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Demonstrations › Acids, Bases, Buffers, Titrations › 16.5

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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 xanh adduct. When acid is added, the reaction is reversed.

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Materials:

500 mL tall form beaker Glass stir rod 1M Copper chloride (CuCl2)‡ 1 M Aqueous Ammonia‡ 1 M Hydrochloric acid (HCl)‡

‡HCl & Ammonia are located in the cabinets under the hood. Copper chloride is located in the thuphikhongdung.vnical storage cabinets.

Procedure:

1. địa chỉ copper chloride solution to lớn the beaker. 1. địa chỉ some ammonia to the copper chloride solution. The solution will turn a deep blue. 2. Add the acid. The reaction is reversed.

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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 lớn 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) –> 2+(aq) +2Cl-

When an acid is added, the ammonia is protonated và the reaction is reversed.

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Disposal:

Make sure the solution is within the proper pH range. The solution can be flushed down the drain with water.

References:

1. None

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