Question
A salt with few drops of conc. HCl gives apple green colour in flame test. The group precipitate of the salt is dissolved in acetic acid and treated with $K_{2}{CrO}_{4}$ to give yellow precipitate. When the sodium carbonate extract of the salt solution is heated with conc. ${HNO}_{3}$ and ammonium molybdate, it resulted a canary yellow precipitate. The cation and anion present in the salt are respectively.
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Solution
Sol. [Key Concept: Apple-green flame $\Rightarrow$ Ba$2 +$; canary-yellow with molybdate $\Rightarrow$ PO$4^{3 -}$.]
(i) ${Ba}^{+ 2}$ gives apple green colour while ${Ca}^{+ 2}$ and ${Sr}^{+ 2}$ gives brick red and crimson red in flame test.
(ii) ${Ba}^{+ 2} + {CrO}_{4}^{2 -} \rightarrow \underset{\text{~}\text{Yellow ppt}\text{~}}{{BaCrO}_{4}}$
(iii) $\begin{matrix} {PO}_{4}^{3 -} + \text{~}\text{Conc}\text{~}{HNO}_{3} + \left( {NH}_{4} \right)_{2}{MoO}_{4} \longrightarrow \left( {NH}_{4} \right)_{3}\left\lbrack P\left( {Mo}_{3}O_{10} \right)_{4} \right\rbrack\underset{\text{~}\text{Canery yellow ppt}\text{~}}{\downarrow} \\ \end{matrix}$
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