Number of Single Bonded Oxygen Atoms in Chromium Peroxide Complex

When an acidified solution of chromate ($\text{CrO}_4^{2-}$) or dichromate ($\text{Cr}_2\text{O}_7^{2-}$) is treated with hydrogen peroxide ($\text{H}_2\text{O}_2$) in the presence of an organic solvent such as amyl alcohol or ether, a deep blue complex of chromium peroxide, $\text{CrO}_5$ (also represented as $\text{CrO}(\text{O}_2)_2$), is formed:

$\text{CrO}_4^{2-} + 2\text{H}^+ + 2\text{H}_2\text{O}_2 \longrightarrow \text{CrO}_5 + 3\text{H}_2\text{O}$

Thus, the chromium(VI) species 'X' responsible for the blue coloration is $\text{CrO}_5$.

Structural Analysis of $\text{CrO}_5$:

1. Geometry & Bonding: $\text{CrO}_5$ exhibits a butterfly-shaped structure with the central chromium ($\text{Cr}$) atom in a $+6$ oxidation state.
2. Types of Oxygen Atoms:
   • 1 Oxo oxygen atom: Attached to the central chromium atom via a double bond ($\text{Cr}=\text{O}$).
   • 4 Peroxo oxygen atoms: Belonging to the two peroxide linkage groups ($-\text{O}-\text{O}-$). Each of these 4 oxygen atoms forms a single covalent bond with the central chromium atom ($\text{Cr}-\text{O}$).

Therefore, the total number of oxygen atoms connected to chromium solely via single bonds in one molecule of 'X' is 4.