Final answer:
Adding nitric acid (HNO3) to a saturated solution of barium carbonate will increase its solubility by reacting with CO32- to form HCO3-, thus shifting the equilibrium to dissolve more BaCO3.
Step-by-step explanation:
To increase the solubility of a saturated solution of the slightly soluble salt barium carbonate (BaCO3), one needs to consider the effects of adding other substances. The addition of sodium carbonate (Na2CO3) introduces more CO32- ions, which due to the common ion effect, decreases the solubility of BaCO3 by shifting the equilibrium to the left. Similarly, adding barium nitrate (Ba(NO3)2) would provide more Ba2+ ions, also decreasing solubility for the same reason. Potassium hydroxide (KOH), a strong base, would not affect the barium concentration but would increase the OH- concentration, possibly precipitating barium as Ba(OH)2. Therefore, the correct answer to increase the solubility of BaCO3 is to add nitric acid (HNO3). Nitric acid increases the H+ ion concentration, which reacts with CO32- to form HCO3-, thereby decreasing the CO32- ion concentration in the solution and shifting the solubility equilibrium to the right to dissolve more BaCO3.