When a solution of `Na_(2)Cr_(2)O_(7)` is treated with amyl alcohol and acidified `H_(2)O_(2)`, the layer of ayl alcohol turns blue. What is the blue colouration?

Options

A. `Cr^(2+)`
B. `CrO_(5)`
C. `CrO_(4)`
D. `Cr^(2+)+CrO_(5)`

Answer

To determine the blue coloration observed when a solution of sodium dichromate (Na₂Cr₂O₇) is treated with amyl alcohol and acidified hydrogen peroxide (H₂O₂), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactants in this reaction are sodium dichromate (Na₂Cr₂O₇), amyl alcohol, and acidified hydrogen peroxide (H₂O₂).

2. **Reaction with Amyl Alcohol**:
- When sodium dichromate is treated with amyl alcohol, it undergoes a reaction that leads to the formation of sodium chromate (Na₂CrO₄) and water (H₂O). The reaction can be summarized as:
\[ \text{Na}_2\text{Cr}_2\text{O}_7 + \text{Amyl Alcohol} \rightarrow \text{Na}_2\text{CrO}_4 + \text{H}_2\text{O} \]

3. **Reaction with Acidified Hydrogen Peroxide**:
- The sodium chromate (Na₂CrO₄) formed in the previous step is then treated with acidified hydrogen peroxide (H₂O₂). In an acidic medium, this reaction results in the formation of chromium pentoxide (CrO₅) and sodium ions:
\[ \text{Na}_2\text{CrO}_4 + \text{H}_2\text{O}_2 \rightarrow \text{CrO}_5 + \text{Na}^+ + \text{H}_2\text{O} \]

4. **Color of Chromium Pentoxide**:
- The chromium pentoxide (CrO₅) produced in the reaction is known to exhibit a blue color. This is the reason why the layer of amyl alcohol turns blue upon the addition of acidified hydrogen peroxide.

5. **Conclusion**:
- Therefore, the blue coloration observed in the layer of amyl alcohol is due to the formation of chromium pentoxide (CrO₅).

### Summary:
The blue coloration is due to the formation of chromium pentoxide (CrO₅) when sodium dichromate reacts with amyl alcohol and acidified hydrogen peroxide.