Advertisements
Advertisements
प्रश्न
Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?
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.
\[\ce{2CrO^2-_4 + 2H+ -> Cr2O^2-_7 + H2O}\]
\[\ce{Cr2O^2-_7 + 2OH- -> 2CrO^2-_4 + H2O}\]
APPEARS IN
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 equation :
`2MnO_4^(-)+6H^++5NO_2^(-)rarr`
Complete the following equations:Cr2O72- + 2OH- →
Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?
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.
Write the formula of an oxo-anion of Manganese (Mn) in which it shows the oxidation state equal to its group number.
Complete the following equations:
`2MnO_4^(-)+16H^++5S^(2-)rarr`
Name a member of the lanthanoid series that is well-known to exhibit +2 oxidation state.
Answer the following question.
When MnO2 is fused with KOH in the presence of KNO3 as an oxidizing agent, it gives a dark green compound (A). Compound (A) disproportionates in an acidic solution to give a purple compound (B). An alkaline solution of compound (B) oxidizes KI to compound (C) whereas an acidified solution of compound (B) oxidizes KI to (D). Identify (A), (B), (C), and (D).
Zinc carbonate is precipitated from zinc sulphate solution by the addition of ___________.
Which of the following is amphoteric oxide?
\[\ce{Mn2O7, CrO3, Cr2O3, CrO, V2O5, V2O4}\]
Potassium permanganate acts as an oxidant in neutral, alkaline as well as acidic media. The final products obtained from it in the three conditions are, respectively.
Why \[\ce{HCl}\] should not be used for potassium permanganate titrations?
Complete the following ionic equation:
\[\ce{Cr2O^{2-}7 + 2OH^- ->}\]
Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] from chromite ore.
Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] from chromite ore.
Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] 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 SO2? Write the ionic equation for the reaction.
