ABSTRACT
It is commonly necessary in laboratory science to create chemical solutions of known concentrations. The SI unit for the amount of a substance is the mole (mol). The SI derived unit of concentration is thus mol m−3. However, the use of the non-SI term, the molar (M) solution, equivalent to 1 mole in 1 liter of water, is widespread, as is ‘millimolar’ (mM). Given that in SI ‘M’ is a prefix (mega), there is some possibility of confusion here, so care must be taken. A solution with a concentration of 1 kmol m−3 is equivalent to a 1 M solution, and 1 mol m−3
is equivalent to a 1 mM solution. Some definitions are useful. The mole is the SI unit of substance. 1 mole of a
chemical compound has a mass equal to its molecular weight in grams. A mole of a chemical compound contains 6.022 × 1023 molecules (this number is known as Avogadro’s number). Moles can also be used to express the amount of atoms and ions, for example.
