Question

Which of the following is a false statement about iron (III) hydroxide?
A. It is a weaker a base than ${\text{Fe}}{\left( {{\text{OH}}} \right)_{\text{2}}}$
B. With concentrated KOH it form a complex ${{\text{K}}_3}\left[ {{\text{Fe}}{{\left( {{\text{OH}}} \right)}_{\text{6}}}} \right]$
C. it gradually lose water and transform into ${\text{F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}$
D. it exhibits amphoteric properties with acidic ones predominating.

Answer 1

Hint: To answer this question we will determine the basicity of iron (III) hydroxide and iron (II) hydroxide based on the electron density. We will write the reaction given in the statement to determine whether the statement is true or not.

Complete step-by-step answer:
Base donates electrons. So, the compound having more electrons will be more basic.
The oxidation state of iron in iron (III) hydroxide, is $ + 3$ and oxidation state of iron in iron (II) hydroxide${\text{Fe}}{\left( {{\text{OH}}} \right)_{\text{2}}}$ in $ + 2$so, the iron (II) hydroxide has more electron so, iron (III) hydroxide is less basic than iron (II) hydroxide ${\text{Fe}}{\left( {{\text{OH}}} \right)_{\text{2}}}$so, statement A is true.
The iron in $ + 3$ oxidation state has ${{\text{d}}^{\text{5}}}$ electronic configuration, so it can form a compound with concentrated potassium hydroxide. The reaction is shown as follows:
${\text{Fe}}{\left( {{\text{OH}}} \right)_3}\,{\text{ + }}\,{\text{3KOH}}\, \to {{\text{K}}_3}\left[ {{\text{Fe}}{{\left( {{\text{OH}}} \right)}_{\text{6}}}} \right]$
So, statement B is true.
The iron (III) hydroxide loses water and forms oxides. The reaction is shown as follows:
${\text{2}}\,{\text{Fe}}{\left( {{\text{OH}}} \right)_3}\, \to {\text{F}}{{\text{e}}_2}{{\text{O}}_3}\, + \,3\,{{\text{H}}_{\text{2}}}{\text{O}}$
So, statement C that it gradually loses water and transforms into ${\text{F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}$, is correct.
Iron (III) hydroxide reacts with hydrochloric acid and gives salt of iron and water. The reaction is as follows:
${\text{2}}\,{\text{Fe}}{\left( {{\text{OH}}} \right)_3}\, + \,6\,{\text{HCl}}\, \to 2{\text{FeC}}{{\text{l}}_3}\, + \,6\,{{\text{H}}_{\text{2}}}{\text{O}}$
So, as the iron (III) oxide reacts with acid and gives salt so, it is basic, not amphoteric. So, statement D is not true.
So, statement D is a false statement about iron (III) hydroxide.

Therefore, option (D) it exhibits amphoteric properties with acidic ones predominating, is the correct answer.

Note: The basicity is determined as the power of accepting a proton, or electrons, or hydroxide donating tendency. Iron (III) hydroxide is more acidic than iron (II) hydroxide because due to the high oxidation state, iron (III) hydroxide has a more electron-accepting tendency. Acidity is directly proportional to the oxidation state of metal and basicity is inversely proportional. Amphoteric substance reacts with both acid as well as a base.