Why is potassium permanganate coloured?

  • Thread starter CrimpJiggler
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In summary, the permanganate ion contains manganese in the +7 oxidation state, making it a d0 ion. Because of this, it does not absorb visible spectrum radiation as there are no electrons available to jump to higher crystal field orbitals. The reason for this is that the ligand donates electrons into the empty d orbitals of Mn(VII). This also explains why chromate, another d0 ion, is colored as well. The cause for absorption of visible radiation in these ions is due to ligand to metal charge transfers, where oxygen transfers electrons to the empty d orbitals of the metal atom. This process is known as LMCT and can be further explored in the provided sources.
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CrimpJiggler
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In the permanganate ion, manganese is in the +7 oxidation state, therefore it is a d0 ion. I thought that d0 and d10 ions don't absorb visible spectrum radiation because there are no electrons to jump to higher crystal field orbitals (or in the case of d10 ions, there are no free orbitals for electrons to jump to). I remember reading months ago an explanation for this that involved something to do with the ligand donating electrons into Mn(VII)s empty d orbitals. Can anyone explain this to me?

EDIT: Also I'd like to know why chromate is coloured. Again Cr(VI) is a d0 ion, therefore its not absorbing radiation due to electrons jumping to higher orbitals in the crystal field. What is causing it to absorb visible radiation?

UPDATE: I found out the answer to this question. Permanganate, chromate and dichromate are coloured for the same reason. Ligand to metal charge transfers. In each case, oxygen transfers electrons to the empty d orbitals on the metal atom. Interesting stuff, I found this info here:
http://www.webexhibits.org/causesofcolor/8.html
 
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1. Why is potassium permanganate purple?

Potassium permanganate is purple because it absorbs all colors of visible light except for purple. The chemical structure of potassium permanganate causes it to reflect purple light, giving it its characteristic color.

2. Is potassium permanganate always purple?

Yes, potassium permanganate is always purple regardless of its concentration or state (solid, liquid, or gas). This is due to its unique chemical properties that result in the absorption and reflection of purple light.

3. Can the color of potassium permanganate change?

The color of potassium permanganate can appear to change depending on its concentration. At higher concentrations, it may appear darker or more vibrant purple, while at lower concentrations it may appear lighter or more pinkish in color. However, the underlying purple color remains the same.

4. Why is potassium permanganate used as a color indicator?

Potassium permanganate is used as a color indicator in chemistry experiments because its purple color is easily distinguishable and can be used to track the progress of a reaction. As the potassium permanganate reacts, its color may change, indicating the completion of the reaction.

5. Does the color of potassium permanganate have any practical uses?

Yes, the color of potassium permanganate has several practical uses. It is commonly used in water treatment plants to remove impurities and in medical settings as an antiseptic. It is also used as a dye in various industries and as a color indicator in chemical reactions.

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