Question

What are chemical twins? How is potassium dichromate preppardfrom chromite ore?

Answer 1

Chemical twins are those in which the properties of some elements are same. Atomic size of  Zr and Hf ,  Nb and Ta are similar. This is due to Lanthanide contraction.
 
Following steps indicate how K2Cr2O7 is obtained from chromite ore 

 

Preparation of sodium chromate


Conversion of sodium chromate into sodium dichromate



Conversion of sodium dichromate to potassium dichromate


Potassium dichromate being less soluble than sodium dichromate can be obtained in the form of orange coloured crystals by treating sodium dichromate with potassium chloride and can be removed by filtration.