THE D-BLOCK TRANSITION ELEMENTS ASSIGNMENT

1. Describe the preparation of potassium dichromate from chromite ore.

2. Describe the preparation of potassium permanganate from pyrolusite. 

3. .Co+2 is stable in aqueous solution but in the presence of complexing reagent it is easily oxidised.

4. .The chemistry of actinoid elements is not so smooth as lanthanoid. Justify this statement. 

 

 

ANSWERS

1. Preparation of sodium chromate
4FeCr2O4 + 16NaOH + 7O2 → 8NaCrO4 + 2Fe2O3 + 8H2O
Conversion of sodium chromate into sodium dichromate
2Na2CrO4 + conc.H2SO4 → Na2Cr2O7 + Na2SO4 + H2O
Conversion of sodium dichromate to potassium dichromate
Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl

2. MnO2 + 2OH− + O2 → MnO42− + H2O
MnO42− + Cl2 → MnO4− + 2Cl−

 

3. In the presence of strong field complexing reagents, it is oxidized to Co (III). Although the 3rdionization energy for Co is high, but the higher amount of crystal field stabilization energy (CFSE) released in the presence of strong field ligands overcomes this ionization energy.

4. Lanthanoids display a limited number of oxidation states because the energy difference between 4f, 5d, and 6s orbitals is quite large. On the other hand, the energy difference between 5f, 6d, and 7s orbitals is very less. Hence, actinoids display a large number of oxidation.

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