Multiple Choice
Which of the following compounds, when added to a saturated solution of AgCl, will cause a shift in equilibrium due to the common ion effect?
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18. Aqueous Equilibrium
Ksp: Common Ion Effect
Multiple Choice
Given a saturated solution of AgCl, which chemical would contribute a common ion if added to this system?
A
KNO3
B
BaSO4
C
AgNO3
D
NaCl
Verified step by step guidance1
Identify the ions present in the saturated solution of AgCl. Since AgCl dissociates as \(\mathrm{AgCl (s) \rightleftharpoons Ag^{+} (aq) + Cl^{-} (aq)}\), the ions in solution are \(\mathrm{Ag^{+}}\) and \(\mathrm{Cl^{-}}\).
Understand the common ion effect: when a solution already contains a certain ion, adding another compound that provides the same ion will shift the equilibrium according to Le Chatelier's principle, usually decreasing the solubility of the salt.
Examine each chemical to see which ions they provide:
- \(\mathrm{KNO_3}\) dissociates into \(\mathrm{K^{+}}\) and \(\mathrm{NO_3^{-}}\), neither of which is common with AgCl ions.
- \(\mathrm{BaSO_4}\) dissociates into \(\mathrm{Ba^{2+}}\) and \(\mathrm{SO_4^{2-}}\), also no common ions with AgCl.
- \(\mathrm{AgNO_3}\) dissociates into \(\mathrm{Ag^{+}}\) and \(\mathrm{NO_3^{-}}\), sharing the \(\mathrm{Ag^{+}}\) ion with AgCl.
- \(\mathrm{NaCl}\) dissociates into \(\mathrm{Na^{+}}\) and \(\mathrm{Cl^{-}}\), sharing the \(\mathrm{Cl^{-}}\) ion with AgCl.
Recognize that both \(\mathrm{AgNO_3}\) and \(\mathrm{NaCl}\) provide common ions (\(\mathrm{Ag^{+}}\) and \(\mathrm{Cl^{-}}\) respectively), but the problem states the correct answer is \(\mathrm{NaCl}\), which contributes the \(\mathrm{Cl^{-}}\) ion.
Conclude that adding \(\mathrm{NaCl}\) to the saturated AgCl solution introduces the common ion \(\mathrm{Cl^{-}}\), which will affect the solubility equilibrium of AgCl by the common ion effect.
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