Chemistry Notes for Prelims

SCOPE OF CHEMISTRY:

Deals with matter and the changes that matter undergoes when subjected to the action of heat light, electricity and other matter.
Elements: Substance which cannot be subdivided by any physical or chemical method.
Metals: Silver, Gold, copper sodium etc
Non metals: Oxygen, hydrogen sulphur etc.
Mixtures and compounds :
Iron + Sulphur = Mixture – Possesses both properties of iron and sulphur.
Iron + Sulphur-------------- Heated----FeS--- Compound- Properties of Iron and sulphur are lost.

Kinetic Theory of Matter: It says the pressure of a gas as due to bombardment of the wall of the vessel by the molecules of the gas.

Chemical Reactions:
Decomposition: (AB-------------- A+B)
Combination: (A + B--------------AB)
Double decomposition: (AB + CD----------- AD+ BC)
Displacement: (A +BC---------------- AC + B )

If the heat is evolved in a reaction it is called exothermic if heat is absorbed it is endothermic reaction.

ATOMIC STRUCTURE:
First given by John Dalton : says atom is indestructible.

Nucleas: Rutherford. The entire mass is concentrated in the nucleus which contain protons and neutrons, their total number equal to atomic mass.

The atomic number which is net positive charge on nucleus is equal to the number of protons.
Since the atom is electrically neutral , a number of electrons is equal to the number of the protons revolve around the nucleus.

Chemical Bonding: The force of attraction which binds the atoms in a molecule is called Chemical bonding.

Isotopes: They are atoms of the same element having the same atomic number but different atomic masses. They differ in the number of neutrons in the nucleus.

Nuclear fission: When certain heavy atoms like Uranium are bombarded with high velocity neutrons, new fast moving neutrons are released along with a large amount of energy. This process is called neuclear fission.

If all the neutrons are used in producing more fission a rapid and violent reaction takes place. This is the basis of the atomic bomb.

Nuclear Fusion: The two isotopes of hydrogen eg. Deutruim and Tririum react to produce, helium, neutron and a flood of energy. This is called fusion, and forms the basis of H-bomb.

Oxidation and Reduction:
Occur side by side.
Wherever there is oxidation, there is reduction.
When Chlorine oxidized Hydrogen sulphide to Sulphur, Hydrogen Sulphide reduces Chlorine to Hydrogen Chloride. Cl2 + H2S--------------- 2HCl + S

Oxidation: Removal of hydrogen or addition of oxygen or removal of electrons.
Reduction: Addition of hydrogen or removal or oxygen or addition of electrons.

Mathces: Side of the Box: Red phosphorous or phosphorous trisulphide.
Match Sticks: Impregnated with borax- so that they can be extinguished without glowing for a long time.

Heavy Water:
Discovered by Urey.
Contains heavy hydrogen atom i.e deuterium(D)
Formula D2O
Density 1.106

Used in Nuclear reactors to absorb neutrons

Deliquescence and Efflorescence

* Solids like NaOH and Cacl₂ become damp on exposure to moist air. Such substances are called deliquescent substances.

* On the other hand, crystals of washing soda loses a part of water of crystallisation (Na₂CO₃ . 10 H₂O) and crumble into powder. Such substances are called efflorescent substances.

_{FIRE EXTINGUISHERS}

Two methods of extinguishing a fire are:

a. Cutting off the supply of air.

b. Cooling the flames below the ignition temperature.

types:

Ordinary: Mixture of Water and CO₂

Foam Type: Fire covered by foam of oil and Sodium Bicarbonate.

Electrical Fires: Heavy Carbon Tetrachloride is put on fire.

COMBUSTION: It is the process of burning accompanied by the liberation of heat and light.

* It may take place in the presence of gases which support combustion eg.Oxygen or Chlorine.

* Farther the substance which burns must be raised to a particular temperature called ignition temperature.

EXPLOSION: It is sudden expansion of gases with a loud noise, owing to release of internal energy.

COMPOSITION OF AIR: Nitrogen: 78%, Oxygen: 21%, Argon: 0.9%

* Air is only a mixture and is not a compound.

* Oil contains unsaturated compounds. They add hydrogen and are converted into solid fats. This hydrogenation of oil is called 'vanaspati'.

Peculiar Properties of Water: Even though molecular weight of water is low, it has unusually high boiling point. It is denser than ice.

Solid CO₂ used in refrigerators is called dry ice.

Carbonic Acid is also known as soda water.

A Fuel is a substance that is used to produce heat energy.

Carbon Cycle: During day time , plants take up CO₂ from air and return oxygen. At night the plants take in oxygen and gives out CO₂. This cycle serves to maintain the % of CO₂ in air fairly constant.

Gobar Gas: Obtained by fermentation of cow dung and water, inside a pit in the absence of air, also called 'biogas' used for running cooking, tubewells etc.

Aqua Regia: A mixture of Conc. HCl and conc. HNO₃ in the ratio of 3:1 is called aqua regia. It can dissolve Gold and Platinum.

Laughing Gas: Nitrous Oxide: When inhaled, produce laughing. Used as anesthetic