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Atmospheric pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m 3, μg/m 3, etc.) at sea level will decrease with increasing altitude because the atmospheric pressure decreases with increasing altitude.
As an example, a measured NO x concentration of 45 ppmv in a dry gas having 5 volume % O 2 is: 45 × ( 20.9 - 3 ) ÷ ( 20.9 - 5 ) = 50.7 ppmv of NO x. when corrected to a dry gas having a specified reference O 2 content of 3 volume %. Note: The measured gas concentration C m must first be corrected to a dry basis before using the above equation.
For example, the conversion factor between a mass fraction of 1 ppb and a mole fraction of 1 ppb is about 4.7 for the greenhouse gas CFC-11 in air (Molar mass of CFC-11 / Mean molar mass of air = 137.368 / 28.97 = 4.74). For volume fraction, the suffix "V" or "v" is sometimes appended to the parts-per notation (e.g. ppmV, ppbv, pptv).
The molar mass is appropriate for converting between the mass of a substance and the amount of a substance for bulk quantities. The molecular mass (for molecular compounds) and formula mass (for non-molecular compounds, such as ionic salts ) are commonly used as synonyms of molar mass, differing only in units ( daltons vs g/mol); however, the ...
11.6 g of NaCl is dissolved in 100 g of water. The final mass concentration ρ(NaCl) is ρ(NaCl) = 11.6 g / 11.6 g + 100 g = 0.104 g/g = 10.4 %. The volume of such a solution is 104.3mL (volume is directly observable); its density is calculated to be 1.07 (111.6g/104.3mL) The molar concentration of NaCl in the solution is therefore
It is a dimensionless quantity with dimension of / and dimensionless unit of moles per mole (mol/mol or mol ⋅ mol-1) or simply 1; metric prefixes may also be used (e.g., nmol/mol for 10-9). [5] When expressed in percent , it is known as the mole percent or molar percentage (unit symbol %, sometimes "mol%", equivalent to cmol/mol for 10 -2 ).
An equivalent (symbol: officially equiv; [1] unofficially but often Eq [2]) is the amount of a substance that reacts with (or is equivalent to) an arbitrary amount (typically one mole) of another substance in a given chemical reaction.
Stoichiometry is not only used to balance chemical equations but also used in conversions, i.e., converting from grams to moles using molar mass as the conversion factor, or from grams to milliliters using density. For example, to find the amount of NaCl (sodium chloride) in 2.00 g, one would do the following: