CHE 101 Lecture Outline Chapter 3 Chapter 3 Stoichiometry Chemical Conversions w formulas equations Material to Learn on Your Own I do not have time to cover Sections 3 1 3 3 in lecture A Pre recorded lecture is located on UB Learns located Gulde Folder PreRecorded Folder Chapter03 Weights of Compounds Gulde Folder PreRecorded Folder Chapter03 Balancing Equations You MUST watch the BOTH prior to your next lecture Turn to Page 5 Chemical Conversion Factors of lecture Notes Weights Formula weight FW of atomic weights of in a chemical formula Unit Can also be called MW if dealing w a molecule FW or MW of Atoms AW What is the MW of 1 H2O molecule Use on Periodic Table Can round answer to Exact or Inexact 1 CHE 101 Lecture Outline Chapter 3 Percent composition Experiment 2 Percent composition contributed by each element in a substance Or each substance in a mixture Composition atoms of element element AW x 100 FW Useful for verifying of a sample B c of elements for a specific compound change What is the percent composition of nitrogen in caffeine C8H10N4O2 2 CHE 101 Lecture Outline Chapter 3 Chemical Reactions and Equations Chemical reactions rxns when chemicals are into new chemicals Chemical equations representation of a chemical rxn Reactants chemical s Products chemical s Phase of matter Law of Conservation of matter matter is neither created nor destroyed only of elements on both sides of a rxn Such equations are said to be 3 CHE 101 Lecture Outline Chapter 3 ALWAYS use to balance equations 4 CHE 101 Lecture Outline Chapter 3 How to Write a Balanced Equation 1 Write correct chemical If an or compound use IONS ion written first 2 Balance each element by adjusting Smallest numbers are preferred no Smallest is desired coefficients Sample Problems 1 Write a balanced equation w phases for when aqueous lead II nitrate reacts with aqueous potassium chloride to produce solid lead II chloride and a solution of potassium nitrate Can keep together when balancing 2 Balance the equation for when liquid phosphorus pentachloride reacts with water to produce hydrochloric acid and phosphoric acid PCl5 l H2O l HCl aq H3PO4 aq 5 CHE 101 Lecture Outline Chapter 3 6 CHE 101 Lecture Outline Chapter 3 Chemical Conversion Factors Most common chemical Conversion Factors 1 Formula ratio 2 Avogadro s 3 Molar mass Remember Never start a calculation w a conversion factor ALL calculations MUST have the chemical formula as part of the unit 1 Ratio Conversion Factor Ratio describes the of atoms or ions in 1 molecule Ex Mg OH 2 1 molecule Mg OH 2 1 Mg atoms 1 molecule Mg OH 2 2 O atoms 1 molecule Mg OH 2 2 H atoms 1 molecule Mg OH 2 1 Mg2 ions 1 molecule Mg OH 2 2 OH ions Exact or inexact exact Sample Problem Sodium phosphate Na3PO4 is used to control the pH of processed foods Calculate the number of molecules present if you have 1 20x1024 sodium ions Look at notes 7 CHE 101 Lecture Outline Chapter 3 2 Avogadro s Number the Mole Convenient to have a word for describing a large fixed numbers of objects 1 dozen 12 1 gross 144 Mole mol of objects in exactly 12 grams of 12 C 1 mol 6 022x10 23 Avogadro s Exact or inexact Exact 1 mole of anything always has 6 022x1023 objects 1 mol baseballs 6 022x1023 baseballs 1 mol Cu 6 022x1023 Cu 1 mol H2 6 022x1023 H2 How to know what your object is Depends on the chemical If have an element ie Cu S Hg object atom If have a compound ie H2 object molecule Diatomics Molecular Ionics or Acids 8 CHE 101 Lecture Outline Chapter 3 Sample Problem How many molecules of diphosphorus pentoxideare are there in 4 58 moles of diphosphorus pentoxide See notes in notebook The mole refers to the same number of objects 1 mole 6 022x10 23 atoms or molecules Same of objects doesn t mean the weights are the same 12 Golf balls weighs 12 baseballs But weight of 12 golf balls should weight of 2nd set of 12 golf balls 9 CHE 101 Lecture Outline Chapter 3 The mole also refers to a specific mass for a specific substance called Molar Mass 10 CHE 101 Lecture Outline Chapter 3 3 Molar Mass Molar mass Mm mass in grams of 1 mole of a chemical Unit grams mole Calculate the same way as FW or MW Mm of H2O look at notes in notebook Exact or Inexact Inexact Sample Problem Calculate how many grams are in 0 2923 mols of Al2 SO4 3 a substance used to purify drinking water Look at notes In notebook SUMMARY of Conversion Factors MOLES ARE the STAR of the show 11 CHE 101 Lecture Outline Chapter 3 Sample Problems 1 Corundum is a naturally occurring form of aluminum oxide but the presence of impurities creates gemstones Cr atoms create rubies and Fe atoms create sapphires Calculate the number of aluminum atoms in 7 61g of pure aluminum oxide Look at notes in notebook 2 If a sample of aluminum foil has 1 20x1024 aluminum atoms calculate how many grams of pure aluminum are present Look at notes in notebook 12 CHE 101 Lecture Outline Chapter 3 13 CHE 101 Lecture Outline Chapter 3 Determining Empirical Molecular Formulas Molecular Formula MF actual formula Empirical Formula EF smallest mole ratio Benzene and Acetylene Molecular formula MF C6H6 C2H2 Empirical formula EF CH CH 1 Difference factor x 6 or 2 C6H6 x x C2H2 x x NOTE MF EF masses differ by x factor Benzene 78 11g mol 13 02g mol x x 6 Acetylene 26 04g mol 13 02g mol x x 2 Must find Empirical before Molecular Get moles of each element If have mass 100g sample Ex If have 51 7 C then you would have 51 7 g C 2 Determine Empirical Formula EF Find smallest mole ratio divide by smallest of moles No decimals May need to multiply each element by an integer to obtain a whole 3 Calculate Molecular Formula MF Use Mm to determine difference factor x 14 CHE 101 Lecture Outline Chapter 3 Sample Problems 1 A 2 50g unknown sample has 2 33g of copper and the remainder is nitrogen What is the empirical formula Look at notes in Notebook 2 Ascorbic acid Vitamin C contains 40 9 C 4 60 H and 54 5 O Determine the empirical molecular formula provided the molar mass of ascorbic acid is 175g mol Look at notes in notebook 15 Molecular formula CHE 101 Lecture Outline Chapter 3 Types of Reactions Many reactions have characteristics in common 5 Basic types 1 Combination 2 Decomposition 3 Combustion 4 Single Replacement 5 Double Replacement 1 Combination Rxn Combination 2 or more reactants form 1 product Also known as synthesis rxn Assume reactants are in their natural state Sample Problem Write the balanced reaction for the combination of solid aluminum and fluorine gas Al s F2 g Al3 F 2Al s 3F2 g