Final answer:
Adding Ba²⁺(aq) ions to a carbonate solution will produce an insoluble compound first because barium carbonate has the lowest solubility and will therefore precipitate before the carbonates of magnesium, calcium, and strontium.
Step-by-step explanation:
If we are adding ions Mg²⁺(aq), Ca²⁺(aq), Sr²⁺(aq), or Ba²⁺(aq) to a solution containing carbonate ions (CO₃²⁻), the ion that will form an insoluble carbonate compound first is the Ba²⁺(aq). This is because, in general, the solubility of the alkaline earth metal carbonates decreases as we go down the group in the periodic table. Therefore, among the given options, barium carbonate (BaCO₃) is the least soluble and will precipitate first when its ions are mixed with carbonate ions.
The tendency of various ions to form a precipitate can be explained by looking at their respective solubility product constants (Ksp). The Ksp is a measure of how much of a compound can be dissolved in a solvent before reaching the saturation point. In this scenario, barium carbonate has a lower Ksp value compared to the other compounds, indicating that it is less soluble and will therefore precipitate out of solution earlier.