Weight concentration

Concentration is often expressed as a weight of solute in a unit volume of solution; for example, gdm 3, or %w/v, which is the number of grams of solute in 100 cm3 of solution. This is not an exact method when working at a range of temperatures, since the volume of the solution is temperature-dependent and hence the weight concentration also changes with temperature.

Whenever a hydrated compound is used, it is important to use the correct state of hydration in the calculation of weight concentration. Thus 10%w/v CaCl2 (anhydrous) is approximately equivalent to 20% w/v CaCl26H2O and consequently the use of the vague statement '10% calcium chloride' could result in gross error. The SI unit of weight concentration is kg m 3 which is numerically equal to g dm 3.

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