Question

Methylene blue is adsorbed on activated charcoal at 25$^{0}C$ from its aqueous solution.
Which is the correct statement for this process?
a.) The adsorption requires activation at 25 $^{0}C$
b.) The adsorption is accompanied by a decrease in enthalpy.
c.) The adsorption increases with increase of temperature.
d.) The adsorption is irreversible

Answer 1

Hint: Methylene blue is represented by the formula ${{C}_{16}}{{H}_{18}}Cl{{N}_{3}}S$. It is prepared by the oxidation of dimethyl-4-phenylenediamine in the presence of sodium thiosulfate.

Complete step by step answer:
Adsorption is the process of adhesion of atoms or ions or molecules of a gas to the surface. Adsorbent is a material which will allow atoms or ions or molecules of a gas to adhere to its surface and adsorbate is the substance whole molecules get adsorbed on the surface.
Methylene blue is adsorbed on activated charcoal at 25$^{0}C$ from its aqueous solution. For this process the adsorption is accompanied by the decrease in the enthalpy. Adsorption of methylene blue is physisorption hence there is no requirement of activation energy for this reaction.
Physisorption is an exothermic process which means that heat is released during the reaction. It is also a reversible process and it decreases with the increase in temperature. Thus the process which does not involve any surface tension is achieved easily and quickly at low temperature.
So, the correct answer is “Option B”.

Additional Information:
Methylene blue is used as an antiseptic in the cases of urinary tract infection.
Methylene blue is also used as an indicator during various types of reactions.
Methylene blue is non- combustible in nature and also acts as an enzyme inhibitor.
Methylene blue is basic in nature and exhibits cardio protective properties.

Note: Do not get confused between adsorption and absorption. Adsorption is a surface phenomenon in which the atoms and molecules from the gas and liquid are stuck into the surface whereas absorption is a bulk phenomenon in which the molecules of the adsorbate enters into the adsorbent.