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Concentration or density is a volume-specific quantity, expressing the number of particles as number per volume, or as properties of the particles in a variety of formats (amount, charge, mass, volume or energy per volume of the system). In chemistry, amount concentration is amount per volume, cB = [B] = nB·V-1 [mol·m-3]. The standard concentration, c°, is defined as 1 mol·dm-3 = 1 mol·L-1 = 1 M.

Concentration {quote}: 1. Group of four quantities characterizing the composition of a mixture with respect to the volume of the mixture (mass, amount, volume and number concentration).

2. Short form for amount (of substance) concentration (substance concentration in clinical chemistry).

{end of quote: IUPAC Gold Book}

A change of concentration of an elementary entity, i, in a system, dci, can be due to internal transformations (advancement per volume,

Abbreviation: c [mol·L-1]

Reference: IUPAC Gold Book

Communicated by Gnaiger E 2018-10-18

Concentration in different formats

Number concentration or number density is the number of particles (entities, objects) per volume,
C = N·V-1 [x·m-3]
Amount concentration
cB = nB·V-1 [mol·m-3]
Charge density in electricity is charge per volume,
ρ = QB·V-1 [C·m-3]
Mass density is the reciprocal of specific volume,
ρ = mB·V-1 [kg·m-3]
Volume density is equivalent to the volume fraction,
ΦB = VB·V-1.

Total concentration

  1. The total concentration of a substance (e.g. ADP) must be distinguished from the concentration of a specific ionic species (e.g. ADP4-, MgADP2-, MgHADP-).
  2. The total concentration of a substance must be distinguished from the free concentration, if unspecific binding occurs to membranes (e.g. TPP) or if a substance is bound to BSA (e.g. fatty acids).
  3. The concentration of a substance (c) differs from the activity (a), except at very high dilution. The activity of dissolved gases is expressed as the (relative) partial pressure (e.g. pO2). The ratio of concentration (e.g. cO2 [µM]) and partial pressure (e.g. pO2 [kPa]) is the solubility (see oxygen solubility).

MitoPedia concepts: MiP concept, Ergodynamics