Question

Which pair of ions among the following can be separated by precipitation method?

• A. Eu(II) and Dy(III)
• B. Gd(III) and Dy(III)
• C. Eu(II) and Yb(II)
• D. Eu(II) and Gd(II)

Hint:

Lanthanide separation: \begin{itemize} \item Similar Ln$^{3+}$ ions hard to separate \item Exceptions: Eu$^{2+}$ and Yb$^{2+}$ \item Use oxidation state differences \end{itemize}

Answer 1

The Correct Option is A

Concept: Separation by precipitation depends on: \begin{itemize} \item Difference in oxidation states \item Difference in solubility of salts \end{itemize} Lanthanides usually show +3 oxidation state, but Eu commonly forms stable +2 state. Step 1: Analyze pairs \begin{itemize} \item Eu(II) vs Dy(III): different oxidation states $\Rightarrow$ different chemistry \item Gd(III) vs Dy(III): similar chemistry $\Rightarrow$ difficult separation \item Eu(II) vs Yb(II): both +2 $\Rightarrow$ similar properties \item Eu(II) vs hypothetical Gd(II): not common \end{itemize} Step 2: Reason Eu(II) forms insoluble salts (like EuSO$_4$), while Dy(III) behaves like typical Ln$^{3+}$. Thus can be separated by selective precipitation. Conclusion: Eu(II) and Dy(III) can be separated.