Inorganic chemistry

What is the equation of normality?

Examples of normality?

Definition of normality equation and examples in chemistry

Definition of normality in chemistry

Normality definition equation and examples are listed here briefly. Normality is a measure of concentration equal to the equivalent weight in grams per liter of solution. The equivalent weight Gram is the measure of the reactive capacity of a molecule . The role of the solute in the reaction determines the normality of the solution. Normality is also known as the equivalent concentration of the solution.

Equation of normality

Normality (N) is  molar concentration c i divided by an equivalence factor f eq :

N = c i / f eq

Another common equation is normality (N) equal to the equivalent weight in grams divided by the number of liters of solution:

N = equivalent weight in grams / liters of solution (often expressed in g / l)

or it can be the molarity multiplied by the number of equivalents:

N = molarity x equivalents

Normality units

The capital letter N is used to indicate concentration in terms of normality. It can also be expressed in eq / L equivalent (equivalent per liter) or in meq / L (milliequivalent per liter of 0.001 N, generally reserved for medical reports).

Examples of normality

For acid reactions, a solution of 1 MH 2 SO 4 will have a normality (N) of 2 N because 2 moles of H + ions are present per liter of solution.

For the precipitation reactions of sulfides, where the ion SO  is the important part, the same solution of 1 MH 2 SO 4 will have a normality of 1 N.

Example problem

Find the normality of 0.1 MH 2 SO 4 (sulfuric acid) for the reaction:

2 SO 4 + 2 NaOH → Na 2 SO 4 + 2 H 2 O

According to the equation, 2 moles of H + ions (2 equivalents) from sulfuric acid react with sodium hydroxide (NaOH) to form sodium sulfate (Na2SO4) and water. Using the equation:

N = molarity x equivalents
N = 0.1 x 2
N = 0.2 N

Do not confuse with the number of moles of sodium hydroxide and water in the equation.

Since you have received the molarity of the acid, you do not need any additional information. All you need to know is how many moles of hydrogen ions are involved in the reaction. Since sulfuric acid is a strong acid, you know that it dissociates completely into its ions.

Potential problems using N for concentration

Although normality is a useful unit of concentration, it cannot be used for all the situations because its value depends on an equivalence factor which can change depending on the type of chemical reaction of interest. For example, a solution of magnesium chloride (MgCl 2 ) can be 1 N for the Mg 2+ ion , but 2 N for the Cl  ion . While N is a good unit to know, it is not used as much as molarity or molality in laboratory work. It has value for acid-base titrations, precipitation reactions and redox reactions. In acid-base reactions and precipitation reactions, 1 / f eqis an integer value. In redox reactions, 1 / f eq can be a fraction.

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