Question

Which one of the following is not explained by adsorption?
(A) When acetic acid solution is shaken with charcoal, the concentration of the acid decreases
(B) The white precipitate of $Mg\left( O{{H}_{2}} \right)$ attains blue colour when precipitated in the presence of magneson reagent.
(C) The air becomes dry in the presence of silica gel
(D) An aqueous solution of $NaOH$ attains pink colour with a drop of phenolphthalein

Answer 1

We know that adsorption and absorption are related with surface chemistry. These two are surface and bulk phenomena. In this question we will check the option by option by basic concepts of absorption and adsorption.

Complete answer:
Absorption is a phenomenon in which assimilation of the molecular system throughout the bulk of the solid or liquid medium takes place. So, it is a bulk phenomenon. It is an endothermic process and temperature change has no effect. This process occurs at a uniform rate and concentration is constant throughout the medium. Adsorption is a surface phenomenon in which accumulation of molecular species at the surface of liquid or solid takes place. It is an exothermic process and this process is influenced by low temperature.
Rate of this process is not uniform; it increases steadily and reaches equilibrium. Concentration is not constant; it is different at the bottom of adsorbent from that in the bulk. Sorption is a physical and chemical process by which one substance becomes attached to another. The charcoal is very good for absorption. The crushing of charcoal increases its surface area. More is the surface area, more will be the solution adsorbed. The concentration is the amount of a substance present in its aqueous solution. If some amount of present substance gets escaped out of the solution, then its concentration decreases. When the charcoal is mixed with acetic acid solution and is then shaken for half and hour. The shaking provides energy and the acetic acid solution gets adsorbed in the charcoal. Thus, the amount of acetic acid gets lowered in the solution. So, the concentration of the solution decreases.
Therefore, the correct answer is option A.

Note:
Remember that there is an opposite process of sorption which is called desorption. We have to remember all the specifications of these processes. So, don’t get confused between these simple mechanisms. The fine charcoal means the charcoal has been crushed into a fine powder.