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Christopher O. Oriakhi

Print publication date: 2009

Print ISBN-13: 9780195367997

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195367997.001.0001

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Measuring Chemical Quantities: the Mole

Chapter:
5 (p.45) Measuring Chemical Quantities: the Mole
Source:
Chemistry in Quantitative Language
Publisher:
Oxford University Press
DOI:10.1093/oso/9780195367997.003.0009

A mole is defined as the amount of a given substance that contains the same number of atoms, molecules, or formula units as there are atoms in 12 g of carbon-12. For example, one mole of glucose contains the same number of glucose molecules as there are carbon atoms in 12 g of carbon-12. The number of atoms in exactly 12 g of carbon-12 has been determined to be 6.02×1023. This number, 6.02×1023, is called Avogadro’s number (NA). Therefore, a mole is the amount of a substance that contains Avogadro’s number of atoms, ions, molecules, or particles. For example: 1 mol He atoms = 6.02×1023 atoms 1 mol CH3 OH molecules = 6.02×1023 molecules 1 mol SO2−4 ions = 6.02×1023 ions The term molar mass is now commonly used as a general term for both formula mass and molecular mass. The molar mass of any substance is the mass in grams of one mole of the substance, and it is numerically equal to its formula mass (expressed in amu). For example, the formula mass of glucose, C6H12O6, is 180.0 amu. So the molar mass or the mass in grams of 1 mol of glucose is 180.0 g. In terms of chemical arithmetic, the mole is the most important number in chemistry. It provides useful stoichiometric information about reactants and products in any given chemical reaction. The quantities commonly encountered in chemical problems include the number of moles of a substance; the number of atoms, molecules, or formula units of a substance; and the mass in grams. These quantities are related and can be readily interconverted with the aid of the molar mass and Avogadro’s number. Calculations based on the mole can be carried out by using conversion factors, or with simple equations based on the conversion factor.

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