ALLCBTs

JEE 2026 Chemistry Solving Questions.

Published on Jul 22, 2025 • Education

Introduction

Welcome JEE aspirants!
In today’s chemistry tutorial, we’ll walk through a solved JEE-level chemistry question involving combustion analysis to calculate the percentage composition of hydrogen and oxygen in an organic compound.

This concept is crucial for excelling in:

• JEE Main Chemistry
• JEE Advanced Chemistry
• CBSE Class 11 & 12 Organic Chemistry
• Engineering entrance exams across India

Let’s proceed with a methodical, exam-focused approach to mastering this core topic.

You can watch the full class in the video below:

Question Overview

Problem:
On combustion, 0.98 g of an organic compound (containing carbon, hydrogen, and oxygen) yields 0.27 g of water (H₂O) and 0.7 g of carbon dioxide (CO₂).

You are asked to calculate the percentage composition of hydrogen and oxygen in the compound.

Step 1: Data Extraction

• Mass of compound = 0.98 g
• Mass of water (H₂O) = 0.27 g
• Mass of carbon dioxide (CO₂) = 0.7 g

Step 2: Determine Mass of Hydrogen

Since hydrogen comes from water, we calculate its mass based on the molecular ratio:

Step 3: Determine Mass of Carbon

Carbon is derived from carbon dioxide (CO₂):

Step 4: Calculate Mass of Oxygen

Step 5: Calculate Percentage Composition

Final Answer

• Hydrogen: 3.06%
• Oxygen: 77.55%

Watch more educational videos and past questions: https://youtube.com/@allcbts

Conclusion

Understanding how to calculate the percentage composition of elements through combustion analysis is a vital skill for success in JEE Main and Advanced Chemistry.

In this tutorial, we:

• Identified the role of water and carbon dioxide in combustion
• Used molar mass ratios to calculate elemental masses
• Applied stoichiometric principles to find percentage composition
• Keep practicing similar questions and focus on concepts like empirical formula, mole calculations, and organic compound identification — all of which are frequently tested in JEE exams.

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