The d-And-f-Block Elements

The d-And-f-Block Elements

Question

Complete the following chemical equations:

straight i right parenthesis space MnO subscript 4 superscript minus straight space left parenthesis aq right parenthesis straight space plus straight space straight S subscript 2 straight O subscript 3 superscript 2 minus end superscript straight space left parenthesis aq right parenthesis straight space plus straight space straight H subscript 2 straight O straight space left parenthesis straight l right parenthesis straight space rightwards arrow
ii right parenthesis space Cr subscript 2 straight O subscript 7 superscript 2 minus end superscript straight space left parenthesis aq right parenthesis straight space plus straight space Fe to the power of 2 plus end exponent left parenthesis aq right parenthesis straight space plus straight space straight H to the power of plus straight space left parenthesis aq right parenthesis straight space rightwards arrow

Or

State reasons for the following:

(i) Cu (I) ion is not stable in an aqueous solution.

(ii) Unlike Cr3+, Mn2+, Fe3+ and the subsequent other M2+ ions of the 3d series of elements, the 4d and the 5d series metals generally do not form stable cationic species.

Answer
straight i right parenthesis space 8 MnO subscript 4 superscript minus straight space left parenthesis aq right parenthesis straight space plus straight space 3 straight S subscript 2 straight O subscript 3 superscript 2 minus end superscript straight space left parenthesis aq right parenthesis straight space plus straight space straight H subscript 2 straight O straight space left parenthesis straight l right parenthesis straight space rightwards arrow 8 MnO subscript 2 straight space plus straight space 6 SO subscript 4 superscript 2 minus end superscript plus straight space 2 OH to the power of minus

ii right parenthesis space Cr subscript 2 straight O subscript 7 superscript 2 minus end superscript straight space left parenthesis aq right parenthesis straight space plus straight space 6 Fe to the power of 2 plus end exponent left parenthesis aq right parenthesis straight space plus straight space 14 straight H to the power of plus straight space left parenthesis aq right parenthesis straight space rightwards arrow 2 Cr to the power of 3 plus end exponent straight space plus straight space 6 Fe to the power of 3 plus end exponent straight space plus straight space 7 straight H subscript 2 straight O
Or

(i) In aqueous solution, Cu+ ion undergoes oxidation to Cu2+ ion. The relative stability of different oxidation states can be seen from their electrode potentials.

Cu+(aq) + e- --> Cu(s) , E0red = 0.52V

Cu2+(aq) + 2e­- ---> Cu(s), E0red = 0.34V

Thus overall reaction is :

2Cu+ (aq) ---> Cu2+ (aq) + Cu(s)

Due to more reduction electrode potential value of Cu+, it undergoes oxidation reaction quite feasibly. Hence, copper (I) ion is not stable in aqueous solution.

(ii) The valence shell electronic configurations of Cr3+, Mn2+, Fe3+ are d3d5 and d3respectively. Owing to the symmetrical distribution of the d electrons, these ions can form stable cationic complexes. The atomic radii of the 4d and 5d transition elements are more than that of the 3d series elements. Hence, generally, they do not form stable cationic species.

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