Ch 4 Stoichiometry Quantitative Information about Chemical Reactions 4 1 Mass Relationships in Chemical Reactions Stoichiometry A balanced chemical equation shows the quantitative relationship between reactants and products in a chemical reaction Mass of reactant mass of products because of the Law of Conservation of Mass of atoms of reactant of atoms of products 1 H2 O2 H2O balance 2 2H2 O2 2H2O 2 3 moles of H2 produce how many moles of water O2 is in excess I want to produce 5 0 moles of H2O how many moles of O2 do I have to start with 3 Clicker Q Given this balanced chemical reaction 3 PbF2 2 PCl3 2 PF3 3 PbCl2 How many moles of PF3 can be made from the reaction of 4 5 moles of PbF2 with excess PCl3 4 In order to solve stoichiometry problems one must go through moles using molar masses and mole ratios as conversion factors One cannot do this without writing a balanced chemical equation first grams moles moles grams Using molar mass Using mole ratios Using molar mass 5 Given this balanced chemical reaction Ca OH 2 2 HCl CaCl2 2 H2O If 37 0 g of Ca OH 2 74 0 g mol are reacted with excess HCl how many grams of H2O can be formed 6 What mass of carbon dioxide can be produced by the reaction of 0 540 mole of iron III oxide with excess carbon monoxide Fe 2 O 3 3 CO 2 Fe 3 CO 2 Clicker Q What is the formula weight for CO2 Clicker Q Mass of CO2 produced 7 What mass of CO is required to react with 146 g of iron III oxide 159 7 g mol Fe 2 O 3 3 CO 2 Fe 3 CO 2 8 What mass of iron III oxide 159 7 g mol reacted with excess carbon monoxide if the carbon dioxide produced by the reaction had a mass of 8 65 grams Fe 2 O 3 3 CO 2 Fe 3 CO 2 9 4 2 Reactions in Which one Reactant is present in Limited Supply Limiting reactant Substance that is used up first is the limiting reactant It limits the amount of product that can be formed Suppose a box contains 87 bolts 110 washers and 99 nuts How many sets each consisting of one bolt two washers and one nut can you construct from the contents of one box 10 Kokosberger 4 eggs 240 g of sugar 320 g of coconut flakes Makes 48 cookies What if I had 6 eggs 120 g of sugar and 350 g of coconut flakes how many cookies would I make Clicker Q What if I had 4 eggs 250 g of sugar and 340 g of coconut flakes how many cookies would I make 11 A Stoichiometry Calculation with a Limiting Reactant At high temperatures ammonia can react with oxygen according to the following unbalanced reaction NH3 O2 NO H2O If 6 55 moles of NH3 react with 15 4 moles of oxygen how many moles of water can theoretically be produced 12 Clicker Q How many moles of HCl can be produced by reacting 4 0 mol of H2 and 3 5 mol of Cl2 Which cpd is the limiting reactant Enter moles of product produced 13 How many g of silver bromide 187 8 g mol can be formed when solutions containing 50 0 g of magnesium bromide 184 1 g mol and 100 0 g of silver nitrate 169 9 g mol are mixed together magnesium nitrate is also produced How many g of the excess reactant remain unreacted 14 Clicker Q What is the maximum mass of sulfur dioxide 64 1 g mol that can be produced by the reaction of 95 6 g of carbon disulfide 76 12 g mol with 110 g of oxygen Carbon disulfide reacts with oxygen to form carbon dioxide and sulfur dioxide 15 Which is the limiting reactant if we start with 50 0 g Al and 50 0 g O2 How much product can you make How much in moles of the excess reagent remains 16 17 4 3 Percent Yield The theoretical yield is the maximum product yield that can be expected based on the masses of the reactants and the reaction stoichiometry The actual yield is the experimentally measured amount of products that results upon completion of the reaction The percent yield is a measure of the extent of the reaction in terms of the actual vs the theoretical yield Yield Actual Yield in grams or moles Theoretical Yield in grams or moles 100 18 19 Fig 4 3 p 166 Clicker Q If a chemical reaction has a yield of 56 3 and the theoretical yield is 80 0 g what is the actual yield in g 20 A 10 0 g sample of ethanol C2H5OH 46 g mol was boiled with excess acetic acid CH3COOH to produce 14 8 g of ethyl acetate CH3COOC2H5 88 g mol What is the percent yield CH3COOH C2 H 5OH CH 3COOC2 H 5 H 2O Clicker Q What is theoretical yield in g 21 Given this balanced chemical reaction BaCl2 s H2SO4 aq BaSO 4 s 2 HCl aq If 97 2 g of BaCl2 208 2 g mol are reacted with 11 4 g of H2SO4 98 0 g mol and 21 9 g of BaSO4 233 4 g mol are made what is the percent yield for this reaction Clicker Q What is the theoretical yield in g 22 How many grams of commercial acetic acid 97 0 C2H4O2 by mass must be allowed to react with an excess of PCl3 to produce 77 7 g of C2H3OCl if the reaction has a 67 8 yield Balanced reaction 3 C2H4O2 PCl3 3C2H3OCl H3PO4 23 Hydrogen peroxide decomposes into H2O and oxygen gas In a certain experiment 71 13 g of hydrogen peroxide decomposed to yield 15 33 g of oxygen gas Calculate the theoretical and percent yields for this experiment Clicker Q What is the yield 24 4 4 Chemical Equations and Chemical Analysis Quantitative Analysis of a Mixture Depends on 2 basic ideas 1 A substance present in unknown amount reacts with a known amount of another substance Stoichiometric ratio known for their reaction then unknown amount can be calculated like a titration 2 Material of unknown composition can be converted to one or more substances of known composition 25 Chemical Analysis A 0 123 g sample of the mineral thenardite contains sodium sulfate along with several inert compounds The sodium sulfate in the sample is converted to insoluble barium sulfate by adding aqueous barium chloride in excess to the dissolved thenardite sample Na2SO4 BaCl2 BaSO4 2 NaCl The mass of recovered barium sulfate is 0 177 g What is the mass percent of sodium sulfate in the mineral 26 0 123 g thenardite contains sodium sulfate convert to 0 177 g barium sulfate 27 A 0 5491 g sample of a pure soluble chloride compound is dissolved in water and all of the chloride ion is precipitated as AgCl 143 3 g mol by the addition of …