In chemistry and biochemistry, a dissociation constant or an ionization constant is a specific type of equilibrium constant used for reversible reactions or processes. That means that it refers to the extent to which a complex, molecule, or salt separates or splits into smaller molecules, ions, or radicals in a reversible manner. The dissociation constant is represented by the symbol K_d. Chemistry (derived from the Arabic word kimia, alchemy, where al is Arabic for the) is the science that deals with the properties of organic and inorganic substances and their interactions with other organic and inorganic substances. ... Biochemistry is the study of the chemistry of life, a bridge between biology and chemistry that studies how complex chemical reactions give rise to life. ... In chemistry, the equilibrium constant is a theoretically-calculated number associated to a reaction which is a useful tool to determine the concentration of various reactants or products in a system where chemical equilibrium occurs. ... A complex in chemistry is a reversible association of molecules, atoms, or ions through weak non-covalent chemical bonds. ... In general, a molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. ... A magnified crystal of salt In chemistry, salt is a term used for ionic compounds composed of positively charged cations and negatively charged anions, so that the product is neutral and without a net charge. ... In chemistry, radicals (often refered to as free radicals) are atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ...

Given the reaction

A_xB_y <=> xA + yB

It is given by the expression

Where [A], [B], and [A_xB_y] indicate the concentrations of A, B, and A_xB_y, respectively.

pK

The pK value is defined as:

where K_d is the dissociation constant.

water dissociation constant(K_d)is often expressed as K_w.

Acid base reactions

For the deprotonation of acids, K is known as K_a, the acid dissociation constant. Stronger acids, for example sulfuric or phosphoric acid, have larger dissociation constants; weaker acids, like acetic acid, have smaller dissociation constants. A molecule can have several acid dissociation constants. In this regard, that is depending on the number of the protons they can give up, we define monoprotic, diprotic and triprotic acids. The first (e.g. acetic acid or ammonium) have only one dissociable group, the second (carbonic acid, bicarbonate, glycine) have two dissociable groups and the third (e.g. phosphoric acid) have three dissociable groups. In the case of multiple pK values they are designated by indices: pK₁, pK₂, pK₃ and so on. For amino acids, the pK₁ constant refers to its carboxyl (-COOH) group, pK₂ refers to its amino (-NH₃) group and the pK₃ is the pK value of its side chain. Deprotonation is a chemistry term that refers to the removal of a proton (hydrogen ion H+) from a molecule, forming the conjugate base. ... An acid (from Arabic Azait meaning oil, often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... In chemistry and biochemistry, acid dissociation constant, the acidity constant, or the acid-ionization constant (Ka) is a specific type of equilibrium constant that indicates the extent of dissociation of hydrogen ions from an acid. ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ... R-phrases S-phrases , , Supplementary data page Structure and properties n, εr, etc. ... Flash point 43 Â°C R-phrases , S-phrases , , , US Permissible exposure limit (PEL) 10 ppm Supplementary data page Structure & properties n, εr, etc. ... Flash point 43 Â°C R-phrases , S-phrases , , , US Permissible exposure limit (PEL) 10 ppm Supplementary data page Structure & properties n, εr, etc. ... ... Carbonic acid is a carbon-containing acid with the formula H2CO3. ... This refers to the bicarbonate ion, for baking soda, see Sodium bicarbonate. ... Glycine (Gly, G) is a nonpolar amino acid. ... R-phrases S-phrases , , Supplementary data page Structure and properties n, εr, etc. ... A carboxyl or carboxylic group is a functional group consisting of a carbon atom and an oxygen atom doubly bonded to each other. ... In chemistry, especially in organic chemistry and biochemistry, an amino group is an ammonia-like functional group. ...

See also

• Acid dissociation constant
• Base dissociation constant
• Receptor (biochemistry)
• Dissociation (chemistry)
• Equilibrium Constant