SUDESHNA PAUL EDUCATIONAL COMPANION

 

 

CHEMISTRY

 

 

 

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   MAGIC FIRE

GOLDEN RAIN

PHOTOCHEMICAL REACTION

BARKING  DOG

MAKE SILVER SHINNY

CHEMICAL BONDS

VOLCANO

 Electrodeposition
Hydrometallurgy Crystal Structure Forms of Corrosion

 

 

 

 

 
 MAGIC FIRE

You can show  magic by creating fire without matches. Just take a pinch of red chromium oxide and touch it with ethanol. The reactions are as follows

2 CrO3 + C2H5OH + 3/2 O2==> Cr2O3 + 2 CO2 + 3 H2O 

In this reaction fire is obtained from strong oxidizing agents by reacting it with inflammable organic components . The process involves a lot of heat as the reaction  is exothermic, it releases huge heat which can ignite ordinary substances like paper

 

 

Prepared by S Paul

 

 

 

 

 

 

GOLDEN RAIN

The same beauty of gold can be obtained by a simple  chemical reaction without using any gold. When lead nitrate reacts with potassium iodide then a golden yellow precipitate of lead iodide is formed. When the precipitate is heated with hot water (70degree) along with little acetic acid  ,  then cooled ,dried and placed in a flask,  attractive shiny golden rays will illuminate its sides. It will appear as rainy golden shower. 

The reaction :-

Pb(NO3)2 + 2 KI ==> PbI2¯ + 2 KNO3                              

 

 

 

 

 

 

 

BARKING  DOG

 

 

THE REACTION BETWEEN  NITROUS-OXIDE OR NITROGEN MONOXIDE AND CARBON DISULPHIDE FORMS AN EXPLOSIVE MIXTURE .

WHEN THE MIXTURE IS IGNITED IN THE TUBE , THE SOUND OF A DOG BARKING COULD BE CLEARLY HEARD, EVEN THOUGH THERE IS NO DOG PRESENT . THE EXPLOSION BECOMES MORE VIOLENT WHEN THE TUBE'S DIAMETER IS INCREASED ,IT IS FOLLOWED BY A BLUE FLAME. THIS PECULIAR SOUND IS HEARD AS THE MIXTURE MOVES MODERATELY IN THE TEST TUBE. THE REACTION :-

3 NO + CS2==> 3/2 N2 + CO + SO2 + 1/8 S8                            

4 NO + CS2==> 2 N2 + CO2 + SO2 + 1/8 S8   

 

 

 

 

 

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MAKE SILVER SHINNY
If you have any objects made from silver or plated with silver, you know that the bright, shiny surface of silver gradually darkens and becomes less shiny. This happens because silver undergoes a chemical reaction with sulfur-containing substances in the air. You can use chemistry to reverse the tarnishing reaction, and make the silver shiny again.

Line the bottom of the pan with aluminum foil. Set the silver object on top of the aluminum foil. Make sure the silver touches the aluminum. To the hot water, add about one cup of baking soda for each gallon of water.  The mixture will froth a bit and may spill over; this is why you put it in the sink. Pour the hot baking soda and water mixture into the pan, and completely cover the silver. All of the tarnish will disappear within  minutes. If the silver is badly tarnished, you may need to reheat the baking soda and water mixture.

When silver tarnishes, it combines with sulfur and forms silver sulfide. Silver sulfide is black. When a thin coating of silver sulfide forms on the surface of silver, it darkens the silver. The silver can be returned to its former luster by removing the silver sulfide coating from the surface.

In the reaction, sulfur atoms are transferred from silver to aluminum, freeing the silver metal and forming aluminum sulfide. Chemists represent this reaction with a chemical equation.

3 Ag2S   +   2 Al   =   6 Ag   +   Al2S3
silver
sulfide
aluminum silver aluminum
sulfide

 

 

 

 

 

 

 

 

 

 

 

 

 

VOLCANO
The orange crystals of ammonium dichromate, if heated to a sufficient temperature, start to decompose producing voluminous green chromium(III) oxide.  Once started the reaction is self-supporting because it does not require any external oxidising or reducing agents.  In fact, both the oxidant (Cr+6) and the reductant  (N-3) are present in the same molecule,

(NH4)2Cr2O7==> Cr2O3 + 4 H2O + N2                            (13.1)

            Normally this demonstration is performed as the classical Volcano experiment, so called because ash produced occupies a far greater volume than that of the original dichromate and so builds a ‘mountain’ of dark green ash with sparks and read heat emanating from a ‘Caldera’ at its summit. 

 

 

 

PHOTOCHEMICAL REACTION

 

 

 

 

The light-initiated reaction of hydrogen and chlorine H2 + Cl2 is  an example of photochemical reaction and also can be used to demonstrate that energy is often required for a reaction to begin. This is a free radical chain reaction which is initiated photochemically by the homolytic cleavage of chlorine molecules to give chlorine atoms.

Cl2 + 245.5 kJ = 2 Cl·

The cleavage of one mole of chlorine by photodissociation requires 1 mole of light quanta (hn).  Since an amount of energy equal to 243.5 kJ corresponds to a wavelength of 491 nm, only blue light or light of even shorter wavelengths can be used, but not longer-wavelength yellow or red light.  Thus the chlorine-hydrogen reaction is initiated by blue light but not red light