Some stinging insects spray formic acid when threatened — and cabbage juice can catch them in the act. You boil red cabbage leaves in water, soak paper towel strips in the purple liquid, and let them dry. When the strips touch an acid, the pigment reacts and the paper turns pink. Place a dry strip over a disturbed anthill, and a color change tells you the ants are spraying acid.

Phosphoric acid is strong enough that dentists already use it to etch teeth before bonding — and the same acid is an ingredient in commercial soda. You soak fifteen wisdom teeth in five different concentrations of phosphoric acid for seven days, then weigh each tooth before and after to measure how much enamel dissolved. The teeth in the strongest solution lost the most weight. Higher acid concentration meant more enamel broken down and carried away.

Red cabbage contains a natural pigment that reacts visibly when it meets an acid or a base. When you add a few drops of the purple juice to vinegar, it turns pink. Touch it to soapy water and it shifts to green or blue. Each color tells you exactly where that liquid falls on the acid-to-base scale.

Spaghetti is denser than water, so it sinks — until baking soda and vinegar change the situation. You dissolve baking soda in water, drop in small pieces of vermicelli, and add vinegar. The two ingredients react and release carbon dioxide gas. Bubbles cling to the spaghetti and lift it to the surface. When the bubbles pop at the top, the spaghetti sinks and the cycle starts again.

Oil and water refuse to mix — but a chemical reaction can push one through the other. You fill a bottle with oil and colored water, drop in baking soda, then add a splash of vinegar. The two ingredients react and produce gas bubbles. Those bubbles carry colored blobs up through the oil, and when they pop at the surface, the blobs sink back down. The cycle repeats as new bubbles form.