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in The d and f Block Elements by (36.2k points)
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Give the method of preparation and two examples for the oxidizing property of K2Cr2O7.

OR

Some d-block elements are given below :

Cr, Mn, Fe, Co, Ni

Identify the element which shows maximum paramagnetic behaviour.

1 Answer

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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.

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