Activity Based Science Learning >Water floating on water


Introduction -  We  see many things happening in the kitchen. For instance, floating of  oil on water and mixing of same type of liquids with one another. Adding a little milk to water it whitens it by getting mixed with the whole of water. Similarly, adding a few drops of ink on a glass filled with water makes the entire water acquire the colour of the ink. But, is it possible that a few drops of ink make only the upper portion of the water coloured? In this experiment we are going to do something of this sort.  

Required material – A drinking glass, red (or some other) colour, coffee heater ( a device used for heating water). 

Procedure –

1.         Fill a drinking glass little more than half with water.

2.         Immense the coffee heater in the glass in such a manner that only some of the upper portion of water is in contact with the heater so that only the upper portion of the water is heated.

3.         Take out the coffee heater from the glass in such a manner that water in the glass is not disturbed.

4.         Now ad a few drops of red (or some other) colour from  the sides of the glass into it so that the water is not disturbed. 

After some time, watch if the entire water or only other upper portion of it acquires the red colour? You will sea that only the upper portion of water becomes red while the lower portion of water remains colourless. i.e. the upper portion of water in the glass floats above its lower portion.  

Discussion : When we throw a piece of wood into water it floats on it. But, when we drop a steel spoon into water it sinks. It is for the simple reason that the density of wood  is less than that of water while the density of steel is greater as compared to water. An object of lower density floats on an object of greater density. The oil because of its low density as compared to water floats on it. In our experiment, the upper portion of the water was heated. Its density, therefore, decreased while the density of the lower portion of water, which did not receive heat, remained the same. So, the upper portion of water kept floating on the lower portion and did not get mixed up with it. As the red colour had first spread over the upper portion of water, it remained there and did not spread to the lower portion. 

Do and think A little more – What will happen when water of the upper portion becomes cold? Will you in that case also observe coloured water in the upper portion and clear water on the lower portion? If we add some colour on a glass filled with cold water, will only the upper portion of water be coloured? Think, if densities of both the liquids are same they should remains where they are and should not get mixed up with each other. However, this does not happen and the two liquids get mixed up making the entire water coloured. This is due to the BROWNIAN motion of the molecular of liquids.

 

 

 





 


Back on top ^