Chemical stoichiometry involves mathematical calculations of the amounts of reactants and products in a chemical reaction. This is one of the first concepts taught to a science student in chemistry, and are very crucial from the examination point of view. They have a significant weightage in JEE including both JEE Main and JEE Advanced. As JEE Advanced 2019 is just a few days away, you must be revising the syllabus. So, we thought of helping you save time in revision by giving you some quick revision tips for stoichiometry.
Basically, stoichiometry deals with the quantitative analysis of chemical reactions. Concepts such as limiting reactant, n-factor, and gravimetric/volumetric analysis are important, and covered in detail. So, how to revise stoichiometric concepts within 10 minutes? Read on!
The mole concept
One mole of a substance is defined as the number of atoms in exactly 12 grams of carbon-12. This number comes out to be 6.023 × 1023, which is equal to the Avogadro number. Therefore, one mole of a substance contains an Avogadro number of atoms.
Equations form a major part of stoichiometry. They represent the reactants and products in a clean and concise manner and enable us to perform mathematical calculations easily and conveniently.
Balancing a chemical equation means making the molecules of a certain substance the same on both the products side and the reactants side of the chemical equation. An example is-
MnO2 + 4HCI →MnCI2 + 2H2O + CI2
Here, the number of molecules of each element on the left side is equal to those on the right-hand side. For instance, the left side contains 4 Cl atoms, and the right side contains 2+2=4 Cl atoms as well.
Limiting reactant in a chemical reaction is the reactant which is completely consumed during the reaction, and stops the production of any more products. The limiting reactant decides the yield of the product, and it is crucial to identify the limiting reactant in a reaction before getting into solving questions. The final yield of the product is decided by the amount of the limiting reactant taken initially.
Gravimetric and volumetric analysis
Here, we relate the mass of given substances with the volumes of two or more gases. For problems involving the mass-volume relationships, the gas equation PV=nRT is used to find out the unknown factors, usually the moles of the gas, and then further calculations are made.
If the relationship is in a volume-volume form, remember that one mole of a gas occupies 22.4 litres of volume at STP. This is a very handy relation for solving questions related to equations with gaseous reactants and products.
The volumetric analysis involves quantitative analysis of substances in a solution through volume measurements. We usually measure these amounts against a standard solution, one whose concentration is known to us and does not change. Titrations are an example of volumetric analysis.
The difference in end point and equivalence point should be very clear to students. The point where titration is stopped is the endpoint, and the point where the reaction is completed is the equivalence point.
We hope that you were able to revise your stoichiometry concepts within 10 minutes! All the best to you for all your exams!