TOPICS FOR HOLIDAY LESSON (CHEMISTRY)

(1) GIANT MOLECULES (POLYMERS)

(2) METALS AND THEIR COMPOUNDS (I) Sodium (ii) Aluminium (iii) Iron (iv) Copper

(3) ALTERNATIVE TO PRACTICALS (i) Titration (ii) Salt Analysis

POLYMERS (GIANT MOLECULES)

Polymers: are chemical compounds made of small molecules that are arranged in a simple repeating structure to form larger molecules.

Polymers are grouped into:- Natural and Synthetic Polymers. (i) Natural polymers e.g. starch, cellulose, proteins and rubber. NOTE:

(i) Fats and oil are not large enough to be grouped as polymers. (ii) All polymers are macromolecules but not macromolecules are

polymers e.g. Diamond is a macromolecules but not a polymer.

SYNTHETIC POLYMERS Synthetic polymers are commonly called plastics. Plastics are synthetic

materials which can be softened by heat or pressure and moulded into any desirable shape. The two types of plastics are:-

(i) Thermoplastic: can be softened repeatedly by heat and remoulded.

(ii) Thermosets: cannot be softened or melted by heat and remoulded once they are formed or set. ADVANTAGES (DESIRABLE QUALITIES) OF PLASTICS)

(1) Plastics are strong but light. (2) They are resistant to chemical and microbial attack.

(3) They can be tailor-made to our exact requirement. (4) Raw materials for the manufacture of plastics are readily and

cheaply available from the refining of crude oil. (5) Plastic items can be produced at very low costs.

(6) Plastic are good insulators of heat and electricity. DISADVANTAGES

(1) Most plastic materials are non-biodegradable hence cause environmental pollution.

(2) Burning of plastic products releases toxic gases into the atmosphere.

(3) There is heavy dependence on crude oil for the production of plastics.

POLYMERIZATION Polymerization is the process whereby two or more monomers link

together to form a compound of high molecular mass called Polymer. Synthetic polymers are made by polymerization. Monomers are the

smaller molecules that combine to form a polymer. For instance, the monomer of starch is glucose, proteins are amino acids, polythene is ethene and PVC is chloroethene.

CONDITIONS FOR POLYMERIZATION (1) High temperature (i.e. presence of heat) (2) Presence of an initiator.

(3) High pressure. (4) Presence of a catalyst.

TYPES OF POLYMERIZATION There are two types which are: (i) Addition polymerization (ii) Condensation polymerization. (i) Addition polymerization: is the process whereby two or more of the same

monomers link together to form the polymer without elimination of any small molecules.

Some examples of addition polymerization are:- (1) Polyethene: If ethene is subjected to a high temperature of about 2500C and

pressure above 1500atm, together with traces of oxygen as an initiator, it polymerizes to polyethene (Polythene).

, where A = monomer

Ethene

Polythene

NOTE: During polymerization, the double bonds in ethene molecules are

removed.

USES OF POLYTHENE For making: (i) Plastic bags. (ii) Kitchen wares.

(iii) Cables insulators. (iv) Boxes (v) Crates. (vi) Dustbins.

(2) Polychoroethene (Polyvinyl chloride, PVC) is manufactured from chloroethene as the monomer.

USES OF PVC

For making: 1. Plastic pipes 2. Cable covering 3. Raincoats

4. Artificial leather cloths 5. Tiles

6. Shower curtains. (3) Polyphenylethene (Polystrene) is made from the monomer phenylethene

(styrene) by refluxing, using a solution of benzoyl peroxide as catalyst.

PVC

When air, coupled with is foaming agent, a blown into heated polystyrene, it expands into a light, white, opaque solid that floats in water. This is known as expanded polytrene or Styrofoam.

USES

1. Styrofoam is used as ceiling tiles and lamp shades because of its lightness.

2. Due to its high compressibility, it is widely used as packing materials or as shock absorbers for fragile objects during transportation.

3. It used for making disposable cups and food containers in fast-food shops.

(4) PERSPEX: Its monomer is methyl 2-methylpropenoate. The monomers are

heated to give poly methylz-methyl propenoate (PMMA). An organic catalyst lauryl peroxide is used in this process.

USES

It is used for making: 1. car rear light.

Phenylethene Polyphenylethene (Polystyrene)

Methylz-methyz propenate

Perspex (Poly methyl-methyl propenate)

2. wind shields 3. window-panes 4. fish tanks 5. contact lenses

6. street-lamp housing (5) Polypropenonitrile:- It is commonly known as polyacrylonitrile. Its monomer

is propenonitrile and the catalyst is organic peroxide.

USES It is used for making textile. That is woolly garments e.g. Orlon.

CONDENSATION POLYMERISATION

Condensation polymerization is the process whereby two or more monomers link together to form the polymer with the elimination of a small molecule. Examples include: 1. Nylon: It is formed from two monomers which are hexane-1, 6 diamine

and hexanedioic acid water molecules are produced in addition to the Nylon.

n + n

n

Propenonitrile

Poly Propenonitrile

hexime – 1, 6 - diamine Hexanedioic acid

n

USES OF NYLON 1. For making all kinds of clothing.

2. Terylene: It is a polyester that is also known as Dacron in USA. It is formed by the condensation of benzene -1, 4 – dicarboxylic acid and ethane 1, 2 – diol, using an acid catalyst.

USES

For making sails of boat where a strong rot-proof material is required. 3. Phenol-methanal: It is commonly known as Bakelite. It is formed by

condensing phenol and methanol in the presence of an acid or an alkali as catalyst.

OH

| + n O

Nylon 6 – 6 (a polyamide)

Benzene 1, 4 dicarboxylic acid Ethene 1, 2 - diol

terylene

Phenol-methanal (Bakelite)

USES: It is used for making

1. plugs 2. switches.

3. utensil handles. 4. telephone casings.

5. sockets. 6. radio housing.

RUBBER When the barked a rubber tree is cut, a thick white liquid called latex oozes

out. If the latex is collected and heated, it changes into an elastic solid called rubber. Chemically, rubber consists of z-methyl buta-z, 3-diene monomers also knows as isoprene.

When the monomers polymenze, they form long polymeric chains which have only a limited number of cross-links between them.

Vulcanization of rubber: is the addition of calculated amount of sulphur to rubber and heating the mixture so as to toughen the rubber. The sulphur atoms form strong cross-linkages which hold the long rubber chains together. This gives rubber greater tensile strength, durability and elasticity over a wide range of temperature.

2 – methylbuta-1, 3-diene

Natural rubber

cross links

rubber sulphur

Synthetic rubber A typical synthetic rubber is poly (2-chloro buta – 1, 3-diene) or neoprene.

Other synthetic rubber includes: (i) styrene butadiene rubber (SBR)

(ii) Thiokol

(iii) poly buta-1, 3-diene (iv) poly 2-methyl propene

SBR is obtained by copolymerization phenylethene (styrene) with three parts of aqueous buta -1, 3-diene. It is vulcanized by carefully heating it with 3% by mass of sulphur.

USESS OF SBR

(1) In making vehicle tyres (2) Soles of footwear