InterviewSolution
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InterviewSolution
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(a) (i) How is the variability in oxidation states of transition metals different from that of the p-block elements ? (ii) Out of Cu^(+) and Cu^(2+), which ion is unstable in aqueous solution and why ? (iii) Orange colour of Cr_(2)O_(7)^(2-) ion changes to yellow when treated with an alkali. Why ? (b) Chemistry of actinoids is complicated as compared to lanthanoids. Given two reasons |
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Answer» Solution :(a) (i) The variability in oxidation state of TRANSITION metal is due to the incomplete FILLING of d-orbitals in such a way, that their oxidation states differ from each other by unity, e.g., `Fe^(2+) and Fe^(3+)` etc. In case of P-block elements, the oxidation state differ by units by two, e.g. `+3 and +5`. MOREOVER, in transition elements, the higher oxidation states are more stable for heavier elements in a group, e.g., `Mo^(+6)` is more stable than `Cr^(4+)`. In P-block elements, the lower oxidation states are more stable for heavier members due to inert pair effect, e.g., `Pb^(2+)` is more stable than `Pb^(4+)`. (ii) `Cu^(+)` is unstable in aqueous solution than `Cu^(2+)`. This is because, although `2^(nd) I.E` of copper is large but hydration enthalpy for `Cu^(2+)` is much more negative than that or `Cu^(+)` and compounds are unstable in aqueous solution and undergo disproportionation. `2Cu^(+) rarr Cu^(2+) + Cu` (iii) Orange colour of `Cr_(2)O_(7)^(2-)` ion changes to yellow when treated with an ALKALI because of the formation of chromate ions `{:(Cr_(2) O7^(2-) + 2OH^(-),rarr,2CrO_(4)^(2-) + H_(2)O),("Dichromate ion",,"Chromate ion"),("(orange)",,"(yeloow)"):}` (b) Chemistry of actinoids is complicated as compared to lanthanoids because: (i) actinoids show wide range of oxidation states i.e., `+3, +4, +5, +6` due to small energy difference between `5f, 6d and 7s` subshells of actinoids. (ii) actinoids are radioactive due to that, chemistry of actinoids is complicated. |
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