Hydrogen Peroxide + Potassium Dichromate

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What actually happens when we add Hydrogen Peroxide to acidified Potassium Dichromate? Do we get a deep blue solution or a green solution? I have read both of them.
Will the result be different if Sodium Peroxide is added instead of Hydrogen Peroxide?

#Chemistry #Inorganic Chemistry

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6 Answers

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Khyati ·2010-10-16 21:16:48

When hydrogen peroxide is added to a acidified solution of dichromate (or any other Cr (+VI) species) , a very complicated reaction occurs. The products depends on the pH and the concentration of Cr.

Cr₂O₇^2- + 2H⁺ + 4H₂O₂â†’2CrO(O₂)₂ + 5H₂O

A deep blue violet coloured peroxo compound is formed. This decomposes rapidly in aq solution into Cr³⁺ and dioxygen.

In less acidic solutions of potassium dichromate an hydrogen peroxide give salts which are violet colored and diamagnetic. These are thought to contain [Cr(O₂)OH^-], but the structure is nt known as the compounds are explosive.

In alkaline solution with 30% hydrogen peroxide, a red-brown compound K₂Cr₃O₈ is formed which is a tetraperoxo species [Cr(O₂)₄]^- and contains Cr(+V).

In ammonia solution the dark red brown compound (NH₃)₃CrO₄ is formed which contains Cr(+IV)

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Aadesh Madnaik Nice answer! Thanks a lot.
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swordfish ·2010-10-17 06:16:57

So that means first deep blue solution is formed and then the compound CrO₅ decomposes to give Cr₃₊ which is green in colour?

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Euclid ·2010-10-17 23:12:41

i think it gives only deep blued solution of CrO₅.....not Cr₂O₃!!!

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swordfish ·2010-10-18 01:40:52

@Euclid
It gives blue solution only in ethereal solutions. In concentrated, it gives green colour

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Euclid ·2010-10-18 11:07:53

ya.....potassium dichromate in acidic medium gives Cr⁺³ but not in presence of H₂O₂...

in less acidic solution K₂Cr₂O₇ and H₂O₂ give salts that are violet coloured and diamagnetic due to formation of [CrO(O₂)(OH)] ^-

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Khyati ·2010-10-18 17:40:09

@ Swordfish what you din understood, sabkuchh toh likha hai in the previous post

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