Mole The mol is the SI unit for amount of a substance. The mol allows chemists to count particles by massing them. 1 mol of any substance contains the same number of particles as there are in exactly 12 g of carbon-12. The number of particles in 12 g of carbon-12 is 6.022 x 1023, this is known as Avogadro’s number. 1 mol of Cu = 6.022 x 1023 atoms 1 mol of H2O = 6.022 x 1023 molecules 1 mole of CaCl2 = 6.022 x 1023 formula units 1 mol of marbles stacked tightly together would cover the USA 70 miles deep! Molar mass Molar mass is the mass in grams per mol of a substance. Molar mass is determined by totaling of the average atomic masses of each element in its chemical formula. For example, the molar mass of sodium is 22.99 grams/mol, the molar mass of H2 equals 2.016 grams/mol (1.008 + 1.008), and the molar mass of water is 18.02 grams/mol (16.00 + 2.016, note the use of significant figures) Determine the molar mass of nitrogen (III) oxide N2O3 2(14.01) + 3(16.00) 76.02 g/mol 1 Determine the molar mass of copper (II) sulfate pentahydrate CuSO4 . 5H2O 63.55 32.06 64.00 + 5(18.02) 249.71 g/mol 2 Molar mass can be used as a conversion factor For example, the number of moles of water in 25.0 grams can be determined as follows. 25.0 g H2O x 1 mol H2O = 1.39 mol H2O 18.02 g How many grams are present in .074 mol of carbon dioxide? .074 mol CO2 x 44.01 g CO2 = 3.3 g CO2 1 mol CO2 Avogadro’s Number can be used as a conversion factor to go between atoms, formula units or molecules and moles How many molecules of water are present in .0416 mol of water? .0416 mol H2O x 6.022 x10 23 molecules H 2 O = 2.51 x 1022 molecules H2O 1 mol H 2 O How many atoms are present in 2.96 g of silver? 6.022 x10 23 atoms Ag 1 mol Ag 2.96 g Ag x x = 1.65 x1022 atoms Ag x 107.87 g Ag 1 mol Ag 3