Multiple Choice
When an ionic compound dissolves in water, what typically occurs at the molecular level?
107
views
6. Chemical Quantities & Aqueous Reactions
Solubility Rules
Multiple Choice
Which of the following statements best explains how lowering the pH affects the solubility of a salt containing a basic anion, such as CaCO3?
A
Lowering the pH decreases the solubility because more H+ ions cause the salt to precipitate.
B
Lowering the pH increases the solubility because the added H+ reacts with the basic anion to form a weak acid.
C
Lowering the pH increases the solubility because it increases the concentration of the salt's cation.
D
Lowering the pH has no effect on the solubility of salts containing basic anions.
Verified step by step guidance1
Identify the salt and its basic anion: In this case, the salt is CaCO\_3, which contains the carbonate ion (CO\_3^{2-}), a basic anion.
Understand the effect of pH on basic anions: Lowering the pH means increasing the concentration of H\^+ ions in solution. These H\^+ ions can react with the basic anion (CO\_3^{2-}) to form its conjugate acid (HCO\_3\^- or H\_2CO\_3), which are weak acids.
Write the relevant equilibrium reaction showing how H\^+ interacts with the basic anion:
\(\mathrm{CO\_3^{2-} + H\^+ \rightleftharpoons HCO\_3\^-}\)
and further
\(\mathrm{HCO\_3\^- + H\^+ \rightleftharpoons H\_2CO\_3}\)
Explain how this reaction affects solubility: By consuming CO\_3^{2-} ions, the equilibrium of the salt dissolution shifts to dissolve more CaCO\_3 to replace the lost CO\_3^{2-}, thus increasing the solubility of the salt.
Conclude that lowering the pH increases the solubility of salts containing basic anions because the added H\^+ ions react with the anion to form weak acids, driving the dissolution equilibrium forward.
Related Videos
Related Practice
