phenolphthalein

thymolphthalein

p-nitrophenol

sodium hydroxide

concentrated sulfuric acid

glycerin

95 % ethanol

Indicators:

RED: 1.5 g phenolphthalein + 3.0 g p-nitrophenol

ORANGE: 0.45 g phenolphthalein + 6.0 g p-nitrophenol

YELLOW: 6.0 g p-nitrophenol

GREEN: 0.6 g thymolphthalein + 6.0 g p-nitrophenol

BLUE: 1.5 g thymolphthalein

VIOLET: 0.9 g phenolphthalein + 0.4 g thymolphthalein

Mix the amounts listed above with 30 mL 95 % ethanol and store in dropping bottles labeled with the color indicated.

Acid-alcohol solution (0.05 M H₂SO₄ mixed with an equal volume of 95% ethanol):

Dilute 2.8 mL of con H₂SO₄ to 1 L with deionized water. Mix with an equal volume (1 L) of 95% ethanol.

H₂SO₄-glycerin solution:

Dilute 10 mL of con H₂SO₄ in 20 mL of glycerol, and transfer to a dropper bottle

Base solution (0.012 M NaOH):

Mix 1.00 g of NaOH with distilled water and dilute to 2.0 L.

Pre-demonstration Preparation:

1. Label the beakers with their color, and place two drops of indicator solution of that color in the center of each beaker. Set them on the light box in rainbow order (ROYGBV) from left to right.

2. Label one of the pitchers as acid and fill completely with acid-alcohol solution. Sit on the top of the table to the right of the light box.

3. Label the other pitcher as base, and fill completely with base solution. Set it on the floor behind the table out of view by the audience.

4. Add 25 drops of H₂SO₄ glycerin solution in the center of the 4 L plastic container and set it to the left of the light box.

5. Set the 30 mL beaker, glue stick stirrer, towel, and dropper bottle of H₂SO₄-glycerin behind the light box and to the left.

6. Set Kermit on the front of the table to one side so that the audience view will not be obstructed.

7. If the indicator solution dries on the bottom of the beakers they will appear cloudy. Add a few drops of 95 % ethanol if this happens to keep them "invisible" on the bottom.

The Demonstration:

Banjo strumming

Clean glasses with towel. There is enough time to do three of them.

Why are there so many songs about rainbows,

And whatís on the other side?

Rainbows are visions, but only illusions,

And rainbows have nothing to hide.

Pour acid alcohol mixture into the glasses. Be done by the end of the verse.

So weíve been told, and some choose to believe it,

I know theyíre wrong; wait and see.

Observe that there is no rainbow. Switch pitchers (i.e. place acid pitcher on the floor behind the table, look closely at the glasses, and pick up the base pitcher)

Someday weíll find it, the rainbow connection;

The lovers, the dreamers, and me.

After looking at the (base) pitcher in wonder, pour about 70 mL of solution into each glass. This is not enough to develop the colors.

Who said that evíry wish would be heard and answered

When wished on the morning star?

Somebody thought of that, and someone believed it;

Look what itís done so far.

Whatís so amazing that keeps us star-gazing

And what do we think we might see?

Someday weíll find it, the rainbow connection,

The lovers, the dreamers, and me.

Starting with red, pour in sequence the colors of the rainbow. Pick up a glass pour in enough base to develop the color (approximately 150 mL), and display the colored glass to the audience. Start with the word "Who" and finish with "me." When finished take a bow!

All of us under its spell;

We know that itís probably magic.

Present the dropping bottle of H₂SO₄-glycerin to the audience.

Have you been half asleep and have you heard voices?

Iíve heard them calling my name.

Add two drops of H₂SO₄- glycerin to each beaker. Finish by "my name."

Is this the sweet sound that calls the young sailors?

The voice might be one and the same.

Iíve heard it too many times to ignore it.

Present the stirrer and stir out the colors of the rainbow in sequence. Finish by "ignore it." Present the colorless glasses and take a bow.

Itís something that Iím poised to be.

Someday weíll find it, the rainbow connection;

The lovers, the dreamers, and me.

Pick up the base pitcher and quickly redevelop the colors in all of the glasses, again in rainbow sequence. You will add about 100 mL of base to each glass.

La-la-la......

As the song ends, remove the center two glasses (yellow and green) from the light box. Replace them with the 4 L container. Pour the contents of the glasses into the 4 L container, two at a time, pouring the last two (red and violet) as the song fades.

Safety Precautions:

The acid alcohol solution is flammable. Keep the container closed. Avoid flames or sparks. The acid (glycerin and acid alcohol) and base solutions can cause burns. Wear safety glasses. If you spill these solutions on yourself, wash it off immediately.

Disposal:

The final solution may be disposed of down the drain.

Reference:

Hutton and Smith, J. Chem. Ed., 61, 172 (1984)