To determine which compound will cause a shift in equilibrium due to the common ion effect, we need to identify which compound can contribute an ion already present in the equilibrium reaction.
The equilibrium reaction is:
[tex]\[ \text{H}_2\text{SO}_4 \Leftrightarrow 2 \text{H}^+ + \text{SO}_4^{2-} \][/tex]
In this reaction:
- [tex]\( \text{H}_2\text{SO}_4 \)[/tex] dissociates into [tex]\( 2 \text{H}^+ \)[/tex] and [tex]\( \text{SO}_4^{2-} \)[/tex].
Let's analyze the compounds one-by-one to determine if they provide the common ion [tex]\( \text{SO}_4^{2-} \)[/tex]:
1. NaCl:
- Dissociates into [tex]\( \text{Na}^+ \)[/tex] and [tex]\( \text{Cl}^- \)[/tex].
- Does not provide [tex]\( \text{SO}_4^{2-} \)[/tex].
2. KNO _3:
- Dissociates into [tex]\( \text{K}^+ \)[/tex] and [tex]\( \text{NO}_3^- \)[/tex].
- Does not provide [tex]\( \text{SO}_4^{2-} \)[/tex].
3. MgSO _4:
- Dissociates into [tex]\( \text{Mg}^{2+} \)[/tex] and [tex]\( \text{SO}_4^{2-} \)[/tex].
- Provides the common ion [tex]\( \text{SO}_4^{2-} \)[/tex].
4. FeCl _3:
- Dissociates into [tex]\( \text{Fe}^{3+} \)[/tex] and [tex]\( \text{Cl}^- \)[/tex].
- Does not provide [tex]\( \text{SO}_4^{2-} \)[/tex].
Thus, among the choices, only [tex]\( \text{MgSO}_4 \)[/tex] provides the [tex]\( \text{SO}_4^{2-} \)[/tex] ion, which is common with the equilibrium reaction.
Therefore, the addition of [tex]\( \text{MgSO}_4 \)[/tex] will cause a shift in equilibrium because of the common ion effect.
