An acid is a substance that donates a proton, and a base is a substance that accepts a proton. A base is a chemical compound that forms OH- ions when dissolved in water and reacts with acids to form salts. An acid is a chemical compound that forms H+ ions when dissolved in water and reacts with bases to form salts.
Acids and bases are chemical opposites. Adding a basic solution to an acidic one neutralize the acid. For example, adding sodium hydroxide (NaOH) to hydrochloric acid (HCl) results in a solution of table salt (NaCl) and water. Antacids, such as sodium bicarbonate, are bases that work by neutralizing stomach acids. The strength of an acid or a base depends upon how completely the H+ or OH- ions disassociate in solution.
The scale for measuring acidity is called the pH scale. Acids have a pH between 7 and 0, with the strongest acids being closest to 0. Bases have a pH between 7 and 14, with the strongest bases being closest to 14. Water, which is neutral, has a pH of 7. While strong acids can be highly corrosive and cause severe burns, weak acids such as acetic acid have almost no corrosive effect and cause no damage to tissue. All acids taste sour, a trait most noticeable in citric acid, the chemical that gives citrus fruits their characteristic tang. Bases have a bitter taste and can feel slippery between the fingers.