Tonight’s Homework
• skim ch 11.2 (373 – 377)
• p 393, # 60 – 64, 67
Homework Review
45. When tin(IV) oxide is heated with carbon in a process
called smelting, the element tin can be extracted.
SnO2(s) + 2C(s)  Sn(l) + 2CO(g)
Interpret the chemical equation in terms of particles, moles,
and mass.
Particles: 1 f.u. SnO2 + 2 atoms C  1 atom Sn + 2 molecules CO
Moles: 1 mole SnO2 + 2 mole C  1 mole Sn + 2 mole CO
Mass: 150.71 g SnO2 + 24.02 g C  118.71 g Sn + 56.02 g CO
Homework Review
49. Solid silicon dioxide, often called silica, reacts with
hydrofluoric acid (HF) solution to produce the gas silicon
tetrafluoride and water.
a. Write the balanced chemical equation for the reaction.
SiO2 (s) + 4 HF (aq)  SiF4 (g) + 2 H2O (g)
b. List three mole ratios, and explain how you would use them
in stoichiometric calculations.
You should have listed 12 mole ratios. They are useful to
convert from moles of one substance to moles of another.
Homework Review
50. Chrome The most important commercial ore of chromium
is chromite (FeCr2O4). One of the steps in the process used to
extract chromium is the reaction of chromite with coke
(carbon) to produce ferrochrome (FeCr2).
2C(s) + FeCr2O4(s)  FeCr2 (s) + 2CO2 (g)
What mole ratio would you use to convert from moles of
chromite to moles of ferrochrome?
1 mole FeCr2 / 1 mole FeCr2O4
Homework Review
53. Antacids Magnesium hydroxide is an ingredient in
some antacids. Antacids react with excess hydrochloric
acid in the stomach to relieve indigestion.
a. Balance the reaction of Mg(OH)2 with HCl.
Mg(OH)2 + 2HCl  MgCl2 + 2H2O
b. Write the mole ratio that would be used to determine
the number of moles of MgCl2 produced when HCl reacts
with Mg(OH)2.
1 mol MgCl2 / 1 mol Mg(OH)2 OR 1 mol MgCl2 / 2 mol HCl
Stoichiometric Calculations
section 11.2
Mass Production (an analogy )
• 2-L bottles of soda
• 100,000 bottles per
order
• Best case scenario, how
many liters of soda
should be “batched” at
a time?
• 200,000 L
Thinking like a chemist…
• “Balanced Chemical Equation”
1bottle + 2liters - of - soda =1filled - bottle - of - soda
• Mole Ratio
2liters - of - soda
1bottle
• Conversion
2liters - of - soda
100, 000bottles ´
= 200, 000liters - of - soda
1bottle
The basics of stoichiometric
conversions…
• Best Case Scenario = Balanced Chemical Eqn.
• The mole ratio is the missing link between the best
case scenario (balanced chemical equation in moles)
and reality (in grams).
– DETERMINE mole ration FROM THE BALANCED EQUATION
• 3 types of conversions
– mole to mole
– mole to mass
– mass to mass
For all of them, GO
TO MOLES FIRST!
• Use molar mass (MM) to convert between moles and
mass.
3 groups – 3 reactions
• https://www.youtube.com/watch?v=oqMN3y
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• https://www.youtube.com/watch?v=Mx5JJWI
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• https://www.youtube.com/watch?v=x2BXuI52
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3 groups – 3 problems
• Determine what type of conversion
– mole to mole
– mole to mass
– mass to mass
• Work through the problem to solve it.
• Outline the steps to solve this type of
problem.
• Be prepared to teach it to your classmates.
Summary –
Determine given and unknown, then…
moles given to
moles unknown
mole give to
mass unknown
mass given to
mass unknown
1. Balance chemical
equation.
1. Balance chemical
equation.
1. Balance chemical
equation.
2. Determine and use the
mole ratio to relate moles
unknown to moles given.
2. Determine and use the
mole ratio to relate moles
unknown to moles given.
2. Convert mass given to
moles given using molar
mass.
3. Convert moles unknown
to mass using molar mass.
3. Determine and use the
mole ratio to relate moles
unknown to moles given.
4. Convert moles unknown
to mass unknown using
molar mass.
= moles given x (moles
unknown/moles known)
= moles given x (moles
unknown/moles known) x
(MM unknown/1mole)
= mass given x
(1mole/MM) x (moles
unknown/moles known) x
(MM unknown/1 mole)
Groups 1 & 2
• Potassium metal reacts vigorously with water
to produce potassium hydroxide and hydrogen
gas. If 0.0400 moles of potassium is used, how
many moles of hydrogen gas is created?
Groups 3 & 4
• Determine the mass of sodium chloride (NaCl)
commonly called table salt, produced when
1.25 moles of chlorine gas (Cl2) reacts
vigorously with excess sodium.
Groups 5 & 6
• Gasohol is a mixture of gasoline and ethanol.
Determine the mass of CO2 produced from the
combustion of 100.0 g ethanol (C2H5OH).