Chapter 11 Notes The Mole I. Measuring Matter A. Counting particles 1. Large numbers are easier to count as groups (dozen roses, ream of paper, pair of shoes) 2. Moles (mol) are used to measure the amount of a substance a. 6.02 X 10 23 particles represents one mole (This is Avogadro’s number) b. Avogadro’s number is a large number that conveys the number of atoms, molecules, or formula units

B. Converting moles to particles 1. Can determine the number of particles present in one mole of a substance 2. Uses the conversion factor of 6.02 X 10 ANSWERS!

23 particles = 1 mole 1 mole 6.02 X 10 23 particles 3. Allows number of moles or number of particles to be determined as you can flip the conversion factor 4. YOU MUST CANCEL UNITS TO OBTAIN CORRECT

II. Mass and the Mole A. Different objects have different masses per unit (dozen eggs vs. a dozen sodas) B. Mass and the mole 1. Masses of elements are in atomic mass units (amu) 2. Mass in grams of one mole of any pure substance is the molar mass a. Has the units of g/mol b. Copper has a molar mass of 63.546 g/mol c. If a sample of 63.546 g is measured it has 6.02 X 10 to grams 23 atoms d. Molar mass can be used to convert from moles 63.546 g Cu OR 1 mole 1 mole 63.546 g Cu

D. Converting mass to atoms 1. Involves Avogadro’s number and molar mass 2. Must use two step conversions to obtain the desired value 3. Mass must always be converted to moles before being converted to any other unit III. Moles of Compounds A. Chemical formulas represent the atoms and the amounts of each type of atom B. A mole of a compound contains Avogadro’s number of molecules regardless of the number of atoms involved 1. 1 mole of H 2 O and C 6 H 12 O 6 both have 6.02 X 10 23 molecules a. 1 mole of H oxygen 2 O has two moles of hydrogen atoms and one mole of oxygen atoms b. 1 mole of glucose has six moles of carbon, twelve moles of hydrogen, and six moles of c. These known quantities can be used in conversion factors

2. Molar mass of a compound can be calculated by knowing the number of moles and multiplying it by the molar mass. Then all masses for each atom is added for the molar mass of the compound 3. Converting moles of a compound to mass a. Same process as with an atom b. Must use molar mass of the compound c. Can use the reverse conversion factor for converting mass to moles 4. Converting mass to particles a. Mass must first be converted to moles using the compound’s molar mass b. Moles are then converted to particles using Avogadro’s number

IV. Empirical and molecular formulas A. Percent composition is the ratio of an element compared to the total compound 1. This comparison is based on mass 2. All that is needed is a chemical formula 3. Use the mass of the given element and divide by the total mass of the compound B. Empirical formulas 1. The formula with the smallest whole-number mole ratio of elements 2. May or may not be the molecular formula 3. Molecular formulas are simple multiples of empirical formulas 4. Percent composition can allow empirical formulas to be determined a. If given percentages, the assumption of 100 grams of the compound must be made b. Percent of the element is equal to the mass it has in 100 grams

C. Molecular formulas 1. Actual number of atoms of each element in one molecule/formula unit 2. May have the same empirical formula or percent composition of other molecules/formula units 3. Properties of each will be different 4. Can be calculated by dividing the determined molar mass of the compound and dividing by the mass of the empirical formula 5. This number will give the number each subscript must be multiplied by for the molecular formula