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When potassium dichromate (K₂Cr₂O₇) is treated with dilute sulfuric acid (H₂SO₄), the acidic medium allows it to act as a powerful oxidizing agent. In this reaction mixture, several active oxidizing species are produced, including chromic acid (H₂CrO₄), chromium trioxide (CrO₃), and nascent oxygen [O].
The overall reaction can be represented as:
K₂Cr₂O₇ + H₂SO₄ → H₂CrO₄ + CrO₃ + [O]
Chromic acid (H₂CrO₄) is one of the key oxidizing species that forms in situ. It directly oxidizes many organic compounds.
Chromium trioxide (CrO₃) is another oxidizing intermediate that can be formed in acidic conditions.
Nascent oxygen [O] is a highly reactive atomic oxygen released during the process, which is responsible for many of the oxidation reactions.
This oxidizing mixture is widely used in organic chemistry for the oxidation of alcohols and other compounds:
Primary alcohols are oxidized to aldehydes, and then further to carboxylic acids.
Secondary alcohols are oxidized to ketones.
Tertiary alcohols are generally resistant to oxidation, but under strong conditions, they may undergo elimination to form alkenes.
In analytical chemistry, acidified potassium dichromate is also used in redox titrations to determine the concentration of reducing agents. A common example is the titration of ferrous ions (Fe²⁺), where Fe²⁺ is oxidized to Fe³⁺.
The orange color of dichromate (Cr₂O₇²⁻) changes to the green color of chromium(III) ions (Cr³⁺) during the reaction, making it easy to follow visually.
Thus, the correct answer is All of these, because the mixture produces H₂CrO₄, CrO₃, and nascent oxygen, all of which contribute to its strong oxidizing behavior.
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