If you had a choice between a glass of lemon juice or apple juice, most folks would pick the sweeter one – apple. Did you know that apples are loaded with malic acid, and are actually considered to be acidic? It’s just that there is so much more sugar in an apple than a lemon that your taste buds can be fooled. Here’s a scientific way (which is much more reliable) to tell how acidic something is.
Acids are sour tasting (like a lemon), bases are bitter (like unsweetened cocoa powder). Substances in the middle are more neutral, like water. Scientists use the pH (power of hydrogen, or potential hydrogen) scale to measure how acidic or basic something is. Hydrochloric acid registers at a 1, sodium hydroxide (drain cleaner) is a 14. Water is about a 7. pH levels tell you how acidic or alkaline (basic) something is, like dirt. If your soil is too acidic, your plants won’t attract enough hydrogen, and too alkaline attracts too many hydrogen ions. The right balance is usually somewhere in the middle (called ‘pH neutral’). Some plants change color depending on the level of acidity in the soil – hydrangeas turn pink in acidic soil and blue in alkaline soil.
There are many different kinds of acids: citric acid (in a lemon), tartaric acid (in white wine), malic acid (in apples), acetic acid (in vinegar), and phosphoric acid (in cola drinks). The battery acid in your car is a particularly nasty acid called sulfuric acid that will eat through your skin and bones. Hydrochloric acid is found in your stomach to help digest food, and nitric acid is used to make dyes in fabrics as well as fertilizer compounds.
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Materials:
- Litmus paper or pH paper (you can cut into strips)
- apple
- lemon
- vinegar
- baking soda
- cup with water
- (Advanced Students only: make your own sodium hydroxide here)
Here’s a video that shows you how to test several different things, including how to safely test stronger acids and bases, should you wish to test your own out.
Some things you can test (in addition to the ones in the video) include: Sprite, distilled white vinegar, baking soda, Vanish, laundry detergent, clear ammonia, powdered Draino, and Milk of Magnesia. DO NOT mix any of these together! Simply add a bit to each cup and test it with your pH strips. Here’s a quick video demonstration:
(Note – we didn’t list the chemicals on the shopping list as there were a LOT of stuff to get for only one experiment, so just sit back and watch!)
No pH strips? The chop up a head of red cabbage and whirl in a blender with water. Pass through a strainer (discard the solids), and pour this new ‘indicator’ into several cups. Add Sprite to one cup and watch for a color change. Add baking soda and watch for another color change. Continue down the line, adding only one chemical per cup into your cabbage juice.
Click here to view another version of this experiment: Chemical Matrix.
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