Day 2: Evidence of Chemical Reactions Lab

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TSWBAT identify four unknown reactions as either a chemical change or physical change based on their knowledge from previous experiments.

Big Idea

Using Pasco probeware, students use previously obtained data to determine whether an unknown "reaction" is chemical or physical change.


Performance Expectation (PE)/Disciplinary Core Idea (DCI)

This lesson is aligned with HS-PS1-7, the uses of mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction; and DCI-PS1.B, the fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions. One important part of predicting chemical reactions is to recognize that a chemical reaction has occurred and not just a physical change.  Recognizing evidence that a chemical reaction has occurred is the first step in understanding chemical properties.  This investigation has students predict whether a change in properties is chemical or physical. 

Science and Engineering Practices (SEP)

Practice 3 Planning and Carrying Out Investigations -- Students plan an investigation test a design collaboratively to produce data to serve as the basis for evidence as part of building and revising models, supporting explanations for phenomena, or testing solutions to problems. Consider possible confounding variables or effects and evaluate the investigation’s design to ensure variables are controlled.

Practice 4 Analyzing and Interpreting Data -- Students analyze data using tools, technologies, and/or computational models in order to make valid and reliable scientific claims or determine an optimal design solution

Crosscutting Concepts (XC)

During this lesson students will recognize Matter and Energy are a part of chemical reactions.  While preforming this investigation students are expected to see that matter is conserved because atoms are conserved in chemical and physical chemical processes.  

The previous day students finished the lesson by categorizing 10 different reaction into the five different reactions types: synthesis, decomposition, single replacement, double replacement and combustion.  To start the class, I have student write down on a single sheet of paper one example of each.  They are told to use their notes to aid them in this.  This will help them recall what was learned from the previous day.  After a five minutes I have them turn it, so that I can look at it after class.


5 minutes

Day 1 of this lab students were introduced to safety procedures, how to use probeware and how to identify evidence of a chemical reaction (using color change, presence of gas change in properties and temperature change).  Most groups got through the first two reactions on day one and were able to see evidence of chemical reactions.  If this lab is to be completed in two day it is imperative that students get started immediately.  As they are logging onto the computer I will instruct the other members of the group that they need to be focused to complete this.  I also show them a copy of how to accurately answer questions and draw the temperature graphs.  Since they are working in groups of four due to number of equipment set-ups, I will instruct another group member to start heating 100 ml of water in a 250 ml beaker.  This will be used in the physical change and unknown sections of the lab.

I also remind them that reactions one and three will need to be saved and the products from those are used in the unknown change section. After completing the evidence of chemical reactions they will perform a series of 4 experiments that will illustrate physical changes.  The experiment portion of the lab is concluded by observing and analyzing four unknowns and identifying characteristics and whether or not the unknown is a physical or chemical change.  Once the unknowns are completed they will clean up their stations and work on the synthesis questions that have them summarize their findings (Evidence of Chemical Reaction Key).

Physical Changes and Unknown Classification

30 minutes

By this time in day two most lab groups have figured out a good understanding of how to work effectively to get the experiments and the data recorded.  All groups work at different paces so some finish with 15 minutes in the class while other groups are struggling to finish the unknowns.  I find that it's important to keep track of the groups that are lagging behind, otherwise they will not collect enough data to complete the synthesis questions.  Again it's important to stay on groups to ensure that all members are participating equally.  Ideally I would prefer smaller groups of 2 or 3 kids per group but equipment is the issue, so I have to make do.


Synthesis and Conclusion

15 minutes

It is encouraged at the beginning of day two to remind students to save all runs and not delete them.  It's not imperative that students save all their runs, but if they don't it's important they have all graphs entered accurately on the data sheet.  Having accurate data will make it easier to answer many of the synthesis questions that are at the end of the lab.  I make note to the students that they do not have to have the lab open to answer the synthesis questions.  These can be answered at home if accurate data has been collected.

I added the synthesis questions verbatim on the data sheet so they could be completed outside of class if needed, make it possible to complete this lab in two days.


 Below is an explanation of student work for day two and expected learning outcome for the lab.