Not Red?! The “Rainbow Ammonia Fountain” That Turns Purple, Green, and Blue
Ken Kuwako, Science Trainer, here. Every day is an experiment!
Normally, the fountain shoots up bright red. But what if it turned purple, green, or blue instead? What would you think? At this year’s school festival, our Science Club put on a variety of science shows. Here, I’d like to share one of them: an experiment where a club member added indicators to create fountains in unexpected colors. It was such a clever twist that it made me say, “Huh, now that’s smart!” Students really can come up with ideas that go beyond anything you’d imagine.
https://youtu.be/UifOtTKTRm8
What Is the Classic “Ammonia Fountain”?
In the ammonia fountain experiment, you fill a flask with ammonia gas, squeeze a little water into it with a dropper, and the water in the beaker shoots up through a tube in a dramatic fountain.
Ammonia is a gas that dissolves in water extremely well. One volume of water can dissolve about 700 volumes of ammonia. When water enters the flask, the ammonia inside dissolves into it all at once, and the pressure in the flask drops. The outside air then pushes the water in the beaker up into the flask like a fountain.
On top of that, water with ammonia dissolved in it becomes alkaline. So if you add an indicator called phenolphthalein to the water being drawn up, the colorless water turns into a fountain of vivid red. This is the classic version of the experiment.
This Year, We Switched Up the Indicators
The method is simple: add an indicator such as BTB to the water that gets drawn up. So, which indicators were used this time? Here’s what the fountains looked like.
Please note that ammonia has a pungent smell. When you try this experiment, make sure the room is well ventilated and wear safety goggles.
Three Fountains, Three Color Changes
First, the solution being drawn up is yellow, and the fountain turns purple.
Next, the starting color is pink, and the fountain turns green.
And finally, the water being drawn up is yellow, and the fountain turns blue.
Beautiful, isn’t it? Now, can you guess which indicators were used?
How the Colors Change, Plus a Few Hints
Indicators are chemicals that change color depending on whether a liquid is acidic, neutral, or alkaline. For example, BTB goes from yellow (acidic) to green (neutral) to blue (alkaline), while phenolphthalein goes from colorless (acidic to neutral) to red (alkaline).
In these fountains, the color before the liquid is drawn up is the acidic-to-neutral color, and the color of the fountain is the alkaline color. The ammonia dissolves and turns the water alkaline, and that’s what causes the color change.
Here are two hints to help you work out the answer:
・Every indicator has its own range where it changes color (the boundary between acidic and alkaline), and its own set of colors.
・An indicator isn’t always a single chemical. Some are mixtures of two, blended to make the color change easier to see.
An Everyday Indicator: Red Cabbage
Indicators aren’t just for the lab. The juice from boiled red cabbage contains a pigment called anthocyanin, which turns red or pink in acid, purple when neutral, and shifts from blue to green to yellow as it gets more alkaline. You can enjoy a color-changing show right in your own kitchen.
Behind everyday color changes like these, the science of acids and alkalis is quietly at work. Why not try different indicators yourself and hunt for a fountain color all your own?
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Science is more fun and more fascinating when it’s close to home! This blog is packed with easy-to-follow science experiments you can do at home, along with tips to make them work. Try searching around and see what you find!
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