Understanding Sodium Nitroprusside Formula

Sodium nitroprusside is a well-known coordination compound. It is often used in medicine and as a chemical reagent. The question asks for its correct chemical formula from the given options.

Identifying the Correct Chemical Formula

Let's look at the chemical formula of sodium nitroprusside. The chemical formula is typically represented as a complex salt.

The generally accepted chemical formula for sodium nitroprusside is Na₂[Fe(CN)₅(NO)].

Let's break down this formula:

• Na₂: This indicates the presence of two sodium ions (Na⁺).
• [Fe(CN)₅(NO)]: This is the complex anion.
  • Fe: Represents the central iron atom.
  • (CN)₅: Represents five cyanide ligands (CN^-).
  • (NO): Represents the nitrosyl ligand. In nitroprusside, the nitrosyl ligand is considered as NO⁺ (nitrosonium ion) or sometimes represented as neutral NO coordinated to iron, but the +1 oxidation state for NO is common in this complex context to balance charges and assign iron's oxidation state.

To balance the charge, let's consider the oxidation states. Sodium ions are each +1, so 2 × (+1) = +2. Cyanide ligands are each -1, so 5 × (-1) = -5. If we consider the nitrosyl ligand as NO⁺ (+1), then the charge on the complex ion is Oxidation State of Fe + 5(-1) + (+1) = Net Charge of Complex Ion. Since the overall compound is neutral, the complex anion must have a charge of -2 to balance the two Na⁺ ions (+2). So, Oxidation State of Fe - 5 + 1 = -2, which gives Oxidation State of Fe - 4 = -2, so the Oxidation State of Iron is +2.

\(\text{Oxidation State of Fe} + 5(\text{charge of CN}^-) + (\text{charge of NO}^+) = \text{Charge of complex ion}\)

\(\text{Oxidation State of Fe} + 5(-1) + (+1) = -2\)

\(\text{Oxidation State of Fe} - 5 + 1 = -2\)

\(\text{Oxidation State of Fe} - 4 = -2\)

\(\text{Oxidation State of Fe} = +2\)

Comparing Formula with Options

Let's compare the correct formula, Na₂[Fe(CN)₅(NO)], with the given options:

1. Na₄[Fe(CN)₅NO₅]: This formula is significantly different, both in the number of sodium ions and the composition of the complex anion.
2. Na₂[Fe(CN)₅(NO)]: This formula exactly matches the correct chemical formula for sodium nitroprusside.
3. NaFe[Fe(CN)₆]: This formula represents sodium ferrocyanide (sodium hexacyanoferrate(II)) or a related Prussian blue type compound, which is different from sodium nitroprusside.

Based on this comparison, the formula Na₂[Fe(CN)₅(NO)] is the correct representation of sodium nitroprusside.