Expressing concentrations
As most biological processes are carried out in the aqueous environment, it is important to know how the concentrations of the solutions are expressed:
Concentrations based on volume : concentrations represented as the amount of substance per unit volume of solution are the most widely used in a biochemical laboratory.
Molarity (M): Molarity is the number of moles of solute per litre of solution. One mole is defined as the amount of substance that contains as many atoms, molecules, or other elementary units as the number of atoms present in 12 g of Carbon 12. One mole is the mass in grams numerically equal to the formula weight of the substance.
Normality (N): Normality is the number of equivalents of solute per litre of solution. One equivalent (or equivalent weight) of an acid or base is the mass that contains one mole of replaceable hydrogen or hydroxyl. One equivalent (or equivalent weight) of a compound involved in oxidation-reduction reaction is the mass that donates or accepts one faraday of electrons (1 mole of electrons).
Weight/volume percent (%w/v): The weight of solute in grams per 100 ml of solution. Osmolarity: Osmolarity is the molarity of the particles in a solution. Osmolarity of 1 M solution of a dissociable molecule is n Osmolar, where n is the number of ions produced per molecule. Ionic strength 
where Mi is the molarity of the ith ion and Zi is the net charge of the ion (sign does not matter). |
: Ionic strength is a measure of all the charges present in a solution: