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A2 Chemistry - Manganese chemistry

I need help.
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oceane
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1) Manganese can form stable compounds with an oxidation number of +7, for example the common laboratory chemical, potassium manganate(vii). Suggest why no other element in the first row of the transition elements can exist with such a high oxidation number, under normal conditions.

2) Suggest why potassium manganate(vii) behaves differently in the presence and absence of a strong acid.

3) When CO2 is bubbled through a green aqueous manganate solution, the solution becomes purple and a brown ppt is formed.

Explain the action of the CO2 in bringing about the reaction.


1.) The electron configuration of Mn is (Argon) 3d54s2 so it has 7 electrons of fairly similar energies it can donate in a reaction. The other transition elements before it in the Periodic Table will have fewer electrons and hence cannot donate so many. As for the elements after it, I imagine the extra protons in the nucleus means too much energy is required to reach as high an oxidation state. Fe manages +6 but I think that's only with very electronegative elements.

2.) Adding an acid makes the manganate (VII) a very potent oxidising agent - the electrode potential for [MnO4- + 8H+], [Mn2+ + 4H2O is +1.5V which is a lot.

From what I can gather on the net, in alkaline solution the manganate (VII) only reduces up to manganate (VI).

3.) The CO2 acts as a disproportionating agent i.e. the manganate (VI) is both oxidised to manganate (VII) which is purple, and MnO2 which is a brown precipitate.

Any1 know how to do superscripts/ subscripts?

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