Question

Account for the following:

Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.

Answer 1

Due to the +I effect of −CH₃ group, methylamine is more basic than water. Therefore, in water, methylamine produces OH⁻ ions by accepting H⁺ ions from water.

\[\ce{CH3-NH2 + H-OH -> H3N+-CH3 + OH-}\]

Ferric chloride (FeCl₃) dissociates in water to form Fe³⁺ and Cl⁻ ions.

Then, OH⁻ ion reacts with Fe³⁺ ion to form a precipitate of hydrated ferric oxide.

\[\ce{FeCl3 -> Fe^{3+} + 3Cl^-}\]

\[\ce{2Fe^{3+} + 6OH^- -> \underset{(Brown precipitate)}{Fe2O3.3H2O}}\]