Amount of substance
|Surname||Amount of substance|
The amount of substance (outdated molar amount or molar number ) with the formula symbol is a basic quantity in the International System of Units (SI) and indirectly indicates the number of particles in a substance portion. Particles can be atoms , ions , molecules , formula units or electrons . Formula symbol and particle type X are given together as n X or n (X).
The unit of measurement for the amount of substance is the mole , an SI base unit. An amount of substance of 1 mol ( = 1 mol) contains that determined by the Avogadro constant ( N A ≈ 6 .022e23 mol −1 ) specified number of particles. The Avogadro constant is theproportionality factorbetween the amount of substance and the number of particles N(X):
Amount of substance and the quantities derived from it, such as concentration of substance , amount of substance and ratio of substance, are important in stoichiometry . The use of the quantity of substance shifts considerations of chemical reactions from the atomic or molecular range to weighable substance masses with a very high number of particles.
Calculating the amount of substance
The amount of substance is calculated
... from the crowd
The calculation from the mass is possible using the equation given above.
... from the volume
One mole of an ideal gas takes up an approximate volume of V m = 22.4 l / mol under standard conditions . This volume is called the standard molar volume (molar volume). The amount of substance results directly from the volume.
Example: How many moles is equivalent to 5 liters of oxygen ?
... from the number of particles
Since the number of particles N is proportional to the amount of substance n (the proportionality factor is the Avogadro constant N A = 6.022 · 10 23 / mol), the amount of substance can be calculated from the number of particles.
Example: Given are N = 10 25 particles.
... out of concentration
Since the concentration c X (mol / l) is a measure of the concentration for solutions , which relates the amount of substance X to the volume V of the solution, this can also be calculated back to the amount of substance.
Example: How many moles of sodium chloride are in 0.22 liters of a 0.6 molar NaCl solution?