What is a Normal Solution?

Normality (N) is another way to quantify solution concentration. It is similar to molarity but uses the gram-equivalent weight of a solute in its expression of solute amount in a liter (L) of solution, rather than the gram molecular weight (GMW) expressed in molarity. A 1N solution contains 1 gram-equivalent weight of solute per liter of solution.

Expressing gram-equivalent weight includes the consideration of the solute's valence. The valence is a reflection of the combining power of an element often as measured by the number of hydrogen atoms it can displace or combine with. A 1.0 gram-equivalent weight is the amount of a substance that will combine with or displace 1 atom of hydrogen.

Divide the GMW of a solute by the valence (number of hydrogen ions that can be displaced).

Example:

The normality of a 1.0 liter NaCl solution that contains 1.0 gram-equivalent weight will be the GMW of NaCl divided by the valence of NaCl:

(Atomic weights of Na = 22.99 and Cl = 35.45)

GMW of NaCl = 22.99 + 35.45 = 58.44 g

N = GMW/valence (the valence for NaCl is 1.0)

58.44 g/1.0 = 58.44 g = 1.0 gram-equivalent weight of NaCl = 1N solution of NaCl

In this situation, because NaCl has a valence of one, the molarity and normality of the solution are the same. Some compounds, however, will not have the same normality as molarity, as in the case of H₂SO₄.

Example:

The normality of a 1.0 liter solution of H₂SO₄ containing 1.0 gram-equivalent weight will be the molecular weight of H₂SO₄ divided by the valence of H₂SO₄:

(Atomic weights of H = 1, S = 32.06, and O = 16)

GMW of H₂SO₄ = 1(2) + 32.06 + 16(4) = 98 g

N = GMW/valence (the valence for H₂SO₄ is 2.0, as there are 2.0 H ions that could be displaced)

98 g /2 = 49 g = 1.0 gram-equivalent weight of H₂SO₄ = 1N solution of H₂SO₄

The molarity of this 1N solution of H₂SO₄ would be 0.5 (M = g /GMW per liter or 49g/98g = 0.5)