Mole Concept for AIIMS BSc Nursing 2026,

Mole concept is a cornerstone of chemistry, providing a practical way to quantify the immense numbers of microscopic entities such as atoms, molecules, and ions involved in chemical processes. Understanding this concept is crucial for aspirants of competitive exams like AIIMS BSc Nursing, as it underpins stoichiometry and various quantitative analyses in chemistry.

Introduction to Atom

An atom is the fundamental building block of matter.

• Historical Context: The discovery of the atom is largely attributed to Dalton.

• Dalton's Atomic Theory and its Limitation: Dalton proposed that an atom is indivisible. This theory, however, faced limitations.

• Modern Definition of Atom: An atom is defined as the smallest entity of the universe that can take part in any chemical reaction.

• Examples of Atoms: Hydrogen atom (H), Nitrogen atom (N), Oxygen atom (O), Sulfur atom (S), Chlorine atom (Cl), etc.

Molecules

Molecules are formed when two or more atoms combine.

• Definition: Molecules are formed by combining atoms of one or more types.

• Examples of Molecules: H₂ (Hydrogen gas), N₂ (Nitrogen gas), P₄ (White phosphorus), S₈ (Sulfur), H₂O (Water), NH₃ (Ammonia), etc.

Ions

Ions are atoms or molecules that carry an electrical charge.

Concept of Mole

To work with the vast numbers of microscopic particles in chemistry, a special unit, the mole, is used.

• Necessity of Mole: Entities like atoms and molecules are microscopic and exist in vast numbers. The mole concept quantifies these large numbers conveniently.

• Analogy for Mole: Similar to how "pair" represents 2 items or "dozen" represents 12 items, a mole represents a very large collection of entities.

• Definition of Mole: A mole is a collection of Nₐ species together.

Avogadro's Number (Nₐ)

Avogadro's Number is a fundamental constant in chemistry.

• Definition: Nₐ is a specific number known as Avogadro's Number.

• Values/Representations:

• 6.023 × 10²³

• 6.022 × 10²³

• For simplified calculations: 6 × 10²³

• Significance: This number is extremely large (greater than a crore cubed). It allows chemists to handle incredibly vast quantities of particles in practical units.

Relationship between Moles and Number of Species

There is a direct relationship between the number of moles and the total number of particles.

• Derivation:

• 1 mole contains Nₐ species.

• 2 moles contain 2 × Nₐ species.

• n moles contain n × Nₐ species.

• Formula: The total number of species (count) = Moles × Avogadro's Number (Nₐ).

• This formula enables conversions:

• To find the number of species given moles: multiply moles by Nₐ.

• To find moles given the number of species: divide the number of species by Nₐ.

Moles and Number of Species Problems

Here are some examples illustrating calculations involving moles and the number of species.

1. Find total number of molecules in 3 mol H₂.

• Given: 3 moles of H₂.

• Concept: Number of molecules = Moles × Nₐ.

• Solution: 3 × Nₐ molecules.

2. Find total moles of glucose (C₆H₁₂O₆) in 6 Nₐ molecules of it.

• Given: 6 Nₐ molecules of glucose.

• Concept: Moles = Number of species / Nₐ.

• Solution: (6 Nₐ) / Nₐ = 6 moles.

3. Find the total number of oxygen atoms in 1.2046 × 10²⁴ molecules of oxygen gas.

• Identify Oxygen Gas: Oxygen gas means O₂.

• Step 1: Calculate moles of O₂ molecules.

• Moles of O₂ = (1.2046 × 10²⁴ molecules) / (6.023 × 10²³ molecules/mol) = 2 moles of O₂ molecules.

• Step 2: Determine oxygen atoms per O₂ molecule.

• One O₂ molecule contains 2 oxygen atoms.

• Step 3: Calculate total number of oxygen atoms.

• Total oxygen atoms = (Number of O₂ molecules) × 2

• Total oxygen atoms = (1.2046 × 10²⁴) × 2 = 2.4092 × 10²⁴ atoms.

• Alternatively, using Nₐ: Total oxygen atoms = (2 moles O₂) × (2 atoms/molecule) × Nₐ = 4 Nₐ atoms.

4. Find the sum of moles of carbon and hydrogen atoms in 2 moles of sucrose.

• Identify Sucrose Formula: Sucrose = C₁₂H₂₂O₁₁.

• Step 1: Determine moles of atoms per mole of sucrose.

• 1 mole of sucrose contains:

• 12 moles of Carbon atoms

• 22 moles of Hydrogen atoms

• 11 moles of Oxygen atoms

• Step 2: Calculate moles of atoms in 2 moles of sucrose.

• 2 moles of sucrose contain:

• Carbon: 2 × 12 = 24 moles of Carbon atoms

• Hydrogen: 2 × 22 = 44 moles of Hydrogen atoms

• Step 3: Calculate the sum of moles of Carbon and Hydrogen.

• Sum = 24 moles (C) + 44 moles (H) = 68 moles.

5. For 0.1 mol of ozone gas, find:

• Identify Ozone Gas Formula: Ozone gas = O₃.

• Given: 0.1 mole of O₃ gas.

• Part 1: Number of Molecules.

• Concept: Number of molecules = Moles × Nₐ.

• Solution: 0.1 × Nₐ molecules.

• Part 2: Total Number of Oxygen Atoms.

• Step 1: Atoms per molecule. One O₃ molecule contains 3 oxygen atoms.

• Step 2: Total atoms. Total oxygen atoms = (Number of O₃ molecules) × 3

• Total oxygen atoms = (0.1 Nₐ) × 3 = 0.3 Nₐ atoms.

• Part 3: Moles of Oxygen Atoms.

• Concept: Moles of atoms = Total number of atoms / Nₐ.

• Solution: (0.3 Nₐ) / Nₐ = 0.3 moles of oxygen atoms.

Effective Study Strategy for Success

Achieving success in competitive exams requires a structured and consistent approach. Here are key strategies to maximize your preparation:

• Attend Live Classes Daily: Make attending all live classes a habit to ensure consistent learning and avoid procrastination.

• Revision: This is a very important aspect. Merely attending classes is passive. Active revision, involving focused self-study and problem-solving, is crucial for deep understanding and retention.

• Practice Questions:

• Solve all questions discussed in class (re-attempt them in a rough copy).

• Review NCERT back exercise questions, as objective questions can often be derived from these.

• Utilize NCERT Exemplar for additional practice.

• Target Score: Aim for 27+ out of 30 marks in Chemistry.

• Importance of Chemistry: Chemistry often acts as the rank-decider in competitive exams. A strong performance in this subject is key for securing admission to institutions like AIIMS.

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