a) Potassium dichromate (K2Cr2 O7 ) is an important compound of chromi

1.	a) Potassium dichromate (K2Cr2 O7 ) is an important compound of chromium. Describe the method of preparation of potassium dichromate from chromite ore.b) The gradual decrease in the size of lanthanoid elements from lanthanum to lutetium is known as lanthanoid contraction. Write anyone consequence of lanthanoid contraction.
Answer» a) K₂Cr₂O₇ is prepared from chromate one Fe Cr₂ O₄. Step I: The powdered ore is heated with molten alkali in free access of air to form soluble sodium chromate. 4 Fe Cr₂O₄ + 16 NaOH + 7O₂ → 8 Na₂CrO₄ + 2 Fe₂O₃ + 8 H₂O Step II: Sodium chromate (Na₂Cr O₄) is filtered and acidified with dil. H₂SO₄ to form sodium dichromate. 2 Na₂CnO₄ + H₂SO₄ → Na₂Cn₂O₇ + Na₂SO₄ + H₂O Step III: Na₂Cn₂O₇ solution is treated with KCI to form K₂Cr₂O₇. Na₂Cn₂O₇ + 2 KCI → K₂Cn₂O₇ + 2NaCI b) Consequences of lanthanoid contraction are Difficulty in separation of lanthanoids due to similanity in chemical properties. The similarity in size of elements belonging to same group of second & third transition series.

a) Potassium dichromate (K2Cr2 O7 ) is an important compound of chromium. Describe the method of preparation of potassium dichromate from chromite ore.b) The gradual decrease in the size of lanthanoid elements from lanthanum to lutetium is known as lanthanoid contraction. Write anyone consequence of lanthanoid contraction.

Answer»

a) K₂Cr₂O₇ is prepared from chromate one Fe Cr₂ O₄.

Step I: The powdered ore is heated with molten alkali in free access of air to form soluble sodium chromate.

4 Fe Cr₂O₄ + 16 NaOH + 7O₂ → 8 Na₂CrO₄ + 2 Fe₂O₃ + 8 H₂O

Step II: Sodium chromate (Na₂Cr O₄) is filtered and acidified with dil. H₂SO₄ to form sodium dichromate.

2 Na₂CnO₄ + H₂SO₄ → Na₂Cn₂O₇ + Na₂SO₄ + H₂O

Step III: Na₂Cn₂O₇ solution is treated with KCI to form K₂Cr₂O₇.

Na₂Cn₂O₇ + 2 KCI → K₂Cn₂O₇ + 2NaCI

b) Consequences of lanthanoid contraction are

Difficulty in separation of lanthanoids due to similanity in chemical properties.
The similarity in size of elements belonging to same group of second & third transition series.