Salary statement

In chemistry and physics, content information - also called content quantities - indicates the content of a substance in a substance mixture ( DIN 1310 ), i.e. quantifies the material proportion of an individual substance in a solid, liquid or gaseous mixture , for example an aqueous solution or an alloy (cf. . Key figure ). Salary information is given using the three basic physical parameters

• Mass m ,
• Volume V and
• Amount of substance n .

Salary sizes are quotient sizes and are defined using size equations. One distinguishes

• Proportions : Size of a component in relation to the sum of the same size of all components (e.g. dissolved substances and solvents): mass fraction , molar fraction , volume fraction .
• Concentrations : size of a component in relation to the final volume of the mixture (solution): mass concentration , molar concentration , volume concentration .
• Ratios : size of a component in relation to the same size of another component to be named (e.g. solvent) ( mass ratio , molar ratio , volume ratio ).

All content quantities that contain volume as a quantity are temperature-dependent. A clear indication of volume proportions, concentrations, volume proportions and volume ratios therefore also includes naming the associated temperature. (For the temperature dependence of the volume concentration, for example alcohol content .)

The content quantities / content information are defined for the solution (solution) of a substance (i or j) in the solvent (LM) by the following size equations.

Specification of the proportion of a component

Mass fraction : ${\displaystyle w\mathrm {(i)} ={\frac {m\mathrm {(i)} }{m\mathrm {(i)} +m\mathrm {(j)} }}}$

Amount of substance : ${\displaystyle \chi \mathrm {(i)} ={\frac {n\mathrm {(i)} }{n\mathrm {(i)} +n\mathrm {(j)} }}}$

Volume fraction : ${\displaystyle \varphi \mathrm {(i)} ={\frac {V\mathrm {(i)} }{V\mathrm {(i)} +V\mathrm {(j)} }}}$

• The specification “mass%” corresponds to the mass fraction x100, the specification “volume%” the volume fraction x100. These ways of naming are unsystematic, but not yet completely extinct; because percent is nothing else than another writing figure for the number 0.01.
• Molenbruch is another, outdated term for the molar fraction.
• For ideal gases i, φ (i) = x (i) applies .

In addition to data in percent (1% = 1: 100 parts) of the total mass or the total volume of mixtures, there are also data in per mille (1: 1000), ppm (1: 1 million), ppb (1: 1 billion or 1 trillion), ppt (1: 1 trillion or a trillion or a thousand) and ppq (1: 1 trillion or 1 quadrillion). However, such terms - except percent and per mille - depend on the cultural context of both the author and the reader, and are therefore not recommended (see parts per million ). They can easily be replaced by the fractions of the units (such as µg / kg), which at the same time reduces the likelihood of incorrect information or interpretation of the intended units. A reasonable but rare alternative is the use of SI prefixes: µ%, p% etc.

V (mixture) and V (solution) can mean the sums of the volumes of the individual components before or after mixing or dissolving. However, since it is not a mixture before mixing, only the mixture should be specified and otherwise the volumes of the components. The volume of a mixture is not equal to the sum of the volumes of the components V (i) + V (LM) before mixing, because a volume contraction or volume expansion ( volume dilation ) occurs when the components are mixed . With a volume contraction the following applies: V (i) + V (LM)> V (solution). Therefore, a distinction must be made between volume fraction φ (i) (in relation to the sum of the individual volumes of the substances) and volume concentration σ (i) (in relation to the volume of the solution after dissolution). It is therefore often inexpedient to state the volume fraction; it is better to state the volume concentration instead.

Specification of the concentration of a component

Mass concentration : ${\displaystyle \beta \mathrm {(i)} ={\frac {m\mathrm {(i)} }{V\mathrm {(Lsg)} }}}$

Amount of substance concentration : ${\displaystyle c\mathrm {(i)} ={\frac {n\mathrm {(i)} }{V\mathrm {(Lsg)} }}}$

Volume concentration : ${\displaystyle \sigma \mathrm {(i)} ={\frac {V\mathrm {(i)} }{V\mathrm {(Lsg)} }}}$

(See note on volume share above)

Molality : ${\displaystyle b\mathrm {(i)} ={\frac {n\mathrm {(i)} }{m\mathrm {(LM)} }}}$

(In addition to this term, there is also the outdated content specification normality in chemistry . Here, the molar concentration c = n / V (outdated: molarity ) has been multiplied by the chemical stoichiometric value z of the reacting substance. A sulfuric acid with c  = 0.5 mol / L therefore has the normality 1.0, for example, which means the following in the DIN standard- compliant representation: If the use of the mole of sulfuric acid particle H ₂ SO ₄ is used, then c = 0.5 mol / L instead, equivalent particles 1/2 (H ₂ SO ₄ ) are used as the basis, because in the case of the chemical reaction under consideration the stoichiometric valence of sulfuric acid is z = 2, c = 1 mol / L; in the outdated parlance: 0.5 -Molar aqueous sulfuric acid solution is 1-normal, provided that the sulfuric acid is used as a bivalent.)

Specification of the ratio of two components

Mass ratio : ${\displaystyle \zeta \ ={\frac {m\mathrm {(i)} }{m\mathrm {(j)} }}}$

Mole ratio : ${\displaystyle r\ ={\frac {n\mathrm {(i)} }{n\mathrm {(j)} }}}$

Volume ratio :. ${\displaystyle \psi \ ={\frac {V\mathrm {(i)} }{V\mathrm {(j)} }}}$

conversion

To convert the salary information you need the following values ​​in particular:

• M = m / n ( molar mass = mass / amount of substance )
• ρ = m / V ( density = mass / volume )
• V _m = V / n ( molar volume = volume / amount of substance).

See also

• Fabric purity
• Titer

Web links

• Klaus-Peter Rueß (Institute for Analytical Chemistry, University of Regensburg, October 2006): Stoichiometric calculation with size equations, page 34 ff. Of 112 (PDF file; 5.8 MB)

Individual evidence

1. ↑ DIN 1310 : 1984-02 - Composition of mixed phases (gas mixtures, solutions, mixed crystals); Terms, symbols.