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Teaching Stoichiometry in 60 Minutes or Less

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## Teaching Stoichiometry in 60 Minutes or Less

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**Teaching Stoichiometry in 60 Minutes or Less**Stacey Cool CSTA, San Jose Oct 2012 Golden Valley High School Merced, CA scool@muhsd.org @CoolChemGal www.tinyurl.com/coolschem**Objective**• Demonstrate a way to teach molar conversions, stoichiometry & other conversions using ratios**Background**• Teach Chemistry & AP Chemistry for 10 years • In Merced, CA • Stoichiometry stumbling blocks CSTA, San Jose 2012; S. Cool**Why?**• Issues with dimensional analysis • Power Standard • CSTA 2 years ago**The Process**• What are you looking for, what are you given? • What you are looking for on top • What you are given on the bottom • Carry the units over • Fill in numbers • Cross multiply • Solve**November**Molar Conversions**22.4 L**Volume (L) The Mole Road Map 22.4 L Mole Molar mass (periodic table) 6.02 x 1023 Mass (grams) Particles (atoms, molecules, formula units)**Some practice problems:**• How many moles is 5.69 g of NaOH?**Some practice problems:**• How many moles is 5.69 g of NaOH? x mol NaOH 1 mol NaOH = 5.69 g NaOH 40.00 g NaOH We need a relationship between grams & moles. Need to figure out the molar mass of NaOH! NaOH = 22.99 g/mol + 16.00 g/mol + 1.01 g/mol Molar mass of NaOH = 40.00 g/mol 1 mole NaOH= 40.00 g NaOH Cross multiply and solve for x. (x mol NaOH) = (5.69 g NaOH)(1 mol NaOH) 40.00 g NaOH = 0.14225 moles NaOH 3 sig figs = 0.142 moles NaOH**Some practice problems:**• Determine the number of moles in 128.14 g of SO2.**Some practice problems:**• Determine the number of moles in 128.14 g of SO2. x mol SO2 1 mol SO2 = 128.14 g SO2 64.07 g SO2 We need a relationship between grams & moles. Need to figure out the molar mass of SO2! SO2 = 32.07 g/mol + 2(16.00 g/mol) Molar mass of SO2 = 64.07 g/mol 1 mole SO2 = 64.07 g SO2 Cross multiply and solve for x. (x mol SO2) = (128.14 g SO2)(1 mol SO2) 64.07 g SO2 = 2 moles SO2 4 sig figs = 2.000 moles SO2**Examples**What would 3.0 moles of carbon weigh?**January**Stoichiometry**22.4 L**Volume (L) The Mole Road Map 22.4 L Mole Molar mass (periodic table) 6.02 x 1023 Mass (grams) Particles (atoms, molecules, formula units)**Mass**(grams) Mass (grams) Molar mass (periodic table) Molar mass (periodic table) mole ratio Volume (L) Volume (L) Mole Mole 22.4 L 22.4 L Particles (atoms, molecules, formula units) Particles (atoms, molecules, formula units) 6.02 x 1023 6.02 x 1023**An Example**Na + Cl2 2NaCl How many grams of sodium chloride are produced from 46 g of sodium and excess chlorine?**An Example**Na + Cl2 2NaCl 2 molx x gNaCl g NaCl 58.5 = 1 molx g Na 46 g Na 23 (x g NaCl)= (46 g Na)(2 mol)(58.5 gNaCl) (1 mol) (23 g Na) = 117 g NaCl**An example...**If 56 g of Fe are added to a solution of Copper (II) Sulfate, how much solid copper (MW = 64) will form? 2Fe + 3CuSO4Fe2(SO4)3 + 3Cu**Mass to Mole**Zn + Cu2SO4 ZnSO4 + 2Cu How many moles of copper can be produced from 446 g of Cu2SO4(molar mass of Cu2SO4= 223 g/mol)?**Volume to Volume**C6H12 + 9 O2 6CO2 + 6H2O How many liters of oxygen are needed to produce 20.0L of carbon dioxide?**Mole to Mole**How many moles of O2 are produced when 3.00 moles of Al2O3 decompose? 2 Al2O3® 4Al+3O2**Practice**2 Al(s) + 6 HCl(aq)2 AlCl3(aq) + 3 H2(g) • When 23.0g of solid aluminum is reacted with excess hydrochloric acid, what volume of hydrogen gas is produced at STP?**Practice**2Al(s) + 6HCl(aq) 2AlCl3(aq) + 3H2(g) • Using the same 23.0g of aluminum as above, how many moles of HCl need to be added in order for it to react completely?**Practice**2Al(s) + 6HCl(aq) 2AlCl3(aq) + 3H2(g) • How many moles of aluminum chloride are produced from 0.60 mol of hydrochloric acid?**Other Applications**• Pressure conversions • Joule-calorie conversions • Metric conversions Remember: You are teaching a problem solving process!**Converting Between Pressures**• 1 atm = 760 mm Hg = 760 torr = 101.3 kPa • Convert 1520 torrto atm**Contact Info**scool@muhsd.org @CoolChemGal www.tinyurl.com/coolschem CSTA, San Jose 2012; S. Cool