Alka Seltzer and Factors that Affect Reaction Rates

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Objective

Students will be able to explain the factors that affect the rate of a reaction as evidenced by performing a lab activity.

Big Idea

Chemical reaction rates depend on various factors including stirring, temperature, surface area, and concentration.

Introduction

In this lesson students have a chance to practice what they learned about reaction rates through performing a lab activity.

  • This lesson covers the Next Generation Science and Engineering Performance Expectation 1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration on the reacting particles on the rate at which a reaction occurs.  It does so because students are performing a lab to test the factors that affect reaction rates.
  • This lesson aligns with several of the Next Generation Science and Engineering Practices including:
    • 2 Developing and Using Models.  It does so because students are modeling why reaction rates increase.
    • 3: Designing and Carrying out Experiments. It does so because students are performing an experiment.
    • 6: Constructing explanations: It does so because in the extension activity students are asked to make a claim and use evidence from an article and from their lab.
  • This lesson aligns with the Next Generation Science and Engineering Crosscutting Concepts including:
    •  1: Patterns.  It does so because the pattern of reaction behavior can be studied and used to understand phenomenon.
  • For this lesson each student group needs the following resources: warm water, room temperature water, a 25mL graduated cylinder, a film canister, 3 Alka Seltzer tables, a knife, and forceps.

Explain

10 minutes

To begin this lesson I go over the lab with students.  

  • To do this I first pass out the alka seltzer and rates lab paper.  
  • I then give students several minutes to read over the lab on their own.  
  • After 3-4 minutes I ask students the goal of the lab.  I ask for volunteers and they let me know that it is to test the factors that affect reaction rates.  
  • I then go over what students will be doing for the prelab and have them spend several minutes doing the prelab on their own.  This is a movie of me going over this with students.
  • I then review safety with students by letting them know that they must wear the goggles at all times and to make sure to not point the film canisters at students because the tops will pop off vigorously.  This is a video of me doing this with students. 
  • Finally I break students into cooperative groups and have them go up to their lab stations.  For more information on how I use cooperative groups see my cooperative groups reflection
  • This is a picture of what a station looks like for the lab. 

Elaborate

40 minutes

In this section of the lesson students are expected to perform the alka seltzer and rates lab.

When they get up to their stations they first finish their data tables, and then begin the lab activity. This is a movie showing one group of students performing one of their trials. 

As students are working I walk around and check for several things...

  1. I make sure that they have their data tables complete BEFORE starting the lab.
  2. I make sure that they are recording observations as well as the time for the canister's top to pop off.
  3. I check that students are ALL wearing their goggles.
  4. I make sure that they understand that the first cylinder is their control; therefore, the one tha they should be comparing their other trials to.  This movie shows me doing this with my students. 

As students complete the lab I have them begin to work on the analysis questions. When all students are done with the lab and working on the analysis questions I have them pause so that we can work on the extension together.

Extend

10 minutes

When most students have completed the lab I lead them in performing the extension activity.  This is found on the last page of their alka seltzer and rates lab.  

For this extension students read an article discussing how aspirin should be taken if someone is having a heart attack.  Basically, it says that the aspirin should be chewed as that it gets into the bloodstream and works faster.   The goal is for students to come up with a claim that the article gives similar results as their lab because they both show that by increasing surface area that reactions happen faster. 

This is a movie of me going over this with one class. 

Evaluate

When students complete their labs I have them turn them in and I grade them using the alka seltzer lab rubric.

Most of my students missed at least one point, and most forgot to revisit their predictions.  These are several examples of some graded labs which show some of the common mistakes by students.

In this first example the student had an incorrect prediction for their prelab, did not refer back to their predictions in the analysis section #1, and did not really come up with a claim in regards to evidence from their lab in the extension.

In this second example the student did not refer back to their predictions when doing analysis part 1, and did not use evidence in the extension section.

In this third example the student did a good job but still did not refer back to their predictions in the first part of their analysis.

Finally in this fourth example the student also did a good job but did not refer back to their predictions int he first part of their analysis.

Because so many students forgot to go back to their predictions I feel that I need to do a better job of helping students with this next time.  Therefore, I made some changes to the lab which I discuss in the reflection, Common Confusions with the Lab.