Ch.2 - Atoms & ElementsWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
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
Additional Practice
Thomson's Cathode Ray Tube Experiment
The Chadwick Neutron Experiment
Mass Spectrometry
Additional Guides
Periodic table Charges (ignore)
Calculating Molar Mass (ignore)
Calculating Grams to Moles
LearnAdditional Practice
Next SectionAtomic Theory

"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.

Previous SectionLaw of Conservation of Mass
Next SectionAtomic Theory
Additional Problems
Drinking alcohol is also called ethyl alcohol or ethanol. Most of the ethanol produced in the USA comes from corn, an obviously natural source. It can also be made in the laboratory from natural gas (CH4) as a starting material. If you wanted to use ethanol from one of these sources, and price were not a consideration, decide which one you would choose. Which of the following laws listed below is most useful to you in making your decision?   a. The Law of Conservation of Mass b. The Law of Definite Proportions c. Dalton’s Atomic Theory d. The Law of Multiple Proportions e. Avogadro’s Hypothesis
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 contains 2.85 g of fluorine? a. 2.71 g b. 4.00 g c. 3.00 g d. 4.50 g e. 6.00 g
A substance composed of 2 or more elements in a fixed, definite proportion is consideredA) a homogeneous mixture.B) a heterogeneous mixture.C) a compound.D) a solution.E) an alloy.
Two samples of carbon tetrachloride were decomposed into their constituent elements. One sample produced 38.9 g of carbon and 448 g of chlorine, and the other sample produced 14.8 g of carbon and 134 g of chlorine. Are these results consistent with the law of definite proportions? Show why or why not. 
The mass ratio of sodium to fluorine in sodium fluoride is 1.21: 1. A sample of sodium fluoride produced 28.8 g of sodium upon decomposition. How much fluorine (in grams) was formed?
Upon decomposition, one sample of magnesium fluoride produced 1.65 kg of magnesium and 2.57 kg of fluorine. A second sample produced 1.32 kg of magnesium. How much fluorine did the second sample produce?
A 7.83-g sample of HCN is found to contain 0.290 g of H and 4.06 g of N. Find the mass of carbon in a sample of HCN with a mass of 3.37 g.
Determine the number of each type of atom in each formula: a. Ca(NO2)2
Determine the number of each type of atom in each formula: b. CuSO4
Determine the number of each type of atom in each formula: c. Al(NO3)3
A sample of ascorbic acid (vitamin C) is synthesized in the laboratory. It contains 1.50 g of carbon and 2.00 g of oxygen. Another sample of ascorbic acid isolated from citrus fruits contains 6.35 g of carbon. How many grams of oxygen does it contain? Which law are you assuming in answering this question?
How many of the indicated atoms are represented by each chemical formula: (a) carbon atoms in C2H5COOCH3
How many of the indicated atoms are represented by each chemical formula: (b) oxygen atoms in Ca(ClO4)2
How many of the indicated atoms are represented by each chemical formula: (c) hydrogen atoms in (NH4)2HPO4?
What is the ratio of oxygen atoms to hydrogen atoms in the mineral aluminite Al2(SO4)(OH)4 . 7H2O?a. 8:4b. 15:18c. 18:15d. 15:11e. 11:15
A sample of H2SO4 contains 2.02 g of hydrogen, 32.07 g of sulfur, and 64.00 g of oxygen. How many grams of sulfur and grams of oxygen are present in a second sample of H2SO4 containing 7.27 g of hydrogen?
Determine the number of each type of atom in each formula: d. Mg(HCO3)2
Two samples of sodium chloride were decomposed into their constituent elements. One sample produced 2.94 g of sodium and 4.53 g of chlorine. Which of the following could be the results of the decomposition of the other sample, being consistent with the law of constant composition (also called the law of definite proportions or law of definite composition)? a. 5.90 g of sodium and 3.54 g of chlorine b. 5.90 g of sodium and 1.47 g of chlorinec. 5.90 g of sodium and 14.8 g of chlorine d. 5.90 g of sodium and 9.09 g of chlorine
Use the law of constant composition to complete the following table summarizing the amounts of nitrogen and oxygen produced upon the sample of dinitrogen monoxide. Enter your answers numerically separated by a comma.