Acids, Bases, Buffers, Titrations
16.5 Lewis Acid/Base reaction (Ammonia + Copper Chloride)
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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.
Materials:
- 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.
Procedure:
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.
Discussion:
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.
Disposal:
Make sure the solution is within the proper pH range. The solution can be flushed down the drain with water.
References:
1. None
