What is the relation between normality ,molarity and n factor? How is it derived from formula of normality?
Answers
Answer:
If you know the Molarity of an acid or base solution, you can easily convert it to Normality by multiplying Molarity by the number of hydrogen (or hydroxide) ions in the acid (or base). For example, a 2 M H2SO4 solution will have a Normality of 4N (2 M x 2 hydrogen ions). ... Equivalent mass for H2SO4 is 98/2 = 49.
Explanation:
Normality, abbreviated as “N,” is a useful way of measuring the concentration of some solutions in the laboratory. While it is used in many areas of a laboratory technician’s world, we in the water and wastewater fields use it almost exclusively to measure the concentrations of acids and bases for such solutions as titrants in acidity and alkalinity analyses and for the pH adjustments of BOD, ammonia, and phosphorus samples.
Normality is similar in concept to molarity (refer to the previous article “Molarity”). Where molarity (M) represents the concentration of an ion or compound in solution, normality (N) goes one step further and represents the molar concentration only of the acid component (usually the H+ ion in an acid solution) or only the base component (usually the OH- ion in a base solution).
Here is a simple example to show the relationships of Normal acid and base solutions: a 1N solution of the acid H2SO4 will completely neutralize an equal volume of a 1N solution of the base NaOH. Even though the H2SO4 provides two (acid) H+ ions per molecule verses only one (base) OH- ion per NaOH molecule, the calculations of N take into account these differences and puts it all into an equivalent scale. In a sense, with normality calculations, you really can compare apples with oranges – acid and base-wise anyway.
If you know the Molarity of an acid or base solution, you can easily convert it to Normality by multiplying Molarity by the number of hydrogen (or hydroxide) ions in the acid (or base).
N = (M)(number of hydrogen or hydroxide ions)
For example, a 2 M H2SO4 solution will have a Normality of 4N (2 M x 2 hydrogen ions). A 2 M H3PO4, solution will have a Normality of 6N.
However, to make a solution of a predetermined normality requires a bit more calculating. First, you must determine the compound’s equivalent mass. This is done by taking the compound’s gram-molecular mass and dividing by the number of hydrogen ions or hydroxide ions. Here are a few examples:
H2SO4, sulfuric acid.
The gram-molecular mass is 98 (From the periodic chart the individual atomic masses are: H=1, S=32, O=16: {1x2}+32+{16x4}=98).
The number of acid hydrogen ions (H+ ) is 2.
Equivalent mass for H2SO4 is 98/2 = 49.
H3PO4, phosphoric acid. The gram-molecular mass is also 98. The number of hydrogen ions (H+ ) is 3. Equivalent mass for H3PO4 is 98/3 = 32.6.
NaOH, potassium hydroxide. The gram-molecular mass is 40. The number of hydroxide ions (OH-) is 1. Equivalent mass for NaOH is 40/1 = 40.
Once the equivalent mass of an acid or base is determined, you can then calculate the amount of grams needed per volume of water for N.