Write the net ionic equation for the precipitation of magnesium carbonate from aqueous solution:
The Correct Answer and Explanation is :
Net Ionic Equation:
[
\text{Mg}^{2+}(aq) + \text{CO}_3^{2-}(aq) \rightarrow \text{MgCO}_3(s)
]
Explanation:
When magnesium carbonate (( \text{MgCO}_3 )) precipitates from an aqueous solution, it occurs through the reaction between magnesium ions (( \text{Mg}^{2+} )) and carbonate ions (( \text{CO}_3^{2-} )) that are present in solution. This reaction leads to the formation of solid magnesium carbonate, which is insoluble in water and precipitates out of the solution.
Step-by-Step Breakdown:
- Dissociation of Reactants:
- Magnesium salts, such as magnesium chloride (( \text{MgCl}_2 )), dissociate into magnesium ions (( \text{Mg}^{2+} )) in solution:
[
\text{MgCl}_2 (aq) \rightarrow \text{Mg}^{2+} (aq) + 2 \text{Cl}^- (aq)
] - Similarly, carbonate salts, such as sodium carbonate (( \text{Na}_2\text{CO}_3 )), dissociate into carbonate ions (( \text{CO}_3^{2-} )):
[
\text{Na}_2\text{CO}_3 (aq) \rightarrow 2 \text{Na}^+ (aq) + \text{CO}_3^{2-} (aq)
]
- Formation of Precipitate:
- When these ions are in the same solution, the magnesium ions (( \text{Mg}^{2+} )) and carbonate ions (( \text{CO}_3^{2-} )) combine to form solid magnesium carbonate (( \text{MgCO}_3 )):
[
\text{Mg}^{2+}(aq) + \text{CO}_3^{2-}(aq) \rightarrow \text{MgCO}_3(s)
] - The solid precipitate, ( \text{MgCO}_3 ), is formed because magnesium carbonate is insoluble in water under typical conditions.
- Net Ionic Equation:
- In a net ionic equation, only the species directly involved in the reaction are shown. Spectator ions, like ( \text{Cl}^- ) and ( \text{Na}^+ ), do not participate in the precipitation and are omitted. Thus, the net ionic equation focuses solely on the interaction between ( \text{Mg}^{2+} ) and ( \text{CO}_3^{2-} ), leading to the formation of solid magnesium carbonate.
This reaction demonstrates a typical precipitation reaction, where two soluble ionic compounds in aqueous solution react to form an insoluble solid, which precipitates out.