Conducting the Reaction Rate Experiment

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Objective

Students will conduct a reaction rate experiment they designed and determine if their results are reasonable based on a calculated theoretical yield.

Big Idea

Reaction rates are influenced by temperature, concentration, and surface area. A theoretical yield from stoichiometry is a good benchmark for determining if experimental data is reasonable.

Introduction

In the previous lesson students worked to write the first sections of a lab report that will document a reaction rate experiment that they designed.

In this lesson students will be able to conduct their experiment when they get approval for that work.

This lesson aligns to the NGSS Disciplinary Core Idea of HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs by giving students the chance to produce this evidence in the form of their reaction rate data.

It aligns to the NGSS Practice of the Scientist of Planning and carrying out investigations because in this lesson students will actually carry out the investigation that they have already planned

It aligns to the NGSS Crosscutting Concept of Cause and Effect because students will be expected to describe the cause and effect relationships by relating what is known about the smaller scale mechanisms (kinetics) with what is observed at the macroscale (reaction rate variance).

In terms of prior knowledge or skills, students should have already learned a number of related topics, including introductory kinetics, collision theory, and the factors that influence reaction rates.

The materials needed for the experiment include the following:

  • Timers
  • Reaction vessels such as 100 ml beaker
  • Graduate cylinders
  • 1M, 3M, and 6M HCl
  • Gloves and safety goggles
  • Calcium carbonate powder and various sizes of calcium carbonate pebbles
  • A wastes disposal container for unreacted HCl
  • An acid neutralization kit for accidental spills
  • Electronic balances

Do Now

5 minutes

Do Now: I ask students to have their reaction rate experiment paperwork out. they have been working with the Reaction Rates Experiment Graphic Organizer and the Reaction Rates Experiment. I then ask them to identify which group they are in:

Group 1: If you not completed the packet up to the data table then continue working on it and identify any questions you have.

Group 2: If you have already turned in work, please come get the work and look it over. If it needs revision, work on it. If not, hold tight.

Group 3: If you are ready to turn in work, please sign up for a conference with me.

I reason that this is a good way to start class because it immediately places students in a position to move forward with the work that was already started in a previous class. I already know what group they are in because I am keeping track of who has been cleared to do their experiment.

Mini-lesson and Guided Practice

10 minutes

Mini-lesson:  I first talk with Group 2. Some students are ready to begin experimenting and I want them to be able to get right to work. I begin by reviewing the safety concerns that we talked about when we did a trial run of the procedure:

  • Wear gloves to protect against acid.
  • Hair must be tied up, and goggles must be worn, at all times.
  • Watch where we are going
  • Dispose of their materials in waste beakers.

 

I then remind them of how we have the materials laid out. There are measuring stations for the different concentrations of HCl, and students need to be sure they are using the correct concentration by reading the labels BEFORE they pour acids. I note that every weigh station is equipped with calcium carbonate.

I note the locations where students can heat their acid. I remind students that if the acid overheats they can suffer serious injury, and the way to prevent this is to heat the acid slowly, and to monitor the temperature of the acid.

I then turn to Group 1 to see if anyone has any questions.

Finally, I tell Group 2 that I will meet with them individually to conference with them about their work.

This instructional choice reflects the fact that different students will be in different places, and I want to meet them where they are. I do not want to slow students down who are ready to conduct the experiment. I also want to send a message to students who are moving slow on the first part of the lab report that time is moving along and some students are already cleared for experimentation.

 

Application

35 minutes

Student Activity: During this section of the lesson my class is very student directed. Some students are working on finishing their experimental design and introduction. Some students are conducting their experiment. Some students are conferencing with me to either get help with revising their experiment or to get cleared so they can begin their experiment.

Most of my evaluation for the first half of the lab report has to occur when students are not working on experiments because I need to be present and aware when students are working with chemicals. In my largest class, which has 27 students in it, I may not be able to conduct any assessment conferences. I may focus my attention more on answering questions.

In my small group of 17 students, it may be more practical to divide my attention. One way I can conference and still have students make progress is to limit the trials to the lowest concentration of acid, and the coldest temperature when I know that my attention will be divided. Students are accustomed to working with 1M HCl, and they know how to act safely in the lab.

The lab feels very dynamic on days like today. Everyone is busy working at their own pace and trying to move their work forward. Time tends to go by quite quickly, and I need to have a timer set so that there is time for clean-up and debrief.

Catch and Release Opportunities: If I see any safety violations, I stop class immediately, or address individuals if that would be more effective. If I see students not keeping the lab tidy, I stop and explain my expectations.

Stopping class to discuss this is important because when many students are trying to get their work done they sometimes forget that keeping the lab neat and organized is a lab safety issue. I remind students that the only thing I believe in more strongly than getting them to do science is getting them to do science safely.

I also take time to watch and interact with as many groups as possible. I do this to maintain relationships, to gather insights as to how the experiments are going, and to engage in scientific dialogue when the opportunity arises. Here is a video of me interacting with students conducting the reaction rate experiment.

Debrief

10 minutes

To wrap this lesson up I ask some students to share their data tables. I am curious to see how the experiment is progressing. I want to evaluate student progress so that I can make adjustments to our schedule if it seems to be taking longer than I anticipated.

More importantly, I want to make sure that student data seems reasonable. I remind students that there is a theoretical yield for the reaction they are conducting. I also remind them that they have a hypothesis. The data should be in a range that we would expect based on the stoichiometry and the hypothesis.  I ask students to assess how reasonable the data is that we are projecting.

Ending class this way allows me the chance to remind students that the goal of the experiment is to generate data that makes sense. If they have a measurement error or some other careless mistake that that makes their data inaccurate, then this will affect their conclusion, and their grade.