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Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate? |
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Answer» Potassium Dichromates are generally prepared from chromates which in turn are obtained by the fusion of chromite ore (FeCr2O4) with sodium or potassium carbonate in free excess of air 4FeCr2O4 + 8Na2CO3 + 7O2 → 8Na2CrO4 + 2Fe2O3 + 8CO2 The yellow solution of Na2CrO4 is filtered and acidified with H2SO4 to give a solution from which orange sodium dichromate Na2Cr2O7 2H2O can be crystallised sodium dichromate is more soluble than potassium dichromate. The latter is prepared by treating the solution of Na2Cr2O4 with KCl. Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl (orange crystals) (b) On increasing the PH of a solution of K2Cr2O7, it behaves like a strong oxidising agent and it oxidises iodide to iodine sulphides to sulphur, tin (II) to tin (IV) and Iron (II) salts to iron (III). |
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