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AP Chemistry
7.12 Common-Ion Effect
7.11 Introduction to Solubility Equilibria
IntermediateMCQGraphicalConceptual15.2k
A line graph with bare axes and no gridlines. The horizontal axis is labeled 'Concentration of Added \(\text{SO}_4^{2-}\) (M)' and begins at 0. The vertical axis is labeled 'Equilibrium \([\text{Ba}^{2+}]\) (M)' and begins at 0. A single smooth, solid black curve starts at a point on the vertical axis above zero, curves downward steeply toward the right, and flattens to approach the horizontal axis asymptotically without touching or crossing it. No other lines, data points, legends, text, or annotations appear.
Equilibrium \([\text{Ba}^{2+}]\) as a function of added \([\text{SO}_4^{2-}]\) at \(298 \text{ K}\).
A student investigates the common-ion effect by measuring the equilibrium concentration of \(\text{Ba}^{2+}\text{(aq)}\) in several saturated solutions of \(\text{BaSO}_4\text{(s)}\) containing different initial concentrations of dissolved \(\text{Na}_2\text{SO}_4\text{(aq)}\) at \(298 \text{ K}\).

\[ \text{BaSO}_4\text{(s)} \rightleftharpoons \text{Ba}^{2+}\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \quad K_{sp} = 1.1 \times 10^{-10} \text{ at } 298 \text{ K} \]

The student's results are shown in the graph below.

Which of the following best explains why the equilibrium concentration of \(\text{Ba}^{2+}\text{(aq)}\) decreases non-linearly and approaches the horizontal axis asymptotically as the concentration of added \(\text{SO}_4^{2-}\text{(aq)}\) increases?

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