Is Cu(OH)2 insoluble or soluble
The Correct Answer and Explanation is:
Copper(II) hydroxide, Cu(OH)2, is generally considered insoluble in water. It has very low solubility, meaning only a small amount of it dissolves when added to water.
The solubility of ionic compounds in water depends on the balance between the lattice energy (the energy required to break apart the ionic solid) and the hydration energy (the energy released when ions are surrounded by water molecules). In the case of Cu(OH)2, the lattice energy is quite large due to the strong electrostatic forces between the Cu²⁺ and OH⁻ ions. This makes it difficult for water molecules to separate these ions.
Even though water can hydrate the copper and hydroxide ions, the lattice energy is strong enough that the solubility of Cu(OH)2 remains low. When Cu(OH)2 is added to water, only a small amount dissolves, and the solution reaches an equilibrium where most of the Cu(OH)2 remains as a solid precipitate. This is why Cu(OH)2 appears as a blue precipitate in water under normal conditions.
To quantify the solubility, the Ksp (solubility product constant) of Cu(OH)2 is relatively low, which further confirms its limited solubility. In fact, the Ksp value for Cu(OH)2 is around 2.2 × 10⁻¹⁴ at 25°C, which is an indication of how little Cu(OH)2 dissolves in water.
However, Cu(OH)2 can dissolve in acidic solutions due to the formation of copper(II) complexes. When the hydroxide ions react with an acid, the copper(II) ions are released into the solution as copper salts, often forming soluble complexes like [Cu(H2O)6]²⁺ or [CuCl4]²⁻. So, while Cu(OH)2 is insoluble in pure water, it can dissolve under certain conditions when exposed to acids or other reagents that facilitate its dissolution.
