In chemistry and biochemistry, acid dissociation constant, the acidity constant, or the acid-ionization constant (K_a) is a specific type of equilibrium constant that indicates the extent of dissociation of hydrogen ions from an acid. While strong acids dissociate practically completely in solution and consequently have large acidity constants, weak acids do not fully dissociate and generally have acidity constants far less than 1. Because this constant differs for each acid and varies over many degrees of magnitude, the acidity constant is often represented by the additive inverse of its common logarithm, represented by the symbol pK_a (similar to the concept of pH, though not related directly). Chemistry (in Greek: χημεία) is the science of matter and its interactions with energy and itself (see physics, biology). ... Biochemistry is the chemistry of life. ... In chemistry, the equilibrium constant is a theoretically-based number that helps chemists determine the concentration of various reactants or products in a reaction where chemical equilibrium exists. ... Dissociation is a psychological state or condition in which certain thoughts, emotions, sensations, or memories are separated from the rest of the psyche. ... Hydronium is the common name for the cation H3O+. Nomenclature According to IUPAC ion nomenclature, it should be referred to as oxonium. ... An acid (often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... A strong acid is an acidic compound which ionizes completely in an aqueous solution. ... A weak acid is an acid that does not fully ionize in solution; that is, if the acid was represented by the general formula AH, then in aqueous solution a significant amount of undissolved AH still remains. ... The additive inverse, or opposite, of a number n is the number which, when added to n, yields zero. ... The common logarithm is the logarithm with base 10. ... pH is a measure of the activity of hydrogen ions (H+) in a solution and, therefore, its acidity or alkalinity. ...

pK_a = −log₁₀K_a

Given a weak acid HA, its dissociation in water is subject to the following chemical equilibrium: Chemical equilibrium is the state in which a chemical reaction proceeds at the same rate as its reverse reaction; the rates of the forward and reverse reactions are equal, and the concentration of the reactants and products stop changing. ...

HA + H₂O ↔ H₃O⁺ + A^– (it is also acceptable to write this as: HA ↔ H⁺ + A^–, the difference being only what theory of acids/bases you are applying. See the Bronsted-Lowry Theory and the Arrhenius Theory for more information)

The acidity constant for the acid HA is the dissociation constant for this equilibrium. In other words, An acid-base reaction is a chemical reaction between an acid and a base. ... An acid-base reaction is a chemical reaction between an acid and a base. ... In chemistry, the equilibrium constant is a theoretically-based number that helps chemists determine the concentration of various reactants or products in a reaction where chemical equilibrium exists. ...

, where [X] denotes the molar concentration of X in the solution

Using this definition, chemists can quickly and easily determine the concentrations of various chemicals in an equilibrium. For example, to determine the pH of a solution of known molar concentrations of sodium hydroxide and hydrofluoric acid, if you know the K_a of the acid at the given temperature (which is easily attainable information) you can determine the concentration of hydrogen ions, which will allow the determination of the pH after taking into account the neutralization due to the base. A molar is the fourth kind of tooth in mammals. ... Concentration is a very common concept used in chemistry and related fields. ... Sodium hydroxide (NaOH), also known as caustic soda or lye in North America, is a caustic metallic base used in industry (mostly as a strong chemical base) in the manufacture of paper, textiles, and detergents. ... Hydrofluoric acid is a highly corrosive solution of the chemical compound hydrogen fluoride in water. ...

Basicity constant of the conjugate base

By analogy, one can define the basicity constant (K_b) and the pK_b of the conjugate base A^–: In the Brønsted-Lowry (protonic) theory of acids and bases, a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. ...

pK_b = −log₁₀K_b

This is the dissociation constant for the equilibrium

A^– + H₂O ↔ HA + OH^–

Analogously to K_a, the magnitude of K_b indicates the relative strength of the base, with K_b > > 1 indicating a strong base. In chemistry, a strong base is a compound with a very high pH value. ...

Relationship between acidity and basicity constants

There exists a relationship between the value of K_a for an acid HA and the value of K_b for its conjugate base A^–. Since adding the ionization reaction for HA and the ionization reaction of A^– always gives the reaction for the self-ionization of water, the product of the acidity and basicity constants gives the dissociation constant of water (K_w), which is 1.0 × 10^-14 M² at 25°C. In other words, The self-ionization of water is the chemical reaction in which two water molecules react to produce a hydronium (H3O+) and a hydroxide ion (OH-): The reaction is also known as the autoionization or autodissociation of water. ... This page refers to concentration in the chemical sense. ...

K_aK_b = K_w

pK_a + pK_b = pK_w

As the product of K_a and K_b remains constant, it follows that stronger acids have weaker conjugate bases, and vice versa.

pKa of some common substances

Measurements are at 25ºC:

• 3.75: Formic acid
• 4.19: Succinic acid
• 4.20: Benzoic acid
• 4.63: Aniline
• 4.74: Acetic
• 4.76: Citrate
• 5.21: Pyridine
• 6.37: Carbonic acid
• 6.40: Citrate
• 6.99: Ethylenediamine
• 7.00: Imidazole
• 9.14: Borate
• 9.25: Ammonia
• 9.33: Benzylamine
• 9.81: Trimethylamine
• 9.99: Phenol
• 10.08: Ethylenediamine
• 10.66: Methylamine
• 10.73: Dimethylamine
• 10.81: Ethylamine
• 11.01: Triethylamine
• 11.09: Diethylamine
• 12.67: Phosphate
• 12.74: Borate

Many more are available here: [1] (http://www.uaf.edu/chem/321Fa04/pkas.html), [2] (http://daecr1.harvard.edu/pdf/evans_pKa_table.pdf) and [3] (http://www.chembuddy.com/?left=BATE&right=dissociation_constants) Formic acid (systematically called methanoic acid) is the simplest carboxylic acid. ... The acid succinic acid has the formula: HOOC-CH2-CH2-COOH At room temperature, pure succinic acid is a solid that forms colorless, odorless prisms. ... Structural formula Benzoic acid, C8H5C(O)OH, is an aromatic carboxylic acid. ... Aniline, phenylamine or aminobenzene (C6H5NH2) is an organic chemical compound which is a primary aromatic amine consisting of a benzene ring and an amino group. ... The chemical compound acetic acid (from the Latin word acetum, meaning vinegar), systematically called ethanoic acid, is the acid that gives vinegar its sour taste. ... Citric acid is a weak organic acid found in citrus fruits. ... Pyridine is a clear liquid with an odor that is sour, putrid, and fish-like. ... Carbonic acid is a weak acid with the chemical formula of H2 C O3. ... Citric acid is a weak organic acid found in citrus fruits. ... Imidazole is a heterocyclic aromatic organic compound. ... Borate is a salt or ester of boric acid. ... Ammonia is a chemical compound with the formula NH3. ... Trimethylamine, also known as NMe3, N(CH3)3, and TMA, is a colorless, hygroscopic, and flammable simple amine with a typical fishy odor in low concentrations and an ammonia-like odor in higher concentrations. ... Phenol, also known under the old name carbolic acid, is a colorless crystalline solid with a typical sweet tarry odor. ... Methylamine is a primary amine with a formula of CH3NH2. ... Safety (MSDS) data for dimethylamine General Synonyms: N-methyl-methanamine Molecular formula: C2H7N CAS No: 124-40-3 EINECS No: 204-697-4 EC index no: 612-001-00-9 Physical data Appearance: colourless gas with strong ammonia-like smell Melting point: -92 C Boiling point: 7. ... Triethylamine is a tertiary amine with formula N(C2H5)3 and a boiling point around 89 C. Categories: Biology stubs | Amines ... In chemistry, a phosphate is a polyatomic ion or radical consisting of one phosphorus atom and four oxygen. ... Borate is a salt or ester of boric acid. ...