# Teaching Stoichiometry in 60 Minutes or Less Stacey Cool CSTA, San Jose Oct 2012 Golden Valley High School Merced,

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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

Power Standard

The Process 1.What are you looking for, what are you given? 2.What you are looking for on top 3.What you are given on the bottom 4.Carry the units over 5.Fill in numbers 6.Cross multiply 7.Solve

MOLAR CONVERSIONS November

22.4 L Mole Volume (L) Mass (grams) Particles (atoms, molecules, formula units) 22.4 L 6.02 x 10 23 Molar mass (periodic table) The Mole Road Map

Some practice problems: How many moles is 5.69 g of NaOH?

We need a relationship between grams & moles. Need to figure out the molar mass of NaOH! Some practice problems: How many moles is 5.69 g of NaOH? 5.69 g NaOH mol NaOH g NaOH = NaOH = 22.99 g/mol + 16.00 g/mol + 1.01 g/mol Molar mass of NaOH = 40.00 g/mol 1 40.00 Cross multiply and solve for x. = 0.14225 moles NaOH3 sig figs = 0.142 moles NaOH 1 mole NaOH= 40.00 g NaOH x mol NaOH (x mol NaOH) = (5.69 g NaOH)(1 mol NaOH) 40.00 g NaOH

Some practice problems: Determine the number of moles in 128.14 g of SO 2.

We need a relationship between grams & moles. Need to figure out the molar mass of SO 2 ! Some practice problems: Determine the number of moles in 128.14 g of SO 2. 128.14 g SO 2 mol SO 2 g SO 2 = SO 2 = 32.07 g/mol + 2(16.00 g/mol) Molar mass of SO 2 = 64.07 g/mol 1 64.07 Cross multiply and solve for x. = 2 moles SO 2 4 sig figs = 2.000 moles SO 2 1 mole SO 2 = 64.07 g SO 2 x mol SO 2 (x mol SO 2 ) = (128.14 g SO 2 )(1 mol SO 2 ) 64.07 g SO 2

Examples What would 3.0 moles of carbon weigh?

STOICHIOMETRY January

22.4 L Mole Volume (L) Mass (grams) Particles (atoms, molecules, formula units) 22.4 L 6.02 x 10 23 Molar mass (periodic table) The Mole Road Map

Mole Volume (L) Mass (grams) Particles (atoms, molecules, formula units) 22.4 L 6.02 x 10 23 Molar mass (periodic table) Mass (grams) Volume (L) Particles (atoms, molecules, formula units) Mole 6.02 x 10 23 Molar mass (periodic table) 22.4 L mole ratio

Na + Cl 2  2NaCl How many grams of sodium chloride are produced from 46 g of sodium and excess chlorine? An Example

Na + Cl 2  2NaCl 46 g Na g NaCl g Na = 58.5 23 = 117 g NaCl x g NaCl (x g NaCl) = (46 g Na)(2 mol)(58.5 gNaCl) (1 mol) (23 g Na) 2 mol x 1 mol x

If 56 g of Fe are added to a solution of Copper (II) Sulfate, how much solid copper (MW = 64) will form? 2Fe + 3CuSO 4  Fe 2 (SO 4 ) 3 + 3Cu An example...

Mass to Mole Zn + Cu 2 SO 4  ZnSO 4 + 2Cu How many moles of copper can be produced from 446 g of Cu 2 SO 4 (molar mass of Cu 2 SO 4 = 223 g/mol)?

Volume to Volume C 6 H 12 + 9 O 2  6CO 2 + 6H 2 O How many liters of oxygen are needed to produce 20.0L of carbon dioxide?

Mole to Mole How many moles of O 2 are produced when 3.00 moles of Al 2 O 3 decompose? 2 Al 2 O 3  Al + 3O 2

Practice 2 Al (s) + 6 HCl (aq)  2 AlCl 3(aq) + 3 H 2(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)  2AlCl 3(aq) + 3H 2(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)  2AlCl 3(aq) + 3H 2(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 torr to atm

Contact Info scool@muhsd.org @CoolChemGal www.tinyurl.com/coolschem CSTA, San Jose 2012; S. Cool

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