To Verify the Law of Conservation of Mass (Class 9 Chemistry Practical)
To demonstrate that the total mass of reactants equals the total mass of products in a chemical reaction.
TL;DR: To demonstrate that the total mass of reactants equals the total mass of products in a chemical reaction.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
Aim: To demonstrate that the total mass of reactants equals the total mass of products in a chemical reaction.
Materials Required
- Balance (accurate)
- Lead nitrate solution
- Potassium iodide solution
- Test tubes
- Beaker
- Distilled water
- Weighing paper
Theory
The law of conservation of mass states that in a chemical reaction, the total mass of reactants equals the total mass of products. No mass is created or destroyed, only rearranged. In the reaction Pb(NO3)2 + 2KI → PbI2 (yellow ppt.) + 2KNO3, the mass before and after reaction is the same.
Procedure
- Take a clean, dry beaker and weigh it on a balance - record this mass
- Add measured quantities of lead nitrate solution and potassium iodide solution to the beaker
- Record the total mass of the beaker plus solutions
- Mix the two solutions thoroughly and observe the formation of yellow precipitate (PbI2)
- Weigh the beaker with all contents after reaction is complete - record this mass
- Compare the mass before reaction with the mass after reaction
- Account for any small differences (water evaporation, weighing errors)
Observation
When lead nitrate solution is mixed with potassium iodide solution, a bright yellow precipitate of lead iodide forms immediately. The mixture becomes turbid. The mass of the system before and after the reaction remains essentially the same.
Result
The law of conservation of mass is verified. Mass before reaction = [value] g, Mass after reaction = [value] g. The small difference (if any) is due to water loss or weighing errors, not loss of chemical mass.
Precautions
- Ensure the balance is calibrated before use
- Use a covered beaker or watch glass to prevent water evaporation
- Record measurements immediately
- Allow reactions to complete before weighing
- Use appropriate quantities of reactants
Viva Questions
State the law of conservation of mass.
The law of conservation of mass states that the total mass of reactants equals the total mass of products in a chemical reaction.
Why is the beaker weighed before adding reactants?
To establish the initial mass of the system so it can be compared with the final mass after reaction.
What is the yellow precipitate formed in this experiment?
The yellow precipitate is lead iodide (PbI2).
What could cause a difference in mass measurements?
Water evaporation, weighing errors, and incomplete transfer of products can cause small differences.
More Class 9 Chemistry Practicals
- To Prepare a True Solution and Observe the Tyndall Effect
- To Find the pH of Samples Using Indicators
- To Study a Double Displacement (Precipitation) Reaction
- To Test Acids and Bases with Indicators
- To Study the Effect of Temperature on Reaction Rate
- To Determine Melting and Boiling Points of a Pure Substance
🤖 Stuck on any of these? Ask Syllab's free AI Tutor to explain step by step →