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Home Ex. Chem.

posted Jan 14, 2016, 8:34 PM by Upali Salpadoru   [ updated Oct 17, 2016, 7:38 PM ]

Home Experiments Chemistry.


1.Making Oxygen.


We have all heard of Oxygen but never seen it; 

‘cause you can’t see it. 

It is a colourless gas and as such invisible as air.

There are different ways to make a sample of this gas.  



Method 1

                               Adult supervision Essential


You need.

  • Condys (Potassium permanganate)   

                                      Can be purchased from a Pharmacy.

  • Hard glass test tube.  

                               A substitute such as from a fused bulb or even a fish tin may be used.                                                                                                                       

  • Test tube holder.         

                                          Can be improvised by splitting a piece of wood.

  • Burner            

                                                A tin may be kept on a hot plate.

  • Joss stick or a thin wood splint


Method.


TT.jpg

Add about a teaspoon of dark purple condys crystals into a hard glass test tube.










Theory:-


Potassium permanganate → Potassium manganate  +  Manganese dioxide + Oxygen.


2KMnO4     →  K2MnO4  +  MnO2  + O2


Nelly.jpg

How do we know that the gas is Oxygen?



Test for Oxygen

The usual test for Oxygen is the glowing splint test.

When you expose a glowing red splint into the gas , it will start burning with a flame.



Method 2.

You need:-

  • Hydrogen peroxide ( solution)

                    (From a pharmacy or a beauty saloon)

  • Empty bottle (medium)

  • Some baker’s yeast.

  • Glowing splint Or a Joss stick.


Theory:

Ox 1.jpg


Hydrogen peroxide is an unstable compound. Oxygen is bound to water very loosely.  So it can decompose as indicated here.

                               H2O2 = H2O + O2

When this solution is used on wounds oxygen bubbles fizzed out. It is due to an enzyme catalase present in blood.

There are many substances that catalyze this reaction. In labs they use a black powder called Manganese dioxide. This substance is present in torch cells mixed with carbon.


For this experiment we suggest the use use of Live yeast.


Method:-

O2 test.jpg

Add a few ml. of Hydrogen peroxide solution into the bottle. Then add the live yeast slowly and watch what happens.

You will soon realise that a gas has been released.

If it is Oxygen  it will  catch fire.

            

      Physical Properties of Oxygen

  Colour……….Colourless

        Odour……….No smell

              Weight………16 times heavy as Hydrogen

                      Solubility ……..  Slightly soluble


2.Making Carbon dioxide.

    This is also a colourless, odourless gas.  Although this is essential for photosynthesis , there is only a very, very small percentage of CO2 (0.03%) in the atmosphere.

The gas that comes out of fizzy drinks is CO2


There are 3 kinds of soda we commonly use. :-

  1. Drinking soda.             This is a solution of CO2 gas in water.

          Warming or reduced pressure will decompose this substance.

                    H2CO3  =   H2O + CO2

  1. Washing soda    Na2CO3      Sodium carbonate  used for washing.

                    All acids have H+  ions. These react to release the gas.

                   2 Na+  +  CO3 - -    +  2 H+   =    H2CO3   +  2 Na+

                                   H2CO3   =  H2O  +   CO2

  1. Baking soda,     NaHCO3       Sodium hydrogen carbonate.( Sodium bicarbonate) Used to raise the dough for making bread.


             This gives the gas when heated,

         2 NaHCO3   =       Na2CO3  +  H2O + CO2


Carbon dioxide may be obtained from any of the above three. Let us use NaHCO3



You need:-


U need 2.jpg

Theory:-

Baking powder has Sodium hydrogen carbonate. Vinegar has about 4% acetic acid.

Sodium bicarbonate + Acetic acid = Sodium acetate +water +Carbon dioxide.

                 NaHCO3 + CH3COOH → CH3COONa + H2O + CO2(g)


Method:-

Nelly.jpg

    Add the baking powder into the bottle up to a height of about 2cm.  Then slowly add the vinegar slowly. Effervescence will start immediately. The gas coming out is carbon dioxide.

The gas may be collected into a balloon.

How do you know?


Testing for Carbon dioxide:-

Release the gas from the balloon slowly to bubble through lime water.(not lime juice) Ca(OH)2


In the presence of Carbon dioxide colourless lime water, changes to a white colour. This can be prepared by dissolving burnt lime ,Calcium oxide or Calcium hydroxide in water.



Co2 test.jpgFig. Passing Carbon dioxide through lime water.


Physical Properties of Carbon dioxide.
Colour -  No colour.
Odour - No smell.
Weight- Slightly heavier than air.
Solubility- Slightly soluble 
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