Question

What is the number of ions in the aqueous solution of ferric hexacyanoferrate(II)?
A. 4
B. 5
C. 6
D. 7

Answer 1

Coordination compounds do not completely dissociate into its all ions, as ions present in the coordination sphere do not dissociate and remain as it is in aqueous solution. Only the compounds attached to the complex form ions.

Complete Step by step solution:
Depending on the number of types of ions the salt possesses, salts are of 2 types namely simple salt and mixed salts. Simple salts have only one type of cation and only one type of anion. For example KCl, NaCl, ${\text{MgC}}{{\text{l}}_2}$.
Mixed salt has more than one type of cation or one type of anion in them. Mixed salts are further of two types namely double salt and coordination compound. Double salts mix with water and it gets completely dissociated into its ion components. For example Cernalite ${\text{KCl}}.{\text{MgC}}{{\text{l}}_2}.6{{\text{H}}_{\text{2}}}{\text{O}}$, Mohr salt ${\text{FeS}}{{\text{O}}_4}.{\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}.6{{\text{H}}_2}{\text{O}}$ .

Coordination compounds do not completely dissociate in water into all its cationic and anionic components. For example ${{\text{K}}_4}\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_6}} \right]$ and $\left[ {{\text{Cu}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}} \right]{\text{S}}{{\text{O}}_4}$.
Ferric hexacyanoferrate(II) has the chemical formula ${\text{F}}{{\text{e}}_4}{\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_6}} \right]_3}$. It is also known as Prussian blue because of its colour. It is a coordination compound so it will completely dissociate into its ionic component. Its coordination sphere does not get dissociated in the aqueous solution. On adding Ferric hexacyanoferrate(II) to water, it will produce 4 ${\text{F}}{{\text{e}}^{ + 3}}$ ion and 3 ${\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_6}} \right]^{ - 4}}$ ion. Thus, a total 7 ions it will produce in its aqueous solution.
Similarly ${{\text{K}}_4}\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_6}} \right]$ , it will produce 4 ${{\text{K}}^ + }$ ion and one ${\left[ {{\text{Fe}}{{\left( {{\text{CN}}} \right)}_6}} \right]^{ - 4}}$ ion. Thereby Potassium hexacyanoferrate(ll) produces a total 5 ions in its aqueous solution.

Thus, the correct option is D.

Note: During IUPAC nomenclature of coordination compound, first cation is written and then anion. During naming of coordination sphere; naming of ligands are done in alphabetical order first and then the central metal atom is named with its oxidation number in roman number.