Molar concentration

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Molar concentration is a measure of the concentration of a solution. It is defined as moles of solute per litre of solution, and has units of mol dm^-3, which is often represented by M.

$C=\frac{N/A}{V}$

Here, N is the number of molecules present in the volume V. This latter is measured in litres. A is the Avogadro's number, 6.022×10²³.

Another formula that may be used is M=n/V, where M is the molar concentration, n is the number of moles and V is the volume in litres.

[edit] Examples

Most proteins are present in the bacteria E. coli at 60 copies or fewer. The volume of the bacteria is 10^-15 litre, which gives us C=10^-7 M = 100 nM. (nM is nanomolar i.e. 10^-9 moles per litre).

If 2 grams of NaCl are dissolved in 5 millilitres of water. As 58 grams of NaCl is 1 mole of molecules, and 1 millilitre is 0.001 litre, this gives C = (2/58)/0.005 = 6.9 M.