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UNIT 8 NOTES- CHEM H- STOICHIOMETRY
STOICHIOMETRY is the study of quantitative relationships between the amounts of
reactants used and the amounts of products formed, in a chemical reaction(equation).
Since matter cannot be created or destroyed in a Chemical reaction, the total mass of
products must be equal to the total mass of reactants (Law of Conservation). For
example, In the reaction below……
2H2
+
O2

2H20
If 4 grams of Hydrogen gas react with 64 grams of oxygen gas, then the amount of water
forming as a product should be 68 grams. Even though atoms have been re-arranged to
form new molecules/compounds (products), there is no loss of mass of starting
materials (reactants).
Also note that the mass ratios are 4: 64 : 68
This is not the same as the ratio of the coefficients used to balance the equation!!!!!
The coefficients tell us the number of molecules (or atoms)…..NOT the MASSES.
Since coefficients represent a quantity of atoms, they can also be used to represent
MOLES, (and even volumes of gases)…..so therefore…..
2 moles H2 (g)
+
1 mole O2 (g) 
2 moles H20 (g)
This reaction always takes place in a mole/molecule/volume ratio of 2 : 1 : 2 no
matter how many molecules. So, In order to determine the amount of product
manufactured, we will always need to express any “GIVEN” information in “MOLES.
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PARALLEL SITUATION
Suppose you work at “Kim Car Company”(as opposed to Kia cars) on the
assembly line. Here is a recipe for the manufacturing of their best vehicle.
1 engine + 4 tires + 6 glass panes + 1 body 
1 car
If you were asked: How many more cars could be made if 21 tires are remaining in the
warehouse?
Since the numbers in the equation represent a quantity ratio, you can use them to
determine your answer.
First: setup the factor label grid w/given and desired info.
21 tires
=
? cars
Second : use the equation to find the theoretical ratio of tires : cars
4 tires
or
1 car
1 car
4 tires
Third : Plug in the correct conversion factor and calculate
21 tires
1car
=
5 . 25 cars = 5 cars
4 tires
Lets try a REAL sample problem .
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STOICHIOMETRY Sample Problem #1
How many grams of water vapor can be manufactured when 20.0 grams of Hydrogen gas reacts with
(excess) oxygen .
First: Write and balance a chemical equation that represents the process. Interpret the equation in
terms of moles
2H2 (g)
+
O2 (g) 
2H20 (g)
Second: Since 20.0 g is a mass, convert it to moles ( a quantity) using the formula weight of
hydrogen gas.
20.0 g H2
1 mole H2
2.0 g H2
Third : Use the equation to establish the ratio between Hydrogen gas (Given) and water vapor
(the desired). Place this conversion into the grid.
20.0 g H2
1 mole H2
2.0 g H2
2 mole H2O
2 mole H2
Fourth: Usually the mass (or volume ) is needed for the second substance, so convert moles of
water back to grams (or liters) of water now using the formula weight of water .
20.0 g H2
1 mole H2
2 mole H2O
18.0 g H2O
2 mole H2
1 mole H2O
= 180.
g H2O
2.0 g H2
STOICHIOMETRY Sample Problem #2
Ammonium Nitrate can be decomposed into water vapor and dinitrogen oxide. How many grams
of Ammonium Nitrate is needed to produce 180.0 g water ?
First: Write and balance a chemical equation that represents the process. Interpret the equation in
terms of moles.
NH4NO3 (s) 
N2O (g)
+
2H20 (g)
Second: Since 180.0 g is a mass, convert it to moles ( a quantity) using the formula weight of
water.
180.0 g H2O
1 mole H2O
18.0 g H2O
Third : Use the equation to establish the ratio between ammonium nitrate (the desired) and
water vapor (the given). Place this conversion into the grid.
180.0 g H2O
1 mole H2O
18.0 g H2O
1 mole NH4NO3
2 mole H2O
Fourth: Usually the mass (or volume ) is needed for the second substance , so convert moles of
ammonium nitrate back to grams (or liters) using the formula weight of ammonium nitrate .
180.0 g H2O
1 mole H2O
18.0 g H2O
1 mole NH4NO
2 mole H2O
80.0 g NH4NO3 = 400.0 g NH4NO3
1 mole NH4NO3
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Worksheet J’JAE’ H Chem
Stoich for starters
Name_____________
I. Complete each of the problems below using the factor label method.
1. How many grams of chlorine gas are required to make 730.0 grams of Hydrogen
chloride, assuming enough H2 gas is present ?
H 2 (g) +
Cl2 (g)
 HCl (g)
2. How many moles of oxygen gas are required to produce 242 grams of Magnesium
Oxide in this reaction ?:
Mg
+

O2 (g)
MgO
3. Silver reacts with Nitric acid as indicated by the following equation:
Ag
+
HNO3 
NO2
+
AgNO3+
HOH
What minimum amount of HNO3 would be required to react with 5.00 grams of silver ?
4. How many grams of oxygen are required to oxidize 140.0 grams of iron to Iron III
Oxide?
Fe
b)
+
O2 (g) 
Fe2O3
How many grams of Fe2O3 are produced ?
5. How many grams of water vapor are produced when 136 grams of ammonia are
burned in excess oxygen ? The reaction is :
NH3
+
O2(g)

N2
+
H2O(g)
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Worksheet KK H Chem
Stoichiometry (moderate)
Name__________________
I. Complete each of the problems below using the factor label method.
Please complete in your notebook.
1. If 120 grams of Sodium carbonate react with calcium hydroxide, how many grams of
sodium hydroxide are formed?
Na2CO3
+
Ca (OH )2
 NaOH +
CaCO3
2. If 90.0 grams of Barium chloride react with sulfuric acid, how many grams of Barium
Sulfate are produced? Complete the equation!!!
BaCl2 +
H2SO4 
3. If 500.0 grams of Potassium Iodide react with lead II acetate, what weight of lead II
iodide is formed? Write the equation.
4. When 80.0 grams of calcium chloride react with silver nitrate, how many grams of
silver chloride are produced ? Write the equation.
5. How many grams of oxygen are produced by heating 400.0 grams of potassium
chlorate ? Write the equation.
6. If 600.0 grams calcium hydroxide react with nitric acid, how many grams of nitric
acid are needed to completely react with the calcium hydroxide ? Write the equation.
7. When 50.0 grams of Mg react with AgNO3 in solution, how many grams of Ag are
prepared ? Write the equation.
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8. How many grams of calcium carbonate are required in the preparation of 50.00 grams
of calcium oxide ? Write the equation. (Classifying the reaction first will help to write it)
9. Determine how much carbon dioxide and water will be produced from the combustion
of 104 g of C2H2.
10. How many moles of aluminum iodide are produced in the reaction between iodine
and 108 g of Al.
11. What mass of sodium hydroxide is needed to produce 16.0 g of magnesium
hydroxide if it reacts with magnesium chloride?
12. How many moles of gallium chloride (Ga+3) are formed from the reaction of 1.50
moles of hydrochloric acid with gallium?
13. Silver can be obtained from the ore KAg(CN)2 and then recovered by the reaction:
KAg(CN)2 + Zn ---> Ag + Zn(CN)2 + KCN (balance). What mass of zinc is
needed to produce 28.0 grams of Ag?
14. What mass of hydrogen is produced by reacting chromium (III) and 1.24 mol of
phosphoric acid?
15. What mass of calcium chloride can be made from 45.4 g of calcium carbonate
according to the equation: CaCO3 + HCl + H2O ---> CaCl2.6H2O + CO2 (balance)
16. What mass of silver oxide is needed to prepare 225 g of AgC10H9N4SO2 from
C10H10N4SO2? Water is also a product?
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EXCESS REAGENT(Reactant)-LIMITING REAGENT(Reactant)
The Limiting reagent limits the extent of a chemical reaction, and thus limits the amount
of product that can be formed in a chemical reaction. The Excess reagent is leftover,
meaning that it remains in the reaction vessel after the reaction has come to a stop .
Let’s go back to our analogy at “Ferrara Car Company”. Here’s the recipe for the
manufacturing of their best vehicle (again).
1 engine + 4 tires + 6 glass panes + 1 body 
1 car
If you were asked: How many cars could be made from 52 tires and 66 glass panes?
Since the numbers in the equation represent a quantity ratio, you can use them to
determine your answer.
Setup the factor label grid w/given and desired info for each reactant.
52 tires
1car =
4 tires
13 cars
66 glass panes 1car
=
6 glass panes
11 cars
Since the 66 glass panes can only produce 11 cars, it is considered to be the limiting
reagent. Once the eleven cars are manufactured, the reaction(assembly line) stops. No
more cars can be made. At this point there are still enough tires left to make 2 more cars.
The tires are considered to be excess reactant. See if you can determine “How many
tires remain?”
Plug in the correct conversion factor and calculate
2 cars
4 tires
1 car
= 8 tires remain
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Sample #3: Excess- limiting reagent (Treuer’s Method)
In the production of disulfur dichloride, molten sulfur reacts with chlorine gas
according to this equation:
S8
+ 4Cl2 
4S2Cl2 (l)
If 200.0 g Sulfur reacts with 100.0 g chlorine, what mass of disulfur dichloride is
produced ?
Step 1 : Determine how many grams of disulfur dichloride is produced by each
reactant.
200.0 g S8
1 mole S8
256.5 g S8
4 moles S2Cl2
1 mole S8
135.0 g S2Cl2 _ = 421 g S2Cl2
1 mole S2Cl2
100.0 g Cl2
1mole Cl2
71.0 g Cl2
4 moles S2Cl2 135.0 g S2Cl2 _ = 190.4 g S2Cl2
4 moles Cl2
1 mole S2Cl2
THE REACTANT THAT PRODUCES THE LESSER MOLE/grams
AMOUNT OF PRODUCT(S2Cl2 in this reaction) IS CONSIDERED TO BE
THE LIMITING REACTANT (REAGENT)
The LIMITING REAGENT DECIDES EVERYTHING ELSE
B) To determine the amount of excess reagent reacted (used up)
…….. start with the actual limiting reagent, chlorine. Treat the excess reagent as the
“desired”
100.0 g Cl2
1mole Cl2
71.0 g Cl2
1 mol S8
256.5 g S8. = 90.42 g S8 used
4 mole Cl2 1 mole S8
C) To determine the amount of excess reagent unreacted, leftover, or unused…
Take the amount that was used, 90.42 g Sulfur reacted, and subtract this amount from the
amount of excess reagent that you had initially. Because 200.0 g of sulfur is available
and only 90.42 g is needed the mass in excess is….
200.0 g S8 - 90.42 g S8 = 109.6 g S8 in excess
There are other ways to determine the same answers:
Try to figure out another way….
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WORHSHEET LL H Chem Name ___________________________
Excess/Limiting Stoich “Have an excess amount of fun with these”
1. How many grams of Al2O3 can be formed when a mixture of 0.36 mol of aluminum
and 0.36 mol of oxygen is ignited?
2. What mass of bromine could be produced from 2.10 g of NaBr and 9.42 g of H2SO4?
2NaBr + 2H2SO4 + MnO2 ----> Br2 + MnSO4 + 2H2O + Na2SO4
*3. If 20.0 g of NaOH react with 30.0 g of H2SO4, how much sodium sulfate will be
produced? How much of the excess remains in grams?
4. If 5.00 g of copper metal react with 20.0 g of silver nitrate, how much silver will be
produced?
5. If 20.0 g of potassium hydroxide react with 15.0 g of ammonium sulfate, calculate the
mass of ammonia (NH3) produced. NOTE: the product ammonium hydroxide
decomposes into ammonia and water. What is in excess? How much excess is there, in
grams?
6. In a reaction between 25.0 g of NH3 and 19.0 g of oxygen how many grams of
nitrogen can be produced? What substance is in excess and how many grams remains?
NH3 + O2 ---> N2 + H2O (balance)
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7. How many grams of iron III oxide can be made from 25.5 g of iron and 25.0 g of
oxygen? What substance is the limiting agent? What substance is in excess and how
many grams remains?
8. Given :
CaCO3
+
2NaCl

Na2CO3
+
CaCl2
How Many grams of calcium chloride are formed when 1000 grams of NaCl react
with 2000 grams of calcium carbonate ? What substance is in excess and how
many grams remains?
9.
Given :
C12H22O11 + 12 O2  12 CO2
+ 11 H2O
34.2 grams of sugar reacts with 32.0 grams of oxygen gas. How many moles of
water is produced ? What substance is in excess and how many grams remains?
10. Iron burns in air(oxygen) to form a black iron oxide, Fe3O4.
56 grams of iron reacts with 64 grams of oxygen. How much iron oxide is
produced ? What substance is in excess and how many grams remains?
11. If 28 g Si reacts with 25 g nitrogen, what mass of Si3N4 will be produced? What
substance is in excess? What substance is in excess and how many grams remains?
12. A very confusing problem. (2 PROBLEMS IN ONE)
Magnesium acetate can be prepared by a reaction involving 15.0 g of iron III acetate
with either 10.0 g of MgCrO4 or 15.0 g of MgSO4. Which reaction will give the greatest
yield of Mg(C2H3O2)2? How many grams of Mg(C2H3O2)2 will be produced?
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PERCENTAGE YIELD (Efficiency)
Quite often in chemistry, chemical reactions do NOT always produce the amount
of product that is calculated (on paper). In the calculations that you have been
practicing, the answer that you obtain on paper is called the Theoretical Yield.
The Theoretical Yield is the maximum amount of product that can be produced
from a given amount of reactant. Since a chemical reaction rarely produces the
theoretical yield (in the real world), the amount of product that is truly produced
in an experiment is called the Actual Yield (Experimental yield).
One way to decide how efficient a chemical reaction is in producing the
desired product is to perform a calculation known as Percent Yield.
Mathematically, percent(age) yield can be expressed as :
Percent Yield = Actual (Experimental.) Yield (from the experiment) x 100%
Theoretical Yield (from stoichiometric calculations)
Sample Problem # 4 Percent yield
a) Determine the theoretical yield of water when 136 grams of ammonia is burned in
excess oxygen ?
b) If 168 grams of water is obtained, calculate the percent yield.
The reaction is :
4NH3 +
3O2

2N2
+
6H2O
The theoretical yield is :
136 g NH3
1 mole NH3
17.0 g NH3
6mole H2O
4mole NH3
18 g H2O
= 216 g H2O (Theo.)
1 mole H2O
The percent yield is :
% Yield = Actual Yield
Theoretical Yield
% Yield = 168 g x 100%
216 g
% Yield =
The percent purity is :
x 100%
% Purity = Mass pure x 100%
Mass pure + mass inert
substance
77.8 %
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Stoichiometry Lab :
Iron - Copper II Sulfate Reaction
Stoichiometry is a Calculation in Chemistry that deals with quantitative relationships
between the reactants, products , and energy in chemical reactions.
In this experiment, you will let iron filings react with Copper II Sulfate solution. An
excess of Copper II Sulfate will be used so that all of the iron filings will be reacted. By
weighing the amount of iron used and the amount of new substance formed, you will be
able to determine a quantitative relationship between reactants and products for this
reaction.
As you do this experiment, record your data carefully and neatly. Take special care to
show the units as an important part of each measurement. Express each measurement
using the correct number of significant figures as determined by the precision of the
measuring instrument.
Before coming to lab, you should plan what you are to do.
DATA TABLE:
1
2
3
4
5
6
7
8
9
10
Mass of 250 ml beaker (g)
Mass of Beaker and CuSO4 (g)(optional)
Mass of CuSO4 used (g)
Mass of weighing dish (g)
Mass of weighing dish and Fe (g)(option)
Mass of Fe used (g)
Mass of filter paper (g)
Mass of filter paper and product (g)
Mass of product (g)
Procedure:
a) weigh a clean, empty 250 ml beaker to the nearest 0.01 gram. Record in table(1)
b) Tare the beaker, add Copper II Sulfate to the beaker until the balance indicates a reading greater
than 10 grams. Record the mass of Copper II Sulfate in the data table precisely to 0.01 g (3)
c) Add about 50 ml of de-ionized water to the copper II Sulfate crystals.
d) Place the beaker on a ring stand with wire gauze. Warm the solution until it just starts to boil.
Be careful not to let the solution boil over!! Remove the burner.
e) Weigh a plastic weighing dish. Record the mass in your data table (4)
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f) Tare the plastic dish and add Fe filings so that the mass is somewhere between 1.50 and 2.10 g of
Iron. Record the exact mass of Iron in the data table (6).
g) Weigh a piece of filter paper on the balance. Record the mass in the data table. Fold the paper
into “quarters” and write your initials on the edge of the paper (in pencil). Set the filter paper up
inside a funnel on a funnel stand.
h) While stirring the hot copper sulfate solution with a glass rod, add the iron filings SLOWLY
AND A LITTLE AT A TIME. After the reaction is complete, slowly pour the contents (beaker is
HOT) of the reaction into the filter paper, insuring that all solids are collected by the paper. Rinse
your beaker out with a de-ionized water wash bottle. Be sure to get out any solids in the beaker by
washing them into the filter paper.
i) After the final washing, the solid must be dried. Carefully remove the filter paper (don’t spill)
and let dry on the side of the room, either in the drying oven or by air drying overnite.
j) After the solid is dry (next lab day) weigh the solid and filter paper on the balance (8)
Calculations/Questions
1. Determine the mass (experimental result) of the product (show Calculation in lab report)
2. What do you think the product is ? Why ?
3. Write a chemical reaction for the experiment.
4. Calculate moles of iron and Copper II Sulfate.
5. Perform calculations that show which reactant is the limiting and Excess reagent ?
6. Assuming the product is pure copper, determine the moles (Experimental result) of copper in the
reaction.
7. Divide the moles of Iron, Fe, by the moles of copper, Cu. Be sure to express your answer as a
decimal and use the correct number of significant figures.
8. Calculate the Theoretical answer for the mass of Copper that should have been produced.
9. Using the Actual mass of Copper (ques #1), determine the percent yield.
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