⚗️ CBSE · Class 11 · Chemistry · Chapter 1

Some Basic Concepts
of Chemistry

Complete chapter resources for CBSE Class 11 Chemistry — mole concept, stoichiometry, laws of chemical combination, atomic and molecular masses, sample questions, and board exam tips.

4Topics
7–9Board marks
8Sample questions
3PYQ included
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Key Formulas — Chapter 1
  • Molar mass: M = mass (g) / moles (mol)
  • Moles from mass: n = m / M
  • Avogadro's number: Nₐ = 6.022 × 10²³ mol⁻¹
  • % composition: % = (mass of element / molar mass) × 100
  • Empirical formula: simplest whole-number ratio of atoms
  • Molarity: M = moles of solute / volume (L)
Chapter Overview

What this chapter covers

Chapter 1 of NCERT Class 11 Chemistry lays the quantitative foundation for all of chemistry. It begins with the classification of matter (pure substances vs. mixtures, elements vs. compounds), the laws of chemical combination — conservation of mass, definite proportions, multiple proportions, Gay-Lussac's law of gaseous volumes, and Avogadro's law — and introduces the atomic theory of Dalton that explains these empirical observations.

The central concept is the mole, the SI unit for amount of substance. One mole of any substance contains exactly 6.022 × 10²³ (Avogadro's number) entities. The mole bridges the microscopic world of atoms and molecules with the macroscopic masses measured in the lab, enabling calculation of molar mass, percentage composition, empirical and molecular formulas, and ultimately stoichiometric relationships in chemical equations.

Stoichiometry — the quantitative relationship between reactants and products in a balanced chemical equation — is the practical payoff of the chapter. Students learn to identify the limiting reagent (the reactant that determines how much product forms), calculate the theoretical yield, and determine the amount of excess reactant remaining. These skills are tested in every Class 11 and 12 board paper and are indispensable for JEE and NEET.

Topics

What's inside Chapter 1

As per NCERT Class 11 Chemistry (CBSE syllabus)

Topic 1
Importance of Chemistry & Classification of Matter
Role of chemistry in daily life. Classification of matter: pure substances (elements and compounds) vs. mixtures (homogeneous and heterogeneous). Physical and chemical properties.
Topic 2
Laws of Chemical Combination & Dalton's Atomic Theory
Law of conservation of mass, law of definite proportions, law of multiple proportions, Gay-Lussac's law of gaseous volumes, and Avogadro's law. Dalton's atomic theory as an explanation.
Topic 3
Atomic and Molecular Masses, Mole Concept
Atomic mass unit (amu), relative atomic mass, molecular mass, formula unit mass. Definition of the mole, Avogadro's number, molar mass. Interconversion of moles, molecules, and grams.
Topic 4
Stoichiometry & Stoichiometric Calculations
Balancing chemical equations. Percentage composition, empirical and molecular formulas. Mole-to-mole and mass-to-mass calculations. Limiting reagent, theoretical yield, and reactions in solution (molarity).
Connections

How this chapter fits in

Useful for setting question difficulty and cross-chapter papers.

Builds on
Class 9 · Matter in Our Surroundings
States of matter, pure substances vs. mixtures, physical changes
Class 10 · Atoms and Molecules
Atomic mass, molecular mass, Avogadro's concept (NCERT Science)
Chapter 1 Basic Concepts
of Chemistry
Leads to
Ch 5 · States of Matter
Mole-based gas law calculations depend on molar mass and molarity concepts
Class 12 · Electrochemistry & Solutions
Molarity, normality, equivalent mass — all rooted in Chapter 1 skills
Board Blueprint

Marks & question-type breakdown

Typical pattern based on CBSE Class 11 Chemistry board papers from the last five years.

Question type Marks Typical count What's usually tested
MCQ / Objective 1 1–2 SI units, laws of chemical combination, or mole concept definition
Very Short Answer 2 1 Moles ↔ grams conversion, percentage composition, or empirical formula
Short Answer 3 1 Stoichiometry problem: mass-to-mass or moles of product from given mass of reactant
Long Answer / Numerical 4–5 1 Limiting reagent identification, theoretical yield, or empirical + molecular formula determination
Total (approximate) 7–9 4–5 Weightage varies across paper sets and years
Sample Questions

8 sample questions — generated by MarksZen AI

Aligned to CBSE Class 11 Chemistry Chapter 1. Covers all question types across Easy, Medium, and Hard difficulty.

Q1 Easy 1 mark MCQ
The SI unit for the amount of substance is: (a) gram (b) mole (c) kilogram (d) litre
Q2 Easy 2 marks Short Answer
Calculate the number of moles in 44 g of carbon dioxide (CO₂). Also find the number of molecules present. (Molar mass of CO₂ = 44 g/mol; Avogadro's number = 6.022 × 10²³ mol⁻¹)
Q3 Medium 2 marks Short Answer
State the Law of Conservation of Mass and the Law of Definite Proportions. Give one example to illustrate each.
Q4 Medium 3 marks Short Answer
Calculate the percentage composition by mass of each element in sulphuric acid (H₂SO₄). (Atomic masses: H = 1, S = 32, O = 16 g/mol)
Q5 Medium 3 marks Word Problem
A compound on analysis is found to contain 40% carbon, 6.67% hydrogen, and 53.33% oxygen by mass. Determine its empirical formula. (Atomic masses: C = 12, H = 1, O = 16 g/mol)
Q6 Hard 4 marks Word Problem
12 g of carbon is burnt in 48 g of oxygen to form carbon dioxide according to the equation: C + O₂ → CO₂ (i) Identify the limiting reagent. (ii) Calculate the mass of CO₂ produced. (iii) Find the mass of the excess reactant left over. (Atomic masses: C = 12, O = 16 g/mol)
Q7 Hard 4 marks Word Problem
An organic compound contains 75% carbon and 25% hydrogen by mass. Its molar mass is determined to be 16 g/mol. (i) Determine the empirical formula of the compound. (ii) Find the molecular formula. (Atomic masses: C = 12, H = 1 g/mol)
Q8 Hard 5 marks Case-Based
A student dissolves 5.85 g of sodium chloride (NaCl) in enough water to make 500 mL of solution. (i) Calculate the moles of NaCl dissolved. (ii) Calculate the molarity of the solution. (iii) How many moles of NaCl are present in 250 mL of this solution? (iv) What mass of NaCl is needed to prepare 1 L of a 2 M solution? (Molar mass of NaCl = 58.5 g/mol)
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Previous Year Questions

From CBSE board examinations

Actual questions from past Class 11 Chemistry board papers — Some Basic Concepts of Chemistry.

Board 20223 marks
Calculate the amount of water (H₂O) produced when 3.2 g of methane (CH₄) is completely burnt in oxygen. Also find the moles of oxygen consumed. (Atomic masses: C = 12, H = 1, O = 16) (CBSE 2022)
Board 20232 marks
A compound contains 4.07% hydrogen, 24.27% carbon, and 71.65% chlorine by mass. Find the empirical formula of the compound. (Atomic masses: H = 1, C = 12, Cl = 35.5) (CBSE 2023)
Board 20204 marks
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of acetic acid. The products were 2.2 g of carbon dioxide, 0.9 g of water, and 8.2 g of sodium acetate. Show that these observations are in agreement with the law of conservation of mass. (CBSE 2020)
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FAQ

Questions teachers ask

How many marks does Some Basic Concepts of Chemistry carry in the CBSE Class 11 board exam? +
Typically 7–9 marks across 3–4 questions — one 1-mark MCQ on SI units or mole concept, one 2-mark question on laws of chemical combination or percentage composition, and one 3–5 mark numerical on stoichiometry or mole-based calculations. This chapter is foundational and its concepts underpin questions across multiple chapters in the paper.
What is the mole concept and why is it the most important topic in this chapter? +
The mole is the SI unit for amount of substance: 1 mole = 6.022 × 10²³ particles (Avogadro's number). It connects the microscopic world of atoms and molecules to measurable macroscopic masses. Virtually every stoichiometry and solution-chemistry calculation in Class 11 and 12 uses the mole concept, making it the single highest-priority topic in this chapter for both board exams and JEE/NEET.
What are the laws of chemical combination that students must know for the board exam? +
CBSE Class 11 requires knowledge of five laws: (1) Law of Conservation of Mass — total mass of reactants equals total mass of products; (2) Law of Definite Proportions — a pure compound always contains the same elements in the same mass ratio; (3) 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 simple whole-number ratio; (4) Gay-Lussac's Law of Gaseous Volumes; (5) Avogadro's Law. The first two appear most frequently in board questions.
How do I solve limiting reagent problems in stoichiometry? +
Step 1: Write and balance the chemical equation. Step 2: Convert all given masses to moles by dividing by molar mass. Step 3: Divide each reactant's mole count by its stoichiometric coefficient. The reactant with the smallest value is the limiting reagent. Step 4: Use the limiting reagent's moles and the balanced equation ratios to calculate the moles of product formed, then convert back to grams. Board questions at the 4–5 mark level often require identification of the limiting reagent plus the amount of excess reactant left over.
How do I generate a custom question paper for Some Basic Concepts of Chemistry using MarksZen? +
Sign up for a free MarksZen account, choose CBSE Class 11 Chemistry, select Chapter 1 (Some Basic Concepts of Chemistry), set your preferred question-type mix (MCQ, short answer, word problem) and total marks — the AI generates a complete board-aligned paper with answer key in under 2 minutes, ready for PDF export.