General Knowledge & General Awareness Notes: General Science - Chemistry

CHEMISTRY

ELEMENTS
- An element may be defined as a substance which is made by same type of atoms and it can neither be broken into, nor built from two or more simpler substances by any known physical or chemical methods, e.g., copper, silver, hydrogen, carbon, oxygen, nitrogen, gold, iron etc.

COMPOUNDS
- A compound may be defined as a substance which contains two or more elements combined in some fixed proportion by weight and which can be decomposed into two or more elements by any suitable method.
- The properties of a compound are entirely different from those of the elements from which it is made.
- Some common examples of compounds are water, sugar, salt, aspirin, chloroform, alcohol and ether.

MIXTURES
- A material containing two or more elements or compounds in any proportion is a mixture.
- The components of a mixture can be separated by physical means like filtration, sublimation and distillation.

ATOMIC STRUCTURE

ATOM
- Atom is the smallest part of the element that takes part in a chemical reaction. Atom of an element can not be changed into that of another element by a chemical or physical means. It does not exist in free state.

MOLECULE
- A molecule is the smallest part of an element or compound that is capable of existing independently.

ACID
According to modern theory, an acid is a compound which yields hydrogen ions (protons) to a base in a chemical reaction. In a water solution, an acid tastes sour, turns blue litmus red and produces free hydrogen ions.

Acid Sources
Citric Acid Lemons or Oranges (Citrus Fruits)
Lactic acid Sour milk
Tartaric acid Grapes
Acetic acid Vinegar
Maleic acid Apples
Oxalic acid Tomato
Formic acid Red ants

BASES
- Such compounds which gives salt and water with acid known as bases. Bitter in taste, turns red litmus paper into blue, contains replaceable hydroxyl group.
- Some important bases are sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide.
- All alkalies are bases but all bases are not alkalies because all bases are not soluble in water.

SALTS
- Salts are ionic compounds containing a positive ion (cation) and a negative ion (anion).
- When an acid reacts with a base, a salt and water are formed. This reaction is called neutralization since the acid and base neutralize each other's effect.

ELECTROLYSIS
- The process of decomposition of an electrolyte by the passage of an electric current through its molten state or its aqueous solution is called electrolysis.
- Device through which electric current is passed known as electrodes.

METALLURGY
- Metals occur in nature, in the native (in free state) as well as in the combined state.
- Naturally occurring materials containing metals are called minerals.
- A mineral from which a given metal is obtained economically is called an ore.
- The process of extraction of a metal in a pure state on a large scale from its ore by Physical and Chemical means is called metallurgy.
- The rocky and siliceous matter that associated with the ore is known as gangue.
- Substance that is added to ore to remove the gangue is known as flux.

ATOMIC WEIGHT (OR ATOMIC MASS)
- The atomic mass of an element is the number of times its atom is heavier than 1/12th of the mass of carbon (C12) atom.
- The unit used to measure atomic mass is called atomic mass unit, i.e., amu.

ELECTRON
- The electron is a fundamental particle of an atom which carries a unit negative charge. It was discovered by J.J. Thomson in 1897.
PROTON
- It is a fundamental particle of an atom carrying a unit positive charge. It was discovered by Rutherford and Goldstein in 1886.

NEUTRON
- It is a fundamental particle of an atom carrying no charge.<br>I. was discovered by Chadwick in 1932.

ISOTOPES
- The atoms of the same element having different mass numbers are called isotopes.

ISOBARS
- Elements having the same atomic mass but differ in atomic number are called isobars.

ISOTONES
- Elements having the same number of neutrons are called isotones.

OXIDATION AND REDUCTION
- Oxidation is a process in which a substance adds on oxygen or loses hydrogen. In modern terms, oxidation is the process in which a substance loses electrons.
- Reduction is a process in which a substance adds on hydrogen or loses oxygen. In modern terms, reduction is the process in which a substance gains electrons.
- Oxidation and reduction always occur simultaneously. If one substance is oxidised, another is reduced. The reaction in which this oxidation-reduction process occurs is called a redox reaction.
- Oxidising agents are substances which bring about the oxidation o f other substances, e.g., Potassium Permanganate, Potassium Dichromate, Nitric Acid, Hydrogen Peroxide, etc.
- Reducing agents are substances which bring about the reduction of other substances, e.g., hydrogen sulphide, hydrogen, carbon, sulphur dioxide, etc.

ACIDS, BASES AND SALTS

ACID
- An acid is any compound that can react with a base to form a salt, the hydrogen of the acid being replaced by a metal. The reaction of an acid with a base is called a neutralization reaction. 
- The process of removal of gangue from the ore is known as concentration.
- Calcination is the heating of the ore in the absence of air.
This method is employed for obtaining the metal oxides from carbonates and hydroxides.
- Roasting is the heating of the ore in the presence of air.
On roasting, part of the ore is oxidised to form an oxide.
This oxide is then reduced to the metal.
- The industrial reduction process for obtaining metal from the treated ore is called smelting.

AMALGUM
- An alloy in which one of the component metals is mercury is known as amalgum.

IRON AND STEEL
- Iron is extracted from its ores by the blast furnace process.
- Iron obtained from blast furnace is called pig iron or cast iron containing about 5% carbon.
- Pure iron is called wrought iron which does not contain carbon more than 0.2%, or any other impurities or constituents.
- Steel contains 0.25% – 2% carbon and varying amounts of other elements.

CARBON AND ITS COMPOUNDS

ALLOTROPY
- Such substances which having the same chemical properties, but differ in physical properties, known as allotropes and this property is called allotropy.

DIAMOND
- Diamond is the purest form of carbon.
- It is non-conductor of heat and electricity.
- It is the hardest natural substance.
- It burns in air at 900°C and gives out CO2.

GRAPHITE (BLACK LEAD)
- It is good conductor of heat and electricity.
- Graphite is used in making lead pencils.
- Graphite is also used as electrodes, lubricant, moderators, electrotyping and carbon arc.

AMORPHOUS FORMS OF CARBON
1. Wood Charcoal – Obtained from wood
2. Sugar Charcoal – Obtained from cane sugar
3. Bone or Animal Charcoal – Obtained from animal bones
4. Coke Charcoal – Obtained from coal

CARBON MONOXIDE (CO)
- Carbon monoxide is an active poison and is very dangerous as it is a colourless and odourless gas and can not, therefore, be easily detected.
- The extremely poisonous nature of carbon monoxide is a result of its combining with the haemoglobin of the blood to form carbo-xyhaemoglobin, which is not decompassed by any of the processes in the body.

HYDROCARBONS
- Com pounds of carbo n an d h ydro gen are called hydrocarbon.
- A natural source of hydrocarbon is petroleum obtained from sedimentary rocks.
- Compounds having the same molecular formula but differ in properties due to different structural formula known as isomers and this property is called isomerism.

SATURATED HYDROCARBONS (ALKANES)
- Containing single covalent bonds only.
- Such compounds are, in general, called alkanes for instance, Methane, Ethane, Propane, Butane. UNSATURATED HYDROCARBONS
- Containing multiple bonds.
- Compounds with double bonds are called alkenes, e.g. ethylene, propyene etc. and triple bond containing compounds are called alkynes, e.g. acetylene, propyne etc.
- Benzene is an unsaturated cyclic hydrocarbon with the structure.
- Compounds derived from benzene are called aromatic compounds.

FUELS

Solid Fuels
- These contain carbon and, during combustion, form mainly carbon dioxide and carbon monoxide with a large amount of heat.
- Examples of solid fuels are wood, coal, coke and paraffin wax.

Liquid Fuels
- These are basically mixtures of several hydrocarbons.
During combustion, they form carbon dioxide and water.
- Liquid fuels are obtained as different fractions during the distillation of petroleum.
- Examples of liquid fuels are kerosene oil, petrol, diesel oil and alcohol.

Gaseous Fuels
- Gaseous fuels do not leave ash on burning and have high content of heat.
- The main gaseous fuels are liquefied petroleum gas (LPG, mainly a mixture of propane and butane and used in homes for cooking, water gas (CO + H2), producer gas (CO+ N2), coal gas (mixture of hydrogen, methane, ethylene, carbon monoxide, nitrogen, oxygen and carbon dioxide) and natural gas (mixture of methane, ethane, propane and butane with traces of higher hydrocarbons obtained from oil well, above petroleum).

PETROLEUM AND NATURAL GAS
- Natural gas contains about 80% methane and 10% ethane, the remaining 10% being a mixture of higher gaseous hydrocarbons.
- Compressed Natural Gas (CNG) is natural gas filled in cylinders under high pressure.
- The quality of petrol for use in car engines is denoted by their anti-knock properties.
- To increase octane number, tetra ethyl lead (TEL) is added to petrol.

HEAVY WATER
- Chemically heavy water is deuterium oxide.
- Heavy water is used in nuclear reactors as a moderator because it slows the fast moving neutrons.

Hard and Soft Water
- Water which produces lather with soap solution readily is called soft water.
- Water which does not produce lather with soap solution readily is called hard water.
- The hardness of water is due to presence of the bicarbonates, chlorides and sulphates of calcium and magnesium.
- Temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium.
- Permanent hardness of water is due to presence of sulphates, chlorides, nitrates of calcium and magnesium.

GLASS
- Ordinary glass is solid mixture of silica, sodium silicate and calcium silicate.
- Soft glass is a soda-lime silicate glass. It melts at low temperature. It is used in manufacturing of bottles, test tubes etc.
- Hard glass is potash lime silicate and melts at high temperature in comparison to soft glass and is used in manufacturing of flask etc.
- Flint glass is a lead potash silicate and is used in manufacturing of prism, lens and optical instruments.
- Pyrex glass is a mixture of sodium aluminium borosilicates.<br>I. is used in manufacturing of high quality equipments in laboratory because it does not melt at very high temperature.
- Safety glass is prepared by placing a layer of transparent plastic glass between two layers of glass by means of a suitable adhesive. It is used in making wind screen of automobiles, aeroplanes, trains etc.

CEMENT
- The approximate composition of Portland cement is:
1. Calcium Oxide  62%
2. Silica  22%
3. Alumina  7.5%
4. Magnesia  2.5%
5. Ferric Oxide  2.5%
- A small amount of gypsum is added to slow down the setting of cement.
- Cement containing excess amount of lime cracks during setting while cement containing less amount of lime is weak in strength.
- Cement containing no iron is white but hard to burn.

POLYMERS AND PLASTICS
- A polymer is a large molecule, built up from many hundreds of thousands of small unit called monomeric units or monomers.
- The process of formation of polymers from monomers is called polymerization.
- Plastics are cross-linked polymers and very tough.
- Some examples of plastics are — Celluloid, Bakelite and Vinyl Plastics.

RUBBER
- Natural and Synthetic rubbers are examples of polymers.
- Natural rubber is isomer of isoprene.
- When the natural rubber is heated along with sulphur called vulcanisation. The resulting rubber is elastic, hard and strong.
- Synthetic rubbers are made by polym erisation of chloroprene, styrene and butadiene mixtures and isobutylene.

SOAPS
- The soaps are sodium salts of higher fatty acids. They are useful only in soft water as they form an insoluble precipitate in hard water. This precipitate consists of salts of calcium and magnesium of higher fatty acids. No lather or emulsion is formed and washing is not possible.

Some Importants Alloys
Alloys - Composition

Brass Cu, Zn
Bronze Cu, Sn
Gun metal Cu, Sn, Zn
Bel metal Cu, Sn
German silver Cu, Zn, Ni
Dutch metal Cu, Zn
Aluminium Al, Cu
Nichrome Ni, Fe, Cr, Mn
Chromium steel Cr, C, Fe

FOOD
- It is a nutritive substance taken by an organism for growth, work, repair and maintaining life processes. It provides energy to do work and maintain body heat, provides materials for the growth of the body, makes necessary materials for reproduction and provides materials for the repair of damaged cells and tissues of our body.

Chemical Formulae, Commercial Name of Chemical Compounds
Commercial Name - Chemical Compounds  - Chemical formulae

Common salt Sodium chloride NaCl
Baking soda Sodium bicarbonate NaHCO3
Washing soda Sodium carbonate Na2CO3 . 10H2O
Caustic soda Sodium hydroxide NaOH
Chilli salt peter Sodium nitrate NaNO3
Soda ash Sodium carbonate Na2CO3
Hypo Sodium thiosulphate Na2S2O3 . 5H2O