Acid-base reactions are chemical reactions that occur between acids and bases. An acid is a substance that, when dissolved in water, has greater hydrogen ion activity than pure water does, while a base is a substance that, when dissolved in water, can accept hydrogen ions. The acidity of a solution is measured based on the pH scale; a substance with a pH less than seven is acidic while a solution with a pH greater than seven is basic. There are many different explanations and forms of acid-base reactions, as they can occur in many different ways and have been studied by a number of different chemists.
There are several different properties that define acids and bases other than whether they can give or receive hydrogen ions. Acids change blue litmus paper to red, have a sour taste, and react with some metals to liberate oxygen. Bases, on the other hand, change red litmus paper to blue, have a bitter taste, and often have a slippery feeling. Both acids and bases conduct electricity.
Typically, when an acid and a base are reacted together, they yield a salt. Salts are the neutral products of acid-base reactions. For example, when hydrochloric acid is reacted with sodium hydroxide, a strong base, the product of the reaction is NaCl, or sodium chloride, which is common table salt and is neither acidic or basic, having a pH of about seven. When salts are dissolved in water, they are known as electrolytes and they conduct electricity. There are several different classifications of salts, as some release hydroxide ions when dissolved, some release hydronium ions, and some release neither.
There are many different kinds of acid-base reactions because there are many different kinds of acids and bases that can all be reacted in different quantities. A strong acid reacted with a weak base will have a different result than a weak acid reacted with a weak base, because strong acids release more hydronium ions into a solution than weak acids and strong bases release more hydroxide ions into a solution than weak bases.
Acid-base reactions are studied at all levels of chemistry, beginning in high school, as they are integral to many careers that involve chemistry. The human body has many different ongoing acid-base reactions that are kept in a delicate equilibrium to moderate various bodily functions. Pharmaceutical companies, then, need to ensure that the drugs they make do not upset such delicate balances.