Presentation on theme: "Mole Concept. 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."— Presentation transcript:
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.
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
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?
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!!!
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
Examples: the molar mass for lithium (Li) = manganese (Mn) = silver (Ag) =
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
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?
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
Example: Determine the percent composition of the elements in copper (II) nitrate.
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
example… What is the formula of a compound that is comprised of 56.4g K, 8.7g C and 34.9g O?
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
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
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.