Normality

When you need to compare solutions on the basis of concentration of specific ions or the amount of charge that the ions have, a different measure of concentration can be very useful. It is called normality.

We will deal with normality more completely in the lesson on acid-base titrations and give it just a cursory mention in this lesson. For that reason you can ignore objectives 6-9 and examples 13-17 in your workbook for this lesson.

The normality of a solution is simply a multiple of the molarity of the solution. Generally, the normality of a solution is just one, two or three times the molarity. In rare cases it can be four, five, six or even seven times as much. The symbol for normality is N or N.

Whether the multiplying factor is one, two or three depends on the formula of the chemical and what it is being compared to. Note that calcium chloride has two moles of chloride ions for every mole of CaCl₂. Because of that, the multiplying factor for calcium chloride is two.

CaCl₂

Ca²⁺ + 2 Cl^-

1 M CaCl₂ = 2 N CaCl₂
2.4 M CaCl₂ = 4.8 N CaCl₂
etc.

Similarly, for aluminum chloride the multiplying factor is three.

AlCl₃

Al³⁺ + 3 Cl^-

1 M AlCl₃ = 3 N AlCl₃
2.4 M AlCl₃ = 7.2 N AlCl₃
etc.

Hopefully, this gives you an idea of the nature and value of normality and its relationship to molarity. As mentioned earlier, it will be covered in more detail in the lesson involving acid-base titrations.

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