Grade Level/Subject
Chemistry grades 10 -12
Unit
Stoichiometry
Enduring Understanding
SOL Standards
Title
I.
Stoichiometry involves quantitative relationships that are based
on mole quantities in a balanced equation.
II.
Dimensional analysis is a way of translating a measurement from
one unit to another unit.
III.
The Law of Conservation of Mass allows us to predict the products
of a chemical reaction.
IV.
The mass of a product can be predicted if two pieces of
information are given: the mass of the reactant and the balanced
equation.
V.
Real reactions do not yield the predicted amount of product –
there is some degree of error/loss – this is quantified in the
percent yield calculation.
Standard CH.4 – The student will investigate and understand that
quantities in a chemical reaction are based on molar relationships.
The Stoichiometry Challenge
Lesson Objective
I.
II.
III.
Students will use their knowledge of stoichiometry and dimensional
analysis to predict the amount of product that remains in a test tube
after sodium bicarbonate is decomposed.
Students will test their prediction (by performing the lab) and analyze
the accuracy of their results.
The intention lab demonstrates that real reactions follow the Law of
Conservation of Mass and, as such, stoichiometry can be used to predict
quantities in chemical reactions.
Inquiry Level
2
Materials Required
Borosilicate (Heat Proof) Test Tubes
Test Tube Clamps and Ring Stands
Bunsen Burners
Sodium Bicarbonate (NaHCO3)/Baking Soda
Mass Balance (only need one or two)
The Stoichiometry Challenge
Teacher Notes
Students will use their knowledge of stoichiometry and dimensional analysis to predict the amount of product that
remains in a test tube after sodium bicarbonate is decomposed. Students will then test their prediction (by performing
the lab) and be awarded a grade based on the accuracy of their results. The intention of this lab is to demonstrate,
through inquiry, that real reactions follow the Law of Conservation of Mass and, as such, stoichiometry can be used to
predict quantities in chemical reactions. The decomposition of baking soda is a fairly simple reaction that provides high
yields.
GRADE LEVEL/SUBJECT:
PREREQUISITE KNOWLEDGE:
First Year Chemistry Course (10th-11th Grade)
Decomposition Reactions, Molar Relationships
UNIT:
Stoichiometry
SOL OBJECTIVES:
Standard CH.4 – The student will investigate and understand that quantities in a
chemical reaction are based on molar relationships.
LEVEL OF INQUIRY:
Level Two – Question and Methods are Given, Solution is Open.
MATERIALS REQUIRED:
Borosilicate (Heat Proof) Test Tubes
Test Tube Clamps and Ring Stands
Bunsen Burners
Sodium Bicarbonate (NaHCO3)/Baking Soda
Mass Balance (only need one or two)
TIMING:
Data Collection ~25 minutes
Analysis and Post Lab ~25 minutes
SAFETY:
All Chemicals are Non-Hazardous
Bunsen Burners provide a Fire/Burn Risk
Check all Glassware for Cracks before Heating
ESSENTIAL UNDERSTANDINGS
 Stoichiometry involves quantitative relationships that are based on mole quantities in a balanced equation.
 Dimensional analysis is a way of translating a measurement from one unit to another unit.
 The Law of Conservation of Mass allows us to predict the products of a chemical reaction.
 The mass of a product can be predicted if two pieces of information are given: the mass of the reactant and the balanced equation.
 Real reactions do not yield the predicted amount of product – there is some degree of error/loss – this is quantified in the percent
yield calculation.
TO PREPARE FOR THE LAB…
 Set out all equipment. Each lab groups needs on large test tube, Bunsen burner, ring stand and test tube clamp.
 Each group will determine how much baking soda to start with (about 5 grams is fine). One box of baking soda can be used for
multiple class periods.
 Set out 1-2 mass balances in an area that you can supervise. Avoid given each group a balance – you do not want them secretly
checking the mass without you present.
Name: __________________________________
Period: ________
The Stoichiometry Challenge
Your challenge in this experiment includes two parts: (1) you must predict the amount of product that will be
left in a test tube after sodium bicarbonate undergoes a decomposition reaction and (2) you will test your
prediction by performing an experiment. Your grade on this lab will be determined based on the accuracy of
your prediction – so be careful and watch your lab technique!
Safety Precautions
Before you begin, inspect the test tube for chips and cracks. When using the Bunsen burner, tie back long hair and do not
wear loose clothing. Never leave lit burners unattended. And remember HOT GLASS looks the same as COLD GLASS.
Procedure
1. Obtain a large borosilicate test tube and weigh it on one of the balances. Record this mass in the
Data Table. Note: Borosilicate is a type of glass that can be subjected to very high (and low)
temperatures without shattering.
2. Go back to your lab station and place one large scoop of baking soda (sodium bicarbonate,
NaHCO3) into the test tube - should be about 5 g.
3. Using the same scale as before, weigh the test tube with the baking soda. Record this mass in the
Data Table.
4. Calculate the mass of the baking soda in the test tube and record the amount in the Data Table.
5. Holding the test tube nearly horizontally shake the baking soda gently so that it spreads out.
6. Tighten the test tube clamp securely around the test tube, just below the rim so that it remains
positioned nearly horizontally.
7. Light a burner and adjust it to a large cool flame so that the outer cone is hitting the bottom
half of the test tube. You may have to raise or lower the height of your test tube and clamp to
be positioned correctly.
8. Record the time you started heating. __________.
Note: This heat will initiate a chemical change (a decomposition reaction) that breaks the
NaHCO3 down, not into its elements but into three separate compounds. Use your knowledge
of decomposition reactions to predict the products. Answer Question 1 Now.
9. Look carefully at the upper half of the test tube. Answer Questions 2–3 Now.
10. Move the burner occasionally to a different spot to ensure a thorough heating of the entire
bottom half of the test tube.
11. Consider the substance that is left in the test tube. It may look just like the baking soda you
put in the test tube, but it has actually been converted into something else—sodium carbonate.
Answer Question 4, keeping an eye on the time.
12. After you have been heating the test tube for 10–12 minutes, turn off the burner and let the
test tube cool for 7–8 minutes.
13. While waiting for the test tube to cool, answer Questions 5–7.
14. If your test tube has been cooling for 7–8 minutes, it should be ready for the official weigh-in!
Bring the test tube, along with this sheet containing your prediction from Question 7, to the
instructor who will weigh it on the same scale you used before. Your grade will be based on how
closely your prediction came to the actual mass (see the Scoring Table).
15. After you have finished all of the above, rinse out the test tube in the sink and place back at
your station.
16. Answer the Post-Lab Questions.
Data Collection
Mass of Test Tube (g)
Mass of Test Tube + Sodium Bicarbonate (g)
Mass of Sodium Bicarbonate (g)
Observation Questions (to be completed during lab)
1. The chemical formula of sodium bicarbonate is NaHCO3. What common oxide could be
produced as it decomposes?
2. What do you observe in the upper half of the test tube (step 9)?
3. What common substance appears to be the second product in this reaction? What test
could you perform to verify the identity?
4. The third product of the reaction is sodium carbonate. What is the correct formula for
sodium carbonate?
5. Write the balanced chemical equation for the reaction that took place in the test tube –
make sure it is balanced. Include states for each substance.
6. PREDICT THE PRODUCT AMOUNT: calculate the mass of sodium carbonate you should
have left in the test tube at the end of the reaction. Also calculate the amount of water
and carbon dioxide that should have been produced. Show proper dimensional analysis.
7. Assuming all the baking soda you started with has been converted into sodium carbonate
(with the product gases driven off), what should the test tube and contents weigh now?
Show your work.
Test Your Prediction
Predicted Amount (g)
Actual Amount (g)
Difference
Sodium Carbonate
Carbon Dioxide
Water
Scoring Table
If you are within…
Your grade will be…
0.03 g
0.10 g
0.20 g
0.50 g
1.00 g
5.00 g
You Tried
Post Lab Questions
10/10
9/10
8/10
7/10
6/10
5/10
4/10
Score
8. Suppose you only heated the test tube for 5 minutes – how would this alter your results
and prediction?
9. Does this reaction follow the Law of Conservation of Mass? Use your data to defend
your answer.
10. Calculate the percent yield of your experiment – showing all your work. If it is not
100%, describe at least three errors that could have contributed to a loss in yield.
Classify
each as either a random or systematic error.
11. Suppose you were an engineer employed by a company to produce sodium carbonate on a
large scale. How could you improve the yield of this reaction? List at least three
suggestions.