Observation of sand and water separation

When sand and water are mixed in equal or unequal proportions, a heterogeneous mixture results.This mixture can be separated by following the processes of:

1)Sedimentation

2)Decantation

 

The mixture of sand and water is taken in a beaker and allowed to stand for sometime. The sand being heavier than water and insoluble in water settles at the bottom of the beaker. Next process is decantation.



Separate sand from water – Decantation

A process by which the clear liquid above the sediment is slowly separated by pouring out the liquid into another container. The clear liquid is called  “supernatent” liquid.



Thus the  separation of the mixture of sand and water can be achieved in two steps viz  sedimentation and decantation.

Separate sand from water – Significance

The separation of a mixture does not  involve any chemical reactions nor does it require any energy input.

The separation of a mixture involves only physical methods and the constituents can be recovered  from the mixture without destroying any of the properties of either of the constituents.

The above methods of separation of sand from water support these observations. The methods of sedimentation and decantation are especially useful when the particle size of the insoluble impurity (sand in this case) is sufficiently big as to be isolated  from the mixture  without affecting the properties of either constituent.

These are some  of the most common methods used in almost every house hold for  many years to isolate the insoluble large particle sized impurities from water or from any solvent.

However the only drawback of this method is that the supernatant liquid is  not obtained in a very pure form and the insoluble impurity has to be dried if it has to be obtained in the pure dry state.

The principle behind the sedimentation is that the insoluble impurities being heavier can easily settle down  under the influence of gravity.

The importance of this process lies in the work of a river as the river flows on the surface of the earth. As the river corrodes the rocks and carries the broken pieces along its path downhill and flows through the plains the larger pieces of the rocks get deposited along the river bed and while it flows through the plains the finer particles get deposited in the river bed and the supernatant water with the soluble salts are carried away to the sea. The final result is large deposits of silt on the plains and the rich deposit

Most likely a is the answer - because  you generate   38 atp's but also consume an atp.   each atp gives approx. less than 4 kcal so probably a is the closest answer.