Equivalent (chemistry)
A Val, also equivalent or gram equivalent ( unit symbol: val ) is an obsolete unit of amount of substance. It stands for that amount of substance of a substance that is able to bind or replace connections in one mole of hydrogen, and therefore calculated using the following numerical value equation:
In words, the amount of substance in Val is equal to the amount of substance in moles times the stoichiometric valence z, because each particle is z -fold as it were counted.
Z is in the character DIN 32625 called " number of equivalents " and referred to as Z *. The numerical value of the hereafter is obtained for a given quantity of a substance in Val is, depending on its 'use' in the considered chemical reaction. From an equivalence is called always when the substances involved in the reaction react completely with each other, so their quantities are mutually equivalent with respect to the particular reaction equation.
Equivalent concentration ( normality ) is a molar concentration at which the amount of substance in Val (deprecated) or is given in moles using Äquivalentteilchen.
Äquivalentteilchen
However, Val is not a SI unit and officially prohibited since 1 January 1978. It is replaced by the unit mole. In the case of a reference to the molar amount of substance on the value one often uses the unit symbol cmol or molc. This is, however, a violation of German law unit, against recommendations of many professional societies and to DIN 32625; cmol is the unit character of Zentimol.
A SI -compliant and standardized continuation of the earlier concept of equivalents together with the SI unit mole is made without additions of unit characters. The background is that the data used for the mole particles must be specified exactly as the mole definition. The Val can therefore be replaced by the mole by instead of the real particle - for example, K2Cr2O7 - whose imaginary fraction 1 / z based on: the " Äquivalentteilchen " 1/6 K2Cr2O7, where z = 6 z can at one and the same particle take on different values in different chemical reactions.
Val and Mol
The difference between Val and moles, which came to light only when one of various valency z, am considered to the following chemical reaction:
- In moles with basis set of molecules called " specified particle ": The reaction of two moles of sodium hydroxide with one mole of sulfuric acid molecules molecules to one mole of sodium sulfate molecules and two moles of water molecules.
- In Val: There react two Val sodium hydroxide with sulfuric acid to two two Val Val sodium sulfate and two moles of water ( the water it is not possible to speak of val, since water itself is neutral ).
- In mole basis in place of Äquivalentteilchen to as "specified particle": There react two moles of sodium hydroxide equivalents with two moles of sulfuric acid H2SO4 equivalents ½ to two moles of sodium sulfate equivalents ½ Na2SO4und two moles of water equivalents.
- , The reaction equation can be interpreted such that the symbols for individual particles, not molar amounts are.
Note: According to the definition of the mole in the SI, the underlying particles must be specified.
The material quantity-based mass that corresponds (in the case of mole called molar mass) a Val, called equivalent mass or earlier also equivalent weight (unit: g / eq).
The equivalent mass is:
The equivalent mass can - as the molar mass - are used for the stated mass; prevent confusion, it was formerly spoken by gram -Val or gram equivalent. In a chemical reaction, this equivalent mass of the mass of the substance that would be fully implemented with the equivalent mass of another substance corresponds (for example, one gram equivalent equal to 49 g of sulfuric acid).
Decimal parts of the Val
1 meq = 0.001 val