Identify the Lewis base in this balanced equation: 6 H2O + Cr(H2O)63+ → Cr3+ + 6 H2O
The Correct Answer and Explanation is:
In this equation:
6H2O+Cr(H2O)63+→Cr3++6H2O6 \text{H}_2\text{O} + \text{Cr(H}_2\text{O)}_6^{3+} \rightarrow \text{Cr}^{3+} + 6 \text{H}_2\text{O}6H2O+Cr(H2O)63+→Cr3++6H2O
The Lewis base is the water molecule (H₂O).
Explanation:
In the context of Lewis acid-base theory, an acid is a substance that accepts a pair of electrons, and a base is a substance that donates a pair of electrons. In this reaction, the complex ion Cr(H2O)63+\text{Cr(H}_2\text{O)}_6^{3+}Cr(H2O)63+ involves chromium(III) (Cr³⁺) surrounded by six water molecules as ligands. The water molecules in this complex are acting as ligands, meaning they donate electron pairs to the metal ion, Cr³⁺, which is the Lewis acid in this case because it accepts those electron pairs.
Here’s a step-by-step breakdown:
- Chromium(III) Ion (Cr3+\text{Cr}^{3+}Cr3+): This ion is a Lewis acid because it has a high charge density, which makes it capable of accepting electron pairs.
- Water Molecule (H2O\text{H}_2\text{O}H2O): The oxygen atom in water has lone pairs of electrons that can be donated to a metal ion like Cr³⁺. Hence, water is acting as the Lewis base by donating electron pairs to chromium.
When the complex Cr(H2O)63+\text{Cr(H}_2\text{O)}_6^{3+}Cr(H2O)63+ dissociates, the chromium ion remains as Cr³⁺, and the water molecules are released as free H₂O molecules. Since the water molecules are donating electron pairs to chromium, they are the Lewis bases in this equation.
To summarize, water (H₂O) is the Lewis base because it donates electron pairs to the chromium ion, which is the Lewis acid.
