Question

If solubility of $NaCl$ at ${{20}^{o}}C$ is $35gm$ per $100ml$ of water. Then, on adding $50gm$ of $NaCl$ to the same volume at the same temperature, the salt remains undissolved is
(A) $15gm$
(B) $20gm$
(C) $50gm$
(D) $35gm$

Answer 1

Hint: Solubility means the ability of the solute to get dissolved in a solvent to form a solution. When a solute is dissolved in water, it can be completely soluble, sparingly soluble, or completely insoluble. When a salt dissolves in a solvent, the interactions between the ions and the solvent must overcome the strong forces of attraction of the solute, which are the lattice enthalpies of its ions.

Complete Step by Step Answer:
A saturated solution is the solution in which the maximum amount of solute is dissolved and no more of the solute can be dissolved in it. It is given in the question that the solubility of $NaCl$ at ${{20}^{o}}C$ is $35gm$ per $100ml$ of water. This means that $35gm$ of $NaCl$can be completely dissolved in $100ml$ of water and if more of $NaCl$is added, then it will remain undissolved.

It is asked that if $50gm$ of $NaCl$ is added to the same volume, that is$100ml$, at the same temperature, then the amount of salt that remains undissolved is
Undissolved salt =$50-35$
= $15gm$
This means that on adding $50gm$ of $NaCl$ to the $100ml$ of water at ${{20}^{o}}C$ the salt remains undissolved is $15gm$.
Correct Option: (A) $15gm$.

Note: There are some substances which can dissolve in all proportions in a particular solvent. The factors on which the solubility of a substance depends are the nature of intermolecular forces between solute and solvent, temperature, and pressure.