Featured

CHE-MYSTERY

This is the post excerpt.

Advertisements

Chemistry is called so because it is fully filled with mysteries; not actually mysteries but the ways that help you to reach at the end of the mysteries that are happening in this universe. Be the one who chase the mysteries……..

post

CORROSION

Slow destruction of metals due to the attack of atmospheric gases and moisture on the surface of the metal resulting in the formation of compounds such as oxides, sulphides, carbonates, is called corrosion. Common examples of corrosion are rusting of iron, tarnishing of silver, development of a green coating of verdigris on the surface of copper etc.

Very reactive metals are prone to corrosion while least reactive metals such as gold, platinum etc. donot undergo corrosion.

PREVENTION OF CORROSION

Some methods of protecting metals from corrosion are detailed below;

1. Sacrificial protection

In this method, iron surface is covered with a layer of a metal which is more active than iron. On exposure to atmosphere, the active metal gets oxidised in preference to iron. So long as the protective metal is present on the surface, it continues to protect iron from rusting. With the passage of time the covering metal gets consumed.

2. Barrier protection

In this method,the metal surface is not allowed to come in direct contact with air by introducing a barrier film on the metal surface.this can be done by the following methods.

a)by painting the metal surface

b)by coating the metal surface with a layer of grease,oil or some chemicals such as bisphenol.

c)by electroplating iron with certain non_corroding metals such as nickel,chromium etc.

3.cathodic protection

in this method,the exposed surface of iron metal is connected by a wire to a plate of more reactive metal such as magnesium or zinc kept near it.magnesium is usually employed in the cathodic protection of iron pipes burried underneath the soil.since magnesium is more reactive(easily oxidised)than iron ,magnesium acts as the anode thereby turning iron into cathode and thus prevents the ionisation of iron atoms.as a result magnesium is consumed by oxidation and iron remains intact.thus this is a special case of sacrificial protection and the anode used is called sacrificial anode.

ATOMIC STRUCTURE AND CHEMICAL BONDING

An atom consists of three subatomic particles namely protones, neutrones and electrones. Since Rutherford and Bohr model of atom had some demerits a new approach named wave mechanics is arrived to explain the bahaviour of electrones in atoms. Two important principles that laid the foundation of wave mechanics are the duel nature of matter and Heisenberg’s uncertainity principle.

DUEL NATURE OF RADIATION

Einstein in 1905 suggested that light has duel character, i.e., it can behave as a particle as well as a wave. Some properties of light such as diffraction, interference etc., can be explained only by assuming the light is a wave. But phenomena such as photoelectric effect, black body radiation etc., can be explained only by assuming that light has particle character.

PHOTOELECTRIC EFFECT

It is the phenomenon of ejection of electrones from the surface of a metal when light of suitable frequency strikes on it. The emitted electrones are called photoelectrones.

PARTICLE NATURE AND PLANK’S QUANTUM THEORY OF RADIATION

The failure of the classical electromagnetic theory of radiation to explain photoelectric effect and black body radiation les Max Plank to propose a theory known as quantum theory of radiation. The main postulates of the theory are given below:

  • Radiant energy is emitted or absorbed discontinuously in the form of small packets of energy called quanta.
  • The amount of energy associated with a quantum of radiation is proportional to the frequency of radiation ie., E=hv where h is a constant known as plank’s constant and v is the frequency of radiation
  • Energy can be emitted or absorbed only in terms of whole number multiples of quantum i.e., E=nhv where n=1,2,3……..

EXPLANATION OF PHOTOELECTRIC EFFECT USING QUANTUM THEORY

In order to explain photoelectric effect Einstein modified Plank’s quantum theory and suggested that light consists of a stream of energy particles called protones.

CHEMICALS IN MEDICINE

Chemical substances used for treatment of diseases and for reducing pain are called medicines or drugs. The chemicals used for the treatment of diseases can be classified as follows:

ANALGESICS

Drugs used for releiving pain are called analgesics. Analgesics are of two types; narcotics and non-narcotics. Aspirin, ibuprofen etc. are analgesics. They act both as analgesic and anti-pyretic. Narcotics induce sleep and thus remove the feeling of pain, though they do not remove the cause of pain. Typical examples are morphine, codeine, heroin and marijuane. However, these narcotics cause addiction, i.e., they are habit forming.

ANTIPYRETICS

Chemical substances used to bring down the temperature of the body during high fever are called antipyretics. Most common antipyretics are aspirin (acetylsalicylic acid), paracetamol (4-acetamidophenol) and phenacetin (p-ethoxyacetanilide).

ANTISEPTICS

Antiseptics are chemical substances which prevent the growth of micro organisms or kill them without causing any serioys harm to the living human tissues. They can be safely applied to wounds, cuts, ulcers and diseased skin surfaces. Disinfectants are chemical substances which kill micro organisms but are not safe to be applied to the living tissues. Antiseptics are also used to reduce odours resulting from bacterial decomposition on the body or in the mouth. Some examples of commonly used antiseptics are dettol, bithional, iodine, etc.

TRANQUILLISERS

These are drugs used to reduce anxiety and to release mention tension. They act on central nervous systemand induce sleep to the patients. Since they are used for the treatment of mental disorders, they are als known as psychotherapeutic drugs. They are also used for making sleeping pills. The mist commonly used tranquillers are barbituric acid and its derivatives such as luminal and seconal. Reserpine, isolated from the plant Rauwolfia Serpentina, is also a powerful tranquilliser. It also slows down the pulse rate and liwers the blood pressure. Chlordiazepoxide and meprobamate are mild tranquillisers are suitable for relieving tension. Equanil is used for controlling depression and hypertension. Valium, serotonin etc. are also used as tranquillisers.

ANTACIDS

Substances which remove the excess acid and raise the pH to appropriate level in stomach are known as antacids. Acid Gastritis is a common ailment associated with digestion and is due to excess of hydrochloric acid in gastei juice. Magnesium trisilicate is also used. Recently omeprazole and lansoprazole are introduced as antacids.

ANTIBIOTICS

These are chemical substances produced by some micro-organisms that can be used to inhibit the growth or even kill other micro-organisms which cause infections. The first antibiotic discovered was penicillin. Penicillin is an effective drug for pneumonia, bronchitis, sore throat etc. However some people are allergic to penicillin. Therefore, it is necessary to test the patient for sensitivity to penicillin before giving them the full dose.

THE SOLID STATE; A NOTE FOR 12th STANDARD STUDENTS

In solids the constituent particles are closely packed and have strong intermolecular force of attraction. As a result the particles are fixed in their position and do not have any freedom of motion except that of vibration about their mean position.

CLASSIFICATION OF SOLIDS

Solids are broadly classified into two types: crystalline solids and amorphous solids.

  1. CRYSTALLINE SOLIDS

A crystalline solid is a substance whose constituent particles are arranged in a definite orderly manner. Some examples are; sodium chloride, sucrose, diamond, quartz etc.

2. AMORPHOUS SOLIDS

An amorphous solid is a substance whose constituent particles do not possess a regular orderly arrangement. Some examples are glass, plastic, rubber,fused silica, starch and proteins

chem3

TYPES OF CRYSTALLINE SOLIDS

There are 4 types of crystalline solids

slide_2.jpg

BRAGG EQUATION

Bragg pointed out that scattering of X-rays by crystals could be considered as reflection from successive planes of constituent particles in a crystal. He derived a simple equation that relates the wavelength of X rays to the distance between the planes in a crystal and the angle of diffraction. This equation is called Bragg equation. nλ = 2 d sin θ

d= distance between the planes of constituent particles in the crystal

λ= wavelenth of X rays used

θ=angle between the incident X ray beam and plane of the crystal

n=1,2,3,……

SPACE LATTICE

Space lattice or crystal lattice is defined as the regular arrangement of points in 3d space corresponding to the constituent particles of a crystal. A unit cell is defined as the smallest repeating unit of the crystal lattice which when repeated regularly in all the three directions results in the entire crystal. A unit cell can be considered as the fundamental building block of the crystal and it represents the shape the entire crystal.

CRYSTAL SYSTEMS

If the unit cell in a crystal lattice has lattice points only at the corners, it is called a simple or primitive unit cell. There are 7 types of primitive unit cell among the crystals. These are called 7 crystal systems.

TYPES OF CUBIC LATTICES

In crystals belonging to cubic system, there are three kinds of lattices depending upon the location of lattice points. They are

  • Simple cubic lattice
  • Body centered cubic lattice
  • Face centred cubic lattice

In a simple cubic lattice , the constituent particles are situated only at the corners of the cube. In body centred cubic unit cell, there is a constituent particle at the centre of the unit cell in addition to the particles at the corners. In a face centred cubic unit cell, each corner and each face centre is occupied by particles.

CLOSE PACKING IN CRYSTALLINE SOLIDS

The packing of constituent particles in a solid takes place in such a way that the available space is used most economically and a state of maximum possible density is reached. This type of packing is called close packing. There are two types of close packing in two diamensions. They are:

  • Square close packing

In this arrangement, the particles in the adjacent rows show horizontal as well as vertical alignment in a plane. Each central sphere or particle is in contact with four other spheres.

  • Hexagonal close packing

In this arrangement, particles of the second row are placed in the depressions between particles of the first row. Similarly, particles in the third row are placed in the depressions of the second row.Here each particle is in contact with six other particles which are arranged hexagonally around it.

THREE DIAMENSIONAL PACKING

Three diamensional packed structure is obtained by arranging the hexagonal close packed layer one over the other.

When a third layer is placed over the second layer two types of arrangements are possible.

Hexagonal close packing

In this type of packing, the third layer is placed in such a way that the particles cover the tetrahedral voids in the second layer. Calling the first layer as A and the second layer as B, such an arramgement is called ABAB pattern and is called three diamensional hexagonal close packing (HCP).

Cubic close packing

In this type of packing, the third layer is placed in such a way that the particles cover the octahedral voids. In such a case the third layer has a different arrangement from the first and second layer. This pattern of arrangement is called ABC ABC pattern and is called cubic close packing (CCP).

CO-ORDINATION NUMBER

In any crystal lattice, the number of nearest neighbours with which a given particle is in contact is called co-ordination number. In the hcp and ccp mode of packing, a spherical particle is in contact with six other particles in its own layer. It also touches three particles in the layer above and three in the layer below. Thus each spherical particle has 12 close neighbours in hcp and ccp arrangements, or the co-ordination number is 12.

CHEMISTRY IN DAY TODAY LIFE

Chemistry plays a vital role in our day today life. We can find somany examples for the use of chemistry in our life from the food we eat, the clothes we ware, the food we eat, the air we breath etc. It is important to say that our body is mostly water which is a combination of Hydrogen and Oxygen. Also there are elements like Carbon, Nitrogen, Calcium, Magnesium, Potassium etc present in our body and all these elements are essential for our existence. The emotions that we feel are also due to the presence of some chemicals that is present in our body.

Let’s have a look on the examples of some chemicals that are inevitable for our daily living.

TOOTHPASTE

Tooth paste is a semisolid substance which is used for the purpose of oral hygiene. It helps in removing dental plaque and food from the teeth and helps to prevent tooth decay. In addition to water, toothpaste contain three main ingredients namely abrasives, fluoride, and detergents.toothpaste

Abrasives are dental polishing agents. The polishing of tooth removes stains but it do not ensure dental health.Fluorides are the most popular and active ingredient in the toothpaste. Fluoride helps in the formation of dental enamel and bones. So it helps in preventing dental cavities. Detergents are foaming agents used for cleansing action.

SOAPS AND DETERGENTS                     

Soaps are inevitable parts of our daily life. Soaps are water soluble sodium or soapspotassium salts of fatty acids. These are made from fats and oils or their fatty acids, and treating them with strong alkali. The fats and oils are taken from animal or plant sources. The commpn alkali used for soap making are Sodium hydroxide, also calles caustic soda. The method of soap making is called saponofication and the process involve heating fats and oils and reacting with them a liquid alkali to produce soap and water.

TALCUM POWDER

Talcum powder is made from talc, a mineral made of mainly the elementtalcum-powder.jpgs magnesium, silicon and oxygen. It helps in absorbing moisture thus keeping the skin dry and helping to prevent rashes. It is widely used in cosmetic products like baby powdres and adult body and facial powders as well as in a number of other consumer products.

PLASTIC PRODUCTS

Plastic is a synthetic or semi synthetic organic Plastic-products1polymer. Polymers are long chain molecules made by combining simple molecules called monomers. These polymers are mixed with chemicals like additives, including colorants, plasticizers, stabilizers, fillers and reinforcements. These additives affect the chemical composition, chemical properties and mechanical properties of a plastic and also affect its cost.