IIT JEE is one of the most difficult examinations conducted at the national level for giving admission to prestigious engineering colleges institutes and colleges in India such as – NITs, IITs and CFTIs. The entrance examination is indubitably tough and students need to grasp study materials properly. There are three subjects—Physics, Chemistry and Mathematics. Each of these subjects requires a thorough study. The concepts of these subjects are vast and students need to study with undivided attention. Here, we will be discussing a very important topic of Chemistry i.e. Normality.
Latest Update – The JEE Main and IIT JEE Advanced exams have been postponed due to the COVID-19 situation. The April session of the JEE Main exam has been postponed. The new exam dates will be announced soon.
What is normality?
“Normality is a measure of concentration which is equal to the gram equivalent weight/ litre of solution. Gram equivalent weight is the measure of the reactive capacity of a molecule. The role of solute in the reactions figures out the normality of solution. Normality is also called as the equivalent concentration of a solution.”It is one of the most important concepts in Chemistry subject. Students need to learn its definitions and its derivation. Many numerical based on it are asked in the JEE entrance examination.
The equation of normality
Normality (N) is the molar concentration ‘ci’ which is divided by an equivalence factor feq. It is represented by
N = ci /feq
Another common equation is normality (N) which is equal to the gram equivalent weight divided by litres of the solution:
N = gram equivalent weight / liters of solution (often expressed in g/L)
Or it may be the molarity multiplied by the number of equivalents:
N = molarity x equivalents
Difference Between Normality and Molarity
Here are the differences between Normality and Molarity and candidates must keep the following points in mind:
|Definition||Number of gram equivalent of solute per liter of solution||Number of moles of solute per liter of solution|
|Measures||Measurement of the gram equivalent in relation to the total volume of the solution||Measurement of the Moles in the total volume of the solution|
|Units||Eq L-1||Moles L-1|
Units of Normality
‘N’ is used for indicating the concentration in terms of normality. It is also expressed as eq/L (equivalent per litre) or meq/L (milliequivalent per litre of 0.001 N).
In order to be clearer with the concept of normality, students need to go through the following examples:
Find the normality of 0.1 M H2SO4 (sulfuric acid) for the reaction:
H2SO4 + 2 NaOH → Na2SO4 + 2 H2O
According to this 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
Students are advised not to be confused by the number of moles of sodium hydroxide and water in the equation. Since students have been given the molarity of the acid, they don’t need any more information. What they need to determine if the number of moles of hydrogen ions taking part in the reaction. As sulfuric acid is a strong acid, it breaks into ions.
Like the above, there will be many such problems that students need to solve with undivided attention. While doing numerical, they should remain attentive. A minor fault can mar the whole problem and they will not be able to get the right value of normality.
What do students need to do?
Prior to solving any numerical based on normality, students need to be clear about its concept and its derivation. Students should bear in mind that normality is a very important concept in the IIT JEE entrance examination and students must take it seriously.