Introduction
This chapter forms the foundation of chemistry and is crucial for understanding all subsequent chapters. It deals with the quantitative aspects of chemistry and introduces the concept of the mole, which is central to chemical calculations.
Chemistry is the science of matter and the changes it undergoes. The basic concepts in this chapter provide the tools for quantifying these changes.
Key Topics
Mole Concept
Avogadro's Number (6.022 × 10²³)
Molar Mass
Number of Moles Calculations
Stoichiometry
Balancing Chemical Equations
Stoichiometric Calculations
Mass-Mass Relationships
Percentage Composition
Mass Percentage
Empirical Formula
Molecular Formula
Limiting Reagent
Concept of Limiting Reactant
Calculations involving Limiting Reagent
Percentage Yield
Important Concepts & Formulas
Mole Concept
Number of moles (n) = Mass (m) / Molar mass (M)
Number of moles (n) = Number of particles / NA
Number of moles (n) = Volume of gas (at STP) / 22.4 L
Avogadro's Number
NA = 6.022 × 10²³ particles/mol. This is the number of atoms in exactly 12g of carbon-12.
Percentage Composition
Mass percentage of an element = (Mass of element in compound / Molar mass of compound) × 100
Empirical and Molecular Formula
Molecular formula = (Empirical formula)n
n = Molecular mass / Empirical formula mass
Laws of Chemical Combination
| Law | Statement | Significance |
|---|---|---|
| Law of Conservation of Mass | Mass is neither created nor destroyed in a chemical reaction | Basis for balancing chemical equations |
| Law of Definite Proportions | A chemical compound always contains the same elements in the same proportion by mass | Helps in determining chemical formula |
| Law of Multiple Proportions | When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers | Supports atomic theory |
| Gay Lussac's Law of Gaseous Volumes | When gases react, they do so in volumes which bear a simple ratio to one another and to the volumes of products | Important for gas stoichiometry |
| Avogadro's Law | Equal volumes of gases at the same temperature and pressure contain equal number of molecules | Basis for mole concept |
Important Points to Remember
Key Points for JEE Main
- The mole concept is the most important topic from this chapter for JEE Main
- Always balance chemical equations before solving stoichiometry problems
- In limiting reagent problems, identify the reagent that produces the least amount of product
- Remember that at STP (Standard Temperature and Pressure), 1 mole of any gas occupies 22.4 L
- Empirical formula gives the simplest whole number ratio of atoms in a compound
- Molecular formula is a whole number multiple of the empirical formula
- Percentage yield = (Actual yield / Theoretical yield) × 100
Do's
Practice numerical problems regularly
Understand the concept of mole thoroughly
Learn to balance chemical equations quickly
Memorize important formulas
Don'ts
Don't ignore significant figures in calculations
Don't confuse molecular mass with formula mass
Don't forget to check if the reagent is limiting
Don't skip the units in your answers
JEE Main Weightage
This chapter typically carries 2-3 questions in JEE Main, making it a high-weightage chapter. Most questions are numerical problems based on mole concept and stoichiometry.
Chapter 1 Weightage in JEE Main
Weightage
High (2-3 questions)