Conejo Quandary
Problem-Based Learning
Denise Agapoff
Environmental Studies Amgen SSI 2004
Objective: To compare two different techniques for treating acidic run-off.
First, determine the amount of base needed to neutralize the acidic run-off.
Second, determine how much water is needed to neutralize the acidic run-off.
The Problem: The Conejo Valley Chamber of Commerce has a decision to
make. Decay Mart wants to set-up a paper mill in the Conejo Valley. The
problem is that the factory emissions of waste water streams directly into the
nearby Wildwood Canyon River. You have been hired as a chemist to eliminate
any environmental impact. To do this you must decide on the best way to
neutralize the waste water before it reaches the river.
Expected Emissions:
2.0 grams of hydrochloric acid per one liter per week
Part 1
Questions/Calculations:
1. What is meant by neutralization?
2. Using the base sodium hydroxide, write out a balanced equation
showing the neutralization process.
3. Determine the quantity (grams) of base needed to carry out this
process.
Show work for credit.
4. Explain in words the process that needs to be done every week for
neutralization to occur.
Part 2
Questions/Calculations
1. Calculate the molarity the acidic emissions given above.
2. Use the following formula to calculate the amount of water needed to
neutralize the week’s emission.
C1V1 = C2V2
C1 = concentration of acidic waste (in moles per liter)
V1 = volume of acidic waste
C2 = concentration of neutralized waste, use 1 x 10-7 moles per liter which is the
concentration of in one liter of water
V2 = volume of neutralized waste
3. How much water is needed to dilute the acidic waste each week?
Part 3
Discussion/Conclusion
1. Look at both possible solutions.
Evaluate each based on cost per week, difficulty to perform, and any side
effects.
Thousand Oaks water costs $1.67 per gallon and there are 3.79
liters in one gallon
Sodium hydroxide costs $6.71 per 100 grams
2. Write a letter to the Conejo Chamber of Commerce with your
recommendation. Include your analysis support of your decision.
California State Standards
Structure of Matter
3. Elements have distinct properties and atomic structure. All matter
is comprised of one or more of over 100 elements.
Reactions
5. Chemical reactions are processes in which atoms are rearranged
into different combinations of molecules.
As a basis for understanding this concept, students know:
a. reactant atoms and molecules interact to form products with different chemical
properties.
b. the idea of atoms explains the conservation of matter: in chemical reactions the
number of atoms stays the same no matter how they are arranged, so their total
mass stays the same.
c. chemical reactions usually liberate heat or absorb heat.
d. physical processes include freezing and boiling, in which a material changes
form with no chemical reaction.
e. how to determine whether a solution is acidic, basic or neutral.
Investigation and Experimentation
9. Scientific progress is made by asking meaningful questions and
conducting careful investigations.