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
- \(+6\)
- \(+5\)
- \(+10\)
- \(+3\)
The Correct Option is A
Approach Solution - 1
The chromyl chloride test is used to confirm the presence of chloride ions (\( \text{Cl}^- \)) in a sample. During this test, the sample reacts to form a yellow solution. This solution is then acidified, and the addition of amyl alcohol and 10% hydrogen peroxide (\( \text{H}_2\text{O}_2 \)) leads to the formation of an organic layer that turns blue. This color change indicates the formation of chromium pentoxide (\( \text{CrO}_5 \)).
Let's break down the formation and characteristics of chromium pentoxide:
- Chromium pentoxide (\( \text{CrO}_5 \)) forms when chromium in the solution is oxidized in the presence of peroxide.
- \( \text{CrO}_5 \) exhibits a distinctive blue color due to its structure, which involves multiple bonds with oxygen.
- The oxidation state of chromium in chromium pentoxide (\( \text{CrO}_5 \)) can be determined by analyzing its chemical structure. Each oxygen atom has an oxidation state of \( -2 \).
Let's calculate the oxidation state of chromium in \( \text{CrO}_5 \):
- \( \text{CrO}_5 \) has 5 oxygen atoms, each with an oxidation state of \( -2 \), contributing a total of \( -10 \) (i.e., \( 5 \times -2 = -10 \)).
- Let the oxidation state of chromium be \( x \). The total charge should be zero for a neutral compound:
- \( x + (5 \times -2) = 0 \)
- Simplifying, \( x - 10 = 0 \), thus \( x = +10 \).
However, in our experience with chromate configurations and the given options, we know the stable oxidation state of chromium in \(\text{CrO}_5 \) should actually be \( +6 \) due to peroxo bonds counteracting to effectively reduce the apparent state.
Therefore, the correct option is:
\(+6\)
Approach Solution -2
- During the chromyl chloride test, the following reaction occurs:
Cl− + K2Cr2O7 + H2SO4 → CrO2Cl2 + Cl−
- In basic medium, this results in a yellow solution due to CrO42−.
- Upon acidification, addition of amyl alcohol, and 10% H2O2, a blue organic layer forms due to the formation of CrO5 (chromium pentoxide).
- The oxidation state of chromium in CrO5 is +6.
So, the correct answer is: +6
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