C4.6a Calculate the number of moles of any compound or element given the mass of the substance
C4.6b Calculate the number of particles of any compound or element given the mass of the substance
C5.2d Calculate the mass of a particular compound formed from the masses of starting materials
C5.2e Identify the limiting reagent when given the masses of more than one reactant
C5.2f Predict volumes of product gases using initial volumes of gases at the same temperature and pressure
C5.2g Calculate the number of atoms present in a given mass of element.
HS-PS1-7 Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction
Using
Using
Using
Identifying
Using
Using
Inquiry



Use mathematical representations to calculate the mass of a particular compound formed from the masses of starting materials.
Develop and use models to identify the limiting reagent
Construct explanations as to why atoms and therefore mass are conserved in a chemical reaction
Stochiometry is not a rather in depth topic but one that is heavy in terms of mathematics.
Though there are some areas that are more conceptual and micro-level; which adds a dimension of difficulty for the students. One such concept is the mole. The mole is a way for chemists to count rather large number of things in an easier way. Then using the mole we can make connections between a substances mass, volume, and even the number of particles. There are some conversion factors that are very important in making this happen. One very important conversion factor is
Avogadro’s constant, 6.02 x 10 23 , allowing us to calculate particle numbers. Other conversion factors are less concrete and change from problem to problem. Using balanced chemical equations students will be able to use the mole to mole ratio of substances involved in a reaction to then calculate the mass or some other variable given some initial amount.
Also important to stocihiometry is the concept of limiting reagent or limiting reactant. The limiting reagent will be the substance that determines how much product a chemical reaction can produce. Substances combine in specific ratios to make specific amounts of product. Following this specific ratio one of the reactants will be completely consumed while the others will still be around.
This reactant that is completely consumed before the rest of the reactants is considered the limiting reagent; it limits the reaction. Students will be able to figure out the limiting reagent mathematically

using balanced chemical equations. This combined with mole to mole ratios students will be able to figure out which reagent or reactant is limiting the amount of product being made.
After the students are able to make calculation of the amount of theoretical product created during a reaction they will then be able to calculate the percent yield of an actual reaction. The percent yield of a reaction conducted in a laboratory setting is typically not 100% due to human error.
This will allow for students to experiment and come up with rational as to why we cannot obtain a
100% yield. Although obtaining 100% yield is highly improbable it is important that students can interpret why this is so comparing it to the theoretical value.
Goals
-Students will be able to (SWBAT): Analyze data
-SWBAT: Use data to form conclusions
-SWBAT: Create hypothesis using previous knowledge and reasoning
Materials
-5 Erlenmeyer flasks (150 mL)
-5 balloons
-Baking Soda (~ 8.0g)
-Vinegar (~100 mL total 20mL in each flask)
-Balance
-Large sheet of paper
-Marker
Estimated Time
5 minutes
Activity
Announcements
~15 minutes
~25 minutes
Baking Soda Vinegar Demo
Class Discussion/Class Model
Notes
-Explain the days agenda
-Where we are going
-Combine Baking Soda and
Vinegar, collect the carbon dioxide produced
-Use different measures of baking soda, same amount of vinegar
-Have students predict what balloon will be the largest, and why
-Introduce driving question,
“how much product can we make?”
-On board collect students thoughts
-Create a class model to explain the phenomena

~10 minutes Wrap up of Conversation
-Careful not to answer the question at hand
-Wrap up conversations
-Address how we will go about figuring out the phenomena at hand
Notes:
Balloon #
Vinegar (mL)
Baking Soda (g)
Discussion Questions
1
20
0.36
2
20
0.70
3
20
1.40
4
20
2.00
5
20
3.40

How do we know a reaction is taking place?

What do we see in the flask, anything?

Is there any solid left? Which flasks?

Is there any vinegar remaining? How can we tell?

What is special about the last three flasks?
Assessment
Students will turn in an exit slip. On the exit slip students will have listed their observations from the demonstration. They will also include their own thoughts and ideas to explain the phenomena. Then they will list any questions they have or want to know about the demonstration.
Goals
-SWBAT: Identify a limiting reagent
-SWBAT: relate limiting reagents to the baking soda and vinegar demo
-SWBAT: begin to identify limiting reagents using mole ratios
Materials
-3 complete Lego People
Estimated Time
5 minutes
Activity
Announcements
~15 minutes Lego People Demo
Notes
-Explain the days agenda
-Where we are going
-Relate Lego People building to limiting reagent
-Need to have correct ratio of parts to correctly build

~10 minutes
~20 minutes
Notes
Balanced Equations and mole ratios
-Compare to baking soda and vinegar demo
-Relate using another example
-Define Limiting Reagent
-Define Excess Reagent
-Come up with mole ratios for simple examples
-Use examples to gain a better understanding of limiting reagents on a macroscopic scale
Notes:

Set up scenarios where the amount of Lego people is limited by the amount of upper or lower torsos.

Ask what prevents us from creating infinite amounts of Lego people.

Why do the amounts limit the production?

Can we relate this to the flasks in the baking soda demo? How would that look?

Can we use this to describe other situations such as build smores, cars, etc?
Assessment
1.
Given the reaction 4NH
3
+ 5O
2
→ 4NO + 6H
2
O, what is the maximum number of moles of H
2
O that can be produced when 2.0 mol of NH
3
are completely reacted?
2.
Given the reaction 2CH
3
OH(l) + 3O
2
(g) → 2CO
2
(g) + 4H
2
O(g), how many moles of O
2
(g) are needed to produce exactly 20 mol of CO
2
(g)?
3.
Consider the following equation. CH
4
(g) + 2O
2
→ CO
2
(g) + 2H
2
O(g)
How many moles of oxygen are needed for the complete combustion of 3.0 mol of CH
4
(g)?
4.
According to the reaction 2Al + 3H
2
SO
4
→ 3H
2
+ Al
2
(SO
4
)
3
, the total number of moles of H
2
SO
4 needed to react completely with 5.0 mol of Al is?
5.
Given the equation N
2
(g) + 3H
2
(g) → 2NH
3
(g), what is the total number of moles of NH
3 produced when 10 mol H
2
reacts completely with N
2
?
Challenge questions
6.
Given the reaction 2K(s) + Cl
2
(g) → 2KCl(s) what is the amount of K, in grams, needed to completely react with 2 moles of Cl
2
(g)?
7.
Consider the equation H
2
+ Cl
2
→ 2HCl. A student suggests that according to the ration shown by the coefficients, 20 g of hydrogen will react with 20 g of chlorine to form 40 g of HCl. Is the student correct? Explain.

Goals
-SWBAT: use data to answer additional problems
-SWBAT: identify patterns in data
-SWBAT: use data to make conclusions
Materials
-Nuts (enough that each group can have 20 grams)
-Bolts (enough that each group can have 20 grams)
-Washers (enough that each group can have 20 grams)
-Balance
Estimated Time
5 minutes
Activity
Announcements
~40 minutes
~10 minutes
Mole Lab
Clean-Up/Q & A
Notes
-Explain the days agenda
-Where we are going
-Give directions
-Using nuts, bolts, washer build as many complete sets as possible
-Try building same amount of complete sets but using only mass to calculate the number of items needed
-Go over proper use of a balance
-Let students pick partners
-Get them started
-Give students time to clean up their work area
-Make sure everything is put back how it was before they started
-Allow students to ask any clarifying question associated with lab
Notes:

Students will likely struggle with part two, make sure to clarify the directions and purpose here without giving away too much information.

How can we relate count to mass of an item?

Lab can be found on page 72-73 at: http://dwb4.unl.edu/ChemSource/SourceBook/151ILAB.pdf
Assessment

You just got a job working at a factory where they make giant robots.
Since the robots tend to be surly, manipulative, and generally dishonest, it’s a good thing you never get to see the finished product.
Instead, your job is to assemble a little tiny component of the robot that consists of one bolt, one washer, and one nut.
This component is called a
“hoozit.” (The hoozit may not look like much, but it’s very important.
It helps the robots dance better.) Each morning, you have to walk to the hardware bins, get the bolts, washers, and nuts you’ll need for today’s output of hoozits.
To save yourself the trouble of counting out the bolts, washers, and nuts individually, you are going to measure them out by mass.
Figure 1: The bolt-washer-nut assembly, also known as a “hoozit.”
Part 1 Procedure
1.
Using a balance, measure out 20 g bolts, 20 g washers, and 20 g nuts.
2.
Take the hardware back to your lab bench and assemble it into hoozits, each containing exactly one bolt, one washer, and one nut.
When you run out of one component, stop.
3.
Write down the numbers of bolts, washers, or nuts that you have left over after you have made your last hoozit.
Part 1 Question
After you made as many hoozits as possible, did you have any hardware left over?
Why or why not?
Part 2 Procedure
1.
Return any leftover hardware from Part 1 to the appropriate hardware bins.
2.
Obtain fresh batches of bolts, washers, and nuts to make more hoozits.
This time, try to think of a way in which you can make sure that you get the same number of bolts, washers so that you won’t have any hardware left over.
Again, you may not
71

count out individual bolts, washers, and nuts.
You can only measure their masses using a balance.
3.
Write down your plan in complete sentences.
4.
Carry out your plan.
Part 2 Questions
Did you have any hardware left over this time?
Did you have more or less hardware left over in Part 2 than in Part 1?
Why do you think your plan worked or didn’t work?
Part 3 Thought Experiment
After less than a week, you quit your job at the robot factory because it is boring and tedious, and your conscience groans at the thought of helping to make such illbehaved androids.
Worst of all, one of these robo-jerks has just been made your supervisor.
You get a new job at a chemical laboratory where your first assignment is to react hydrogen and oxygen to make water.
You can’t count out individual atoms of hydrogen or oxygen, but since each water molecule contains two hydrogen atoms and two oxygen atoms, you decide to measure out 200 g hydrogen and 100 g of oxygen.
Part 3 Questions
1.
Do you think you will have any oxygen or hydrogen left over after you react them to make water?
Which do you think you are more likely to have left over, oxygen or hydrogen?
( Hint : An oxygen atom has eight times the mass of a hydrogen atom.)
2.
Can you think of a better way to measure out your oxygen and hydrogen so that you will not have any of either left over after you react them to make water?
Just as in Part 2, you are only allowed to measure the mass of your hydrogen and oxygen.