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 SI base 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 (atoms, molecules, 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
Molar Mass mass (in grams) of one mole of any substance is based on the mass of a carbon atom (12.01 amu) 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 C 6 H 12 O 6
Using Molar Mass in Conversions Example: Determine the mass of 0.0450 mol of chromium. Example: Determine the mass of 0.0450 mol of chromium.
Example: 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?
Example 2- Determine the empirical formula for methyl acetate, which is known to have the following percent composition: 48.64% carbon, 8.16% hydrogen, and 43.20% oxygen.
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… Succinic acid is a substance produced by lichens. Chemical analysis indicates that it is composed of 40.68% C, 5.08% H, and 54.24% oxygen and has a molar mass of 118.1g/mol. What is the molecular formula?