Teaching Stoichiometry in 60 Minutes or Less

Stacey CoolCSTA, San Jose Oct 2012

Golden Valley High SchoolMerced, CA

scool@muhsd.org@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

CSTA, San Jose 2012; S. Cool

Contact Info

scool@muhsd.org

@CoolChemGal

www.tinyurl.com/coolschem