Acids and Bases
. Acids and Bases, two classes of chemical compounds that display generally opposite characteristics. Acids taste sour, turn litmus (a pink dye derived from lichens) red, and often react with some metals to produce hydrogen gas. Bases taste bitter, turn litmus blue, and feel slippery. When aqueous (water) solutions of an acid and a base are combined, a neutralization reaction occurs. This reaction is characteristically very rapid and generally produces water and a salt.