A concentration measures the amount of a dissolved compound (solute) in a solution. Commonly used molar concentration, or molarity, represents the number of moles of the solute in 1L (liter) of the solution. Normality (denoted as “N”) is similar to molarity, but it refers to the number of chemical equivalents rather than moles. For instance, one molecule of sulfuric acid, H2SO4, produces two hydrogen ions in the solution, and hence can react with two molecules of another compound. As a result, one molar solution of H2SO4 will have the normality of 2. As an example, calculate the mass (in grams) of H2SO4 in 240ml of the 2.5 normal (N) solution.
Find the atomic weights of the elements that compose the dissolved compound from the periodic table of the elements (see Resources). In the example, the atomic weights of hydrogen (H), sulfur (S) and oxygen (O) are 1, 32 and 16, respectively.
Sum up the atomic weights of all atoms in the molecule to compute its molecular mass. In this example, the molecular mass of H2SO4 is (1 x 2) + 32 + (4 x 16) = 98g/mole.
Divide the molecular mass by the number of hydrogen ions produced during the compound dissociation to calculate the compound mass equivalent. In the example, the molecular mass of H2SO4 should be divided by 2, so 98/2 = 49g/equivalent. Note that the dissociation of H2SO4 follows the equation H2SO4 = 2H+ SO4(2-).
Divide the volume of the solution (in ml) by 1,000 to convert it to liters (L). In the example, 240ml will convert to 0.24L.
Multiply the normality by the mass equivalent and the volume of the solution (in L) to calculate mass (in grams) of the dissolved compound. In this example, the mass of H2SO4 is 2.5 N x 49g/equivalent x 0.24L = 29.4g.
- “Chemistry”; K.W. Whitten, R.E. Davis, L. Peck and G.G. Stanley; 2009
- Chem Buddy: Normality