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The d & f Block Elements — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe d & f Block Elements5 Marks
Question
Answer the following questions:
Give reasons:
  1. d-block elements exhibit more oxidation states than f-block elements.
  2. Orange solution of potassium dichromate turns yellow on adding sodium hydroxide to it.
  3. Zirconium (Z = 40) and Hafnium (Z = 72) have almost similar atomic radii.
✓

Answer

  1. d–block elements exhibit more oxidation states because of less energy gap between d and s subshell whereas f-block elements have large energy gap between f and d subshell.
  2. On adding NaOH, pH of solution increases and the orange colour of the solution changes to yellow due to conversion of dichromate ion to chromate ion.
$\text{Cr}_2\text{O}^{2-}_7+2\text{OH}^-\rightleftharpoons2\text{CrO}^{2-}_4+\text{H}_2\text{O}\\\text{Dichromate}\ \ \ \ \ \ \ \ \ \ \ \ \ \text{Chromate}\\\text{(Orange)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (\text{yellow})$
  1. This is due to filling of 4f-orbitals which have poor shielding effect (Lanthanoid contraction).

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