it is a lab question, Compare the relative solubilities of BaCrO4 and BaCr2O7. Explain why?………………………………………………………………………………………..
The Correct Answer and Explanation is :
The solubilities of BaCrO₄ (barium chromate) and BaCr₂O₇ (barium dichromate) are quite different, with BaCrO₄ being much less soluble in water compared to BaCr₂O₇.
Solubility Comparison:
- BaCrO₄ (Barium Chromate): BaCrO₄ is known for its low solubility in water. It is classified as an insoluble salt. The solubility product constant (Ksp) of BaCrO₄ is very small, indicating that only a tiny amount of BaCrO₄ dissolves in water. The low solubility is due to the strong ionic lattice formed between Ba²⁺ and CrO₄²⁻ ions, which makes it difficult for water molecules to break the lattice and dissolve the compound.
- BaCr₂O₇ (Barium Dichromate): BaCr₂O₇, on the other hand, is more soluble in water. This can be attributed to its ability to dissociate into two chromate ions (Cr₂O₇²⁻) per barium ion. The chromate ion, Cr₂O₇²⁻, has a relatively larger solubility product compared to the CrO₄²⁻ ion, making BaCr₂O₇ more soluble.
Reason for Difference in Solubility:
- Ion Interaction: BaCrO₄ is less soluble because it involves the chromate ion (CrO₄²⁻), which has a smaller dissociation constant and a higher tendency to form a stable crystal lattice structure. In comparison, BaCr₂O₇ dissociates into two Cr₂O₇²⁻ ions, which increases the disorder (entropy) of the system, leading to greater solubility.
- Chemical Structure: The structure of Cr₂O₇²⁻ (dichromate) is more complex, and it has a higher charge density, meaning that the ions interact more favorably with water molecules, aiding in dissociation. In contrast, CrO₄²⁻ (chromate) is simpler and interacts less effectively with water molecules, making it less soluble.
- Precipitation Behavior: BaCrO₄, due to its low solubility, tends to form precipitates in solutions containing Ba²⁺ and CrO₄²⁻ ions. In contrast, BaCr₂O₇ can dissolve more easily when placed in a solution, especially in acidic conditions, where the dichromate ion is more stable than the chromate ion.
Thus, the difference in solubility is due to the different properties of the chromate and dichromate ions and their ability to interact with water molecules, leading to the solubility disparity between BaCrO₄ and BaCr₂O₇.