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Lanthanide contraction: The steady decrease in the atomic and ionic (M3+) radii of the lanthanides from lanthanum to lutetium with increasing atomic number is called lanthanide contraction. It is due to the poor shielding of the increasing nuclear charge by the 4f electrons.

Acidified K2Cr2O7 with H2S: H2S is oxidised to sulphur (pale yellow) and the orange dichromate is reduced to green Cr3+.

K2Cr2O7 + 4H2SO4 + 3H2S → K2SO4 + Cr2(SO4)3 + 3S + 7H2O

Ionic form: Cr2O72− + 8H+ + 3H2S → 2Cr3+ + 3S + 7H2O

Doubtly AI · 29 Oct 2026 AI-generated · not yet verified Report
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