Coin-Operated Reaction (Demonstration)
(Reference: Perkins, R.I. Journal of Chemical Education, 1986, 63, 783.)

This would be good to do toward the end of the term; there is a lot of chemistry here!

Acids & Bases    :    Pressure

Purpose:
Illustrate the properties of acids and bases, indicators and pressure in one system
 

Safety:
Safety goggles should always be worn in the lab.  Nitric acid is corrosive.  Use pennies before 1982 because zinc reacts violently with nitric acid..  Nitrogen dioxide is highly toxic and should be contained until it fully dissolves in the solution.  You may also want to wear gloves and a chemical resistant apron.
 

Materials:
3 500 mL Erlenmeyer flasks
1 1-hole stopper
4 L-shaped glass tubes
2 2-hole stoppers
15 mL 16 M HNO3
3 shiny (pre-1982) pennies
600 mL 0.01 M HNO3
Flexible cold pack
200 mL 0.35 M NaOH
Phenolphthalein
 

Procedure:
Apparatus set-up:

1. Pour 15 mL concentrated nitric acid into A and secure the 1 hole stopper

2. Place 1mL phenolphthalein (22 drops) into B and fill completely with dilute nitric acid and secure with 2-hole rubber stopper

3. Pour 200 mL sodium hydroxide solution into C

4. Remove stopper from A and drop 2 or 3 pennies into A, quickly secure stopper

5. Reaction may take about 10 minutes.

6. In order to increase the flow a flexible cold pack can be placed under A.
 

Explanation:
Copper reacts with nitric acid to form NO2 gas and cupric nitrate.  The gas is forced into B, and subsequently the solution in B is forced into C.  B contained the indicator so now C will turn pink.  As the nitric in A is consumed the reaction slows and A cools (use cold pack now).  This creates a vacuum effect on B so the dilute nitric from B enters A and dilutes out the blue copper nitrate solution.  Then half of the red C enters B, in B it changes back to clear, so A is blue, B is clear and C is red.
 

Clean-up:
Copper pennies can be rinsed and re-used.  All solutions can be flushed down the drain with excess water.
 
 

Ginger Chateauneuf, 2000,
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