classXII chem                                                     DATE: 25.06.12

Subjective Ques. from d- and f- blocks

1.Explain the following observations:

(i) Transition elements generally form coloured compounds.

(ii) Zinc is not regarded as a transition element.



2.How would you account for the following?

(i) The atomic radii of the metals of the third (5d) series of transition elements are virtually the same as those of the corresponding members of the second (4d) series.

(ii) The E° Value for the Mn3+/Mn2+ couple is much more positive than that for Cr3+/Cr2+ couple or Fe3+/Fe2+ couple.

(iii) The highest oxidation state of a metal is exhibited in its oxide or fluoride.


3.(a) What is meant by the term lanthanoid contraction? What is it due to and what consequences does it have on the chemistry of elements following lanthanoids in the periodic table?

(b) Explain the following observations:

(i) Cu+ ion is unstable in aqueous solutions.

(ii) Although Co2+ ion appears to be stable, it is easily oxidised to Co3+ ion in the presence of a strong ligand.

(iii) The value for manganese is much more than expected from the trend for other elements in the series.


4.Explain the following observations about the transition/inner transition elements:

(i) There is in general an increase in density of element from titanium (Z = 22) to copper (Z = 29).

(ii) There occurs much more frequent metal−metal bonding in compounds of heavy transition elements (3rd series).

(iii) The members of the actinoid series exhibit a larger number of oxidation states than the corresponding members of the lanthanoid series.


5.Give an explanation for each of the following observations:

(i) The gradual decrease in size (actinoid contractions) from element to element is greater among the actinoids than among the lanthanoids (lanthanoid contraction).

(ii) The greatest number of oxidation states are exhibited by the members in the middle of a transition series.

(iii) With the same d-orbital configuration (d4) Cr2+ ion is a reducing agent but Mn3+ ion is an oxidising agent.