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# Law of Definite Proportions

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Sections
The Atom
Subatomic Particles
Isotopes
Ions
Atomic Mass
Periodic Table: Classifications
Periodic Table: Group Names
Periodic Table: Representative Elements & Transition Metals
Periodic Table: Element Symbols
Periodic Table: Elemental Forms
Periodic Table: Phases
Periodic Table: Charges
Calculating Molar Mass
Mole Concept
Law of Conservation of Mass
Law of Definite Proportions
Atomic Theory
Law of Multiple Proportions
Millikan Oil Drop Experiment
Rutherford Gold Foil Experiment

"Different samples of a pure chemical compound always contain the same proportions of elements by mass."

###### Proust's Law of Definite Proportions

Concept #1: Law of Definite Proportions

Example #1: Two unknown compounds are examined. Compound A contains 2.0 grams of hydrogen and 32.0 grams of oxygen. Compound B contains 15.0 grams of hydrogen and 120.0 grams of oxygen. Do Compounds A and B represent the same compound?

Example #2: A compound contains only calcium and fluorine. A sample of the compound is determined to contain 2.00 g of calcium and 1.90 g of fluorine. According to the Law of Definite Proportions, how much calcium should another sample of this compound contain if it possesses 2.85 g of fluorine?

Practice: A 7.74 g sample of HCN is found to contain 0.287 g of H and 4.01 g N. Find the mass of carbon in a sample of HCN with a mass of 3.43 g.