Question

Explain why hydrogen chloride gas in methyl benzene does not liberate hydrogen gas with magnesium metal while hydrogen chloride gas in water liberate hydrogen gas with magnesium?

Answer 1

Explanation:

Hydrogen chloride, outside of water, is not an acid in the sense that an acid is an entity that gives rise to a free proton. When hydrogen chloride is in an aqueous environment the following occurs:

HCl + H2O = H3O+ + Cl_

ie, a free, solvated proton is produced from the strongly dissociated acid and a chloride ion in equimolar amounts. Thus, the litmus turns red.

Methylbenzene, on the other hand, is incapable of associating with hydrogen from the hydrogen chloride to produce a free proton. Bear in mind that H+ does not exist, although, for convenience, the solvated proton is often written as H+. The hydrogen chloride remains as a covalent molecule without conferring acidity to the methylbenzene. The mixture of HCl and C6H5CH3 remains with each molecule retaining its non-reacted and independent entity.