- The given equilibrium system is \(H_2SO_4(aq) \rightleftharpoons 2H^+(aq) + SO_4^{2-}(aq)\).
- The common ion effect occurs when a substance adding an existing ion (\(H^+\) or \(SO_4^{2-}\)) is introduced to the system.
- Evaluating the options, \(MgSO_4\) dissociates to produce \(SO_4^{2-}\), which is present in the equilibrium expression.
- According to Le Chatelier's principle, this increase in product concentration shifts the equilibrium toward the reactants, thus identifying the correct choice as d.
- Final Answer: \(\boxed{d}\)
Explanation
- Analysis of the Equilibrium and Common Ion Effect
The equilibrium of sulfuric acid in an aqueous solution is given by the following equation:
\[H_2SO_4(aq) \rightleftharpoons 2H^+(aq) + SO_4^{2-}(aq)\]
The common ion effect is a phenomenon where the addition of a solute that provides an ion already present in the chemical equilibrium mixture shifts the equilibrium position according to Le Chatelier's principle. In our system, the ions present at equilibrium are the hydrogen ion (\(H^+\)) and the sulfate ion (\(SO_4^{2-}\)). To identify the compound that causes a shift in the equilibrium due to the common ion effect, we must look for a substance that dissociates to release either \(H^+\) or \(SO_4^{2-}\).
- Evaluating the Options
Let us examine the dissociation of each option in water:
A\(FeCl_3\) dissociates as: \(FeCl_3(aq) \to Fe^{3+}(aq) + 3Cl^-(aq)\)
B\(KNO_3\) dissociates as: \(KNO_3(aq) \to K^+(aq) + NO_3^-(aq)\)
C\(NaCl\) dissociates as: \(NaCl(aq) \to Na^+(aq) + Cl^-(aq)\)
D\(MgSO_4\) dissociates as: \(MgSO_4(aq) \to Mg^{2+}(aq) + SO_4^{2-}(aq)\)
Comparing these to our equilibrium system (\(H^+\) and \(SO_4^{2-}\)), we see that only \(MgSO_4\) provides an ion that is already present in the equilibrium, which is the sulfate ion (\(SO_4^{2-}\)).
- Applying Le Chatelier's Principle and Conclusion
According to Le Chatelier's principle, if a product of a chemical reaction at equilibrium is added to the system, the reaction will shift to oppose the change, effectively shifting toward the reactants. By adding \(MgSO_4\), we increase the concentration of the product \(SO_4^{2-}\). Consequently, the equilibrium \(H_2SO_4(aq) \rightleftharpoons 2H^+(aq) + SO_4^{2-}(aq)\) will shift to the left to reduce the excess sulfate concentration. Therefore, \(MgSO_4\) is the compound that causes a shift in equilibrium due to the common ion effect. The correct option is d.
Examples
The common ion effect is widely used in analytical chemistry, such as in the precipitation of slightly soluble salts. For example, if you have a saturated solution of lead(II) chloride (\(PbCl_2\)) and you add a salt like sodium chloride (\(NaCl\)) that provides common chloride ions, the solubility of the lead(II) chloride decreases. This principle allows chemists to control the solubility of compounds, optimize yields in industrial processes, and selectively precipitate specific ions from a mixture, demonstrating the practical application of equilibrium control in everyday science.