Chemical Reactions I: Net ionic equations
4.2 Copper Compound Solubility
Subjects: Chemical reactions, solubility Ksp, net ionic equations
Description: This reaction demonstrates the difference of solubility of copper chloride in water, and then with addition of sodium hydroxide.
- Copper Chloride(s), CuCl2‡
- 1 100 mL beaker
- 1 400 mL beaker
- watch glass
- stir plate*
- stir bar
- 1M NaOH‡
- wash bottle with water
*Shared item. This item is located in the top drawer opposite the chemical storage cabinets. There are also larger stir plates on the bench top.
‡ Copper chloride is located in the general chemical storage cabinets. Sodium hydroxide is located in the cabinet under the hood.
- Add some water to the 300 mL beaker and place on a stir plate with a stir bar.
- Place some copper chloride on a watch glass.
- Add enough water to dissolve the solid.
- Transfer the solution to the beaker of water on a stir plate. Stir using a stir bar.
- Add NaOH to get a precipitate of copper hydroxide.
Copper chloride is soluble in water. It dissociates as follows:
CuCl2(s) → Cu2+(aq) + 2Cl-(aq)
Adding sodium hydroxide produces a precipitate of copper hydroxide.
CuCl2(aq) + 2NaOH (aq) → Cu(OH)2(s) + 2NaCl(aq)
Net ionic equation:
Cu2+ (aq) + 2OH-(aq) → Cu(OH)2(s)
Based on the solubility rules copper hydroxide is not soluble in water while copper chloride is.
The solubility product constant (Ksp) is an equilibrium constant relating the ionization products of a dissolved substance and allows us to understand why copper hydroxide is seemingly insoluble in water. Ksp is determined experimentally by measuring the concentrations of ions in solution. Copper hydroxide does dissolve a tiny amount in pure water and an equilibrium is established. The equation for the equilibrium of copper hydroxide in water is given below:
Cu(OH)2(s) ⇔ Cu2+(aq) + 2OH-(aq)
The solubility product constant, which is the product of the ion concentrations, and has been determined experimentally, is given below:
Ksp = [Cu2+][OH-]2 = 2.2 x 10-20
Ksp is very small meaning that copper hydroxide dissociates very little in water, while the vast majority remains a solid.
Safety: Copper chloride is corrosive. Sodium hydroxide is extremely corrosive and can cause severe burns. Wear proper protective equipment including gloves and goggles.
Disposal: Copper hydroxide in solution can be saved for demo 4.10 Hydroxide clean-up. To dispose, add some hydrochloric acid to dissolve the hydroxide and dispose in the appropriate aqueous waste container.
- Prof. Botch