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.

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:

 

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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.