Test
You have 15 minutes to finish your test!
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Chapter 8- Stoichiometry
Big, Scary name….
Just calculations chemists do!
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Quantitative Analysis
Composition stoichiometry- mass relationships of
elements in compounds.
Reaction Stoichiometry- involves mass
relationships between the reactants and
products in reactions
3
What do the coefficients mean?
Mole Ratios
Coefficients indicate the amount of each material
(Moles or molecules) present in a reaction.
C6H12O6 + 6O2
6CO2 + 6H2O
So… when looking at a balanced equation we can derive a
whole set of conversion factors!
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Mole Ratio- The Definition…
A conversion factor that relates the amounts in
moles of any two substances involved in a
chemical reaction.
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Go to the WS
Finish the back for HW
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You will be working in groups of 3- be sure to exchange
contact info and be sure to communicate if you will be absent.
Jobs Rotate- Write you job at the top of each lab.
1. Leader- Keeps all on task and makes sure
directions are followed.
2. Scientist- Follows directions and is in charge of
making sure no mistakes occur.
3. Mathematician- insures calculations are correct.
I will pick one lab per group to grade-- you get
whatever score they get…make sure everyone in
your group is completing the lab!
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Copper Series- Lab Concerns
Use the same scales for each lab… they mass slightly
different.
Be sure to record any lab mistakes… too much
reactant, lost product, other booboos.
You will be calculating percent error and trying to
explain the errors.
You may never say that you made a mistake in your
calculations-- there are 3 of you working, there
should be no mistakes!
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Copper Series- Lab 1
Write and balance the equation for the reaction of copper
(Cu) plus nitric acid (HNO3) to produce Copper (II)
nitrate (Cu(NO3)2) plus water (H2O) and nitrogen dioxide
(NO2).
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Procedure- Using the sharpie.. Put your period
and lab station on the beaker. Ex: 2-1
1.
2.
3.
4.
Determine the mass of your empty beaker.
Determine the mass of the copper.
Send your scientist to the stock room to put
20mL of HNO3 into the beaker
Put on the watch glass and place on the hot
plate in the fume hood.
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Warm Up:
Mole to Mole Calculations….
Fe2O3 + 3CO
2Fe + 3CO2
1. How many mol CO are necessary to react with 2.2
mol Fe2O3?
2. How many mol Fe are produced if 1.8 mol CO is
used?
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Fe2O3 + 3CO
2Fe + 3CO2
1. How many mol CO are necessary to react with 2.2
mol Fe2O3?
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Mole Ratios
Fe2O3 + 3CO
2Fe + 3CO2
b) How many mol Fe are produced if 1.8 mol CO is
used?
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How did you do on HW?
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The following chart summarizes the
conversions we can do:
Number of particles of A
Mass of A
Moles of A
Volume of gaseous A
Number of particles of B
Moles of B
Mass of B
Volume of gaseous B
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So, can we use stoichiometry to determine
the amount of product made in types of
reactions lab?
We used 0.2 g of CuCO3 in the decomposition
reaction.
How much CuO was produced?
CuCO3
CuO + CO2
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Can we determine the amount of magnesium
oxide (g) were produced in the synthesis reaction?
We used about 0.5 g of Mg.
Mg + O2
MgO
a. Balance the equation.
b. Place the mass of Mg used in the upper left.
c.
Use DA to determine the theoretical mass of
MgO.
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Important Vocabulary Terms
Theoretical yield- the maximum amount of
product that can be produced from a given
amount of reactant.
Actual Yield- measured amount of a product
obtained from a reaction (in lab).
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What is the theoretical yield (in grams) of both
products in the following reaction if 2.5 g of HCl is
used?
Zn + HCl
a.
b.
c.
d.
ZnCl2 + H2
Balance the equation
Put 2.5g HCl in the upper left
Solve for g of zinc chloride.
Solve for g of hydrogen.
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Let’s make sure you are doing the lab
calculations correctly.
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On your copper lab, #5 asks you to determine
the theoretical yield for Cu(NO3)2. Do the
calculation using the mass determined in #1.
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Copper Lab- Series 2
1.
2.
3.
4.
5.
6.
Obtain the mass of your Cu(NO3)2
Add about 20 ml of distilled water.
Add 30 ml of NaOH
Obtain the mass of your filter paper!!!
Filter the mixture- rinse it well with distilled
water.
Wash out your original beaker (check to be
sure it is still marked with your period and
lab station.)
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Warm Up- Friday 2/8
Sodium reacts with Magnesium carbonate.
a.
Write the reactants and predict the products.
b.
How much magnesium is produced when 3.6 g
of sodium reacts with excess MgCO3?
c.
How much MgCO3 is needed to react with
exactly 3.6g of Na?
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There are a bunch of other calculations
we can do using the flow chart…
Number of particles of A
Mass of A
Moles of A
Volume of gaseous A
Number of particles of B
Moles of B
Mass of B
Volume of gaseous B
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Stoichiometric Conversions
How many grams of oxygen are produced when
17.5g of H2O2 decompose according to the
following equation?
H2O2
H 2O +
O2
(Don’t forget to balance the equation!)
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Volume to Volume Calculations
How many liters of water are produced when
3.0L of Hydrogen react with excess oxygen?
H2(g)
+
O2(g)
→
H2O(g)
(Don’t forget to balance the equation!)
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Volume to Volume Calculations
How many liters of oxygen are necessary to
make 5.6L of water?
H2(g)
+
O2(g)
→
H2O(g)
(Don’t forget to balance the equation!)
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Now you try
CH4(g)
a.
b.
+
O2(g)
→
H2O(g)
+
CO2(g)
Balance the equation.
If 5.62L of methane react with excess oxygen,
determine the theoretical yield (L) of both
products.
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Try one on the Volume/Volume WS
This is homework…. Don’t forget!!
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Molecule to molecule calculations
How many molecules of H2O2 are needed to
make 3.5 x 1023 molecules of water?
2H2O2
2H2O + O2
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What if you don’t start with
molecules… use the flow chart!
How many molecules of H2O2 are needed to
make 5.00 g of water?
2H2O2
→
2H2O + O2
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Try these!
CaCO3 + Mg
→
MgCO3
+
Ca
a) How many molecules of Ca are produced if 39.4g of
MgCO3 are also produced?
b) How many grams of Mg are necessary to react with
0.97 mol CaCO3?
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Warm Up- Monday/Tuesday
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Mixed Stoichiometry Problems
CaCO3 + Mg
→
MgCO3
+
Ca
a. How many molecules of calcium carbonate are
needed to react with 5.2g of Magnesium?
b. How many grams of Ca are produced when 7.6
x 1024 atoms of magnesium react?
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Percent Yield

In a perfect world, every student would get a perfect
score on every test.
Alas, we do not live in a perfect world
How do we determine the score you got on the test?
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Percent Yield (cont’d)
In a perfect world, every reaction would produce the
amount of material it is supposed to.
Alas, we do not live in a perfect world.
Percent yield = the ratio comparing the amount of
material actually generated in a reaction to the
maximum amount possible.
l
Percent Yield = Actual Yield x 100
Theoretical Yield
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Percent Yield (cont’d)

The theoretical yield is calculated using
stoichiometry.

The actual yield is found by experimentation.

Key Point: You can never predict the actual
yield or the percent yield.
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Percent Yield
2Mg + O2 → 2MgO
3.2 g of Magnesium reacted with excess
oxygen. 4.9g of MgO was produced in the lab.
Calculate the percent yield.
1.
2.
3.
Balance Equation
Calculate Theoretical Yield
Calculate % Yield
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You Try!
Sb2S3(s) + 3Fe(s) → 2Sb(s) + 3FeS(s)
When 22.3g of Sb2S3 reacts with excess of Fe, 12.7g
Sb is produced in the lab. What is the percent yield?
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Copper- Series 3
1.
2.
3.
4.
5.
6.
7.
8.
9.
Determine the mass of the Cu(OH)2. Don’t forget to subtract the
mass of the beaker and filter paper!
Open up the filter paper containing your product and transfer as
much of the copper hydroxide as you can into the large beaker.
Put the filter paper in too.
Add 100 ml of distilled water.
Put the large beaker on the hot plate and heat to a gentle boil.
Use forceps to remove the filter paper
Use the squirt bottle to rinse the filter paper.
Decant as much water as possible.
Transfer back into your beaker.
Allow product to settle and decant more water.
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Warm Up
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Limiting Reagent
Let’s think about a peanut butter sandwich…
The recipe calls for 2 pieces of bread and 2 Tsp.
of peanut butter.
Write the reaction:
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Now, we only have so much of each
reactant…
Huge tube o Skippy
12 pieces of bread
How many sandwiches can we make?
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Limiting Reagent (cont’d)

Chemical reactions are much the same way. The
balanced chemical equation is the recipe, telling you
how much of each thing you need.

Often, chemicals are not mixed in the correct
amounts, implying that one chemical will run out
before the others.

The chemical that runs out first is called the limiting
reagent.
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Limiting Reagent (cont’d)
Ex: 5.00g of HCl is mixed with 4.00g of NaOH according to
the following reaction:
HCl(aq) + NaOH(aq)
NaCl(aq) + H2O(l)
a)What is the limiting reagent?
b) How much of the other reactant is left over?
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Limiting/Excess
You react 54.8g of silver nitrate with 22.2g of
calcium chloride according to the following rxn.
AgNO3 + CaCl2 →
1.
2.
3.
4.
AgCl
+
Ca(NO3)2
Balance the equation.
Determine the limiting.
Calculate the maximum amount of AgCl
Calculate the excess.
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