Red, White, and Blue Colors

Description

Aqueous ammonia is added to each of three beakers in which reactions take place to form products that are colored red, white, and blue, respectively.

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This demonstration illustrates several equilibria. This series of reactions takes advantage of both the NH₃ and OH^- species present in an aqueous ammonia solution.

HPhenolphthalein + OH^- H₂O + Phenolphthalein^-

colorless

pink (red)

Pb²⁺ + 2 OH^- Pb(OH)₂

colorless

white

Cu²⁺ + 4 NH₃ Cu(NH₃)₄²⁺

blue

deep blue

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1. Set up 3 clean 150-mL beakers. Add 5 drops of 1% ethanolic phenolphthalein to the beaker at the left. Add 10 drops saturated aqueous lead nitrate to the beaker in the center. Add 10 drops saturated aqueous copper sulfate to the beaker at the right.
2.  Pour 400 mL of 1.0 M aqueous ammonia into a 600-mL beaker. Use the large beaker of 1.0 M ammonia as a source. Pour approximately 75 mL of ammonia solution into each beaker starting from the left.
3. Note the evidence for reaction.

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Name ___________________________ Class ________

Teacher__________________________

DoChem 053 Red, White, and Blue Colors

This series of reactions takes advantage of both the NH₃ and OH^- species present in an aqueous ammonia solution.

1. Watch the movie.
2. Write a balanced chemical equation for each of the reactions observed.

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Purpose

To illustrate three colorful equilibrium reactions.

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•  1% ethanolic phenolphthalein with dropper (dissolve 1 g phenolphthalein in 50 mL 95% ethanol, and add to 50 mL of distilled water)
• saturated lead nitrate (3 g lead nitrate/10 mL water) with dropper
• saturated copper sulfate with dropper (30 g CuSO₄•5H₂O per 100 mL distilled water)
• 3 150-mL beakers
• 500 mL 1.0 M aqueous ammonia (add 33 mL of concentrated aqueous ammonia to 470 mL of distilled water)
• 600-mL beaker

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• Prepare only the amount of saturated lead nitrate solution that you will use.

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Preparation of solutions: 40 minutes

Teacher preparation: 10 minutes

Presentation: 5-15 minutes

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The chemicals used are toxic.

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• Do not ingest the chemicals. Provide adequate ventilation; avoid inhaling ammonia vapors.
• Do not pour any solution containing lead down the drain.

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• Store the lead-containing ammonia solution under the hood. Allow the precipitate to settle, filter, and collect for disposal with other heavy metal wastes.
• Prepare a small amount of saturated lead nitrate, and save the solution in a stoppered bottle for use at a later time. Do not discard any saturated lead nitrate stock solution at the sink.
• The phenolphthalein and copper solutions may be disposed of safely at the sink.

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Closure Questions:

1. Write a balanced chemical equation for each of the reactions observed.

Answers to Closure Questions:

1. HPhenolphthalein + OH^- H₂O + Phenolphthalein-

   Pb²⁺ + 2 OH^- Pb(OH)₂

   Cu²⁺ + 4 NH₃ Cu(NH₃)₄²⁺

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• equilibrium reaction
• coordination compounds
• complex ions
• ph indicator
• acid base
• precipitate

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