Question

What difference did you see in water with salt and water with chalk powder after keeping for some time?

Answer 1

Hint: The miscibility of different substances with water depends upon various factors such as particle sizes, the type of solid, the nature of bonds present in the compound, the hydration enthalpies and the temperature at which the experiment is being carried out.

Complete answer:
Common salt is chemically known as sodium chloride. It is an ionic compound made up of sodium metal cations and chloride anions. Ionic compounds have a tendency to dissociate into their constituent ions upon dissolution and remain in the solution in the hydrated form.
Thus when water and salt are mixed, the salt particles occupy the vacant spaces in between particles and give a crystal clear solution with no residues left behind.
Chalk power mainly consists of calcium carbonate and has low solubility in water. Upon dissolving in water, the large particles of chalk powder that remain undissolved remain dispersed in the solution for initial few minutes but settle down at the bottom of the container after allowing the solution to rest for a few minutes.
Therefore the difference between salt and chalk powder dissolved in water is that the salt and water mixture is a homogenous solution that remains crystal clear throughout but the mixture of salt and water forms a suspension in which the white chalk powder eventually settles down (a heterogeneous mixture).

Note:
The low solubility of calcium carbonate in water is associated with the large size of both calcium and carbonate ions. Their comparable sizes lead to high lattice enthalpy yet low hydration enthalpy that effectively reduces the solubility of chalk powder in water.