The d-And-f-Block Elements

The d-And-f-Block Elements

Question

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).
                                  
                                                OR
Complete space the space following space chemical space equations colon
left parenthesis straight i right parenthesis space 8 MnO subscript 4 superscript minus space plus 3 straight S subscript 2 straight O subscript 3 superscript 2 minus end superscript space plus straight H subscript 2 straight O space rightwards arrow
left parenthesis ii right parenthesis space Cr subscript 2 straight O subscript 7 superscript 2 minus end superscript space plus 3 Sn to the power of 2 plus end exponent space plus 14 straight H to the power of plus rightwards arrow

Answer
Chromite space ore comma space on space fusion space with space NaOH space gives space sodium space chromate space which space is space yellow space in space colour colon
4 FeCr subscript 2 straight O subscript 4 space plus 16 NaOH space plus 7 straight O subscript 2 space rightwards arrow stack 8 Na subscript 2 CrO subscript 4 with left parenthesis straight A right parenthesis below space plus 2 Fe subscript 2 straight O subscript 3 space plus 8 straight H subscript 2 straight O
Sodium space chromate space left parenthesis straight A right parenthesis space on space acidification comma space gives space sodium space dichromate space left parenthesis straight B right parenthesis colon
2 Na subscript 2 CrO subscript 4 space plus straight H subscript 2 SO subscript 4 space rightwards arrow stack Na subscript 2 Cr subscript 2 straight O subscript 7 with left parenthesis straight B right parenthesis below space plus Na subscript 2 SO subscript 4 space plus straight H subscript 2 straight O
Sodium space dichromate space left parenthesis straight B right parenthesis space on space reaction space with space KCl space forms space potassium space dichromate space which space is space orange space in space colour colon
Na subscript 2 Cr subscript 2 straight O subscript 7 space plus 2 KCl space rightwards arrow stack straight K subscript 2 Cr subscript 2 straight O subscript 7 space with left parenthesis straight C right parenthesis below plus 2 NaCl
Potassium space dichromate space is space powerful space oxidising space agent. space It space is space used space prepartion space of space azo space compounds.

Or
left parenthesis straight i right parenthesis space 8 MnO subscript 4 superscript minus space plus 3 straight S subscript 2 straight O subscript 3 superscript 2 minus end superscript space plus straight H subscript 2 straight O space rightwards arrow space 8 MnO subscript 2 space plus 6 SO subscript 4 superscript 2 minus end superscript space plus 2 OH to the power of minus
ii right parenthesis space Cr subscript 2 straight O subscript 7 superscript 2 minus end superscript space plus 3 Sn to the power of 2 plus end exponent plus 14 straight H to the power of plus space rightwards arrow 2 Cr to the power of 3 plus end exponent space plus 3 Sn to the power of 4 plus end exponent space plus 7 straight H subscript 2 straight O

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