Acid

An acid (from Latin acidus, meaning sour or tart) is a chemical compound generally defined by its reactions with complementary chemicals, designated bases (see Acid-base reaction theories). An acid tends to give a proton and can be represented by the generic formula AH. In water, there is the following reaction:

<math>\mbox{AH} +\mbox{H}_2\mbox{O} \Leftrightarrow \mbox{A}^- + \mbox{H}_3\mbox{O}^+</math>

There is a distinction between weak acids and strong acids. For a strong acid, no AH remains in solution:

<math>\mbox{AH} +\mbox{H}_2\mbox{O} \rightarrow \mbox{A}^- + \mbox{H}_3\mbox{O}^+</math>

That is why the acidity constant is only defined for weak acids:

Ka = [A-][H₃O⁺]/[AH].

Some of the stronger acids include the hydrohalic acids - HCl, HBr, and HI - and the oxyacids, which tend to contain central atoms in high oxidation states surrounded by oxygen - including HNO₃, H₂SO₄, HClO₄.

Acidity is typically measured using the pH scale.

Acidic (chemistry), the opposite to basic, reacting with basics to form salts. Acidic (geology), of rock: containing more than 65% of silica.

Table of contents 1 Characteristics 2 Acids in Food 3 Different Definitions of Acid/Base 4 Other meanings

Characteristics

Acids are generally:

• Taste: sour when dissolved in water
• Touch: strong acids have a stinging feeling
• Reactivity: acids react violently with many metals
• Electrical Conductivity: acids are electrolytes

Acids in Food

• citric acid: found in citrus fruits
• lactic acid: found in diary products[?] such as yogurt and sour milk
• carbonic acid: found in carbonated beverages[?]
• acetic acid: found in vinegar

Different Definitions of Acid/Base

The word acid comes from the Latin acidus meaning sour. Chemically though the term acid has a more specific meaning.

The Swedish chemist Svante Arrhenius defined an acid to be a substance that gave up hydrogen ions (H+) when dissolved in water, while bases are substances that give up hydroxide ions (OH-). Notice that this definition limits acids and bases to substances that can dissolve in water. Later on, Bronsted[?] and Lowry[?] defined an acid to be a proton donor and a base to be a proton acceptor. In this definition, even substances that are insoluble in water can be acids and bases. The most general definition of acids and bases is the Lewis definition. A Lewis acid is an electron acceptor, while a Lewis base[?] is an electron donor. Acid/base systems are different from redox reactions in that there is no change in oxidation state.

Other meanings

• "Acid" is also a slang word referring to LSD.
• "Acid" is also the sound that a Roland TB-303 music synthesizer makes, and is where the terms Acid Jazz[?] and Acid House originate. A very important term in electronic music, often confused with the LSD meaning.
• ACID is an acronym that expands to four essential properties of a database management system.