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Published byTerence Daniel Modified over 4 years ago

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Mole Concept

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Counting Units A pair refers to how many shoes? A dozen refers to how many doughnuts or eggs? How many pencils are in a gross? How many pieces of paper are in a ream? In chemistry, a counting unit called a mole is used to keep track of the number of atoms, molecules, or formula units that are in a sample of a substance.

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Mole Unit used to measure the amount of a pure substance (abbreviated mol) 1 mol = 6.022 x10 23 representative particles representative particles are the smallest piece of any pure substance Element – atoms Covalent compounds – molecules Ionic compounds - formulas units 6.022 x10 23 is known as Avogadro’s number 6.022 x10 23 can be used as a conversion factor to determine the number of particles in a substance

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Avogadro’s Number How big is Avogadro’s Number? How big is Avogadro’s Number? If you have a mole of pennies (i.e. Avogadro’s number) and divide them equally among the 6 billion people on Earth, how many dollars would each person get?

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Avogadro’s Number 6.022 X10 23 pennies $1x10 12 $1x10 12 6 x 10 9 people x 1 $ = 100 100 Each person would get ~ $ 1 trillion!!!

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Molar Mass mass (in grams) of one mole of any substance units are grams per mole (g/mol) molar mass of any element = the AAM of the element from the periodic table

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Examples: the molar mass for lithium (Li) = manganese (Mn) = silver (Ag) =

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molar mass of a molecule or formula unit – number of atoms of each element multiplied by the mass of each element Examples: H2OH2OH2OH2O Mg(OH) 2

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Mole Conversions Examples: Examples: 1.Determine the mass of 0.0450 mol of chromium. 2.How many moles are in 3.25 g of water? 3.How many particles are there in 2.6 moles of potassium nitrate? 4.How many molecules of glucose, C 6 H 12 O 6, are found in a 5.37 g sample?

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mole

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Percent Composition is the percent by mass of any element in a compound uses molar mass for elements and compounds is found by using the following formula: % of element = mass of element x 100 mass of compound mass of compound

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Example: Determine the percent composition of the elements in copper (II) nitrate.

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Empirical Formulas Empirical formula – smallest whole number mole ratio of elements in a compound Solving Empirical Formula Problems 1.Grams to moles – use the molar mass to convert the grams of each element to moles 2.Divide by small – divide the number of moles of each element by the smallest number of moles

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example… What is the formula of a compound that is comprised of 56.4g K, 8.7g C and 34.9g O?

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Empirical and Molecular Formulas Molecular formula – the actual number of atoms in a molecular compound Example: glucose molecular formula: C 6 H 12 O 6 empirical formula: C 1 H 2 O 1 ratio of the elements is the same in both formulas, just reduced in the empirical formula

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To solve molecular formula problems… Calculate the empirical formula divide empirical molar mass into the given molecular molar mass, then distribute whole number answer through empirical formula

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example problem… Find the molecular formula for a compound that is known to contain 26.7% phosphorus, 12.1% nitrogen, and 61.2% chlorine. Molecular mass of the compound is known to be 695 g/mol.

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