Question

(i) Scandium (z = 21) is a transition element but zink (z = 30) is not. Explain.
(ii) Calculate the equivalent weight of $KMn{O}_4$in acidic medium.
(iii) What do you mean by Lanthanoid contraction ?

Answer 1

(i) On the basis of incompletely filled 3d orbitals, in case of $Sc$ atom in it's ground state $\left({3d}^1\right)$, it is regarded as transition element. On the other hand, $Zn$ atom has completely filled d orbitals $\left({3d}^{10}\right)$ in it's ground state as well as in this oxidised state, Hence, not regarded as transition element.

(ii) The molar mass of ${KMnO}_4$ is 158 g/mol. To find equivalent mass, divide that molar mass by mole of electrons taken in it's half $rxn$. That would be $5.\frac{158}{5}=31.6$ gms/equivalent.

(iii) Lanthnoid contraction is steady decreases in ionic radii of the elements in the lanthandie series from atomic number 57, lanthanum (to) 71, lutetium.