In the wet tests for detection of various cations by precipitation,...

${Ba}^{2 +}$ belongs to ${V}^{\text{th}}$Group and hence they are precipitated with ${CO}_{3}^{2 -}$ to give ppt of ${BaCO}_{3}$. In Wet tests for cations, $( {NH}_{4}{)}_{2}{CO}_{3}$ is used as a group reagent for fifth group cations$( {Ba}^{2 +}, {Ca}^{2 +}, {Sr}^{2 +} )$.

${Ba}^{2 +} + ( {NH}_{4}{)}_{2}{CO}_{3} \to {BaCO}_{3} + {{NH}_{4}}^{⊕}$