Indicate the steps in the preparation of (i) ...

NCERT Class XII Chemistry
Chapter - The d- and f-Block Elements
Questions with Solutions

Question : 26 of 49

Marks: +1, -0

Indicate the steps in the preparation of

(i)

\mathrm{K_2Cr_2O_7}

from chromite ore

(ii)

\mathrm{KMnO_4}

from pyrolusite ore.

Solution:

(i)

4\mathrm{FeCr_2O_4} + 8\mathrm{Na_2CO_3} + 7\mathrm{O_2} \rightarrow 8\mathrm{Na_2CrO_4} + 2\mathrm{Fe_2O_3} + 8\mathrm{CO_2}

2\mathrm{Na_2CrO_4} + 2\mathrm{H}^{+} \rightarrow \mathrm{Na_2Cr_2O_7} + 2\mathrm{Na}^{+} + \mathrm{H_2O}

\mathrm{Na_2Cr_2O_7} + 2\mathrm{KCl} \rightarrow \mathrm{K_2Cr_2O_7} + 2\mathrm{NaCl}

(ii)

2\mathrm{MnO_2} + 4\mathrm{KOH} + \mathrm{O_2} \xrightarrow[]{\Delta} 2\mathrm{K_2MnO_4} + 2\mathrm{H_2O}

3\mathrm{MnO_4}^{2-} + 4\mathrm{H}^{+} \rightarrow 2\mathrm{MnO_4}^{-} + \mathrm{MnO_2} + 2\mathrm{H_2O}

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