What is the Oxidation Number of Cyanide (CN)?

In coordination chemistry and redox reactions, identifying the correct oxidation number of ligands and ions is crucial. The Cyanide ion ($CN^-$) is one of the most common polyatomic ions you will encounter in Class 11 and 12 Chemistry.

Question (Click to Flip)

What is the oxidation state of Iron in $K_4[Fe(CN)_6]$?

Answer

Let Iron be x. Potassium (K) is +1, CN is -1. Equation: 4(+1) + x + 6(-1) = 0. Solving this gives x = +2. So, Iron is in the +2 oxidation state.

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Key Facts

Cyanide is highly toxic because it binds to iron in the blood, preventing cells from using oxygen.

The carbon and nitrogen atoms in $CN^-$ are held together by a strong triple covalent bond.

Hydrogen cyanide (HCN) is a volatile and deadly gas.

1. Overall Charge of Cyanide

The Cyanide ion is a polyatomic ion with the chemical formula $CN^-$. Because it has a single negative charge, the overall oxidation number of the entire CN group is -1.

2. Individual Oxidation States

If a question asks for the specific oxidation states of the Carbon (C) and Nitrogen (N) atoms inside the cyanide ion, we must look at their electronegativity.

Nitrogen is more electronegative than Carbon.
In the $C \equiv N$ triple bond, Nitrogen pulls the shared electrons towards itself.
Therefore, Nitrogen (N) has an oxidation state of -3.
To make the total charge -1, Carbon must balance it out. Let Carbon's oxidation number be $x$. $x + (-3) = -1$ $x = +2$
Therefore, Carbon (C) has an oxidation state of +2 in the cyanide ion.

3. Role in Coordination Compounds

In complex coordination compounds (like Potassium ferrocyanide, $K_4[Fe(CN)_6]$), the CN group acts as a strong-field ligand. When calculating the oxidation state of the central metal atom (like Iron), you will always use -1 as the oxidation number for each CN ligand.

Questions and Answers

What is the oxidation state of Iron in $K_4[Fe(CN)_6]$?+

Let Iron be x. Potassium (K) is +1, CN is -1. Equation: 4(+1) + x + 6(-1) = 0. Solving this gives x = +2. So, Iron is in the +2 oxidation state.

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