Varnish (Short Note) | Inter – Class Chemistry Notes

Varnish (Short Note)

Varnish is a mixture of resin, volatile organic solvents and drying oils. To prepare Varnish such as resin (plastic in liquid state) is dissolved in volatile organic solvents, such as ether or alcohol and then drying oil such as linseed oil is added to it.

The drying oils such as linseed oil consist of esters of highly unsaturated acids containing two or more double bonds. When exposed to air, these oils absorb oxygen and form hard and tough film. The film is insoluble in water.
When a Varnish is applied to the surface, the volatile organic solvents evaporate quickly and the drying oil absorbs oxygen and a hard tough glossy film is obtained. The glossy appearance of the film is due to the presence of resin. Varnish differ from paints in such a manner that, it does not has any added pigment.

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Tin Plating (Short Note) | Inter – Class Chemistry Notes

Tin Plating (Short Note)

Definition

The art of coating a metal with tin is called Tin-Plating.

Those metals which are coated with tin are called tin-plated metals.

Purpose And Examples of Tin Plating

The purpose of tin plating is to protect metals from corrosion and food poisoning. Iron is often tin-plated to protect it from rusting. The common cooking oil containers are made of tin-plated iron. The household utensils of copper and brass are tarnished in moist air due to the formation of thin layer of oxides and carbonates of copper. These are poisonous, due to these problems, utensils are coated with tin.

Method of Tin Plating

Tin plating is carried out by the following methods.

1. Hot Dipping or Mechanical Method

In this method, clean iron or steel sheets are dipped in the bath of molten tin. A layer of tin accumulates on the iron sheet and it gets coated.

2. Electrolytic Method or Electro-Plating

This method is based on electrolytic process. An electrolytic cell is developed, which contains metals to be tin-plated as cathode and pure tin as anode. The electrolytic solution consists of salt of tin such as tin chloride or tin sulphate and an acid such as hydrochloric acid. On passing electric current through the electrolytic cell tin deposits on the metal sheet. Through this method a uniform layer of tin is coated on zinc.

3. Classical Method

In this method, the clean hot surface of a utensil is polished with tin metal with a rag. Copper and Brass utensils are tin-plated by this method. The utensils are heated and rubbed with ammonium chloride before they are tin plated. This is done to remove the oxide from the utensils.

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Silvering Of Mirror (Short Note) | Inter – Class Chemistry Notes

Silvering Of Mirror (Short Note)

Mirror

A mirror is a glass plate coated with silver film on one side.

Silvering of Mirror

Coating a glass plate with silver is called silvering of mirror.

Explanation

When ammonical silver nitrate solution is treated with an aldehyde or other organic reducing agent on the surface of a glass plate the silver (I) is reduced to silver (0). This metallic silver is deposited on the glass plate as a fine film.

The chemical reactions that occur are as follows.

AgNO3 + 2NH4OH —-> [Ag(NH3)2]+ + NO3- + 2H2O

[Ag(NH3)2]+ + RCHO + H2O —-> Ag0↓ + RCOOH + 2NH4+

Method

The process of silvering of mirror is carried out through the following steps.

1. A solution of silver nitrate and ammonia is prepared in distilled water.

2. The aqueous solution of ammonia is slowly added to the solution of silver nitrate until brown precipitates of silver oxide form and dissolve.

3. The mixture is ammonical silver nitrate solution. This solution is mixed with a solution of an organic reducing agent such as glucose.

4. After mixing all the compounds thoroughly, the solution is poured on to the centre of a clean glass surface.

5. The reaction immediately starts and thin film metallic silver deposited on the surface of the glass.

6. The silver film is then coated with either shellae of copal varnish. Finally it is painted with some colour, normally red.

Spraying Method

Silvering of mirror can also be carried out by spraying method. In this technique, the mixture of chemicals is sprayed onto the glass sheet.

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Proteins (Short Note) | Inter – Class Chemistry Notes

Proteins (Short Note)

Definition

Proteins are polymers of amino acids in which different amino acids are linked together through peptide bonds.

Explanation

Proteins consists of one or more polypeptides chain. In general, protein molecules consist of forty to ten thousands or more amino acids units.
The word protein is derived from the Greek word Proteins which means first or of primary importance, in fact proteins are the primary materials of life.
Proteins have very high molecular mass, for e.g. the molecular mass of egg albumin is about 43,000 a.m.u and that of serum albumin is 7,000 a.m.u.

Plants form Proteins from the simple inorganic substances and phosphates. Animals cannot synthesize proteins from inorganic substance. Therefore, they depend upon plants and other animals for dietary Proteins. Animals prepare their own proteins from simple organic molecules. Proteins are necessary for growth and for maintaining existing tissues.

Classification of Proteins

Millions of kinds of proteins exist. The human body may contain as many as five million different kinds of Proteins.

Commonly proteins are classified into the following three classes.

1. Simple Proteins

2. Conjugated Proteins

3. Derived Proteins

1. Simple Proteins

The Proteins which on hydrolysis gave only amino acids or their derivatives, are called simple proteins. They are further classified into following six classes.

a. Albumins

These Proteins are water soluble, and are coagulated by heat. They may be precipitated by saturating their solution with Ammonium Sulphate.
For Example, Egg albumin and serum etc.

b. Globulins

These Proteins are insoluble in water but soluble in dilute salt solution and in dilute solution of strong inorganic acids and basis. They are coagulated by heat.
For Example, Serum Globulins and tissues etc.

c. Prolamins

These Proteins are insoluble in H2O or salt solution, but are soluble in dilute acids and alkalis.

For Example, Zein, Gliadin and Hordein etc.

d. Glutelins

These Proteins are insoluble in water or dilute salt solution but are soluble in the dilute acids and basis. These are coagulated by heat.
For Example, Glutelin and Oryzenin etc.

e. Albuminoids

These Proteins are insoluble in water or salt solution but are soluble in concentrated acids and base.

For example, Keratins and Fibroin etc.

f. Basic Protein

These proteins are strong basic.

For example, Keratins and Fibroin etc.

2. Conjugated Proteins

Those Proteins which contain a non proteinic group attached to the proteinic group are called conjugated proteins. The non proteinic group is called Prosthetic group. This group may be separated from the proteinic part by careful hydrolysis.

Conjugated Proteins are further divided into the following five groups.

a. Nucleo Proteins

The prosthetic group is a nucleic acid. This protein is present in the nuclei of living cell.

b. Chromo Proteins

These are coloured protein. The colour is due to the prosthetic group.

c. Glyco Proteins

In these proteins the prosthetic group contains a carbohydrate or a derivative of carbohydrate.

d. Lipo Proteins

In these proteins prosthetic group is a lipid.

e. Phospho Protein

In these proteins the prosthetic group contains a phosphoric acid.

3. Derived Proteins

The derived proteins are the degradation products obtained by the action of acids, bases or enzymes on proteins. These includes peptones polypeptides and Proteose.

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Polymerization (Short Note) | Inter – Class Chemistry Notes

Polymerization (Short Note)

Definition

The phenomenon in which simple and small molecules are converted into large and complex molecules is known as Polymerization.

The simple and small molecules are known as monomer, where as large and complex molecules are called polymers.

Classification of Polymerization

Polymerization has been classified the following.

1. Addition Polymerization

2. Condensation Polymerization

1. Addition Polymerization

The process of Polymerization in which molecules are added into each other is called Addition Polymerization.

Examples

In presence of traces of oxygen when is heated at about 200ºC under 100 atm pressure, then Polymerization takes place. As a result, monomers add together to form polymer i.e. Polyethene or Polythene.

Diagram Coming Soon

Similarly the Polymerization of Vinyl Chloride to Poly Vinyl Chloride (PVC) and Polymerization of Vinyl Acetate to Poly Vinyl Acetate (PVA) are the examples of Addition Polymerization.

2. Condensation Polymerization

The process of Polymerization in which removal of water molecule takes place with the formation of polymer is called Condensation Polymerization.

Example

Bakelite Plastic is the Polymer that is obtained by the polymerization of Phenol and formaldehyde. During this process removal of water molecule takes place.

Diagram Coming Soon

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Plastic (Short Note) | Inter – Class Chemistry Notes

Plastic (Short Note)

Definition

Plastics are macromolecules, which are formed by the polymerization of simple molecules.

Explanation

In other words we can say that plastic are the polymers formed from monomers. The phenomenon in which simple and smaller molecules are combined together to form complex and large molecules, is called polymerization. The simple and smaller molecules are called monomers and the large and complex molecules are called polymers.

Types of Plastic

There are the following two types of plastics.

1. Thermo Plastic

2. Thermosetting Plastic

1. Thermo Plastic

Thermo plastic is also known as Thermo-softening plastic. This type of plastic is manufactured by heating, softening melding and cooling the raw materials, this process can be repeated and it does not effect the properties of plastic.

2. Thermosetting Plastic

Thermosetting plastics are those materials, which cannot be heated, only once before they set, i.e. they cannot be reworked.

Examples of Plastic

1. Polyethene (Polythene)

In presence of traces of oxygen, when ethene is heated at 200ºC, under 100 atm pressure then polymerization takes place. As a result, polyethene is formed, which is commonly known as polythene.

Diagram Coming Soon

Uses

Polythene is the most common plastic used to form polythene bags and to package food.

2. Poly Vinyl Chloride (PVC)

PVC or Poly Vinyl Chloride is the polymer of vinyl chloride. When vinyl chloride is heated at 80ºC in the presence of catalyst hydrogen peroxide, then polymerization takes place. As a result, Poly Vinyl Chloride is formed.

Uses

PVC is used for insulating covering for electrical cables, for the manufacture of gramophone, records, suitcase covering etc.

3. Poly Vinyl Acetate (PVA)

Poly Vinyl Acetate (PVA) is the polymer of vinyl acetate.

Uses

PVA is used in the manufacture of chewing gums and in the water proofing of textiles.

4. Bakelite

Bakelite is a polymer of phenol and formaldehyde. By the condensation of two molecules of phenol with formaldehyde, a polymer Bakelite is obtained.

Diagram Coming Soon

Uses

Bakelite is used to make buttons, switches, electrical boards, camera, radio, telephone etc.

Quality of Plastics

During the polymerization, some other components are also mixed to improve the quality of the plastic. For example, plasticizer is mixed with the polymer. It reduces the brittleness and improves the elasticity of plastic. Fillers are also mixed with the polymer, which usually increases the mechanical strength of plastics, Some pigments or dyes are added to get various coloured plastics.

Plastic Industry of Pakistan

The plastic industry in Pakistan essentially consists of moulding of plastic powders into various articles of daily use.

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Plaster Of Paris (Short Note) | Inter – Class Chemistry Notes

Plaster Of Paris (Short Note)

Definition

The hemi hydrate form of calcium sulphate is known as Plaster of Paris.

Molecular Formula

The molecular formula of Plaster of Paris is

CaSO4. 1/2 H2O

Preparation of Plaster of Paris

When Gypsum (CaSO4.2H2O) is heated to about 100ºC, it loses some water of crystallization and is converted to Plaster of Paris.

Uses of Plaster of Paris

1. At high temperatures gypsum loses all the water of crystallization to give anhydrous calcium sulphate.

2. It is used in manufacture of H2SO4.

3. It is used in making of cement.

4. It is used in the preparation of moulds used in surgery and castings.

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Pigments (Short Note) | Inter – Class Chemistry Notes

Pigments (Short Note)

Definition

Pigments are the substances which are used to give the proper colour to paints.

Types of Pigments

Lead forms various types of pigments. Some of them are given below.

1. White lead Pigment

2. Red lead Pigment

3. Chrome Yellow Pigment

4. Chrome Red Pigment

5. Turner’s Yellow Pigment

1. White Lead Pigment

White lead Pigment is a basic lead carbonate.

Molecular Formula

[2PbCO3. Pb(OH)2] or [Pb3(OH)2.(CO3)2]

Colour

This lead pigment is white in colour.

Properties

The white colour gradually darken due to the formation of Pbs with Atmospheric H2S. It is also poisonous.

2. Red Lead Pigment (Sandhur)

Molecular Formula

Pb3O4 – Triplumbic Tetra Oxide

2PbO.PbO2 – Lead-Sesqui Oxide

Colour

It is used as red coloured pigment, which varies from orange red to brick red dur to particle size and impurities.

Properties

It is soluble in water but soluble in acids.

3. Chrome Yellow Pigment

Molecular Formula

PbCrO4 – Lead Chromate

It occurs in nature as crocoite.

Colour

It is used as yellow coloured pigment.

Properties

It is insoluble in water but soluble in nitric acid and caustic alkalis.

4. Chrome Red Pigment

Molecular Formula

PbCrO4.PbO – Basic Lead Chromate

Pb2CrO5 – Basic Lead Chromate

Colour

It is used as dark red pigment in paints.

5. Truner’s Yellow Pigment

Molecular Formula

PbCl2.4PbO

Other Pigments

Except above pigments, yellow lead monoxide (massicot) and red lead monoxide (litharge or Murda-sang) are also used in paints.

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Paints (Short Note) | Inter – Class Chemistry Notes

Paints (Short Note)

Definition

Paints are fluids that are applied on a surface to form a hard continuous film on it for protection or decoration.

Wooden and metallic articles are coated with paints to decorate them as well as to protect from corrosion or rusting.

Composition of Paints

Paints are usually composed of three components.

1. Pigments

2. Binders

3. Volatile Solvent

To make a paint, a suitable solvent is used in which both the binder and the pigment are dissolved.

1. Pigments

The pigment of paint gives it colour, it also gives hardness and bulk. Common pigments are titanium dioxide – TiO2 (white), Iron oxide – Fe2O3 (brown or red), Carbon Black – C (black), Chrome Yellow – PbCrO4 (yellow) and organic dyes of various colours.

2. Binders

The binder or vehicle is the part of the paint that carries the pigment particles and hold the entire film of the paint on the surface. Generally some plant oils such as linseed oil, natural and synthetic resin (liquid plastics) are used as binders.

3. Volatile Solvents

To make paint a suitable solvent is selected in which both the pigment and binder are dissolved. The solvent evaporates after the paint is applied. Solvent does not effect the quality of dry paint. Commonly, water or turpentine is used as solvent.

Classification of Paints

On the basis of nature of solvent, the paints are classified into the following two classes.

1. Oil Based Paints

2. Water Based Paints

1. Oil Based Paints

In these paints turpentine is used as solvent. Turpentine is a liquid mixture of hydrocarbon that is obtained from pine trees.

2. Water Based Paints

In these paints, water is used as solvent. Both binders and pigments form a suspension in water.

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