Brief Notes on Normality Equations

Let us begin with the question: what is normality? In a chemical solution, normality is defined as the gramme equivalent weight of solute per litre of solution. Normality is also known as equivalent concentration. It is denoted by the letters “N” or “eq/L.” (equivalents per litre). To calculate the gramme equivalent weight, one must first figure out how many hydrogen ions (H+ or H3O+), hydroxide ions (OH–), or electrons (e–) are carried in a reaction, as well as the chemical species’ valence, you must first figure out how many hydrogen ions (H+ or H3O+), hydroxide ions (OH–), or electrons (e–) are transferred. In other cases, the ratio of a substance’s molar mass to its valence determines its equivalent weight. Valence is also known as the equivalence factor.

Normality formula

Having had an idea about ‘what is normality?’ Let us understand the ways to calculate it. 

There are numerous ways for determining the normality of a solution, the best and most practical of which is to compare the solution (with unknown concentration) to a standard-normal solution. To do so, a main standard solution is created first, followed by titration against the secondary solution until the endpoint is reached.

In titrimetry, the endpoint, as well as equivalence points, are critical. However, during titration, we only care about visual endpoints with appropriate chemical indicators.

Calculation of normality by acid-base titrations

It’s critical to pick the right counteractive species solution (acid against a base). These chemical compounds are utilised as an indirect indicator of a solution’s normality. Volumes of both counter-active species, as well as the normality of the reference solution, are necessary for this.

N1V1=N2V2

N1= Normality of the first chemical

V1= Volume of the first chemical

N2= Normality of the second chemical

V2= Volume of the second chemical

Molarity (M) to Normality (N)

Now consider the relationship between molarity and normality. Molarity and normality are two ways to represent the concentration of a solution. Molarity pertains to the number of moles of solute in one litre of solution. Then, what is normality? Normality refers to the number of equivalents of solute per litre of solution. The equivalency ratio links the two expressions, which is the number of equivalents of solute per mole of solute.

To compute normality from given molarity, multiply the number of chemically active species by the molarity value to obtain normality. The equation below depicts the relationship between molarity and normality.

Molarity=n * Normality

Where n denotes the number of H+ ions in an acid, the number of OH- ions in a base, and the charge in ionic forms in a salt.

Percentage purity (%) to Normality (N)

The following formula can be used to compute normality from a substance’s % purity:

Normality=%purity* density *10Gram equivalent weight of the substance

A 37 percent HCL solution, for example, is accessible as a laboratory reagent. It has a gramme equivalent weight of 36.461 g and a density of 1.49 kg/m3. When the normality is computed, the result is 15.120 N.

Normality Examples

Normality examples will best help us understand ‘what is normality?’ So, here let us take a look at a few basic normality examples.

• HCl Normality

HCl (hydrochloric acid) is a crucial laboratory chemical. A known concentration solution of this acid is normally required during titration. Its gramme equivalent weight is 36.5 g, and each molecule contains one active species (H+). As a result, one normal HCL gas solution includes 36.5 grammes of HCL gas dissolved per litre of solution.

• Sodium Thiosulphate normality

Consider the following redox equation to determine the normality (N) of sodium thiosulfate:

2Na2​S2​O3​+I2​🡪 Na2​S4​O6​+2NaI

2S2​O32− 🡪 S4​O62−​+2e−

Two moles of thiosulphate ions lose two electrons on average (n=1) in this equation, implying that their molarity and normality are identical. Because it has a gramme equivalent weight of 248.18 g/eq, wt, it dissolves 248.18 grams per litre to make 1N and 1M solutions.

Conclusion

Having known ‘what is normality?’ it is important for one to know that normality isn’t the most suitable unit of measurement in some situations. The first step is to determine an equivalency factor. Second, the normality of a chemical solution is not a fixed value. Its value depends greatly on the chemical process under investigation. A solution of CaCl2 that is 2 N in terms of the magnesium (Mg2+) ion is only 1 N in terms of the chloride (Cl–) ion. While it can be beneficial in acid-base titrations and redox reactions, the International Union of Pure and Applied Chemistry opposes its usage in chemistry courses and laboratories.