C11_C_Fats & Rubber(S) Carbon coumpound

8/8/2019 C11_C_Fats & Rubber(S) Carbon coumpound

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4541 CHEMISTRY Chapter 11

2.11 FATS

1. Fats and oils are esters.

Fats ; a natural ester found in animal and human tissue (solid at room temperature).

Oils ; a natural ester found in fish tissue and plants (liquid at room temperature).

Formed by esterification of glycerol (alcohol) / 1,2,3-propanetriol ( alcohol with

3 hydroxyl -OH) with fatty acid (organic acid with long carbon chain,

CnH2n+1COOH , n is about 10 to 20).

(i) Esterification reaction between glycerol and fatty acid :

………... + fatty acid oil or fat + water

H O H O

H C O H H O C R H C O C R

O O

H C O H + H O C R’ H C O C R’ + 3H2O

O O

H C O H H O C R” H C O C R”

H H

(ii) R, R' and R" represent hydrocarbon chains (alkyl groups) that are the same or

different.

(iii) Fats are triesters (triglyceride).

2. The importance of oils and fats :

Fats and oil provide energy for our bodies.

Build membrane cell and certain hormones.

Dissolve certain vitamins for absorption.

3. Source of fats and oils :

• Fats found in animals like cow and goat, are ………………… at room temperature.

Example of animal fats are butter, cheese and lard.

• Oils from plants are ………………… at room temperature. They are called ………

Example of oils are peanut oil, soya bean oil and corn oil.

Chapter 11 Carbon Compounds47

1 mol of glycerol 3 mol of fatty acid 1 mol of fat or oil 3 mol of water




4. Saturated and unsaturated fat :

• Fat and oil molecules are made up of two parts i.e derived from ……………………….

and derived from ………………………..

• Saturated fats molecules are esters of saturated fatty acids. Saturated fatty acids contain

……………………….. carbon- carbon (- C - C - ) covalent bonds.

Example :

Glyceryl tristearate

H O

H C O C (CH2)16 CH3

O

H C O C (CH2)16 CH3

O

H C O C (CH2)16 CH3

H

• Unsaturated fats molecules are esters of unsaturated fatty acids that contain

……………………….. and ……………………….. covalent bonds between carbon

atoms in their hydrocarbon chain.

Example :

Glyseryl trilinolate

H O

H C O C (CH2)7CH=CH-CH2-CH=CH-(CH2)4-CH3

OH C O C (CH2)7CH=CH-CH2-CH=CH-(CH2)4-CH3

O

H C O C (CH2)7CH=CH-CH2-CH=CH-(CH2)4-CH3

H


Derived from glycerol

Derived from stearic acid ( fatty acid )

fatty acids contain single

carbon- carbon (-C-C- )covalent bonds

Derived from glycerol

Derived from linolic acid (fatty acid)

fatty acids

contain double carbon-carbon

(-C = C- )

covalent bonds




If there is only one double bond in a fatty acid molecule, the fats formed are

monounsaturated fat.

If there are more than one double bonds in a fatty acid molecule, the fats formed arepolyunsaturated fats.

Example : [SPM 2008]

• The fats and oils are a mixture of saturated and unsaturated fats molecules.

An oil or fat is classified as a saturated/unsaturated* if it has more saturated fat

molecules compared to unsaturated fat molecules; for example animal fats.

An oil or fat is classified as an saturated/unsaturated* if it has more unsaturated

fat molecules compared to saturated fat molecules; for example vegetable oils

except coconut oil.

5. Converting unsaturated fats to saturated fats

The double covalent bonds between carbon atoms in unsaturated fats are easily

oxidized. When this happen, the fat has turn rancid ( sour ).

Unsaturated fats can be converted to saturated fats by ……………………………

process for example in the manufacture of margarine.


CH(CH2)

7CH C

O

OH

CH3

(CH2)

7

C

O

OH

CH3

(CH2)

14

CH(CH2)

7CH C

O

OH

CH3

(CH2)

4CH

2CH CH

………..…saturated








2.12 NATURAL RUBBER

1. Natural rubber is a natural polymer .

Natural polymers are polymers that exist in nature and are not man made.

Example :

Natural polymer Monomer

Protein Amino acid

Carbohydrate Glucose

Natural rubber Isoprene

2. The Structure of Rubber

• Rubber is formed from the monomer isoprene. Molecular formula of

isoprene is C5H8

• Isoprene molecules are joined together by addition

………………………….. process to form the polymer of natural rubber, polyisoprene :

. H H CH3 H H H CH3 H

C = C – C = C C - C = C - C

H H H H

Isoprene (2-methylbut-1,3-diene) Polyisoprene

3. Coagulation of latex

• Latex is milk like liquid obtained from tapped rubber tree. Latex is a

…………… which contains suspension of rubber particles in water.

• The rubber particles are made up of long chain rubber polymers

[(C5H8)n] surrounded by a …………………………….. The protein membrane is

………… charged. The forces of repulsion between negatively charged particles

prevent them from combining or coagulate.


n is a large number

n

n

Protein membrane

Rubber molecule

Negative charge

Repulsion force




• Latex coagulates when :

Acid is added to it such as methanoic acid (formic acid), ethanoic acid (acetic

acid) or any other weak acids.

or

Left aside for 1 - 2 days due to bacterial action on latex. Bacteria produces acid

that contains hydrogen ions (H+) which causes coagulation of latex.

Coagulate latex is semi solid.

• When acid is added to latex, coagulation of latex occurs :

Positively charged hydrogen ions from the acid neutralises the negative charges

on the surface of the protein membrane. A neutral rubber particle is formed.

The neutral particles no longer repel each other. These neutral particles collide

with each other, causing the membrane to break. The rubber polymers are freed

and they coagulate by combining together to form large lump of rubber polymer

(solidified). The latex has coagulated.

• Coagulation of latex can be prevented by adding alkali (ammonia) to

it. The ammonia solution (containing OH- ions) will neutralise any acids that may be produced by the bacteria.

Activity 22 :-

Describe how the presence of an alkali can prevent the coagulation process of latex.

……………………………………………………………………………………………………….


Rubber polymer

chain

Positive charge

carried by H+

Membrane

break

Rubber polymers

are coagulate




……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

4. Properties and Uses of Natural Rubber

Activity 23 :-

Complete the following table :

Property Description Uses

Elastic

When it is stretched, it straighten out.

It return back to its original shape once the

stretching force is released.

Rubber tube, gloves,

rubber bands, shoe

soles, natural latex

modified concrete and

natural rubberised

bitumen for surfacing

roads.

Not resistance

to oxidation /

Easily oxidised

The natural rubber polymers are easily

oxidised due to presence of double bonds.

Effect of heat

When it is heated, it is soften and become

sticky.

When it is cooled, it becomes hard and brittle.

Effect of

solventNatural rubber is soluble in organic solvents,

alkaline and acidic solutions.

The properties of natural rubber can be improved through the vulcanisation process.

5. Vulcanisation of rubber :

• Natural rubber is elastic.(return to its original shape after stretching force released).

• When the rubber is over stretched, the rubber molecules do not returnto its original position. The rubber has lost elasticity.

• Natural rubber becomes more stronger and elastic after vulcanisation.


VULCANISATION

Sulphur is heated together

with natural rubber.

Rubber stripe is soaked in

sulphur monochloride solution in

methylbenzene for a few hours

and then dried.

In industry In school laboratory




Activity 24 :-

Compare the properties of natural rubber and vulcanised rubber.

Natural rubber Vulcanised rubber

In vulcanised rubber :

The sulphur atoms form cross link between the long rubber molecules.


S

S

S

SS

S

S

S

S

S

Crosslink

S

S

S

SS

S

S

S

S

S




This reduces the ability of the polymers to slide over each other.

The rubber molecules return back to its original positions after beingstretched.

END OF CHAPTER 11


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C11_C_Fats & Rubber(S) Carbon coumpound