Primary standards are compounds with known stoichiometry, high purity, and high stability. Standard solutions can be prepared using primary standards by accurately weighing a known quantity of the compound, followed by dilution to a precise volume. For example, a weighed sample of 0.15 g sodium chloride contains 2.6 x 10 moles of sodium chloride. The following dilution of this sample in a 50-mL volumetric flask will result in a concentration of 0.51 M.