Textbook Question
Disilane, Si2Hx, is analyzed and found to contain 90.28% silicon by mass. What is the value of x?
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Ch.3 - Mass Relationships in Chemical Reactions
McMurry8th EditionChemistryISBN: 9781292336145
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Table of contents
- Ch.1 - Chemical Tools: Experimentation & Measurement170
- Ch.2 - Atoms, Molecules & Ions160
- Ch.3 - Mass Relationships in Chemical Reactions169
- Ch.4 - Reactions in Aqueous Solution199
- Ch.5 - Periodicity & Electronic Structure of Atoms102
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory92
- Ch.7 - Covalent Bonding and Electron-Dot Structures61
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure59
- Ch.9 - Thermochemistry: Chemical Energy122
- Ch.10 - Gases: Their Properties & Behavior155
- Ch.11 - Liquids & Phase Changes54
- Ch.12 - Solids and Solid-State Materials73
- Ch.13 - Solutions & Their Properties120
- Ch.14 - Chemical Kinetics98
- Ch.15 - Chemical Equilibrium125
- Ch.16 - Aqueous Equilibria: Acids & Bases110
- Ch.17 - Applications of Aqueous Equilibria147
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium86
- Ch.19 - Electrochemistry154
- Ch.20 - Nuclear Chemistry96
- Ch.21 - Transition Elements and Coordination Chemistry156
- Ch.22 - The Main Group Elements187
- Ch.23 - Organic and Biological Chemistry51
Chapter 3, Problem 101
The stimulant amphetamine contains only carbon, hydrogen, and nitrogen. Combustion analysis of a 42.92 mg sample of amphetamine gives 37.187 mg of H2O and 125.75 mg of CO2. If the molar mass of amphetamine is less than 160 g/mol, what is its molecular formula?
Verified step by step guidance1
Calculate the moles of carbon in CO2 by using the molar mass of CO2 and the mass of CO2 produced.
Calculate the moles of hydrogen in H2O by using the molar mass of H2O and the mass of H2O produced.
Determine the mass of carbon and hydrogen in the sample using their respective moles and atomic masses.
Subtract the mass of carbon and hydrogen from the total mass of the sample to find the mass of nitrogen.
Convert the masses of carbon, hydrogen, and nitrogen to moles, find the simplest whole number ratio, and use the molar mass to determine the molecular formula.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Combustion Analysis
Combustion analysis is a technique used to determine the elemental composition of organic compounds. In this process, a sample is burned in excess oxygen, producing carbon dioxide and water. The masses of these products are measured, allowing for the calculation of the amounts of carbon, hydrogen, and other elements in the original sample.
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01:29
Combustion of Non-Hydrocarbons
Empirical Formula
The empirical formula represents the simplest whole-number ratio of the elements in a compound. To derive it, the moles of each element are calculated from the mass of the products obtained in combustion analysis. This formula provides essential information about the composition of the compound, which is a stepping stone to determining the molecular formula.
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02:26Empirical vs Molecular Formula
Molecular Formula
The molecular formula indicates the actual number of atoms of each element in a molecule of a compound. It can be derived from the empirical formula by multiplying it by a whole number, which is determined by the molar mass of the compound. In this case, knowing that the molar mass of amphetamine is less than 160 g/mol helps in identifying the correct molecular formula based on the empirical formula.
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02:08Determining Molecular Formulas
Related Practice
Textbook Question
A certain metal sulfide, MS2, is used extensively as a high-temperature lubricant. If MS2 is 40.06% sulfur by mass, what is the identity of the metal M?
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Textbook Question
Combustion analysis of a 31.472 mg sample of the widely used flame retardant Decabrom gave 1.444 mg of CO2. Is the molecular formula of Decabrom C12Br10 or C12Br10O?
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Textbook Question
Heating elemental cesium and platinum together for two days at 973 K gives a dark red ionic compound that is 57.67% Cs and 42.33% Pt. (a) What is the empirical formula of the compound?
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