Class 10 Computer Science Chapter 1: Office Tools (Notes & Online Test) - PSEB

SOME BASIC CONCEPTS OF CHEMISTRY

NCERT Masterclass & NEET Study Module

1. Nature of Matter & Laws of Chemical Combination

Matter is anything that has mass and occupies space. It can exist in three physical states: solid, liquid, and gas. At the macroscopic level, it is classified as mixtures (homogeneous or heterogeneous) and pure substances (elements or compounds).

Laws of Chemical Combination:

• Law of Conservation of Mass (Antoine Lavoisier): Matter can neither be created nor destroyed.
• Law of Definite Proportions (Joseph Proust): A given compound always contains exactly the same proportion of elements by weight.
• Law of Multiple Proportions (John Dalton): If two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in the ratio of small whole numbers.
• Gay Lussac’s Law of Gaseous Volumes: When gases combine, they do so in a simple ratio by volume (provided T and P are constant).
• Avogadro’s Law: Equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules.

2. Atomic Mass & Molecular Mass

One atomic mass unit (amu or 'u') is defined as a mass exactly equal to one-twelfth ($1/12^{th}$) the mass of one Carbon-12 atom.

$$1 \text{ amu} = 1.66056 \times 10^{-24} \text{ g}$$

Average Atomic Mass: Many elements have multiple isotopes. The average atomic mass is calculated by taking the fractional abundance of each isotope into account.

3. The Mole Concept and Molar Masses

A mole is the amount of substance that contains as many elementary entities (atoms, molecules, ions) as there are atoms in exactly 12 g of the Carbon-12 isotope.

Avogadro Constant ($N_A$): $6.022 \times 10^{23} \text{ mol}^{-1}$

Key Formulas:

• Number of Moles ($n$) = $\frac{\text{Given Mass}}{\text{Molar Mass}}$
• Number of Moles ($n$) = $\frac{\text{Number of Particles}}{N_A}$
• For Gases at STP: $n = \frac{\text{Volume at STP}}{22.4 \text{ L}}$

4. Percentage Composition & Empirical Formula

Mass % of an element: $\frac{\text{Mass of element in 1 mole of compound}}{\text{Molar mass of compound}} \times 100$

Empirical Formula: Represents the simplest whole number ratio of various atoms present in a compound.

Molecular Formula: Shows the exact number of different types of atoms present in a molecule.
Molecular Formula = $n \times$ Empirical Formula, where $n = \frac{\text{Molecular Mass}}{\text{Empirical Formula Mass}}$.

5. Stoichiometry and Limiting Reagent

Stoichiometry deals with the calculation of masses (or volumes) of the reactants and the products involved in a chemical reaction based on a balanced chemical equation.

Limiting Reagent: The reactant which is completely consumed when a reaction goes to completion. It determines the maximum amount of product that can be formed. The reactant which is not completely consumed is the Excess Reagent.

6. Reactions in Solutions (Concentration Terms)

• Mass Percent (w/w %): $\frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100$
• Mole Fraction ($x_A$): $\frac{\text{No. of moles of A}}{\text{Total no. of moles in solution}}$
• Molarity ($M$): No. of moles of solute present in 1 Litre of solution. (Depends on Temperature).
  $M = \frac{n}{V (\text{in L})}$
• Molality ($m$): No. of moles of solute present in 1 kg of solvent. (Independent of Temperature).
  $m = \frac{n}{\text{Mass of solvent (in kg)}}$

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🚀 NEET CHEMISTRY MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Mole Concept, Stoichiometry, and Solutions.

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