Correct!

Chrome alum contains the hexaquo cation: [Cr(H₂O)₆]³⁺

Chromium(III) chloride contains the dichloro cation: [CrCl₂(H₂O)₄]⁺

According to ligand field theory (LFT), the 5-fold degeneracy of the metal d orbitals is lifted when a metal atom is surrounded by a set of negative charges or the negative end of dipoles. That is to say, the five d orbitals no longer have the same energy and split. The pattern of splitting depends on the arrangement of the ligands. In an octahedral complex, the d orbitals split into e_g and t_2g orbitals.

The different ligand environments cause a different amount of splitting between the chromium ion's e_g and t_2g orbitals and it is this that results in different colours for the two compounds.

Now try some of the experiments!

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