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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
  1. With reference to structural variability and chemical reactivity, write the differences between lanthanoids and actinoids.
  2. Name a member of the lanthanoid series which is well known to exhibit +4 oxidation state.
  3. Complete the following equation:

$\text{MnO}_{4}^{-}+\text{8H}^{+}+\text{5e}^{-}\rightarrow$

  1. Out of Mn3+ and Cr3+, which is more paramagnetic and why?

(Atomic nos: Mn = 25, Cr = 24).

✓

Answer

  1.  
Lanthanoids
Actinoids
Atomic/ionic radii does not show much variation/+3 is the most common oxidation state, in few cases +2 & +4.
Atomic/ionic radii show much variation/Besides +3 oxidation state they exibit +4,+5,+6,+7 also.
They are quite reactive.
Highly reactive in finely divided state.
  1. Cerium (Ce4+).
  2. $\text{MnO}_{4}^{-}+\text{8H}^{+}+\text{5e}^{-}\rightarrow\text{Mn}^{2+}+\text{4H}_{2}\text{O}$.
  3. Mn3+ is more paramgnetic.

Because Mn3+ has 4 unpaired electrons (3d4) therefore more paramagnetic whereas Cr3+ has 3 unpaired electrons (3d3).

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