Which of the following compounds is soluble in water?
Cs2O
CaS
Al2S3
Hg2Cl2
NiO
The Correct Answer and Explanation is :
Among the compounds listed, CaS (calcium sulfide) is soluble in water.
Explanation:
To determine the solubility of these compounds, we consider the solubility rules for ionic compounds in water. Water solubility depends on the lattice energy of the compound, the charge on the ions, and the interaction between those ions and the solvent (water).
- Cs₂O (cesium oxide):
- Cesium is an alkali metal, and alkali metal oxides are generally soluble in water. However, cesium oxide forms an alkaline solution (basic) and reacts with water to form cesium hydroxide (CsOH). So, while it may dissolve, the solubility might be accompanied by a strong exothermic reaction, making it somewhat difficult to consider in typical dissolution scenarios. It is soluble but reacts vigorously.
- CaS (calcium sulfide):
- Calcium sulfide is an ionic compound. According to solubility rules, sulfides of alkaline earth metals (like calcium) are typically soluble in water. In this case, CaS dissolves to form Ca²⁺ and S²⁻ ions in water. The solubility of CaS is not as high as some other salts, but it is still considered soluble in water.
- Al₂S₃ (aluminum sulfide):
- Aluminum sulfide is insoluble in water. When it reacts with water, it forms aluminum hydroxide (Al(OH)₃) and hydrogen sulfide (H₂S) gas. The reaction is not a simple dissolution; it involves chemical changes, indicating that Al₂S₃ does not dissolve readily in water.
- Hg₂Cl₂ (mercury(I) chloride):
- Mercury(I) chloride is very poorly soluble in water. It forms a sparingly soluble solid, and only a small amount dissolves, generally resulting in a precipitate in most aqueous solutions. It’s considered practically insoluble in water.
- NiO (nickel(II) oxide):
- Nickel(II) oxide is insoluble in water. It is a basic oxide, but it does not dissolve easily in water. Nickel(II) oxide will react with acids to form soluble nickel salts, but it does not dissolve directly in water.
Thus, CaS is the only compound in this list that is notably soluble in water.