Question

Write the balanced equations in the manufacture of K₂Cr₂O₇ from cromite ore?

Answer 1

Manufacture of K₂Cr₂O₇ from chromite ore involves the following steps 

Step-1: Conversion of chromite ore into sodium chromate: Chromite ore is heated with Na₂CO₃ in the presence of excess of air to form sodium chromate 

4FeOCr₂O₃ + 8Na₂CO₃ + 7O₂→ 8Na₂CrO₄ + 2Fe₂O₃ + 8CO₂ 

Step-2: Conversion of sodium chromate into sodium dichromate. 

The yellow solution of sodium chromate is filtered and acidified with H₂SO₄ to give a mixture of Na₂Cr₂O₇ and sodium sulphate 

2Na₂CrO₄ + H₂SO₄ → Na₂Cr₂O₇ + Na₂SO₄ + H₂O 

The less soluble Na₂SO₄ is removed by filtration. 

Step-3: Conversion of sodium dichromate into potassium dichromate: The solution of sodium dichromate is treated with KCl to give potassium dichromate. 

Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl