Advertisements
Advertisements
प्रश्न
Indicate the steps in the preparation of K2Cr2O7 from chromite ore.
Advertisements
उत्तर
Dichromates are generally prepared from chromate, which in turn is obtained by the fusion of chromite ore (FeCr2O4) with sodium or potassium carbonate in free air. The reaction with sodium carbonate occurs as follows:
\[\ce{4FeCr_2O_4 + 8Na2CO3 + 7O_2 ->8Na_2CrO_4 + 2Fe_2O_3 + 8CO2}\]
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.
\[\ce{2Na_2CrO_4 + 2H^+ -> Na_2Cr_2O_7 + 2Na^+ + H_2O}\]
Sodium dichromate is more soluble than potassium dichromate. Therefore, the latter is prepared by treating the solution of sodium dichromate with potassium chloride.
\[\ce{Na_2Cr_2O_7 + 2KCl -> K_2Cr_2O_7 + 2NaCl}\]
Orange crystals of potassium dichromate crystallise out. The chromates and dichromates are interconvertible in an aqueous solution, depending on the pH of the solution. The oxidation state of chromium in chromate and dichromate is the same.
\[\ce{2CrO^{2-}_4 + 2H^+ -> Cr2O^{2-}_7 + H2O}\]
\[\ce{Cr2O^{2-}_7 + 2OH^- -> 2CrO^2-_4 + H2O}\]
Hence, when the pH is increased, making the solution alkaline, dichromate ions (orange in colour) are converted into chromate ions, and the solution becomes yellow.
APPEARS IN
संबंधित प्रश्न
Complete the following chemical equation
8MnO4- + 3S2O32- + H2O →
Complete the following equations : MnO4- + 4H+ + 3e- →
Complete the following chemical equation
Cr2O72- + 3Sn2+ + 14H+ →
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.
Give an example and suggest a reason for the following feature of the transition metal chemistry:
A transition metal exhibits the highest oxidation state in oxides and fluorides.
Indicate the steps in the preparation of KMnO4 from pyrolusite ore.
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`
On addition of small amount of \[\ce{KMnO4}\] to concentrated \[\ce{H2SO4}\], a green oily compound is obtained which is highly explosive in nature. Identify the compound from the following.
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) \[\ce{2MnO^{-}4 + 3Mn^{2+} + 2H2O -> 5MnO2 + 4H^{+}}\]
Which of the following is amphoteric oxide?
\[\ce{Mn2O7, CrO3, Cr2O3, CrO, V2O5, V2O4}\]
When \[\ce{Cu^2+}\] ion is treated with \[\ce{KI}\], a white precipitate is formed. Explain the reaction with the help of chemical equation.
Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] from chomite ore.
Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] from chromite ore.
Indicate the step in the preparation of K2Cr2O7 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.
