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ICSE Class 8 Chemistry Question 11 of 13

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Question 13

State the 'law of conservation of mass'. State the main points of Landolt's experiment for experimental evidence of the law. State the limitations of the law.

Answer

Law of conservation of mass

Law of conservation of mass states that whenever a chemical change takes place, the total mass of the reacting substances is exactly equal to the total mass of the products, [provided masses are measured under similar conditions].

Main points of Landolt's experiment

  • In an 'H' shaped tube as shown in the figure, Landolt introduced a solution of sodium chloride [NaCl] and silver nitrate [AgNO3] in the limbs of the tube and sealed it and weighed it.
  • The solutions were mixed by shaking to obtain a white precipitate of silver chloride.
  • The tube was again weighed after the experiment.
State the law of conservation of mass. State the main points of Landolts experiment for experimental evidence of the law. Matter, Simplified Chemistry Dalal Solutions ICSE Class 8.

Result : Weight of H tube + reactants = Weight of H tube + products.

Hence, total mass of reactants = total mass of products

Limitations of the law

  • Chemical energy stored up in the reactants is released in the form of heat and light.
  • Hence, mass is converted to energy and thus mass and energy are to be considered together.
  • Hence, a very slight error in the experiment was observed.