To an acidified dichromate solution, a pinch of `Na_(2)O_(2)` is added and shaken. What is observed ?

Options

A. Blue colour
B. Orange colour changing to greeen directly
C. Copious evolution of oxygen
D. Bluish-green precipitate

Answer

To solve the question regarding the observation when a pinch of sodium peroxide (Na₂O₂) is added to an acidified dichromate solution, we can break down the process step by step:

### Step 1: Understanding the Reactants
- We start with an acidified dichromate solution, which typically contains potassium dichromate (K₂Cr₂O₇) dissolved in sulfuric acid (H₂SO₄). The dichromate ion (Cr₂O₇²⁻) is orange in color.

### Step 2: Adding Sodium Peroxide
- When a pinch of sodium peroxide (Na₂O₂) is added to the acidified dichromate solution, a reaction occurs. Sodium peroxide acts as a strong oxidizing agent.

### Step 3: Formation of Chromate Peroxide
- The reaction produces chromate peroxide (CrO₅), which is a deep blue compound. The balanced reaction can be represented as:
\[ 2 K_2Cr_2O_7 + 6 H_2SO_4 + 4 Na_2O_2 \rightarrow 2 CrO_5 + 2 K_2SO_4 + 6 H_2O + 4 Na_2O_2 \]
- This results in the formation of a deep blue color in the solution due to the presence of CrO₅.

### Step 4: Color Change
- Over time, the deep blue color fades. This occurs because CrO₅ decomposes in the presence of sulfuric acid to form chromic sulfate (Cr₂(SO₄)₃), which is colorless or pale green. The reaction can be represented as:
\[ 4 CrO_5 + 6 H_2SO_4 \rightarrow 2 Cr_2(SO_4)_3 + 6 H_2O + 3 O_2 \]
- During this reaction, a significant amount of oxygen gas (O₂) is released.

### Step 5: Final Observations
- Initially, a deep blue color is observed due to the formation of CrO₅.
- The deep blue color fades as chromic sulfate is formed.
- There is copious evolution of oxygen gas during the reaction.

### Conclusion
- The final observations are:
1. A deep blue color appears initially.
2. The blue color fades over time.
3. There is abundant evolution of oxygen gas.