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प्रश्न
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).
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उत्तर
Potassium permanganate is prepared by fusion of MnO2 with an alkali metal hydroxide and an oxidizing agent like KNO3. This produces the dark green K2MnO4 which disproportionates in a neutral or acidic solution to give permanganate.
\[\ce{2MnO2 + 4KOH + O2 -> \underset{\text{(A) Dark Green}}{2K2MnO4}+ 2H2O}\]
\[\ce{3MnO^2-_4 + 4H^+ ->\underset{\text{(B) purple}}{2MnO^-_4} + MnO2 + 2H2O}\]
In acid solutions:
Iodine is librated from potassium iodine:
\[\ce{10I^- +\underset{\text{(B)}}{2MnO^-_4}+ 16H^+ -> 2Mn^2+ + 8H2O +\underset{\text{(D)}}{5l2}}\]
In neutral or faintly alkaline solution:
A notable reaction is the oxidation of iodine to iodate:
\[\ce{\underset{\text{(B)}}{2MnO^-_4}+ H2O + I^- -> 2MnO2 + 2OH^- + \underset{\text{(C)}}{IO^-_3}}\].
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).
Indicate the steps in the preparation of KMnO4 from pyrolusite ore.
Complete the following chemical equations :
Cu + H2SO4(conc.) →
Account for the following :
Manganese shows maximum number of oxidation states in 3d series.
E0 value for Mn3+ Mn2+ couple is much more positive than that for Cr3-/ Cr2-.
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) \[\ce{2MnO^{-}4 + 3Mn^{2+} + 2H2O -> 5MnO2 + 4H^{+}}\]
When orange solution containing \[\ce{Cr2O^{2-}7}\] ion is treated with an alkali, a yellow solution is formed and when \[\ce{H^+}\] ions are added to yellow solution, an orange solution is obtained. Explain why does this happen?
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.
