Question

In chromyl chloride test for confirmation of Cl^-, a yellow solution is obtained. Acidification of the solution and addition of amyl alcohol and 10% H₂O₂​ turns organic layer blue indicating formation of chromium pentoxide. The oxidation state of chromium in that is

• A. \(+6\)
• B. \(+5\)
• C. \(+10\)
• D. \(+3\)

Answer 1

The Correct Option is A

The chromyl chloride test identifies chloride ions (\( \text{Cl}^- \)). A sample treated in this test forms a yellow solution. Acidification followed by the addition of amyl alcohol and 10% hydrogen peroxide (\( \text{H}_2\text{O}_2 \)) produces an organic layer that turns blue, signifying the formation of chromium pentoxide (\( \text{CrO}_5 \)).

Regarding chromium pentoxide (\( \text{CrO}_5 \)):

1. \( \text{CrO}_5 \) is formed by the oxidation of chromium in the presence of peroxide.
2. Its blue color is attributed to its structure, which features multiple oxygen-chromium bonds.
3. The oxidation state of chromium in \( \text{CrO}_5 \) can be derived from its chemical structure, given that each oxygen atom has an oxidation state of \( -2 \).

The oxidation state calculation for chromium in \( \text{CrO}_5 \) is as follows:

• \( \text{CrO}_5 \) contains 5 oxygen atoms, each with an oxidation state of \( -2 \), totaling \( -10 \) (\( 5 \times -2 = -10 \)).
• Let the oxidation state of chromium be \( x \). For a neutral compound, the sum of oxidation states is zero:
• \( x + (5 \times -2) = 0 \)
• This simplifies to \( x - 10 = 0 \), yielding \( x = +10 \).

However, based on typical chromate configurations and available options, the stable oxidation state of chromium in \( \text{CrO}_5 \) is understood to be \( +6 \). This is due to peroxo bonds that effectively modify the apparent oxidation state.

Consequently, the correct oxidation state is:

\(+6\)