Acids, Bases, Buffers, Titrations
16.5 Lewis Acid/Base reaction (Ammonia + Copper Chloride)
Subjects: Acids/Bases, Lewis Acid-base reactions, complex ions, equilibrium, Le Chatlier’s principle
Description: Ammonia is added to a solution containing copper chloride, producing the deep blue adduct. When acid is added, the reaction is reversed.
- 500 mL tall form beaker
- Glass stir rod
- 1M Copper chloride (CuCl2)‡
- 1 M Aqueous Ammonia‡
- 1 M Hydrochloric acid (HCl)‡
‡HCl and Ammonia are located in the cabinets under the hood. Copper chloride is located in the chemical storage cabinets.
1. Add copper chloride solution to the beaker.
1. Add some ammonia to the copper chloride solution. The solution will turn a deep blue.
2. Add the acid. The reaction is reversed.
A Lewis acid is a substance that can accept a pair of electrons, while a Lewis Base can donate a pair of electrons. Lewis acid/base reactions produce an acid-base adduct, with coordinate covalent bonds. Ammonia is a good example of a Lewis Base. It has one lone pair of electrons to donate. Metal cations can act as Lewis acids. Thus the reaction between copper (II) and ammonia is a Lewis acid-base reaction that produces a colorful complex ion with four ammonia molecules surrounding the central copper ion. The reaction is shown below:
CuCl2(aq) + 4 NH3 (aq) –> [Cu(NH3)4]2+(aq) +2Cl-
When an acid is added, the ammonia is protonated and the reaction is reversed.
Make sure the solution is within the proper pH range. The solution can be flushed down the drain with water.