K2Cr2O7 is prepared from chromate ore Fe Cr2O4 .
Step I : The powdered ore is heated with molten alkali to form soluble sodium chromate.
4 Fe Cr2 O4 + 16 NaOH + 7O2 → 8Na2CrO4 + 2Fe2O3 + 8H2O
Step II : Sodium chromate (Na2Cr2O7) is filtered and acidified with dil.H2SO4 to form sodium dichromate.
2Na2CrO4 + H2SO4 → Na2Cr2O + Na2SO4 + H2O
Step III : Na2Cr2O7 solution is treated with KCI to form
K2Cr2O7.
Na2Cr2O7 + 2 KCI —» K2Cr2O7 + 2NaCI
OR
Magnetic moment,
µ = \(\sqrt{n(n+2)}\) BM
Cr; n = 6 µ = \(\sqrt{48}\) = 6.93 BM
Mn; n = 5 µ = \(\sqrt{35}\) = 5.92 BM
Fe; n = 4 µ = \(\sqrt{24}\) = 4.90 BM
Co; n = 3 µ = \(\sqrt{15}\) = 3.87BM
Ni; n = 2 µ = \(\sqrt{8}\) = 2.83 BM
∴ Cr has maximum paramagnetic behaviour.