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प्रश्न
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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उत्तर
Potassium dichromate is prepared from chromate, which in turn is obtained by the fusion of chromite ore (FeCr2O3) with sodium or potassium carbonate in free excess of air. The reaction with sodium carbonate occurs as follows:
\[\ce{4FeCr2O4 + 8Na2CO3 + 7O2 -> 8Na2CrO4 + 2Fe2O3 + 8CO2}\]
The yellow solution of sodium chromate is filtered and acidified with sulphuric acid to give a solution from which orange sodium dichromate, Na2Cr2O7.2H2O can be crystallised.
\[\ce{2Na2CrO4 + 2H+ -> Na2Cr2O7 + 2Na+ + H2O}\]
Sodium dichromate is more soluble than potassium dichromate. The latter is therefore prepared by treating the solution of sodium dichromate with potassium chloride.
\[\ce{Na2Cr2O7 + 2KCl -> K2Cr2O7 + 2NaCl}\]
Orange crystals of potassium dichromate crystallise out. The chromates and dichromates are interconvertible in an aqueous solution depending upon the pH of the solution. The oxidation state of chromium in chromate and dichromate is the same.
\[\ce{2CrO^2-_4 + 2H+ -> Cr2O^2-_7 + H2O}\]
\[\ce{Cr2O^2-_7 + 2OH- -> 2CrO^2-_4 + H2O}\]
संबंधित प्रश्न
When chromite ore FeCr2O4 is fused with NaOH in presence of air, a yellow-coloured compound (A) is obtained, which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KCl forms an orange coloured crystalline compound (C).
(i) Write the formulae of the compounds (A), (B) and C.
(ii) Write one use of compound (C).
Complete the following chemical equation
8MnO4- + 3S2O32- + H2O →
Complete the following equations : 2 Na2CrO4 + 2 H + →
Complete the following chemical equation
Cr2O72- + 3Sn2+ + 14H+ →
Name the oxometal anions of the first series of the transition metals in which the metal exhibits the oxidation state equal to its group number.
Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with iron (II) ions? Write the ionic equation for the reaction.
Give an example and suggest a reason for the following feature of the transition metal chemistry:
The lowest oxide of transition metal is basic, the highest is amphoteric/acidic.
Complete the following equation :
Write the ionic equation showing the oxidation of Fe(II) salt by acidified dichromate solutions.
Using IUPAC norms, write the formula of potassium trioxalatochromate(III).
Which of the following reactions are disproportionation reactions?
(a) \[\ce{Cu^{+} -> Cu^{2+} + Cu}\]
(b) \[\ce{3MnO^{-}4 + 4H^{+} -> 2MnO^{-}4 + MnO2 + 2H2O}\]
(c) \[\ce{2KMnO4 -> K2MnO4 + MnO2 + O2}\]
(d) \[\ce{2MnO^{-}4 + 3Mn^{2+} + 2H2O -> 5MnO2 + 4H^{+}}\]
What is the effect of pH on dichromate ion solution?
The oxidation state of manganese in the product obtained in a reaction of potassium permanganate and hydrogen peroxide in a basic medium is ______.
In the two tetrahedral structures of dichromate ion, ______.
Indicate the steps in the preparation of \[\ce{K2Cr2O2}\] from chromite ore.
Indicate the steps in the preparation of K2Cr2O7 from chromite ore.
Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] from chromite ore.
Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with oxalic acid? Write the ionic equation for the reaction.
