Chemistry Notes for Prelims-2

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