their polar hydrophilic carboxylate groups, on
the other hand, tend to remain in contact with
the surrounding water molecules.
• Driven by these two forces, soap molecules
spontaneously cluster into micelles.
– A soap micelle: nonpolar (hydrophobic) hydrocarbon
chains cluster in the inside and polar (hydrophilic)
carboxylate groups lie on the surface.
micelle: A spherical arrangement of organic
molecules in water clustered so that their
hydrophobic parts are buried inside the sphere
and their hydrophilic parts are on the surface of
the sphere and in contact with water.
when soap is
mixed with waterinsoluble grease,
oil, and fats, the
nonpolar parts of
the soap micelles
“dissolve” these
nonpolar
dirt
molecules
and
they are carried
away in the polar
wash water.
• Soaps form water-insoluble salts when used in
water containing Ca(II), Mg(II), and Fe(III) ions
(hard water).
-
2 CH3 ( CH2 ) 1 4 COO Na
+
+
Ca
2+
A sodium soap
(soluble in water as micelles)
-
[ CH3 ( CH2 ) 1 4 COO ] 2 Ca
Calcium salt of a fatty acid
(insoluble in water)
2+
+
2 Na
+
The molecules of detergents are sodium or
potassium salts of long-chain sulphonic acids.
They do not form water-insoluble salts when
used in water containing Ca(II), Mg(II), and
Fe(III) ions (hard water).
1 . H2 SO 4
2 . NaOH
CH 3 ( CH2 ) 1 0 CH 2
Dodecylbenzene
CH 3 ( CH2 ) 1 0 CH 2
-
SO 3 Na
Sodium 4-dodecylbenzenesulfonate
(an anionic detergent)
+