Basic Stoichiometry Problems

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Basic Stoichiometry Problems
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Example 1

• If 35.80g of aluminum chloride reacts with excess
  silver nitrate, how many grams of the ppt will be
  formed?
• 1AlCl3(aq) 3AgNO3(aq) Al(NO3)3(aq)
  3AgCl(s)
• 35.80g AlCl3 1mol AlCl3 3mol
  AgCl 143.32g AgCl
• 132.76g AlCl3
  1mol AlCl3 1mol AgCl
• 115.9g AgCl

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Example 2

• 12.01g of ammonium carbonate reacts with excess
  ferrous bromide. How many grams of the ppt will
  be formed?
• 1(NH4)2CO3(aq) FeBr2(aq) 2NH4Br(aq)
  1FeCO3 (s)
• 12.01g(NH4)2CO3 1mol (NH4)2CO3 1mol FeCO3
  115.86g
• 96.11g 1mol (NH4)2CO3
  1mol FeCO3
• 14.48g FeCO3

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Instructions This is a work along tutorial.
Each time you click the mouse or touch the space
bar on your computer, one step of the problem
solving occurs. Pressing the PAGE UP key will
backup the steps.
Get a pencil and paper, a periodic table and a
calculator, and lets get to work.
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Converting grams to moles.
Determine how many moles there are in 5.17 grams
of Fe(C5H5)2.
Goal
Given
units match
5.17 g Fe(C5H5)2
moles Fe(C5H5)2
0.0278
Use the molar mass to convert grams to moles.
Fe(C5H5)2
2 x 5 x 1.001 10.01
2 x 5 x 12.011 120.11
1 x 55.85 55.85
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Stoichiometry (more working with ratios)
Ratios are found within a chemical equation.
2HCl Ba(OH)2 ? 2H2O BaCl2
1
1
coefficients give MOLAR RATIOS
2 moles of HCl react with 1 mole of Ba(OH)2 to
form 2 moles of H2O and 1 mole of BaCl2
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Mole Mole Conversions
When N2O5 is heated, it decomposes
2N2O5(g) ? 4NO2(g) O2(g)
a. How many moles of NO2 can be produced from 4.3
moles of N2O5?
2N2O5(g) ? 4NO2(g) O2(g)
4.3 mol
? mol
Units match
4.3 mol N2O5
moles NO2
8.6
b. How many moles of O2 can be produced from 4.3
moles of N2O5?
2N2O5(g) ? 4NO2(g) O2(g)
4.3 mol
? mol
4.3 mol N2O5
mole O2
2.2
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gram ? mole and gram ? gram conversions
When N2O5 is heated, it decomposes
2N2O5(g) ? 4NO2(g) O2(g)
a. How many moles of N2O5 were used if 210g of
NO2 were produced?
2N2O5(g) ? 4NO2(g) O2(g)
210g
? moles
Units match
210 g NO2
moles N2O5
2.28
b. How many grams of N2O5 are needed to produce
75.0 grams of O2?
2N2O5(g) ? 4NO2(g) O2(g)
75.0 g
? grams
75.0 g O2
grams N2O5
506
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Gram to Gram Conversions
Aluminum is an active metal that when placed in
hydrochloric acid produces hydrogen gas and
aluminum chloride. How many grams of aluminum
chloride can be produced when 3.45 grams of
aluminum are reacted with an excess of
hydrochloric acid?
Al(s) HCl(aq) ? AlCl3(aq)
H2(g)
2 6 2
3
First write a balanced equation.
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Gram to Gram Conversions
Aluminum is an active metal that when placed in
hydrochloric acid produces hydrogen gas and
aluminum chloride. How many grams of aluminum
chloride can be produced when 3.45 grams of
aluminum are reacted with an excess of
hydrochloric acid?
Al(s) HCl(aq) ? AlCl3(aq)
H2(g)
2 6 2
3
? grams
3.45 g
Now lets get organized. Write the information
below the substances.
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gram to gram conversions
Aluminum is an active metal that when placed in
hydrochloric acid produces hydrogen gas and
aluminum chloride. How many grams of aluminum
chloride can be produced when 3.45 grams of
aluminum are reacted with an excess of
hydrochloric acid?
Al(s) HCl(aq) ? AlCl3(aq)
H2(g)
2 6 2
3
? grams
3.45 g
Units match
3.45 g Al
g AlCl3
17.0
Lets work the problem.
We must always convert to moles.
Now use the molar ratio.
Now use the molar mass to convert to grams.