Copper(II) Bromide, represented by the chemical formula \(\text{CuBr}_2\), is a chemical compound that readily dissolves in water. Specifically, about 55.7 grams of the anhydrous form of \(\text{CuBr}_2\) can dissolve in 100 milliliters of water at 20°C, confirming its status as a highly soluble salt.
Identifying Copper(II) Bromide and Its Solubility
The compound \(\text{CuBr}_2\) is an ionic substance, also known as cupric bromide. In its solid, anhydrous state, Copper(II) Bromide typically appears as grayish-black or dark crystalline powder. This solid form contains the copper cation (\(\text{Cu}^{2+}\)) and the bromide anion (\(\text{Br}^{-}\)) held together in a fixed crystal lattice.
This high solubility is expected for most bromide salts, as the bromide ion (\(\text{Br}^{-}\)) generally forms soluble compounds. Copper is not one of the few exceptions that would render the compound insoluble, such as silver, lead, or mercury(I). The ready dissolution of \(\text{CuBr}_2\) is a direct result of the strong attractive forces between the water molecules and the ions in the crystal.
The Mechanism of Dissolution in Water
The process by which Copper(II) Bromide dissolves in water is driven by the interaction between the ionic solid and the polar water molecules. Copper(II) Bromide is held together by strong electrostatic forces between the positively charged copper ions and the negatively charged bromide ions. For dissolution to occur, the water must overcome these forces.
Water (\(\text{H}_2\text{O}\)) is a polar solvent, meaning it has a partial negative charge near the oxygen atom and partial positive charges near the hydrogen atoms. When \(\text{CuBr}_2\) is placed in water, the partially negative oxygen ends of the water molecules are attracted to the positive \(\text{Cu}^{2+}\) ions. Conversely, the partially positive hydrogen ends of the water molecules are attracted to the negative \(\text{Br}^{-}\) ions.
These attractions pull the ions away from the solid crystal lattice and into the solution. As the ions separate, the surrounding water molecules encapsulate them, a process known as hydration. The hydration shells formed by the water molecules surrounding the now-free \(\text{Cu}^{2+}\) and \(\text{Br}^{-}\) ions stabilize them in the solution. This stabilizing effect of hydration provides the energy necessary to break the strong ionic bonds within the solid, making the dissolution process energetically favorable and highly effective.
Characteristics of the Copper(II) Bromide Solution
Once dissolved, the resulting mixture is a homogeneous liquid solution. A notable characteristic of this solution is its distinctive blue-green color. The color arises from the solvated Copper(II) ions, represented as \(\text{[Cu}(\text{H}_2\text{O})_6]^{2+}\) complexes, which absorb and reflect light in the visible spectrum. The intensity of the blue-green color is directly related to the concentration of the dissolved \(\text{Cu}^{2+}\) ions.
Because the compound fully dissociates into free-moving charged particles (\(\text{Cu}^{2+}\) and \(\text{Br}^{-}\)) upon dissolution, the solution is classified as an electrolyte, allowing it to conduct an electrical current effectively. The solution is also slightly acidic, as the hydrated \(\text{Cu}^{2+}\) ion can react with water molecules in a hydrolysis reaction, releasing a small amount of hydrogen ions (\(\text{H}^{+}\)) into the solution. This resulting acidic property is characteristic of many salts formed from a strong acid and a weak base.