MnSTEP Teaching Activity Collection > MnSTEP Activities > Investigating Factors Influencing Rates of Chemical Reactions

Investigating Factors Influencing Rates of Chemical Reactions

Paula Derickson
Red Rock Central High School
Lamberton, MN 56152

Based on an original activity found at www.alkaseltzer.com.
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Summary

In this investigation, students will observe the rate at which aluminum replaces hydrogen in a hydrochloric acid solution. Based on what they have learned about rates of reaction, they will then form a hypothesis about what factors in this experiment could influence the rate of reaction. They will then write a modified procedure to test their hypothesis. Data will be collected and compared to draw a conclusion.

Learning Goals

1. The student will review the factors that influence rates of reaction.
2. The student will develop a procedure to test his/her hypothesis about the factors influencing the rate of this reaction.
3. The student will work cooperatively with a partner to complete the activity.
4. The student will present data in an understandable format.
5. The student will draw a conclusion based on his/her data.
Vocabulary: rate of reaction, concentration, temperature, reactants, products
Key concepts: 1) The rate of reaction depends on the frequency of collisions between particles (atoms or ions) of the reactants. 2) When temperature increases, particles (atoms or ions) move more rapidly and frequency of collisions increases. (ie. temperature ↑, rate ↑) 3) Concentration is directly proportional to the rate of reaction. (ie. concentration ↑, rate ↑)

Context for Use

This laboratory activity is intended for a secondary school physical science course. It could also be used in a chemistry course. I have not used it yet but I think it will be possible to complete the data collection in 1-2 regular class periods or 1 block period. It would more interesting (and exact) if one were to quantify the amount of H2 gas produced over time, but as long as the student is carefully collecting and recording his/her data it should still show the trend. Students should already be familiar with lab safety procedures before completing this activity. This activity will be used when we are learning about rates of reaction. I want the students to do the activity as presented the first time, but then realize that there really isn't a useful conclusion until one of the variables is changed – namely either the heat or the concentration of the HCl. Then modify the procedure, run it once again, collect the data, compare it to the first run, and draw a conclusion.

Subject: Chemistry:General Chemistry:Chemical Reactions
Resource Type: Activities:Lab Activity
Grade Level: High School (9-12)

Description and Teaching Materials

Adapted from an activity found at Alka-Seltzer.com. The original can be found at the following link:
http://www.alka-seltzerplus.com/as/student_experiment3.html
My changes include a few minor material changes and some additional questions. I have submitted these as a separate file attachment.
In short, the student does the activity basically as outlined in the Alka Seltzer activity. As I ask more questions of them, they will realize that they don't have enough data to actually draw a conclusion about what is affecting the rate at which hydrogen gas is being generated in this reaction system. They will then modify the procedure to test another factor that could be affecting the rate of their reaction (temperature or concentration of acid) and run the activity again. They will compare their two sets of data and draw a conclusion. Rate of Reaction Lab (Microsoft Word 27kB Aug1 09)

Teaching Notes and Tips

Teaching Notes –
I have not yet had opportunity to use this activity in my classroom but a few possible issues or concerns that come to mind are –
- Will the amount of either reactant affect the rate at which the gas is produced? i.e. if we don't measure out exactly the amount of aluminum and the amount of HCl each time can the results really be compared? I have addressed the acid, but not the metal.
- Will not having a heat source slow the rate so much that the reaction won't be measurable?
- I can think of two ways to modify the procedure – 1) take away the heat OR 2) lower the concentration of HCl. Are there other ways to modify it that I haven't thought of yet?

Assessment

I will collect lab notebooks and writeups after the lab is complete. These will be graded. Of course there will also be test questions pertaining to this topic on the unit test. Formative assessments can be used when one-on-one with students in the lab, and especially when checking the students' modified procedures in the middle of the lab.

Standards

9C.2.1.3.6 – describe factors that affect the rate of a chemical reaction.

References and Resources

http://www.alka-seltzerplus.com/as/student_experiment3.html

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