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Teaching Stoichiometry in 60 Minutes or Less
Stacey CoolCSTA, San Jose Oct 2012
Golden Valley High SchoolMerced, CA
[email protected]@CoolChemGal
www.tinyurl.com/coolschem
Objective
• Demonstrate a way to teach molar conversions, stoichiometry & other conversions using ratios
CSTA, San Jose 2012; S. Cool
Background
• Teach Chemistry & AP Chemistry for 10 years
• In Merced, CA• Stoichiometry stumbling blocks
Why?
• Issues with dimensional analysis• Power Standard• CSTA 2 years ago
Power Standard
The Process1. What are you looking for, what are
you given?2. What you are looking for on top3. What you are given on the bottom4. Carry the units over5. Fill in numbers6. Cross multiply7. Solve
MOLAR CONVERSIONS
November
22.4 LMole
Volume(L)
Mass(grams)
Particles(atoms,
molecules, formula units)
22.4 L
6.02 x 1023
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/molMolar 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 SO2.
We need a relationship between grams & moles. Need to figure out the molar mass of SO2!
Some practice problems:• Determine the number of moles in
128.14 g of SO2.
128.14 g SO2
mol SO2
g SO2
=
SO2 = 32.07 g/mol + 2(16.00 g/mol)Molar mass of SO2 = 64.07 g/mol
1
64.07
Cross multiply and solve for x.
= 2 moles SO2 4 sig figs= 2.000 moles SO2
1 mole SO2 = 64.07 g SO2
x mol SO2
(x mol SO2) = (128.14 g SO2)(1 mol SO2)
64.07 g SO2
ExamplesWhat would 3.0 moles of carbon weigh?
STOICHIOMETRY
January
22.4 LMole
Volume(L)
Mass(grams)
Particles(atoms,
molecules, formula units)
22.4 L
6.02 x 1023
Molar mass (periodic table)
The Mole Road Map
MoleVolume(L)
Mass(grams)
Particles(atoms,
molecules, formula units)
22.4 L
6.02 x 1023
Molar mass (periodic table)
Mass(grams)
Volume(L)
Particles(atoms,
molecules, formula units)
Mole
6.02 x 1023
Molar mass (periodic table)
22.4 L
mole ratio
Na + Cl2 2NaCl
How many grams of sodium chloride are produced from 46 g of sodium and excess chlorine?
An Example
An ExampleNa + Cl2 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 + 3CuSO4 Fe2(SO4)3 + 3Cu
An example...
Mass to MoleZn + 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 MoleHow many moles of O2 are
produced when 3.00 moles of Al2O3 decompose?
2 Al2O3 ® 4Al + 3O2
Practice2 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?
Practice2Al(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?
Practice2Al(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 conversionsRemember: 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