Find the % by mass of oxygen in water Two things you need to know Mass of part Mass of whole H2O 2 atoms of hydrogen 1 atom of oxygen 2 x 1.0 g/mol 1 x 16.0 g/mol 16.0 g/mol oxygen 2.0 g/mol hydrogen 2.0 g/mol + 16.0 g/mol = 18.0 g/mol for H2O 16.0 g/mol 88.9% oxygen x 100% = 18.0 g/mol Episode 702

NaHCO3 + HCl  NaCl + CO2 + H2O Lab Excerise We are going to react sodium bicarbonate with hydrochloric acid NaHCO3 + HCl  NaCl + CO2 + H2O Measure and determine the mass of CO2 produced in the reaction Determine the % carbon in the CO2 produced Determine the % carbon in the NaHCO3 used Episode 702

Find the % carbon in sodium bicarbonate (NaHCO3) Remember: (mass of element in 1 mol of compound ÷ molar mass of compound) x 100% Na 1 x 23 g/mol = 23 g/mol H 1 x 1 g/mol = 1 g/mol C 1 x 12 g/mol = 12 g/mol O 3 x 16 g/mol = 48 g/mol 84 g/mol NaHCO3 12 g/mol 14.3% carbon x 100% = 84 g/mol Episode 702

Find the % composition of aluminum oxide Write formula Al2O3 Calculate molar mass Al 2 x 27 g/mol = 54 g/mol O 3 x 16 g/mol = 48 g/mol 102 g/mol 54 g/mol x 100% = 52.9% aluminum 102 g/mol 48 g/mol 47.1% oxygen x 100% = 102 g/mol Episode 702

Empirical Formula Simplest whole number ratio of elements in a compound Example Find the empirical formula for a compound containing 56.6g K, 8.7g C, and 34.7g O Step 1: Convert each mass into moles of the element. 56.6g K 1mol K K1.45C0.73O2.17 = 1.45 mol K 39.1g K Step 2: Divide by the smallest to find a simple whole number. 8.7g C 1mol C = 0.73 mol C 12g C K2CO3 34.7gO 1mol O = 2.17 mol O 16gO Episode 702

Na2SO4 Na1.41S0.705O2.81 32.37g Na 22.64g S 44.99g O 100 g 1.41 mol Na 100 % (Hint: When % are given, assume you have 100g of the compound, and the % changes to grams.) 32.37g Na 22.64g S 44.99g O 100 g 1.41 mol Na 0.705 mol S 2.81 mol O Step 1: Convert each mass into moles of the element. Na1.41S0.705O2.81 Step 2: Divide by the smallest to find a simple whole number. Na2SO4 Episode 702

PxOy 10.15 g sample 4.433 g P Determine the grams of oxygen in the sample. 10.15g – 4.433g = 5.717g oxygen Step 1: Convert each mass into moles of the element. 4.433g P 1 mol P 5.717g O 1mol O = 0.143 mol P = 0.357 mol O 31g P 16g O P0.143O0.357 Step 2: Divide by the smallest to find a simple whole number. PO2.5 (Hint: If the ratio is still not whole numbers, multiply both subscripts by a number, such as “2” to get rid of fraction.) P2O5 Episode 702