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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. Complete the following chemical equations:
  1. $ \text{MnO}_{4}^{-}\text{(aq)}+\text{S}_{2}\text{O}_{4}\text{(aq)}+\text{H}_{2}\text{O}\text{(l)}\rightarrow$
  2. $\text{Cr}_{2}\text{O}_{4}^{2-}\text{(aq)}+\text{Fe}^{2+}\text{(aq)}+\text{H}^{+}\text{(aq)}\rightarrow$
  1. Explain the following observations:
  1. $La^{3+} (Z = 57)$ and $Lu^{3+} (Z = 71)$ do not show any colour in solutions.
  2. Among the divalent cations in the first series of transition elements, manganese exhibits the maximum paramagnetism.
  3. $Cu^+$ ion is not known in aqueous solutions.
✓

Answer

  1.  
  1. $8MnO_4^- + 3S_2O_3^{2-} + H_2O 8MnO_2 + 6SO_4^{2-} + 2OH^-.$
  2. $Cr_2O_7^{2-} + 14H^+ + 6Fe^{2+} 2Cr^{3+} + 6Fe^{3+} + 7H_2O.$
  1.  
i. In $La ^{3+}$, there is no $f$ electrons while in $Lu ^{3+}$, there is presence of $f ^{14} /$ absence of unpaired electron/due to d-d transition.
ii. $Mn ^{2+}$ has $3 d^5$ configuration having 5 unpaired electrons.
ii. $Cu ^{+}$undergoes disproportionation in aqueous solution.
Alternate answer

$2Cu^+​​​​​​​$ $\rightarrow$ $Cu^{2+} + Cu.$

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