Demonstration

PHYSICS

Aim : To show that heat transfer in water is due to convection.

 

Materials Needed : A beaker, water, candle, match box, potassium permanganate crystals/ artificial food colouring and a spoon.

 

Procedure :  

1) Fill the beaker to the half way mark with clear water.

2) Take a pinch of the potassium permanganate crystals/food colouring and drop it gently to the bottom of the beaker.

3) Let it settle for few minutes.

4)You will see that the water at the bottom of the beaker is coloured, but the water at the top is quite clear. Light the candle and pick up the beaker very gently and hold it on top of the candle flame.

 

Observation :

You will see columns of coloured liquid rise up in the beaker.

 

Conclusion :

This is due to convection. Water molecules at the bottom get heated and rise up, carrying the heat energy with them.

 

 

CHEMISTRY 

Aim : Burning of magnesium ribbon.

 

Materials Needed : Magnesium ribbon, candle, matchbox, litmus paper, sand paper,watch glass and water

 

Procedure :  

1) Take a small piece of magnesium ribbon and clean it with sand paper.

2) Light the candle and bring tip of Mg ribbon near a candle flame.When the Mg ribbon is burnt completely collect ash in a watch glass. [Reaction : Magnesium(Mg) + Oxygen(O2) = Magnesium oxide(MgO)]

3) Mix the ash with small amount of water. Stir the mixture well. [Reaction :

Magnesium oxide(MgO) + water()H2O) =Magnesium hydroxide[Mg(OH)2]

4) Test the mixture with blue and red litmus paper.

5) If red litmus turns blue then base and blue turns red then acid.  

Observation :

You will see red litmus paper turns blue.

 

Conclusion : 

It means Magnesium hydroxide is a basic solution.

 

  BIOLOGY 

Aim: to study effect of saliva on starch.

 

Materials needed : Two test tubes, boiled rice, iodine solution, boiled chewed rice and water.

Procedure :

1) Take two test tubes. Label them 'A' and 'B'.

2) In test tube 'A' put one teaspoonful of boiled rice, and in test tube 'B' put one teaspoonful of boiled rice chewed for 2-3 minutes.

3) Add 3-4ml of water in both the test tubes.

4) Now pour 2-3 drops of iodine solution in both the test tubes and observe.

Observation : The solution in test tube 'A' turns blue-black in colour. However, the solution in test tube 'B' does not change colour.

 

Conclusion : The solution in test tube 'A' turns blue-black in colour indicating the presence of starch. However, the solution in test tube 'B' does not change colour indicating the absence of starch. This shows that the starch in test tube 'B' has been digested by by the digestive juices present in the saliva.