Unit 5: Stoichiometry Moles and Molar Mass
The Mole 1 dozen = 12 eggs 1 ream = 500 sheets of paper 1 hat trick = 3 goals 1 mole = 6.022 x 1023 of something Or 602,200,000,000,000,000,000,000 Also known as “Avogadro’s number”
The Mole 1 mole of hydrogen = 6.022 x 1023 atoms 1 mole of carbon = 6.022 x 1023 atoms 1 mole of gold = 6.022 x 1023 atoms 1 mole of calcium = 6.022 x 1023 atoms See the pattern?
Understanding Check Suppose we invented a new collection unit called a “mep”. One mep contains 8 objects. A. How many paper clips in 1.0 mep? B. How many oranges in 2.0 meps? C. How many meps contain 40 gummy bears?
Molar Mass 1 mole of C atoms = 12.011 g 1 mole of Mg atoms = 24.305 g Molar mass: number of grams of one mole of an element or compound 1 mole of C atoms = 12.011 g 1 mole of Mg atoms = 24.305 g 1 mole of Cu atoms = 63.546 g What is the molar mass of the following? 1 mole of Br atoms? 1 mole of Sn atoms?
Molar Mass of Compounds We can also find the molar mass of compounds by ADDING the molar masses of each element Molar masses have units of g/mol Questions to ask yourself: 1. How many of each atom? 2. Molar mass of each element? 3. Total mass from each element? Then add them all together!
Molar Mass of Compounds Example #1 Find the molar mass of magnesium chloride, MgCl2 Questions to ask yourself: 1. How many of each atom? 2. Molar mass of each element? 3. Total mass from each element? Then add them all together!
Molar Mass of Compounds Example #2 Find the molar mass of calcium hydroxide Questions to ask yourself: 1. How many of each atom? 2. Molar mass of each element? 3. Total mass from each element? Then add them all together!
Molar Mass Practice
More Practice with Molar Mass For each of the compounds below, determine the number of atoms for each element: 1. Cu3PO4 2. Fe2(SO2)3 3. potassium phosphide Used as a quick review on Day 2
More Practice with Molar Mass For each of the compounds below, determine the molar mass of the compound: 1. MnBr2 2. Sr(NO3)2 Used as a quick review on Day 2
Calculations with Molar Mass Grams Moles
Converting Grams to Moles Aluminum is often used for the structure of light-weight bicycle frames. How many moles of Al are in 81.0 grams of Al? 81.0 grams Al = ? moles Al Use the box method! grams 81.0 g molar mass 26.982 g/mol moles down = divide
Converting Grams to Moles Practice How many moles does a 25.2 gram sample of CaCl2 contain? grams molar mass moles
Converting Moles to Grams The decomposition of hydrogen peroxide (H2O2) provides sufficient energy to launch a rocket. How many grams of H2O2 are needed for rocket launch that requires 5.00 moles H2O2? 5.00 moles H2O2 = ? g H2O2 Use the box method! grams molar mass 34.0138 g/mol moles 5.00 moles up = multiply
Converting Moles to Grams Practice Aluminum satellite dishes are resistant to corrosion because the aluminum reacts with oxygen in the air to form a coating of aluminum oxide (Al2O3). This tough, resistant coating prevents any further corrosion. What is the mass of 9.45 mol of Al2O3? grams molar mass moles