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CHEM 1127Q (29)
Chapter 3

CHEM 1127Q Chapter 3: Pre-lecture 3: Chapter 3

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University of Connecticut
CHEM 1127Q
Joseph De Pasquale

3 Composition of Substances and Solutions 3.1 Formula Mass and the Mole Concept Formula mass the sum of the average atomic masses of all the atoms represented in the substances formula Formula Mass for Covalent Substances Formula massmolecular mass represents the numbers and types of atoms composing a single molecule of the substance Average molecular mass the sum of the average atomic masses of these atoms Formula Mass for Ionic Compounds Similar to formula mass of covalent substances average masses of neutral sodium and chlorine atoms were used in this computation, rather than the masses for sodium cations and chlorine anions But its ok The Mole Mole defined as the amount of substance containing the same number of discrete entities units like pair, dozen, gross, etc Avogadros number (NA) 6.02214179 1023 Per mole 6.022 1023mol molar mass of an element (or compound) is the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (gmol) 1 mole of any element contains the same number of atoms as 1 mole of any other element masses of 1 mole of different elements are different atomic mass and molar mass are numerically equivalent 3.2 Determining Empirical and Molecular Formulas How to derive the chemical formulas of unknown substances from experimental mass measurements Percent Composition Percent composition the percentage by mass of each element in the compound Can determine percent composition from formula mass Determination of Empirical Formulas sample of compound determined to contain 1.71 g C and 0.287 g H 1. Deriving the number of moles of each element from its mass
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