Question

Which of the following methods is adopted for preparing a dilute solution of ?
(A) Addition of conc. to water
(B) Addition of water to conc. ${{H}_{2}}S{{O}_{4}}$
(C) Dissolution of $S{{O}_{3}}$ in excess water
(D) Dissolution of $S{{O}_{3}}$ in excess ${{H}_{2}}S{{O}_{4}}$

Answer 1

Hint: Recollect the basic concepts of science we learnt in school. One of them was, for dilution of an acid, add acid to water and never water to acid. Use this context in this problem and then determine the correct option.

Complete step by step solution:
- A dilute solution is a solution which is unsaturated and has less concentration of solute dissolved in the solvent. Dilution is the addition of water or solvent in a solution to reduce the concentration of solute.
- Generally, to prepare dilute solution of mineral acids, it is always said to pour acid to water and not the other way around.
- Basically when we are diluting any substance, a solvation effect takes place.
- Solvation or hydration effect is the ability of water molecules to dissolve the solute by forming intermolecular forces of interactions like hydrogen bonding, dipole-dipole interaction, etc.
- So, dilution is a bond making process and therefore, it is exothermic in nature.
- In an exothermic reaction, energy is released due to formation of bonds in the form heat and light.
- Now, if conc. acid is added to water, there is a chance of acid to be splashed out of the beaker due to release of energy and chances of burns.
- Also, due to exothermic reactions, the glass beaker will become very hot and there are chances that the beaker may break or crack.
- Therefore, while diluting strong concentrated acids like sulphuric acid, hydrochloric acid, etc. always add acid to water.

- Therefore, addition of conc. ${{H}_{2}}S{{O}_{4}}$ to water is the method adopted to prepare dilute sulphuric acid and the correct option is (A).

Note: Always remember dilutions are exothermic in nature. Therefore, whenever you need to prepare dilute solutions of acids, always take some amount of water in the beaker or volumetric flask and then carefully with the help of an automated pipette, add the required volume of concentrated acid directly into the water and then dilute that mixture with water up to the mark to get the desired dilution.