Class 11 Chemistry

Chapter 1: Some Basic Concepts of Chemistry (Mole Concept) (Part - 2)

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Class 11 Chemistry Chapter 1 Mole Concept MCQs | NEET & JEE Chemistry | Chemistry Achievers Academy

Master Class 11 Chemistry Chapter 1 – Some Basic Concepts of Chemistry (Mole Concept). Learn the important topics, NEET/JEE weightage, frequently asked concepts, chapter-wise MCQs, PYQs, formula sheet, and revision notes.

📚 Chapter 1: Some Basic Concepts of Chemistry (Mole Concept)

📖 Chapter Introduction

Chemistry is often called the Central Science because it connects Physics, Biology, Environmental Science, and Medicine. The first chapter, Some Basic Concepts of Chemistry, forms the foundation for almost every other chapter in Class 11 and Class 12 Chemistry.

This chapter introduces the language of chemistry through concepts such as the mole, Avogadro constant, molar mass, empirical and molecular formulae, stoichiometry, and chemical calculations. These topics are essential for solving numerical problems in NEET, JEE Main, JEE Advanced, CUET, CBSE Board Exams, and other competitive examinations.

Students who master this chapter will find it much easier to understand later topics such as Atomic Structure, Chemical Bonding, Thermodynamics, Equilibrium, Electrochemistry, and Organic Chemistry.

🎯 Important Topics & Frequently Asked Questions from This Chapter

The following concepts are repeatedly tested in NEET, JEE Main, JEE Advanced, and CBSE Board examinations:

1. Nature of Matter

Characteristics of matter
Physical and chemical properties
Classification of matter

2. Laws of Chemical Combination

Law of Conservation of Mass
Law of Definite Proportions
Law of Multiple Proportions
Gay-Lussac's Law of Gaseous Volumes
Avogadro's Law

3. Dalton's Atomic Theory

Postulates
Limitations

4. Atomic Mass

Relative Atomic Mass
Average Atomic Mass
Molecular Mass
Formula Mass

5. Mole Concept ⭐⭐⭐⭐⭐

Frequently Asked:

Definition of Mole
Avogadro Number
Mole–Mass Relationship
Mole–Volume Relationship
Mole–Particles Relationship

6. Molar Mass

Frequently Asked:

Gram Molecular Mass
Gram Atomic Mass
Conversion Problems

7. Percentage Composition

Frequently Asked:

Percentage by Mass
Numerical Problems

8. Empirical Formula

Frequently Asked:

Determination from Percentage Composition
Numerical Questions

9. Molecular Formula

Frequently Asked:

Relation Between Empirical and Molecular Formula
Molecular Formula Calculations

10. Stoichiometry ⭐⭐⭐⭐⭐

Frequently Asked:

Balanced Chemical Equations
Mole Ratio
Limiting Reagent
Excess Reagent
Percentage Yield
Atom Economy (Basic)

11. Concentration Terms

Frequently Asked:

Molarity
Molality
Mole Fraction
Mass Percentage
Parts Per Million (PPM)

12. Significant Figures

Frequently Asked:

Rules
Addition & Subtraction
Multiplication & Division
Rounding Off

13. Scientific Notation

Frequently Asked:

Exponential Form
Unit Conversion

⭐ Why This Chapter is Important?

This chapter carries significant weight in almost every entrance examination.

NEET

Usually 1–2 questions every year.
Mostly numerical and concept-based.

JEE Main

Numerical calculations.
Stoichiometry.
Mole concept.
Significant figures.

JEE Advanced

Multi-concept numerical problems.
Limiting reagent.
Empirical & molecular formula.
Advanced stoichiometry.

Board Examinations

Definitions.
Derivations.
Numerical problems.
Formula-based questions.

Common Mistakes Students Make

Confusing mole and molar mass.
Incorrect unit conversions.
Errors in balancing equations.
Ignoring significant figures.
Wrong stoichiometric ratios.
Mistakes while calculating empirical formula.

Preparation Tips

Learn every formula thoroughly.
Practice NCERT examples first.
Solve previous year NEET questions.
Practice at least 30–50 numerical problems.
Revise dimensional analysis regularly.

📊 Chapter Weightage

Examination	Expected Questions
NEET	1–2
JEE Main	1–2
JEE Advanced	1–2
CBSE Board	High
TN State Board	High

🎯 High-Weightage Topics for NEET/JEE 2027

✅ Mole Concept

✅ Avogadro Constant

✅ Stoichiometry

✅ Empirical Formula

✅ Molecular Formula

✅ Percentage Composition

✅ Significant Figures

✅ Limiting Reagent

✅ Molarity

✅ Molality

✅ Mole Fraction

What is a Mole?

A mole is the SI unit for the amount of substance. One mole contains 6.022 × 10²³ elementary entities (atoms, molecules, ions, or electrons).

This number is called Avogadro's Number (Nₐ).

Important Formulae

Number of Moles = Mass / Molar Mass
Mass = Number of Moles × Molar Mass
Number of Particles = Number of Moles × 6.022 × 10²³
Number of Moles = Number of Particles / 6.022 × 10²³
At STP:
- 1 mole of any gas = 22.4 L
Density = Mass / Volume

Molar Mass

Molar mass is the mass of one mole of a substance.

Examples:

H₂ = 2 g mol⁻¹
O₂ = 32 g mol⁻¹
CO₂ = 44 g mol⁻¹
H₂O = 18 g mol⁻¹
NH₃ = 17 g mol⁻¹
NaCl = 58.5 g mol⁻¹
CaCO₃ = 100 g mol⁻¹
H₂SO₄ = 98 g mol⁻¹

Avogadro's Number

One mole contains:

6.022 × 10²³ atoms
6.022 × 10²³ molecules
6.022 × 10²³ ions
6.022 × 10²³ electrons

NEET JEE Chemistry – Chapter 1: Mole Concept (Part 2)

MCQs 26–50 (NEET/JEE Level)

26. How many moles are present in 9 g of H₂O?
A) 0.25
B) 0.50
C) 1.00
D) 2.00

27. Number of atoms present in 2 moles of helium is
A) 6.022 × 10²³
B) 12.044 × 10²³
C) 18.066 × 10²³
D) 24.088 × 10²³

28. Number of oxygen atoms present in 1 mole of O₂ is
A) 6.022 × 10²³
B) 12.044 × 10²³
C) 3.011 × 10²³
D) 2.408 × 10²⁴

29. Number of molecules in 22 g of CO₂ is
A) 6.022 × 10²²
B) 3.011 × 10²³
C) 6.022 × 10²³
D) 1.204 × 10²⁴

30. Mass of 0.5 mole of NaOH is
A) 10 g
B) 20 g
C) 30 g
D) 40 g

31. Number of moles in 46 g of ethanol (C₂H₅OH) is
A) 0.5
B) 1
C) 2
D) 3

32. One mole of methane contains
A) 6.022 × 10²³ carbon atoms
B) 6.022 × 10²³ hydrogen atoms
C) 3.011 × 10²³ carbon atoms
D) 12.044 × 10²³ hydrogen atoms

33. The molar mass of Ca(OH)₂ is
A) 72 g mol⁻¹
B) 74 g mol⁻¹
C) 76 g mol⁻¹
D) 78 g mol⁻¹

34. Number of moles present in 74 g of Ca(OH)₂ is
A) 0.5
B) 1
C) 2
D) 4

35. One mole of NH₃ contains hydrogen atoms equal to
A) 6.022 × 10²³
B) 12.044 × 10²³
C) 18.066 × 10²³
D) 24.088 × 10²³

36. Number of molecules present in 2 g of H₂ is
A) 6.022 × 10²³
B) 3.011 × 10²³
C) 12.044 × 10²³
D) 1.204 × 10²⁴

37. Molar mass of glucose (C₆H₁₂O₆) is
A) 160 g mol⁻¹
B) 170 g mol⁻¹
C) 180 g mol⁻¹
D) 190 g mol⁻¹

38. Number of moles in 90 g of glucose is
A) 0.25
B) 0.50
C) 1.00
D) 2.00

39. Number of atoms in one molecule of glucose is
A) 18
B) 20
C) 24
D) 30

40. Number of oxygen atoms in one molecule of H₂SO₄ is
A) 2
B) 3
C) 4
D) 5

41. Number of moles present in 32 g of O₂ is
A) 0.5
B) 1
C) 2
D) 4

42. At STP, the volume occupied by 2 moles of an ideal gas is
A) 11.2 L
B) 22.4 L
C) 44.8 L
D) 67.2 L

43. Number of molecules in 44.8 L of O₂ at STP is
A) 6.022 × 10²³
B) 12.044 × 10²³
C) 18.066 × 10²³
D) 24.088 × 10²³

44. Mass of one mole of calcium is
A) 20 g
B) 40 g
C) 60 g
D) 80 g

45. Number of electrons present in one mole of Na atoms is
A) 6.022 × 10²³
B) 11 × 6.022 × 10²³
C) 23 × 6.022 × 10²³
D) 46 × 6.022 × 10²³

46. Which of the following contains the greatest number of molecules?
A) 18 g H₂O
B) 44 g CO₂
C) 2 g H₂
D) All contain the same number of molecules

47. Number of atoms present in 18 g of H₂O is
A) 6.022 × 10²³
B) 12.044 × 10²³
C) 18.066 × 10²³
D) 1.8066 × 10²⁴

48. One mole of SO₂ contains oxygen atoms equal to
A) 6.022 × 10²³
B) 12.044 × 10²³
C) 18.066 × 10²³
D) 24.088 × 10²³

49. Number of moles in 58.5 g of NaCl is
A) 0.5
B) 1
C) 2
D) 3

50. The number of formula units present in 3 moles of NaCl is
A) 6.022 × 10²³
B) 12.044 × 10²³
C) 18.066 × 10²³
D) 24.088 × 10²³

Answer Key

🚀 How to Score Full Marks from This Chapter

Read every NCERT line carefully.
Memorize all definitions.
Learn all formulas.
Practice unit conversions daily.
Solve previous year NEET and JEE questions.
Practice assertion–reason and statement-based questions.
Revise important numerical problems before the exam.

💬 Motivation Corner

Thirukkural

"எண்ணித் துணிக கருமம்; துணிந்தபின் எண்ணுவது இழுக்கு."

திருக்குறள் – 467

Meaning (English):

Think carefully before starting any task. Once you begin, don't hesitate.

NEET/JEE Message:

Plan your preparation wisely, and once you start, stay committed without giving up.

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