A student has an unknown basic radical in a solution. Addition of to a portion of the solution yield — Qualitative and Quantitative Analysis Chemistry Question
Question
A student has an unknown basic radical in a solution. Addition of $K_2CrO_4$ to a portion of the solution yields a yellow precipitate insoluble in acetic acid. Another portion of the solution yields a white precipitate with dilute $H_2SO_4$. The solution gives NO precipitate with dilute $HCl$ or aqueous $NaCl$. The basic radical is most likely:
💡 Solution & Explanation
The yellow precipitate with $K_2CrO_4$ points to $Ba^{2+}$ (forms $BaCrO_4$) or $Pb^{2+}$ (forms $PbCrO_4$). The white precipitate with $H_2SO_4$ confirms either $BaSO_4$ or $PbSO_4$. However, $Pb^{2+}$ belongs to Group I and would form a white precipitate of $PbCl_2$ with dilute $HCl$ or $NaCl$. Since no precipitate forms with $NaCl$, $Pb^{2+}$ and $Ag^+$ are ruled out. Thus, the cation is Barium ($Ba^{2+}$), which belongs to Group V.