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Thursday, 26 May 2011

Law of Conservation of Mass

Antoino Lavoisier (Known as Father of Chemistry) in 1774 established this law, which states, “Whenever a chemical change or physical change takes place the total mass of reacting species (reactants) is exactly equal to the total mass of the products of the reaction.”

 Thus, according to this law there is no increase or decrease in total mass of matter during a chemical or a physical change. In other words, “Matter can neither be created nor destroyed.” Hence this law is also known as “Law of Indestructibility of Matter”.

Experimental Verification              

Landolt Experiment

                  Landolt verified the law by various experiments conducted by him. In one of the experiment, Landolt took two solutions (i) sodium chloride, NaCl and (ii) Silver nitrate AgNO3. Separately in the two limbs of H – shaped glass tube known as Landolt Tube. The two limbs were sealed and the tube was weighed. The tube was tilted to mix two solutions. Sodium chloride reacts with silver nitrate and precipitate of silver chloride was formed.

                        AgNO3  +  NaCl    AgCl¯  +  NaNO3

The tube was again weighed, Landolt observed that total mass remained practically constant after the reaction.

                  In all the chemical reactions, energy is evolved or absorbed which would be at the expense of change in mass. In ordinary chemical reactions, this change in mass is so small that it can not be registered on the most sensitive balance. This suggests that some matter of the reaction mixture gets converted into energy such as light, heat etc. Thus mass and energy are interconvertible. The mass is converted to energy by Einstein’s relation E = mc2.

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