ICSE Class 9 Answered

Law of conservation of mass: It states that mass can neither be created nor destroyed in a chemical reaction. 
During any change, physical or chemical, the matter is neither created nor destroyed. However, it may change from one form to another.

Experimental Verification of Law of Conservation of Mass 
Requirements: H-shaped tube called Landolt's tube, Sodium chloride solution, silver nitrate solution, etc.

Procedure: A specially designed H-shaped tube is taken. Sodium chloride solution is taken in one limb of the tube and silver nitrate solution in the other limb as shown in the figure. Both the limbs are now sealed and weighed. Now the tubes are averted so that the solutions can mix up together and react chemically. The reaction takes place and a white precipitate of silver chloride is obtained.

The tube is weighed again. The mass of the tube is found to be exactly the same as the mass obtained before inverting the tube. Thus, this experiment clearly verifies the law of conservation of mass