Weighing out solids

Solutions can be prepared directly by weighing out solids and making up to the desired volume with solvent. However, it is more usual that concentrated stock solutions are used to prepare the required solution simply by standard dilution. This is much more convenient than making up every solution freshly, and also avoids the problem of storage of large volumes of diluted solutions. It should, however, be borne in mind that many of the physical and chemical characteristics of a solution (e.g., pH and chemical stability) can be altered when a stock solution is diluted. 

The main vessels used for weighing out solids in environmental analyses are weighing bottles, plastic weighing dishes or weighing boats. These containers are used to accurately weigh the solid, using a four-decimal-place balance, and to transfer a soluble solid directly into a volumetric flask. If the solid is not totally soluble it is advisable to transfer the solid to a beaker, add a suitable solvent, e.g. deionized or distilled water, and stir with a clean glass rod until all of the solid has dissolved. It may be necessary to heat the solution to achieve complete... 

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