In ancient times, acids and bases were mostly defined by their properties. We will be looking at modern definitions more in a forthcoming section, however these properties are still useful to talk about. Many of the ways in which we interact with acids and bases on an every day basis as well as determine acid or base properties in the laboratory setting are related to these properties which will be explored in this section. 12.1.1: Acids- Properties and Examples Acids are very common in some of the foods that we eat. Citrus fruits such as oranges and lemons contain citric acid and ascorbic acid, which is better known as vitamin C. Carbonated sodas contain phosphoric acid. Vinegar contains acetic acid. Your own stomach utilizes hydrochloric acid to digest food. Acids are a distinct class of compounds because of the properties of their aqueous solutions. 12.1.2: Bases- Properties and Examples A base is thought of as a substance which can accept protons, or any chemical compound that yields hydroxide ions (OH-) in solution. It is also commonly referred to as any substance that can react with an acid to decrease or neutralize its acidic properties, change the color of indicators (e.g. turn red litmus paper blue), feel slippery to the touch when in solution, taste bitter, react with acids to form salts, and promote certain chemical reactions (e.g. base catalysis).