Question:
When \(H_2O_2\) is added to an acidified \(K_2Cr_2O_7\) solution
When \(H_2O_2\) is added to an acidified \(K_2Cr_2O_7\) solution
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This blue color is temporary. Without a stabilizing solvent like ether, it eventually decomposes into green \(Cr^{3+}\) ions and oxygen gas.
Updated On: Apr 29, 2026
- A green colour solution is obtained
- A yellow solution is obtained
- A blue-violet solution is obtained
- A green precipitate is formed
- A yellow precipitate is formed
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The Correct Option is C
Solution and Explanation
Concept:
The reaction between acidified potassium dichromate and hydrogen peroxide is a characteristic test for chromium. It involves the formation of an unstable, deep-blue colored compound.
Step 1: Identify the chemical reaction.
When \(H_2O_2\) is added to an acidified solution of \(K_2Cr_2O_7\), chromium peroxide (\(CrO_5\)) is formed: \[ Cr_2O_7^{2-} + 2H^+ + 4H_2O_2 \rightarrow 2CrO_5 + 5H_2O \]
Step 2: Observe the physical change.
The resulting \(CrO_5\) (Chromium pentoxide) is a deep-blue/blue-violet colored compound. However, it is unstable in water and decomposes quickly.
Step 3: Stability factors.
To stabilize this blue color during a laboratory test, ether or amyl alcohol is often added. The \(CrO_5\) dissolves in the organic layer, forming a stable blue-violet layer.
Step 1: Identify the chemical reaction.
When \(H_2O_2\) is added to an acidified solution of \(K_2Cr_2O_7\), chromium peroxide (\(CrO_5\)) is formed: \[ Cr_2O_7^{2-} + 2H^+ + 4H_2O_2 \rightarrow 2CrO_5 + 5H_2O \]
Step 2: Observe the physical change.
The resulting \(CrO_5\) (Chromium pentoxide) is a deep-blue/blue-violet colored compound. However, it is unstable in water and decomposes quickly.
Step 3: Stability factors.
To stabilize this blue color during a laboratory test, ether or amyl alcohol is often added. The \(CrO_5\) dissolves in the organic layer, forming a stable blue-violet layer.
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