Question

The structure of potassium ferrocyanide is:
A.Tetrahedral
B.Octahedral
C.Square planar
D.Linear

Answer 1

Hint:
Solve this question by breaking up the name of the compound. The given compound is a salt made up of potassium and ferrocyanide ions. Potassium is the cation, whereas cyanide is an anion.

Complete step by step answer:
Potassium ferrocyanide is an inorganic compound with the molecular formula – \[{{K}_{4}}[Fe{{(CN)}_{6}}]\]. It occurs as a lemon-yellow monoclinic crystal and is therefore also known as yellow potash prussiate.
It is a coordination compound. From the name, we can decipher that the compound is made of a cation (potassium) and cation (ferrocyanide). Now, let us break the term ferrocyanide –
‘ferro’ stands for ferrous, i.e., the element iron with an oxidation state of +2.
‘cyanide’ stands for a compound made up of C and N which is triple bonded to each other. The structure of cyanide is as given below –

Cyanide has an overall charge = -1.
Therefore, the overall charge of ferrocyanide = (+2) + 6(-1) = -4.
From here, we can see, 4 potassium ions are needed to balance these.
The structure of potassium ferrocyanide can be drawn as –

The geometry of the compound is dependent on ferrocyanide. A coordination compound with six ligands is always octahedral. It is known as the octahedral because it has eight faces.
Therefore, the answer is – option (b) – The structure of potassium ferrocyanide is octahedral.

Additional Information:
The IUPAC name of this compound is potassium hexacyanoferrate (II).

Note:
 Do not confuse potassium ferrocyanide with potassium ferricyanide. In potassium ferricyanide, the iron atom has an oxidation state of +3. Iron is a d-block element with atomic number 26. It has two oxidation states - +2 (ferrous) and +3 (ferric).