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Lecture 6

Lecture 6. Nomenclature Chapter 9 24-September Suggested HW 9.1, 9.5, 9.7, 9.11, 9.15, 9.17, 9.25, 9.29, 9.35, 9.39, 9.43, 9.51, 9.55, 9.57, 9.67, 9.69, 9.71, 9.73, 9.75, 9.79, 9.89, 9.95, 9.99, 9.101, 9.105, 9.109, 9.113, 9.115, 9.117, 9.119, 9.123, 9.127, 9.137, 9.139a.

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Lecture 6

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  1. Lecture 6 Nomenclature Chapter 9 24-September Suggested HW 9.1, 9.5, 9.7, 9.11, 9.15, 9.17, 9.25, 9.29, 9.35, 9.39, 9.43, 9.51, 9.55, 9.57, 9.67, 9.69, 9.71, 9.73, 9.75, 9.79, 9.89, 9.95, 9.99, 9.101, 9.105, 9.109, 9.113, 9.115, 9.117, 9.119, 9.123, 9.127, 9.137, 9.139a

  2. Law of Definite Proportions Compounds Combinations of two or more elements connected through ionic or covalent bonds Cannot be broken down by physical means, but the atoms can be separated by chemical processes Definite and constant elemental composition Law of Definite Proportions In a pure compound, the elements are ALWAYS present in the same definite proportion by mass How much Blue if we have a sample that is 8 g red? 2g blue 4g red Mass Percent = Mass of blue in compound Total mass of compound

  3. Law of Definite Proportions

  4. Law of Definite Proportions

  5. Formula Mass Sum of atomic masses of all atoms present in one formula unit of a substance, expressed in atomic mass units cobalt 27 Co 58.933 Calculate the formula mass of: CH4 NH4+ NH4(OH) Riboflavin  C17H20N4O6

  6. The mole and Avogadro's Number The mass of 1 atom is WAY too small to be useful on a regular basis Avogadro’s Number (NA) 1 mol = 6.022 x 1023 units How many atoms are present in 0.05 moles of CH4? How many moles is 1 x 106 atoms of CH4

  7. The mole and Formula Mass So why is this useful to chemists? Argon 18 Ar 39.95 Formula mass = g mol-1 The mass of 1 Argon atom is 39.95 amu 1 mole of Argon atoms = 39.95 g How many moles of Ar are present in 25 g? Conversion factor! How many Aratoms are present in 25 g?

  8. Molar Mass Molar Mass = Formula Mass For a given molecule, the molar mass is the sum of atoms involved CH4 NH4+ NH4(OH) Riboflavin  C17H20N4O6

  9. The Mole and Chemical Formulas How many moles of Oxygen in 1 mole of: CO CO2 CO32- Na2CO3

  10. Summary of Mole Calculations Molar Mass Avogadro’s Number Number of molecules Moles of the molecule Mass of the molecule Mass Percent Formula Subscript Formula Subscript Molar Mass Avogadro’s Number Moles of Atoms In a Compound Number of atoms Mass of the atom

  11. Some Sample Problems You measure 10 g of sodium in a sample of Na2CO3. How many moles of oxygen are present?

  12. Sample Problems What is the mass of Silicon (in grams) in: 4.444 x 1023 atoms of Si 1764 molecules of SiH4

  13. Sample Purity For every 100 g of a sample, only 72 g is K2SO4 If a 63 g sample of K2SO4 is 72% pure: How much of the sample is not K2SO4? How many moles of oxygen are present in the pure K2SO4?

  14. Empirical Formulas Chemical formulas that gives lowest whole number ratio of atoms Molecular Formula Empirical Formula C2H6 C2H6O C2H6O4 C10H30O16 C10H30O17 C1.67H2 C0.5H1O0.5 C0.25Cl1 C2.33H1.67O

  15. Determining Empirical Formulas Freon is 9.933% carbon 58.63% chlorine 31.44% fluorine What is the Empirical Formula of Freon? Assume 100g of freon Determine the moles of each element Divide all by the lowest number of moles Multiply each number by an integer to get all to whole numbers

  16. Determining Empirical Formulas A compoundis 26.85% potassium 35.35% chromium 38.06% oxygen What is the Empirical Formula

  17. Determining Molecular Formulas You determined the empirical formulaof a compound to be C2HCl. This compound has a molecular formula 181.44 amu. What is the molecular formula? You determined the empirical of a compound to be SNCl2. This compound has a molecular formula 350.94 amu. What is the molecular formula?

  18. Empirical and Molecular Formulas Molar Mass Whole Number Ratio Molecular Formula Empirical Formula Moles of each Element Mass Percentages or Actual Masses Combustion Analysis

  19. Combustion Reactions Combustion reactions occur when compounds react with O2 to produce CO2 and H2O (and sometimes another biproduct) CH4 + O2 CO2 + H2O If 18.032 g of methane is combusted, how much CO2 is produced? How much H2O is produced?

  20. Combustion Reactions If a combustion reaction produces 0.294 g of CO2 and 0.120 g of H2O, what is the empirical formula of the hydrocarbon? CxHy + O2 CO2 + H2O

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