Red cabbage juice is a natural indicator that changes color when it touches an acid or a base. You boil cabbage leaves to extract the purple liquid, then soak paper towel strips in it and let them dry. When you hold a strip near a disturbed anthill, the strip turns pink — showing that the ants are spraying formic acid into the air.

One way to measure vitamin C is to watch for a color change. You use an indicator solution that starts blue, then add drops of orange juice one at a time until the blue disappears. Fewer drops means more vitamin C was present — the indicator's shift from blue to clear reveals how much ascorbic acid each juice contains.

Iodine solution works as a simple detector: it turns dark brown or blue-black the moment it touches starch. That color shift happens within seconds, and it tells you exactly which foods contain hidden starch and which show no change at all.

Different indicator solutions each reveal a different nutrient through a distinct color change. Iodine turns blue-black when it finds starch. Benedict's solution changes color based on how much sugar is present. Biuret reagent turns pink-purple around protein. Each one reacts with a single specific nutrient, making the invisible composition of food visible through color — and together they map out what plant foods and animal foods are actually made of.

Red cabbage contains a natural pigment that shifts color depending on the pH — the acidity level — of whatever liquid it touches. You boil grated cabbage in water, strain out the solids, and add a few drops of the dark purple juice to household liquids. Vinegar turns it pink. Soapy water turns it green or blue. Each color tells you where that liquid falls on the acid-to-base scale.

An iodine-starch solution turns dark purple, and when fruit juice is added, that purple color begins to fade. The more it fades, the more vitamin C is present in the sample. By comparing how much the raw and cooked versions of tomatoes and cherries change the indicator's color, you can see directly whether heating destroys the vitamin C or concentrates it.

Baking soda is a base, and it dries clear on paper — invisible once it's there. When you paint grape juice over the dried writing, the juice changes color wherever it touches the base. Your hidden words appear as a different color against the purple background, revealed by a simple acid-base reaction.

Red cabbage juice is a natural pH indicator that shifts color when it meets acids or bases. When you layer it with oil in a tall container and drop in an Alka-Seltzer tablet, the tablet fizzes and sends colored blobs rising through the oil. Adding a small amount of acid or base mid-reaction changes the color of those blobs as they move — making the chemical change visible in real time.