Verification of “Law of Conservation of mass”
A solution of sodium chloride and silver nitrate are taken separately in the two limbs of an 'H' shaped tube. The tube is sealed and weighed precisely. The two reactants are made to react by inverting the tube.
The following reaction takes place.
AgNO3(aq) + NaCl (aq) à AgCl (s) + NaNO3 (aq)
The whole tube is kept undisturbed for sometime so that the reaction is complete. When the tube is weighed again it is observed that: Weight before the reaction = Weight after the reaction
(b) The law of constant proportions which is also known as the law of definite proportions was stated by Proust as “In a chemical substance the elements are always present in definite proportions by mass”.
E.g. In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen
is always 1:8, whatever the source of water. Thus, if 9 g of water is decomposed, 1 g of hydrogen and 8 g of oxygen are always obtained.
According to Dalton’s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms. The postulates of this theory may be stated as follows:
(i) All matter is made of very tiny particles called atoms.
(ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.
(iii) Atoms of a given element are identical in mass and chemical properties.
(iv) Atoms of different elements have different masses and chemical properties.
(v) Atoms combine in the ratio of small whole numbers to form compounds.
(vi) The relative number and kinds of atoms are constant in a given compound