Question

In potassium trioxalatoferrate(III), what are the primary and secondary valency of central atom respectively?

• A. 3, 6
• B. 3, 3
• C. 6, 3
• D. 6, 6

Hint:

Primary valency means oxidation state, while secondary valency means coordination number. For bidentate ligands, each ligand contributes two coordination positions.

Answer 1

The Correct Option is A

Step 1: Write the formula of the complex.
Potassium trioxalatoferrate(III) is written as \(\mathrm{K_3[Fe(C_2O_4)_3]}\). Here, the complex ion is \(\mathrm{[Fe(C_2O_4)_3]^{3-}}\), and the central metal atom is iron in the \(+3\) oxidation state.
Step 2: Understand primary valency.
According to Werner's theory, the primary valency corresponds to the oxidation state of the central metal atom. In this complex, iron is present as \(\mathrm{Fe^{3+}}\). Therefore, the primary valency of the central atom is \(3\).
Step 3: Understand secondary valency.
The secondary valency corresponds to the coordination number of the central metal atom. Oxalate ion \(\mathrm{(C_2O_4)^{2-}}\) is a bidentate ligand, which means one oxalate ion coordinates through two donor atoms. Since there are three oxalate ligands attached, total coordination number becomes:
\[ 3 \times 2 = 6 \] So, the secondary valency of iron is \(6\).
Step 4: Conclusion.
Thus, in potassium trioxalatoferrate(III), the primary valency is \(3\) and the secondary valency is \(6\).
Final Answer:3, 6.