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The Mole Essential Question To what extent is it advantageous to look at chemical composition in terms of moles instead of mass? How do we measure matter? Mass o Buy potatoes by the kilogram, pound, gram, or ounce Volume o Gasoline – gallon, liter o Liquid medicine – milliliter Count o Soda – 6, 12, 24, or 36 packs Sometimes we use specific words to mean a certain amount o Pair – 2 o Dozen – 12 Conversion factors o We use conversion factors everyday Example – 1 dozen = 12 eggs this can be set-up like this to be used as a conversion factor. The format you use depends on how you are using the conversion factor. Example 2 – Apples Example Problem, if 0.20 bushel is 1 dozen apples and a dozen apples has a mass of 2.0 kg, what is the mass of 0.50 bushel of apples? Assume 2.0 kg of apples is 1 dozen and that each apple has 8 seeds. How many apple seeds are in 14kg of apples? Mole – 6.02 x 1023 representative particles of a substance Avogadro’s number (SI unit for measuring the amount of a substance) What is a representative particle? Ionic compound – formula unit Molecular compound (covalently bonded) – molecule Ion – ion example Ca+2 Element – atom 1 mole of any substance contains Avogadro’s number of representative particles Converting # of particles to moles What is the conversion factor? Example problem 1: Magnesium is a light metal used in the manufacture of aircraft, automobile wheels, tools, and garden furniture. How many moles of magnesium is 1.25 x 1023 atoms of magnesium? Example Problem 2: How many moles of 2.17 x 1023 representative particles of bromine? Converting moles to number of particles What is the conversion factor? Example problem 3: Propane is a gas used for cooking and heating. How many atoms are in 2.12 mol of propane (C3H8)? Example Problem 1 Answer: Example Problem 2 Answer: Example Problem 3 Answer: Molar Mass Element On the periodic table the atomic mass of an element is reported in amu. (atomic mass units). Relative to the mass of C-12. o Why are these not whole numbers? Since we cannot use units of amu in the lab, this scale has been converted to masses measured in grams. The mass of an element is expressed in grams/mole. The mass is the number of grams of 1 mole of that element. Molar mass Molar mass of a compound (Also can be called gram formula mass, gram atomic mass, gram molecular mass, molecular weight) You need: The formula of the compound Atomic numbers of the elements in the compound Must account for the number of atoms of each element Example 4: The decomposition of hydrogen peroxide (H2O2) provides sufficient energy to launch a rocket. What is the molar mass of hydrogen peroxide? Molecular formula: H2O2 H = 1.01 g/mol O = 15.99 g/mol (1.01 g/mol x 2) + (15.99g/mol x 2) = 34.00 g/mol or 2.02 g H + 31.98 g O = 34.00 g/mol