Here we are providing the short notes on Chemistry which will be help to crack science part in may examinations like SSC, Railway and other competitive exams.
MATTER AND ITS NATURE
- Matter can exist in three states-
- The forces of attraction between the particles(inter-molecular force) are maximum in solids, intermediate in liquids and minimum in gases. The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases.
- The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.
- The process of melting, that is, change of solid state into liquid state is also known as fusion.
- Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state. The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed. Evaporation causes cooling.
- Burning of coal, wood or leaves is a chemical change. Explosion of a firework is a chemical change. If you leave a piece of iron in the open for some time, it acquires a film of brownish substance. This substance is called rust and the process is called rusting. The process of rusting can be represented by the following equation: Iron (Fe) + Oxygen (O2, from the air)water (H2O) rust (iron oxide-Fe2O3) For rusting, the presence of both oxygen and water (or water vapour) is essential. It is a chemical change.
- Prevent iron articles from coming in contact with oxygen, or water, or both. One simple way is to apply a coat of paint or grease. Another way is to deposit a layer of a metal like chromium or zinc on iron. This process of depositing a layer of zinc on iron is called galvanisation.
- Stainless steel is made by mixing iron with carbon and metals like chromium, nickel and manganese. It does not rust.
- A solution is a homogeneous mixture of two or more substances. The major component of a solution is called the solvent, and the minor, the solute. Lemonade, soda water etc. are all examples of solutions. We can also have solid solutions (alloys) and gaseous solutions (air).
- The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed, that is, a solution is stable.
- The concentration of a solution is the amount of solute present per unit volume or per unit mass of the solution/solvent. A suspension is a heterogeneous mixture.
- Colloids are heterogeneous mixtures in which the particle size is too small to be seen with the naked eye, but is big enough to scatter light.
- The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium.
Metals & Nonmetals
- Metals are generally good conductors of heat and electricity.
- Silver is the best conductor of heat followed by copper.
- Mercury offers a very high resistance to the passage of electric current.
- Metals are generally hard but sodium and potassium are so soft that they can be easily cut with a knife.
- Metals are malleable and ductile. Gold and silver are most malleable and best ductile metals.
- Metals are solids at room temperature except mercury (mp – 39°C) which is liquid, caesium (mp 28.4°C) and gallium (mp 29.8°C) are liquid above 30°C.
- Metals are electropositive in nature, they ionize by the loss of electrons and form positive ions.
- Almost all the metal oxides are basic in nature but zinc oxide and aluminium oxide are amphoteric.
- Lithium, sodium, potassium, rubidium and caesium are alkali metals. Alkali metals are stored under kerosene or liquid paraffins to protect them from action of air.
- Metallic sodium is prepared by the electrolysis of molten mixture of 40% sodium chloride and 60% calcium chloride in a Down’s cell.
- Sodium bicarbonate, baking soda is used in effervescent drinks and fruit salts in fire extinguishers and it is also used in the form of sesquicarbonate. It is used for wool washing.
- Sodium carbonate washing soda is used in the manufacturing of glass, soap, washing powder and for softening hard water.
- Mixture of sodium carbonate and potassium carbonate is known as fusion mixture.
- Sodium sulphate is Glauber’s salt. It is used as purgative.
- Sodium thiosulphate or Hypo It is used in the photography as a fixing agent.
- Potassium superoxide used in space capsules, submarines and breathing masks as it produces oxygen and removes carbon dioxide and carbon monoxide.
- Potassium cyanide (KCN) is used in the extraction of silver, gold and as a germicide in agriculture. KCN is more poisonous than sodium cyanide.
- Potassium hydroxide (KOH) is known as caustic potash used in the preparation of soft soap. Its aqueous solution is known as potash lye.
- Potassium carbonate is potash or pearl ash.
De-icing of Roads after snowfall
De-icing in the process of removing ice from a surface by using salts on the surface. Now-a-days, liquid and are also used for this purpose.
Alkaline Earth Metals and their Compounds
Beryllium, magnesium, calcium, strontium, barium and radium are collectively known as alkaline earth metals. Be is amphoteric in nature. Mg is called milk of magnesia and used as an antacid.
Calcium oxide (CaO) is also called quick lime. It is used in the manufacturing of glass, calcium chloride, cement, bleaching power, calcium carbide, slaked lime, in the extraction of iron and as a drying agent for ammonia and alcohol.
Calcium hydroxide, slaked lime is used in the manufacturing of caustic soda, sodalime and for softening of hard water.
Calcium sulphate, gypsum loses a part of its water of crystallization when heated upto 120°C to from which is known as plaster of Paris.
Plaster of Paris is a white powder, which sets into hard mass on wetting with water and it is used in making statues, toys, etc., in medical applications of setting fractured bones in right positions and indentistry.
Some Important Metals and their Uses
It is a semimetal (metalloids). In the nature, it occurs in combined state as borax.
Boron and boron carbide rods are used to control the nuclear reactions.
Boron carbide is hardest, known as an artificial substance after diamond and is known as Norbia.
Orthoboric acid is used as an antiseptic and eye wash under the name boric lotion.
It is a third most abundant element of Earth’s crust. It is extracted from bauxite . Aluminium powder is used in fireworks, flash light powder, thermite welding.
Ammonal (a mixture of aluminium powder and ammonium nitrate) is used as an explosive.
Ruby and sapphire are essentially Ruby is red due to the presence of Cr and sapphire is blue due to Fe and Ti. Emerald is green, it contains Ca/Cr and aluminium silicates .
The important ore of tin is cassiterite or tin stone. In cold countries, white tin is converted to grey tin (powder), the process is known as tin disease or tin plague. Tin plating is done to prevent the rusting of iron. Tin amalgam is used in making mirrors. Pentahydrate of stannic chloride , is called butter of tin used as mordant in dyeing.
Lead is mainly found in the form of sulphide ore called galena (PbS). Red lead (minium or sindhur) is used for making protective paint for iron and in match industry.
It is used for making core of nuclear reactors and for making pumps, valves and heat exchangers.
Vanadium pentoxide is a very good catalyst for manufacturing of sulphuric acid by contact process.
Tungsten filaments are used in electric bulbs. Calcium tungstate is used in X-ray tube.
It is extracted from its haematite ore.
Cast iron It is the most impure form of iron and contains 2.5–4% carbon.
Wrought iron or Malleable iron is the most purest form of iron and contains minimum amount of carbon (0.12–0.5%)
Iron (II) is present in haemoglobin (blood).
Mild steel contain 0.25%–0.5% carbon while hard steels contains 0.5%–1.5% carbon. Soft steels contain carbon upto 0.25%.
Stainless steel is an alloy of iron (Fe), chromium (Cr) and nickel (Ni). Ferric chloride is used as stypic to stop bleeding from a cut. Ferrous sulphate is used in making blue black ink.
Copper, Silver and Gold (Cu, Ag and Au)
These are called coinage metals. Silver is used as amalgam for filling teeth and in silvering mirrors. Silver bromide (AgBr) is used in photography. is called lunar caustic used in preparing marking inks and hair dyes.
is called blue vitriol or nila thotha and is called fool’s gold.
Mercuric sulphide (HgS) is used as a cosmetic in Ayurvedic medicine as Makardhwaja.
It is used in galvanization to prevent rusting of iron. Zinc sulphide is used in the preparation of X-ray screens.
Zinc oxide is known as philosopher’s wool. Zinc sulphate is white vitriol.
The process of extraction of metals from their ores is called metallurgy.
Minerals, Ores and Gangue
The natural substance in which metals and other impurities found in combined state, are called minerals.
The minerals from which metal can be extracted conveniently and beneficially, are called ores. Gangue or matrix are the impurities associated with the ore.
Chile salt petre
Some Important Alloys and their Uses
These may be solid, liquid or gas (bromine is the only liquid non-metal).
These are soft, non-lustrous, brittle, non-sonorous and non-conductor of heat and electricity. These have low melting and boiling points. These from oxides with oxygen which are generally acidic. Their examples include noble gases, i.e. helium (He), neon (Ne), argon (Ar), krpton (Kr), xenon (Xe) and some other p-block elements like chlorine , bromine and phosphorus (P) etc.
Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods.
Pure metals have poor mechanical properties. Hence, they are not used in their pure form in industry. Their properties are modified by adding other elements.
Characteristics of alloys:
Alloys are harder and tougher than the base metal and are resistant to corrosion.
They are inert to commonly used chemicals and are magnetisable and ductile.
Alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition.
Alloys of mercury with other metals like sodium, potassium,gold and zinc…etc are called amalgams.
Amalgams stored in iron bottles as iron cannot form amalgam with mercury.
Rold Gold is a metal, such as brass, coated with a thin layer of gold, usually of above 9 carat purity.
Composition- zinc 30%, copper 70%
uses- In making of utensils, pipes and radiator statues etc.
composition – Cu 67%, Zn 33%
uses – Hardware items
Composition – Copper 90%, Tin 10%
uses – In making of coins, ornaments, utensils and statues.
composition – Fe 82%,(Ni + Cr) 18
uses – In making of surgical instruments, watches and utensils etc.
composition- Al 95% ,Mg 5%
uses – In making light articles and physical balance etc.
composition- Al 95%, Cu 4% ,Mn 0.5%
uses -In making parts of aeroplane and ship etc.
composition – Al 8-12% , Ni 15-26% , Co 5-24% ,Cu 6%
Remaining: Fe, Tl
uses – It is useful in making of magnets.
composition – Cu 60% ,Zn 20%, Ni 20%
uses – It is useful in electroplating and making of utensils.
composition – silver 92.5%, copper 7.5%
uses – jewelry, art object
composition – Cu 88%, Sn 10%,Zn 2%
uses – It is useful in making of guns, machine parts and canons.etc
composition – Pb 50%, Sn 50%
uses – It is mainly useful to join electric wires.
composition – copper – 77%, tin – 23%
uses- casting of bells
coin metal –
composition – copper 75%, nickel 25%
uses – U.S coins
composition – Bi 50%, Pb 25%, Sn 12.5%, Cd 12.5%
uses – fuse plugs, automatic sprinklers.
composition – Ni 67%,and copper, with small amounts of iron, manganese, carbon, and silicon.
uses – It is resistant to corrosion and acids and thus used for making valves, pumps, shafts, fittings, fasteners, and heat exchangers.
composition – Pb 67%, sn 33%
uses- soldering joints.