Composition for Class 9 ICSE — Simplified Chapter 1
Matter and its composition for class 9 ICSE begins with one of chemistry’s most tested ideas: the Law of Conservation of Mass. This chapter from the Simplified Chemistry book shows what matter is made of, and why its total mass never changes during a reaction. You will trace the law from John Dalton’s atomic theory to Lavoisier’s experiments, then learn to check it with simple arithmetic. The chapter PDF below gives you the full text for revision.
Download Matter and Its Composition Law of Conservation of Mass Class 9 ICSE Chemistry Chapter 1 PDF
Download the Matter and Its Composition Law of Conservation of Mass Class 9 ICSE Chemistry chapter PDF from the Simplified textbook to revise offline or print for practice. It is the full chapter as printed in the book — 10 pages, 4 sections, 41 questions.
What is inside Chapter 1
10 pages · 4 sections · 1 worked examples · 41 exercise questions
| Section | Title |
|---|---|
| 1 | INTRODUCTION |
| 2 | LAW OF CONSERVATION OF MASS – Statement |
| 3 | EXPLANATION |
| 4 | EXPERIMENT – 1 |
- Questions: 1 questions
- Additional Questions: 40 questions
1 INTRODUCTION
The law rests on two scientific foundations. John Dalton proposed in his atomic theory that atoms can neither be created nor destroyed, but only change from one form to another. Since all matter is built from atoms, matter itself must behave the same way. That idea gives the law its theoretical base.
Lavoisier in 1789 supplied the experimental proof. He heated tin with air inside a closed vessel and measured the total mass before and after. The mass of tin and air before the chemical change matched the mass after tin oxide formed, as long as the temperature stayed constant. Before and after the experiment, the mass remained the same.
These two roots matter for the rest of the Class 9 ICSE chemistry course. Dalton gave the reason; Lavoisier gave the evidence. Together they turned a guess into a law you can test in a lab.
2 LAW OF CONSERVATION OF MASS – Statement
The law says that in any chemical reaction, the total mass of the substances that react equals the total mass of the products formed. One condition is attached to this statement: the masses must be measured under similar conditions.
Why does that condition matter? Temperature and pressure change how gases behave and how much they weigh in practice. Measuring before and after at the same conditions keeps the comparison fair. Without it, the law would be impossible to verify in a real laboratory.
3 EXPLANATION
The law has a simple algebraic form. If A and B react to form C and D, then:
\text{Mass of A} + \text{Mass of B} = \text{Mass of C} + \text{Mass of D}
You can check it with any balanced reaction. Take the formation of carbon dioxide. 12 g of carbon combines with 32 g of oxygen to give 44 g of carbon dioxide.
12 + 32 = 44
The left side equals the right side. No mass appears or vanishes. The same ratio check works for every reaction you will meet in this ICSE chapter.
4 EXPERIMENT – 1
The simplest verification uses phosphorus. A sealed tube containing phosphorus is weighed, then heated carefully until the phosphorus burns completely. After cooling, the tube is weighed again. The weight before and after is the same. No change is detected.
EXPERIMENT – 2: Landolt’s experiment
Landolt tested the law with a double decomposition reaction. He placed sodium chloride solution in one limb of a U-shaped tube and silver nitrate solution in the other, then sealed both limbs. The tube was weighed. He tilted it to mix the solutions. Sodium chloride reacts with silver nitrate to form a precipitate of silver chloride. The tube was weighed again. The weight stayed the same.
\text{NaCl} + \text{AgNO}_3 \rightarrow \text{AgCl}\downarrow + \text{NaNO}_3
Check the masses. Reactants: NaCl is 23 + 35.5 = 58.5, and AgNO₃ is 108 + 14 + 48 = 170. Total reactants: 58.5 + 170 = 228.5. Products: AgCl is 108 + 35.5 = 143.5, and NaNO₃ is 23 + 14 + 48 = 85. Total products: 143.5 + 85 = 228.5. Each side totals 228.5. The mass of reactants equals the mass of products.
Worked example — the 0.58 g check
Take a numerical version of Landolt’s experiment. Dissolve 0.58 g of NaCl in 250 g of water, and 1.71 g of AgNO₃ in another 250 g of water. Mix the two solutions. The products are 1.44 g of AgCl and 0.85 g of NaNO₃. Show that the results follow the law.
Total mass before the chemical change:
0.58 + 1.71 + 500 = 502.290\ \text{g}
Total mass after the chemical change:
1.44 + 0.85 + 500 = 502.290\ \text{g}
The totals match. The reaction is in accordance with the Law of Conservation of Mass.
A common mistake is dropping the 500 g of water from both totals. The water does not react, but it is part of the system being weighed. Include it on both sides, and the check works.
Other reactions that prove the law
The same apparatus verifies the law with other solutions. Mixing lead acetate with sodium sulphate gives lead sulphate:
\text{Pb(CH}_3\text{COO)}_2 + \text{Na}_2\text{SO}_4 \rightarrow \text{PbSO}_4\downarrow + 2\text{CH}_3\text{COONa}
Mixing iron(II) sulphate with silver sulphate gives silver:
2\text{FeSO}_4 + \text{Ag}_2\text{SO}_4 \rightarrow 2\text{Ag}\downarrow + \text{Fe}_2(\text{SO}_4)_3
Each reaction shows the same conclusion. In a chemical change, matter is neither created nor destroyed. There is only a transformation of material substances. That is why the Law of Conservation of Mass is also called the Law of Conservation of Matter. This law sets up the next topic, chemical changes and reactions, which you will study later in Class 9 ICSE chemistry.
Limitations
Chemical reactions release energy as heat and light. That energy is the chemical energy stored in the reactants. When it is released, an extremely small amount of mass converts into energy. So the law is not strictly valid unless mass and energy are considered together.
Conservation of mass and conservation of energy are two aspects of one larger law. The total quantity of mass and energy together remains constant throughout a chemical reaction. This agrees with Dalton’s atomic theory, in which atoms keep their individuality and are not created or destroyed.
What to practise from Composition for Class 9 ICSE
- Questions — 1 question, the 1994 board question asking for a common substance that exists in all three states of matter.
- Additional Questions — 40 questions covering matter and its characteristics, the kinetic theory postulates, differences between solids, liquids and gases, change of state terms, and numerical checks of the Law of Conservation of Mass.
The board’s official site at cisce.org carries the current syllabus and specimen papers for Class 9.
Composition for Class 9 ICSE frequently asked questions
What is matter and its composition for class 9 ICSE?
Matter is anything that has mass and occupies space. This chapter explains how matter is built from atoms and particles, how the three states differ, and how the Law of Conservation of Mass governs every chemical change.
Why is the Law of Conservation of Mass in Class 9 ICSE also called the Law of Conservation of Matter?
In a chemical change, matter is neither created nor destroyed; it only transforms from one substance to another. Since the total matter stays constant, the same law is given both names.
Why must masses be measured under similar conditions for the Law of Conservation of Mass to hold?
Temperature and pressure affect how substances, especially gases, behave and weigh. Measuring before and after under the same conditions keeps the comparison fair and makes the law testable in a lab.
Does the Law of Conservation of Mass fail because heat and light are released during a reaction?
Not exactly. A tiny amount of mass converts into the energy released. The law holds strictly only when mass and energy are treated together as one conserved total.
Reference: ICSE Class 9 Chemistry textbook material, chapter 1: Matter and Its Composition Law of Conservation of Mass — CISCE-aligned.
More from this book
Explore Class 9 Chemistry Notes
Related chapters: