Question

You are given a mixture of salt and sand. Can you separate them by picking?

Answer 1

Hint: For the picking method the two or more substances must have a considerable difference in their size so that they can be separated easily. The size of particles of salt and particles of sand has almost the same size.

Complete answer:
Hand-picking is a method used for the separation of a mixture. The size of the particle of one component must be large enough so that it is distinguished from the size of the particle of another component. The size of particles of salt and sand is almost the same.
So, the mixture of salt and sand can be separated by the solubility process.
We know that the salt is soluble in water but the sand is not soluble in water. In other words, salt dissolves in water, but sand does not dissolve in water. So, this difference in solubility is used to separate the mixture of salt and sand.
First, add some water to the mixture of salt and sand, the salt will dissolve into the water but the sand does not dissolve. The solubility of salt in water increases with an increase in the temperature of the water. So, you will require less water. Once the salt is completely dissolved, filter the solution to separate sand. Now, this salty water can be separated by heating the solution until all the water gets evaporated and the only salt is left.
So, the mixture of salt and sand cannot be separated by picking.

Note:
The mixture of salt and sand can also be separated by melting point, salt (sodium chloride, $NaCl$), and sand (silicon dioxide, $Si{{O}_{2}}$) have different melting points. The melting point of salt is ${{801}^{\circ }}C$ and that of sand ${{1710}^{\circ }}C$. When the mixture is heated the salt will melt first and get separated first.