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Exploration Sum: The Mole: Conversions, Mass Determination

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Exploration Sum: The Mole: Conversions, Mass Determination, & Exploration Sum: The Mole: Conversions, Mass Determination, & Hydrates This Exploration contains targeted background content to prepare... you for performing the exercises in this lesson. Learning Objectives Define the concept of a mole. Distinguish between the terms: atomic mass, molecular mass, and molar mass. Convert between mass, moles, atoms, and molecules. Define and name hydrates by the number of moles of water held in a compound. Explore The Mole A single atom or a single molecule is so small that chemists are seldom able to work with one at a time. Even when weighing the smallest quantities of substances, numerous atoms and molecules are present. A unit of measure called a mole is used to combat this problem, allowing for successful work with defined quantities of atoms and molecules. *****A mole (n) is a unit of measure, describing the amount of a chemical substance that contains as many atoms, molecules, or formula units as there are in exactly 12 grams of pure carbon (12C). This amount of particles (6.022 × 1023) is referred to as Avogadro’s number. *****The atomic masses shown on the periodic table are the average masses of the various isotopes of each element, expressed in atomic mass units, or amu. The atomic mass unit was standardized to be equal to exactly 1/12th the mass of one carbon-12 (12C) atom; thus, one 12C atom has a mass of 12.000 amu. However, carbon has three isotopes (12C, 13C, and 14C) that contain six protons each, but the isotopes vary in the number of neutrons. The different number of neutrons leads to variation in the amu of each isotope. Since natural carbon (C) is composed of some of each isotope, it has an average atomic mass of 12.011 amu, as shown on the periodic table in Figure 1.Figure 1. Periodic Table of Elements.******The atomic mass (atomic weight) of an element is equal to the mass in grams required to equal 1 mole of the substance. Because atomic mass units and the mole are defined from the same reference (carbon-12), the value on the periodic table can represent the mass of a single atom in atomic mass units or the mass of a mole of substance in grams. Thus, the atomic mass units shown on a periodic table are numerically equivalent to the ****** molar masses of the elements or the mass in grams of each element that contains one mole of atoms of that element. For example, the element nitrogen has a molar mass of 14.007 grams, thus 1 mole of nitrogen is equal to 14.007 grams. Likewise, the compound H2O has a molar mass of 18.015 (H + H + O = 1.008 + 1.008 + 15.999), thus 1 mole of H2O is equal to 18.015 grams. The mass of one mole of a substance (molar mass) is equal to either its atomic mass expressed in grams (if it is a monoatomic element) or its ******molecular mass expressed in grams (if it is a diatomic element or compound). [Show More]

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