Name: Reaction Between Ferrous Ion and Potassium Dichromate
Uploaded: 2019-07-19
Duration: 4 min 21 s
Description: This video explains the excellent oxidising agent, potassium dichromate. One mole of potassium dichromate can oxidise six moles of ferrous sulphate molecules...

Question

Explain why

{[Mn (H_{2} O)_{6}]}^{2 +}

is pale pink.

{MnO}_{2}

is black and

{MnO}_{4}^{-}

is intensely coloured purple.

Accepted Answer

The colour of the compound arises due to electronic excitation. During the excitation of electrons, there should be a set of the rule should obey. The rules are the spin selection rule and Laporte selection rule. All the transitions are Laporte forbidden. In the spin selection rule $∆ s = 0$ and in Laporte selection rule, there should be a change in dipole moment during the electronic transition. If all the selection rules are obeying, then the colour will be very intense.

In ${[Mn (H_{2} O)_{6}]}^{2 +}$ , the manganese is in $+ 2$ oxidation state. The electronic transition happens, which is both spin forbidden $(∆ s \neq 0)$ and Laporate forbidden selection rule. Hence, the colour is pale pink. In ${MnO}_{2}$ , the manganese is in $+ 4$ oxidation state and there will be three unpaired electrons in $d$ orbital. So the transition is spin allowed $(∆ s = 0)$ and Laporate forbidden; hence, the colour is black. Hence, the transition happened due to the $d - d$ transition. In ${MnO}_{4}^{-}$ , the manganese in $+ 7$ oxidation state and there is no electron in valence shell. So, here the colour is due to the charge transfer. It is occurred by an electron come from the $p$ orbital of oxygen is gone to $d$ orbital in $Mn$ . So, the energy is absorbed from the visible light and transition happens due to non $d - d$ transition. Hence, ${MnO}_{4}^{-}$ is intensely coloured purple.

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Explain why ${[Mn (H_{2} O)_{6}]}^{2 +}$ is pale pink. ${MnO}_{2}$ is black and ${MnO}_{4}^{-}$ is intensely coloured purple.

Important Questions on Group 7 - the Manganese Group

Learn and Prepare for any exam you want !

Explain why Mn(H2O)62+ is pale pink. MnO2 is black and MnO4- is intensely coloured purple.

Important Questions on Group 7 - the Manganese Group

Learn and Prepare for any exam you want !

Explain why ${[Mn (H_{2} O)_{6}]}^{2 +}$ is pale pink. ${MnO}_{2}$ is black and ${MnO}_{4}^{-}$ is intensely coloured purple.