CHEMISTRY

ELEMENT

It cannot be split simpler substances, e.g., iron, sulphur, oxygen, gold. There are about 106 elements.

COMPOUND

It can be split into simpler substances and is formed by the union of two or more elements in definite proportions by weight, e.g.,

1. Water can be split into hydrogen and oxygen.
2. Iron sulphide is split into iron and sulphur.
3. Chalk is made of calcium, carbon and oxygen.
4. Carbondioxide is made up of carbon and oxygen.

MIXTURE

It is one in which two or more substances are mixed together in any ratio without altering their properties.

1. Sand and salt.
2. Sugar and water.
3. Air is a mixture of nitrogen and oxygen.
4. Gun-Powder is a mixture of nitrate, charcoal and sulphur.

AIR

It consists of nitrogen, oxygen, water vapour carbon dioxide and traces of argon, ozone and some other gases and dust particles. Dry air contains these gases in the following proportions, by volume : Nitrogen 78.06%, Oxygen 21%, Argon 0.94%, 1 litre of air at 0°C and 760 mm of mercury (pressure) weights 1.2932 grams.

It is mixture and not a compound because its composition varies from place to place.

Presence of water vapours in the air : If a glass cleaned from outside and containing ice, is placed in the open air, the outer surface gets covered with water drops. This is due to the condensation of water Vapours from the atmosphere on the cooler surface of glass as the air gets saturated, when its temperature falls.

Presence of carbon dioxide in the air : Similarly lime water placed outside turns milky due to absorption of carbon dioxide from the atmosphere. The milky colour is due to the formation of chalk.

Chemical Composition of water : Water consists of hydrogen and oxygen, in the ratio of 2:1 volume and 1:8 by weight.

When an electric current is passed through water for every one volume of oxygen two columns of hydrogen are evolved.

Water can be prepared by combining oxygen and hydrogen with the help of an electric current and it is seen that for every one part by weight, of hydrogen required to prepare water, 8 parts of oxygen by weight are required.

ACID

Acid is substance which with a base gives salt and water, e.g., hydrochloric acid; nitric acid and sulphuric acid, etc Hydrogen is an essential constituent of acid.

They have sour taste, turn blue litmus red, react with metals giving hydrogen gas, and decompose carbonates giving carbon dioxide.

BASE

Base is a substance which with an acid produces salt and water, for example, calcium hydroxide, magnesium hydroxide, etc A hydroxide is an essential constituted of a base.

ALKALIES

Those bases which are soluble in water are called alkalies such as caustic soda, caustic potash.

They have a soapy touch, bitter taste. They turn red litmus blue, and also turn yellow turmeric paper brown.

Salt is a substance obtained by reacting together an acid and a base.

There are varieties of salts. They can be prepared by the action of acids on metals. Their oxides or bases, e.g., Calcium sulphate. Potassium nitrate. Sodium chloride (Common salt or table salt).

CARBON

Carbon occurs in various forms : diamond, graphite and amorphous carbon. Such forms are known as allotropic forms.

Diamonds occur in nature and also be made artificially by melting coal and solidifying the same under higher pressure. It is the hardest substance known, and is the purest form of carbon. It does not allow heat and electricity to pass through it. It resists the action of chemicals, but gives out carbon dioxide when it is burnt.

In India, diamonds are found in the Central India diamonds mines. Panna mines of M.P. are the most famous.

Other sources of diamonds are South Africa, Brazil, Australia and Congo.

Koh-i-noor is one of the most precious and famous diamond in the world.

The value of diamond depends upon its weight and its purity.

It is used as a gem in jewellary and also for cutting glass.

GRAPHITE

It is a soft grayish black substance with soapy touch, has a metallic shine and allows heat and electricity to pass through it.

It is used in the manufacture of lead pencils and crucibles. Graphite is also used as a solid lubricant, in railway carriage wheels.

AMORPHOUS CARBON

There are many varieties: Wood charcoal is obtained by heating wood and also as a fuel.

Animal charcoal is obtained by destructive distillation of bones and is used for refining sugar.

COAL

It is obtained by slow decomposition of vegetable matter in the absence of air. It is used as a fuel and for the manufacture of coal gas.

Coke is the residue left after the destructive distillation of coal out of contact with air.

LAMPBLACK

It is obtained a soot, when oil burns in a limited supply of air. It is used for the preparation of inks, paints and boot polish

All the above varieties of carbon give carbon dioxide on burning.

CARBON DIOXIDE

It is found in the atmosphere as a result of burning of materials containing carbon, and also as a result of respiration. It is prepared by the action of dilute acids on carbonates or by fermentation of sugar.

It is formed by burning wood, charcoal, etc., in a free supply of air.

In the laboratory it is prepared by treating marble pieces with dilute hydrochloric acid.

 + 2 HCI =  +  + O

Properties : The gas is colourless and has a faint smell. It is heavier than air. It is acidic. It does not help burning. It turns lime water milky.

Uses : It is also used in the preparation of aerated waters. It is used for extinguishing fire. In solid state it is used in curing local sores.

HARD AND SOFT WATER

Hard Water is that water which does not produce lather with soap easily.

Soft Water produces lather with soap very easily. There are two kinds of hardness :

• Temporary,       (2) Permanent

Temporary is due to the bicarbonates calcium and magnesium.

Permanent is due to the sulphates and chlorides of calcium and magnesium.

Temporary hardness can be removed by  (1) boiling, (2) addition of line.

Permanent hardness can be removed by (1) addition of washing soda, or (2) by distillation.

CHEMICAL NAMES

Substance                                            Chemical Name

1. Green Vitriol Iron sulphate and oxygen
2. Litharge Leas monoxide
3. White vitriol Zinc sulphate
4. Caustic lotion Silver nitrate
5. Candy fluid Potassium permanganate
6. Blue vitriol Copper sulphate
7. Kansi (Alloy) Bronze
8. Pital(Alloy) Brass
9. Shora or nitre Potassium nitrate
10. Caustic potash Potassium hydroxide
11. Chile (salpetre) Sodium nitrate
12. Baking soda Sodium
13. Washin soda Sodium carbonate
14. Common salt Sodium chloride
15. Caustic soda Sodium hydroxide
16. Gluber’s salt Sodium sulphate
17. Iron pyrites Iron sulphate
18. Galena Lead sulphide
19. Gypsum Calcium sulphate
20. Epsom Magnesium

NUCLEAR FISSION

It is nuclear reaction in which the nucleus of an atom (e.g., Uranium 235, Plutonium) captures a neutron, and the unstable nucleus so produced breaks into two nearly equal fragments. Also released in the process are several neutrons and a lot of energy. In case one of the neutrons released is captured by another uranium atoms, it too splits. This process if carried on results in self sustaining nuclear fission and is called chain reaction.

Nuclear Fusion : The ability of two light nuclei to combine and form a heavier nucleus is called fusion. The reaction occurs with a release of energy. A typical nuclear fusion reaction involves the interaction of Deuterium nuclei to produce Helium nuclei. To obtain a net gain in energy from the process, temperature must be raised to and held at millions of degrees Celsius which brings in its wake problems of metallurgy. Because of such nuclear energy, without any radioactive by products of the kind produced in fission.

Atomic Reactor : It is a kind of nuclear reactor which besides producing energy by the fission process also produces (breeds) more nuclear fuel simultaneously. In a typical reaction, a neutron induces fissin of a U-235 nucleus which breaks up its two medium sized nuclei and some neutrons; one of the latter then enters a U-238 nucleus (U-238 is always present with U-235 in Uranium fuel) which then decays radioactively into Plutonium which again is a useful fuel and can be fissioned).

Difference between Thermal Reactor and Fast Reactor : In a Thermal Reactor, neutrons released in the chain reaction are slowed down using a moderator like heavy water or graphite. In a Fast Reactor, slowing down of neutrons is not required and thus light water is used. Thermal Reactors use natural uranium as fuel (a mixture of U-238 and some U-235) while Fast Reactors use enriched uranium, in which the proportion of U-235 has been increased.

IMPORTANT LAWS IN SCIENCE AND SOME DEFINITIONS

Periodic Law : If all the elements be arranged in the order of their increasing atomic numbers, those possessing similar properties reoccur at regular intervals.

Valency is the number of atoms of hydrogen with which an atom of the substance can combine chemically. For example, one atom of carbon can combine with four atoms of hydrogen and hence carbon has a valency four.

Electrovalency : When atoms lend or borrow electrons to complete each other’s orbit – this kind of valency is called covalency.

Covalency : When atoms lend or borrow electrons to complete each other’s orbit – this kind of valency is called covalency.

Law of Conservation of Matter : The matter can neither be created nor destroyed.

Law of Constant Composition : A chemical compound always consists of the same elements combined together in the same proportion by weight.

Law of Multiple Proportion : When two elements combine to form more than one compounds, the weight of one which combines with the fixed weight of the other bears simple ratio to each other.

Gay Lussac’s Law of Combining Volumes : When gases react together they do so in volumes which bear simple whole number ratios to one another and to the volumes of the products, If gaseous, all the volumes being measured under simple conditions of temperature and pressure.

Boyle’s law : Temperature remaining constant, the volume of a given mass of any gas is inversely proportional to its pressure.

Gay Lussac’s Law : Volume remaining constant, the pressure of a given mass of a gas varies directly proportional to its absolute temperature.

Ohm’s Law : The current flowing through a conductor between any two points is proportional to the potential difference between them, provided physical conditions remain unaltered.

Atom is the smallest particle of matter, which can take part in a chemical reaction.

Molecule is the smallest particle of matter which can exist freely and has the same properties as the substance.

Dalton’s Law of Partial Pressures : The total pressure exerted by the gaseous mixture is the sum of the pressures, which the gases would exert individually, if each one of them alone had occupied the whole volume, provided they do not react with each other.

Molecular weight of a substance is the average relative weight of its molecule compared with the weight of an atom of oxygen taken as 16.

Equivalent weight of a substance is the number of parts by weight of a substance which combines with or displaces one part by weight of hydrogen, or 8 parts by weight of oxygen or 35.5 parts by weight of chlorine.

Atomic weight of an element is the average, relative weight of its atom compared with the weight of an atom oxygen taken as 16.

Law of Mass Action : The rate of a chemical reaction is proportional to the molecular concentration of each of the reacting substances.

Le Chatelier’s Principle : When a system in equilibrium is subjected to a change of temperature, pressure or concentration the equilibrium automatically shifts in the direction which tends to undo the effect o the change imposed.

Solubility : It is the maximum amount of the substance which can be dissolved in 100 grams of the solvent of a particular temperature.

Water of Crystallisation : It is the number of molecules of water which gives the substance crystalline shape.

Faraday’s Laws of Electrolysis : (1) The products of water which gives the substance crystalline shape.

Weight is proportional at the various electrodes are proportional to their chemical equivalents.

Dulong and Petit’s Law : The product of the atomic weight of a substance and its specific heat is approximately equal to 64.