Concepts of Molecular Weight, Moles and Empirical Formula | CHM 115, Study notes of Chemistry

Download Concepts of Molecular Weight, Moles and Empirical Formula | CHM 115 and more Study notes Chemistry in PDF only on Docsity! Important Concepts in Chapter 3 1) How to calculate molecular weights for compounds 2) How to convert between grams, moles, and # of atoms 3) How to convert a chemical analysis to an empirical formula 4) For a balanced chemical reaction, what is the limiting reagent and theoretical yield But why is this important? Automobile Air Bags ____ NaN3(s) à ____ Na(s) + ____ N2(g) Molecular Weight and Formula Weight (Section 3.1) Molecular Weight (MW) – Units: amu Formula Weight (FW) – Units: amu What is the molecular weight of P4O10? What is the formula weight of Fe2(SO4)3? mol g mole grams or mole mass MassMolar = Molar Mass Molar Mass (MM) – mass (in grams) of one mole of a substance Units: For all substances, the molar mass (g/mol) is equal to the formula weight in atomic mass units (amu) Formula Weight of Fe2(SO4)3 = 399.880 amu Molar Mass of Fe2(SO4)3 = 399.880 g/mol 1 mole of Fe2(SO4)3 = 399.880 g Fe2(SO4)3 Mole Calculations What is the mass of 5.0 mol Cu? How many moles of PbCrO4 (MM = 323 g/mol) are there in 98.5 g of PbCrO4? The molar mass of aspirin is 180.2 g/mol. How many aspirin molecules are present in one 250-mg tablet? grams moles # of atoms, molecules, … Percent Composition (Section 3.3) Percentage composition – Mass percentage – Example: Calculate the mass percentages (to 3 Sig Figs) of the elements (N, H, and O) in ammonium nitrate, NH4NO3. %100 whole theof mass wholein theA of mass A % Mass ×= Empirical Formula and Molecular Formula – Cont. Problem 3.65. Putrescine is a substance produced by decaying animals. It has an empirical formula of C2H6N. The molecular weight of putrescine is approximately 90 amu. What is the molecular formula for putrescine? Empirical Formula and Molecular Formula – Cont. An elemental analysis of an unknown compound shows that it contains 44.9% K, 18.4% S, and 36.7% O. What is its empirical formula? What is the molecular formula of this unknown compound if the molar mass was experimentally determined to be approximately 175 g/mol? Important Concepts in Chapter 3 1) How to calculate molecular weights for compounds 2) How to convert between grams, moles, and # of atoms 3) How to convert a chemical analysis to an empirical formula 4) For a balanced chemical reaction, what is the limiting reagent and theoretical yield But why is this important? Automobile Air Bags ____ NaN3(s) à ____ Na(s) + ____ N2(g) Molecular Weight and Formula Weight (Section 3.1) Molecular Weight (MW) – Units: amu Formula Weight (FW) – Units: amu What is the molecular weight of P4O10? What is the formula weight of Fe2(SO4)3? mol g mole grams or mole mass MassMolar = Molar Mass Molar Mass (MM) – mass (in grams) of one mole of a substance Units: For all substances, the molar mass (g/mol) is equal to the formula weight in atomic mass units (amu) Formula Weight of Fe2(SO4)3 = 399.880 amu Molar Mass of Fe2(SO4)3 = 399.880 g/mol 1 mole of Fe2(SO4)3 = 399.880 g Fe2(SO4)3 Mole Calculations What is the mass of 5.0 mol Cu? How many moles of PbCrO4 (MM = 323 g/mol) are there in 98.5 g of PbCrO4? The molar mass of aspirin is 180.2 g/mol. How many aspirin molecules are present in one 250-mg tablet? grams moles # of atoms, molecules, … Percent Composition (Section 3.3) Percentage composition – Mass percentage – Example: Calculate the mass percentages (to 3 Sig Figs) of the elements (N, H, and O) in ammonium nitrate, NH4NO3. %100 whole theof mass wholein theA of mass A % Mass ×= Empirical Formula and Molecular Formula – Cont. Problem 3.65. Putrescine is a substance produced by decaying animals. It has an empirical formula of C2H6N. The molecular weight of putrescine is approximately 90 amu. What is the molecular formula for putrescine? Empirical Formula and Molecular Formula – Cont. An elemental analysis of an unknown compound shows that it contains 44.9% K, 18.4% S, and 36.7% O. What is its empirical formula? What is the molecular formula of this unknown compound if the molar mass was experimentally determined to be approximately 175 g/mol? Empirical Formula and Molecular Formula – Cont. Elemental analysis shows an unknown carbohydrate contains 20.0 g carbon, 3.36 g hydrogen, and 26.7 g oxygen. What is the empirical formula for this unknown carbohydrate? What is the molecular formula of this unknown carbohydrate if the molar mass was experimentally determined to be approximately 178 g/mol?