Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?
Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?
Solution and Explanation
Potassium dichromate is prepared from chromite ore (FeCr2O4) in the following steps
Step (1): Preparation of sodium chromate
4FeCr2O4+16NaOH+7O2 \(\rightarrow\) 8Na2CrO4+2Fe2O3+8H2o
Step (2): Conversion of sodium chromate into sodium dichromate
2Na2CrO4+conc.H2SO4 \(\rightarrow\) Na2Cr2O7+Na2SO4+H2o
Step(3): Conversion of sodium dichromate to potassium dichromate
Na2Cr2O7+2KCl \(\rightarrow\) K2Cr2O7+NaCl
Potassium dichromate being less soluble than sodium chloride is obtained in the form of orange coloured crystals and can be removed by filtration.
The dichromate ion (Cr2O72-) exists in equilibrium with chromate CrO2-4 ion at pH 4. However, by changing the pH, they can be interconverted.
2CrO2-4-ââ€'-
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The d-block elements are placed in groups 3-12 and F-block elements with 4f and 5f orbital filled progressively. The general electronic configuration of d block elements and f- block elements are (n-1) d 1-10 ns 1-2 and (n-2) f 1-14 (n-1) d1 ns2 respectively. They are commonly known as transition elements because they exhibit multiple oxidation states because of the d-d transition which is possible by the availability of vacant d orbitals in these elements.
They have variable Oxidation States as well as are good catalysts because they provide a large surface area for the absorption of reaction. They show variable oxidation states to form intermediate with reactants easily. They are mostly lanthanoids and show lanthanoid contraction. Since differentiating electrons enter in an anti-penultimate f subshell. Therefore, these elements are also called inner transition elements.
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