Certain parts of a tongue are more sensitive to a particular type of flavor. The sides of our tongue better sense sour-tasting substances, while the back of our tongue is better at picking up bitter flavors.
Some solutions change colors when they are mixed with sour or bitter substances.
Each one has it's own unique color scheme. They can also come in a number of different forms, such as a liquid or a dye dried on a piece of paper. The pH scale tells us how acidic or basic a substance is. A substance with a pH of 7 is neutral, meaning that it is not an acid or a base. Mixing acids and bases can result in a neutral solution because the two neutralize each other.