Solids, liquids, and gases may dissolve in water to form solutions. The amount of solute present may vary below certain limits, so-called solubility. The strength of a solution can be expressed in two ways:
(1) weight (lb) of active solute per 100 pounds (i.e. %) and
(2) weight of active solute per unit volume (gallons or liters) of water.
Either expression can be computed to the other if the density or specific gravity is known. If the solution is dilute (less than 1%), the specific gravity can be assumed to be 1.0; i.e. 1 L of solution is equal to 1 kg and 1 gal of solution equals 8.34 lb.
In water chemistry, molarity is defined as the number of gram-molecular weights or moles of substance present in a liter of the solution. If solutions have equal molarity, it means that they have an equal number of molecules of dissolved substance per unit volume. The weight of substance in the solution can be determined as follows:
The molarity (M) of a solution can be expressed as:
M (mol/L) = moles of solute (mole) / 1.0 L of solution
For uniform purpose,
the Normality (N) is used for preparation of laboratory solutions. The
normality can be written as:
N (eq/L or meq/L) = equivalent of solute (eq or meq) / 1.0 L of solution