Law of constant proportions
The law of constant proportions states that the elements in a certain chemical compound always occur in the same mass ratio . The mass ratio in sodium chloride, for example, is always 39% sodium to 61% chlorine .
This rule, established by Joseph-Louis Proust in 1797 and called Proust's law after him, is the starting point for the development of stoichiometry . John Dalton extended it to the law of multiple proportions .
These observations made by Proust and others were an essential step in Dalton's development of the atomic hypothesis . It is the easiest way to explain the constant mass ratio of the elements in sodium chloride: Sodium chloride is made up of the same number of sodium and chlorine particles . A chlorine particle is half the weight of a sodium particle. Other examples would be copper (I) sulfide {mass ratio m (Cu): m (S) about 4: 1, molar ratio n (Cu): n (S) = 2: 1; a copper particle is twice as massive as a sulfur particle) or sulfuric acid (with n (H): n (S): n (O) = 2: 1: 4, see figure and - in contrast to the difference in mass and quantity - below the order of magnitude (Amount of substance) }.
See also
literature
- Entry on Proust's law. In: Römpp Online . Georg Thieme Verlag, accessed on June 14, 2014.