Incorporating Engineering in High School Science and Math
Chemical Reactions and Stoichiometry Module
ACOS: Grade 9-12, Chemistry Standard 6:
Solve stoichiometry problems involving relationships among the number of
particles, moles, and masses of reactants and products in a chemical reaction.
Engineering Connection:
Chemical and Environmental Engineers are routinely involved in environmental
decisions such as assessing different chemicals’ effects on the surrounding
environment. Engineers in general are also heavily involved in finding areas where
cost-reduction can be obtained. One example is determining the most cost-effective
way of disposing of a chemical. Chemical engineers also use the properties of
chemicals involved in reactions to design more useful forms of the chemicals.
Identifying the Problem:
One of the byproducts of The Chemical Company’s Production Line A is
hydrochloric acid. Environmental regulations require neutralization of this acid
before disposal. Your department has been assigned the task of determining the most
cost effective method of neutralization.
Design Constraints:
In addition, it would be beneficial if the product of this neutralization reaction
may also be profitable for the company, therefore you need to develop a method
which results in a high percent yield. Your group will be assigned one of the following
bases to test in neutralizing the acid.
Base A: Sodium hydroxide: Cost-$57.17/1kg
Base B: Sodium carbonate: Cost-$13.11/1kg
Base C: Sodium bicarbonate: Cost-$18.92/1kg
Day One- Prelab:
1. Complete the Webquest on Acids and Bases so that you have enough
background knowledge to continue.
2. Predict which of the bases presented in the problem will be the most cost
effective for your company to use in neutralizing the acid. Below are the pH
values for various common acids and bases. Use these facts to support your
prediction.
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Chemical
Molarity
pH
Acid, Benzoic
Saturated
2.8
Acid, Boric
0.1 M
5.3
Acid, Citric
0.1 M
2.1
Acid, Hydrochloric
0.1 M
1.1
Acid, Oxalic
0.1 M
1.3
Acid, Salicylic
Saturated
2.4
Ammonia Water
0.1 M
11.3
Borax
0.1 M
9.2
Sodium Bicarbonate
0.1 M
8.3
Sodium Carbonate
0.1 M
11.5
Sodium Hydroxide
0.1 M
12.9
Day Two- Neutralization of Acid:
In this reaction you will measure the mass of solid reactant assigned and that of the
solid product. You will also measure the volume of hydrochloric acid neutralized.
You will then determine the actual, theoretical, and percent yields of the reaction
and share with your department to determine which of these bases is most cost
effective.
Safety:
Wear safety goggles and aprons. If any acid should spill on you, immediately flush
the area with water and notify the teacher. Be careful handling the glassware
during heating.
Objectives: After completing this experiment the student will be able to:
a.
Set up a GLX pH meter for titration.
b.
Titrate an acid with a strong base to determine the volume
needed for neutralization.
Materials:
Analytical balance
Spatula
Assigned Base
50 mL beaker
Graduated cylinder
Buret
1 M HCl
Distilled Water
Weigh boat
Buret Clamp
GLX and adaptor
2-250 mL Beakers
Funnel
pH sensor
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Testing and Evaluating:
Procedure:
1.
2.
3.
4.
5.
Place a weigh boat on the balance. Zero the balance with the weigh boat in
place.
Add approximately 0.50 grams of your assigned base to the weigh boat. Record
this mass in the DATA TABLE.
Remove the weigh boat from the balance and place the solid in a beaker.
Add 10 mL of distilled water and stir to dissolve the base.
Set up the ring stand and buret as directed by your instructor.
6.
Plug in GLX with the power adaptor. Attach the pH sensor in Channel 1. Do
not remove the buffer solution yet.
7.
8.
Turn on the GLX using the
.
Obtain a beaker for wash water and a wash bottle containing distilled (or
deionized) water.
Always rinse the electrode with distilled water into a beaker labeled as "Waste
Beaker".
Fill the buret past the 0.00 mL mark with the 1M HCl standard solution and
deliver the excess into a waste beaker while ridding the buret tip of air
bubbles. Adjust the HCl standard solution to the 0.00 mark of the buret.
Remove the buffer solution container. (Place it in a 50 mL beaker so that it
will not spill.) Keep the ‘O’ ring and buffer lid on the electrode. Slide them up
on the electrode so that they will not be in the way during titration.
Rinse the buffer off of the electrode with distilled water into the waste
container and blot. Immerse the electrode in the base solution.
On the GLX pH value should be visible. If you do not have a pH reading, use
arrow keys to move right to highlight the Meter box.
Begin adding the HCl slowly, about ½ mL at a time. Stop frequently intervals
to swirl the solution and observe the pH.
When the pH reaches 8.0 begin adding dropwise.
When the pH reaches 7.0 or slightly below and stays there for about 1 minute,
your solution is neutral.
Record the total volume of acid used in the data table.
Write your group name on a vial. Pour your neutral solution into the container
and set aside in a designated area for further experimentation.
Rinse off the pH electrode and replace it in the buffer solution.
Wash the buret completely (including the tip) with deionized water at least
three times.
Leave the buret open and inverted in the buret clamp so that it will drain
optimally.
Wash all used glassware and rinse with deionized water.
Wash your hands well before leaving the lab.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
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Day Three- Evaporation to Determine Salt Yield:
Safety:
Wear safety goggles and aprons. If any acid should spill on you, immediately flush
the area with water and notify the teacher. Be careful handling the glassware
during heating.
Objectives: After completing this experiment the student will be able to:
a. investigate mass and mole relationships in reactants and products of a
reaction.
Materials:
Neutralized solution from Day 2
1.
2.
3.
4.
5.
6.
7.
8.
Analytical balance
Spatula
Gauze Square
Tongs
Evaporating dish
Hot mitt
Hotplate
Watch glass
Weigh the evaporating dish and watch glass together and record in Data Table
2.
Pour one half of your neutralized solution into the evaporating dish.
Reweigh the evaporating dish and watch glass with the neutral solution and
record on Data Table 2.
Place the evaporating dish on a hotplate with the watch glass on top. Turn the
hotplate on 5. Heat the reaction mixture until a dry solid remains. If it starts
to boil, turn the hotplate down to 3 or 4. Make sure no water droplets remain
on the underside of the watch glass.
Allow the evaporating dish and watch glass to cool for about 15 minutes.
Determine the mass of the dish, residue, and the watch glass and record in the
DATA TABLE.
If time permits, reheat the evaporating dish and contents for two minutes more
to be sure all the liquid has been driven off. Cool and re-weigh.
Rinse the residue down the sink. Clean up your lab area and wash your hands
before leaving the lab.
Complete calculations and questions.
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STUDENT WORKSHEET: Chemical Reactions and Stoichiometry Module
Student Name:___________________
DATA TABLE 1:
Base Used:______________________
Mass of Reactant, Base
g
Initial pH
Volume of HCl
ml
Final pH
1. Write a correctly balanced equation for your neutralization reaction.
Extension/Quality Control:
1. Based on the volume of acid neutralized and the cost of your assigned base,
calculate the cost of neutralizing 10 L of 1 M HCl using this base. SHOW ALL
WORK BELOW.
Cost of Neutralizing 10 L of 1 M HCl =
A. Cost of Base Used = (Mass of Reactant Base)( 1 Kg
1
1000g
)(Cost of base)
1 Kg
B. Cost Per Volume = Cost of Base Used
Volume of acid neutralized
C. Cost Per 10L HCl = (Cost Per Volume)(10,000 mL)
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DATA TABLE 2:
Mass of dish, glass, and neutral solution
g
Mass of dish, glass, and residue after 1st
heating
g
Mass of dish, glass, and residue after 2nd
heating
g
Mass of dish and glass
g
Calculations: SHOW ALL WORK.
1. Calculate the mass of reactant (base) used.
2. Calculate the mass of product (NaCl). REMEMBER to multiply the mass of
residue by two since you only evaporated one half of the original neutralized
solution
3. Calculate the theoretical yield of NaCl based on the amount of base used and
the balanced equation.
4. Calculate the percentage yield of the NaCl.
CALCULATIONS TABLE
1. Mass of Reactant, Base
g
2. Mass of Product, NaCl (Actual Yield
multiplied by 2)
g
3. Theoretical Yield of NaCl
g
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4. Percentage Yield of NaCl
g
Extension/Quality Control:
2. What are some plausible reasons why your percent yield is less than 100%?
What are some plausible reasons why your percent yield is more than 100%?
3. Compare your final cost and percent yield results with the other groups to
determine the most cost effective method of acid neutralization for the class
as a whole.
BASE A
Cost/10L
% Yield
HCl
NaCl
BASE B
Cost/10L
% Yield
HCl
NaCl
BASE C
Cost/10L
% Yield
HCl
NaCl
AVG:
AVG:
AVG:
AVG:
AVG:
AVG:
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