Transcript Laws of Definite Proportions & Multiple Proportions

Laws of Definite Proportions &
Multiple Proportions
PreAP Chemistry
Law of Definite Proportion
• Put forth by Joesph Louis Proust
(1754-1816) in 1800
• States that different samples of the
same compound always contain its
constituent elements in the same
proportion by mass regardless of the
source.
• It is an intensive property.
–
–
–
–
Example CO and CO2
CO = O/C = 1/1
CO2 = O/C =2/1
CO to CO2 = 1:2
Calculation
• Mass Fraction = Mass of element
Mass of Compound
• Mass Percent = Mass of element x 100
Mass of Compound
• Mass of element in a sample =
Mass of compound x Mass of element in a sample
Mass of Compound
Law of Multiple Proportions
• Derived by John Dalton (1766-1844) in
between 1803-1807.
• States if two elements A and B
combine to form more than one
compound, the masses of B that can
combine with a given mass of A are in
a ratio of small whole numbers.
• It is an intensive property.
– Example – H2O and H2O2
Example
Compound
Mass of
Tin (Sn) in
g
Mass of
Oxygen (O)
in g
Ratio of O
mass with a
constant mass
of Sn
Tin (II) Oxide
SnO
119 g
16 g
1
Tin (IV) Oxide
SnO2
119 g
32 g
2
Difference between Laws of multiple
proportions and definite proportions
• Both laws have to do with relating to Dalton's Atomic
Theory. The only difference is that the Law of Definite
Proportions deals with elements combining to form
ONE compound in a simple whole number ratio. The
• Law of Multiple Proportions is comparing the same 2
elements that make up 2 different compounds, the
division of these 2 ratios should equal a simple whole
number ratio.
– For example: Carbon and oxygen can combine to form
carbon monoxide and carbon dioxide. If you calculated
each compounds ration of oxygen to carbon you would
get the following ratios: compound A would equal a
combining ratio of 1.34:1 (O:C). Compound B would
equal a combining ratio of 2.67:1 (O:C).
– If you divided the bigger ratio by the smaller ratio you
would have that oxygen combines with a ratio of
2.67/1.34 which would equal 1.99:1, which is close
enough to 2:1.