Mole Problems 6.022 x 1023 particles = 1 mole of something 6.022 x 1023 atoms = 1 mole of an element Example: 20.456 x 1023 atoms of carbon = __?__ moles of carbon Set up a T-chart with your starting info in the upper left hand corner: 20.456 x 1023 atoms___ 1 mole______ 6.022 x 1023 atoms = 3.4 moles carbon 1. 12.589 x 1023 atoms of hydrogen = _2.09_ moles of hydrogen 2. 50.459 atoms of lithium = _8.38 x 10-23__ moles of lithium 3. 1289 atoms of barium = _2.14 x 10-21_ moles of barium Formula Mass Example: What is the formula mass of H2O? = (H x 2) + (O) = (1.00794)(2) + (15.9994) = 18.015 grams 1. What is the formula mass of NaCl? (22.98977) + (35.453) = 58.44277 grams 2. What is the formula mass of Na2CO3? (2)(22.98977) + (12.011) + (3)(15.9994) = 105.98874 grams 3. What is the formula mass of Al2(SO4)3 = (2)(26.98154) + (3)(32.06) + (12)(15.9994) = 342.13588 grams Percent Composition Problems 1. Calculate the percent composition of the following: a. NH3 Formula mass = 17.03052 grams N: 82.24% H: 17.76% b. C6H6 Formula mass = 78.11364 grams C:92.26% H: 7.74% c. N2H4 Formula mass = 32.04516 grams N: 87.42% H: 12.58% d. P2O5 Formula mass = 141.9445 grams P: 43.64% O: 56.36% 2. Calculate the percent composition of copper (I) sulfide. Cu2S Formula Mass: 159.152 grams Cu: 79.86% S: 20.14% 3. Calculate the percent composition of sucrose, C12H22O11, and glucose, C6H12O6. Formula Mass of C12H22O11: 342.300 grams Formula Mass of C6H12O6: 180.15768 C: 42.10% H: 6.48% O: 51.52% C: 40.01% H: 6.71% O: 53.28% 4. Determine the percent of water by mass in sodium carbonate decahydrate, Na2CO3 • 10H20. Formula mass of Na2CO3 • 10H20= 286.14164 grams H20: [(20)(1.00794) + (10)(15.9994) ] /( 286.14164) x 100 = 62.96% 5. A sample of an unknown compound with a mass of 0.2370 g is extracted from the roots of a plant. Decomposition of the sample produces 0.09482 g of carbon, 0.1264 g of oxygen, and 0.0158 g of hydrogen. What is the percent composition of the compound? C: 0.09482 / 0.2370 x 100 = 40.01% O: 0.1264 / 0.2370 x 100 = 53.33% H: 0.0158 / 0.2370 x 100 = 6.67% 6. Find the percent composition of a compound that contains 2.3 g of sodium, 1.6 g of oxygen, and 0.1 g of hydrogen in a sample of 4 g of the compound. Na: 2.3 / 4 x 100 = 57.5% 1.6 / 4 x 100 = 40.0% 0.1 / 4 x 100 = 2.5% 7. A sample of an unknown compound with a mass of 0.562 g has the following percent composition. 13% carbon, 2.2% hydrogen, and 84.8% fluorine. When this compound is decomposed into its elements, what mass of each element would be recovered? C: (0.562)(0.13) = 0.07306 grams H: (0.562)(.022) = 0.012364 grams F: (0.562)(.848) = 0.476576 grams