Investigating What We Cannot See

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SWBAT make inferences as to the contents of a "black box" based on observations they make.

Big Idea

In chemistry, often we are observing results of reactions and then making inferences.

Why This Lesson?

My students, like many high school students, have difficulty understanding that many of the observations we make in chemistry are indirect observations--we can see and measure results of chemical reactions, but we do not actually see individual molecules reacting.  I use this particular activity to draw parallels between making observations of things we cannot see and drawing inferences to try and figure out what it looks like.

I have a set of 17 "Ob-scertainers" from Lab-Aids (a kit is available here).  The ob-scertainer is basically a "black box" that holds a steel ball inside.  Different ob-scertainers have different plastic shapes inside that might block the ball from moving thereby causing different sounds.


I tape my ob-scertainers closed so that students cannot open them, even when the activity is over.  I want them to continue questioning their final hypotheses and at a later date, when one of them asks, we can re-visit the containers and open them.  My goal for this lesson is not that my students are correct in their conclusions, but that they learn that we will not always be able to directly make observations nor will we always know whether our conclusions are correct or not.

I use the set slightly differently than the accompanying instructions suggest.

This lesson addresses two different Science and Engineering Practices, SEP 3 - Planning and Carrying Out Investigations and SEP 7 - Engaging in Argument from Evidence.  SEP 3 is specifically addressed because students have to develop their own procedures for investigating the ob-scertainers.  There is no step-by-step procedure that they can follow absent-mindedly.  Students have to plan and carry out their investigations without a specified procedure.  SEP 7 is addressed when students have to work together to reach a consensus as to what the inside of their ob-scertainer may look like.  They also need to find a "match" with other groups, so every time a student is making a claim, another student who disagrees might ask why, which naturally forces students to provide the evidence for their reasoning.


5 minutes

While I take attendance, students do a warm-up activity in their composition Warm-Up/Reflection books. (To read more about Warm Up and Reflection Books please see the attached resources.) This warm-up is specifically to get students in the frame of mind to do an investigation of things they cannot see.

Today's Warm-Up: "How can we observe things we cannot see?"

In this case, the warm-up is asking students to draw from prior experience or knowledge.  The warm-up is preparing them for today's activity during which they will use observation techniques other than vision to determine the contents of a black box container.

For this lesson, as it is the first time I am asking students to use their Warm-Up/Reflection Books, I walk around with a self-inking stamp to stamp the completed warm-ups indicating participation, but not necessarily accuracy.  On days when there is too much business keeping, I do not stamp.  Students have been told that warm-ups are occasionally immediately checked and other times not.  At the end of each unit, Warm-Up/Reflection Books are collected and spot-checked.  

Intro to the Activity

15 minutes

I like to add an air of mystery to this particular activity and deliberately have the ob-scertainers stacked on a lab station in my room.  Students ask what they are, even as they are walking into the room and working on their warm-up question, which indicates they are curious--exactly what I want!  I continue to withhold a layout of the day's instructions while walking around the room numbering my students.  

First, I tell the class that they will get a number and that it is very important that they remember their individual numbers.  Then, I walk around the room assigning numbers 1 - 17 (because that is the number of ob-scertainers that I have).  This allows greater interaction between students who are not sitting together because I am going to have students with like numbers work in small groups together.  My chemistry classes consist of 42-44 students this year, so some groups will have two students and some will have three.  Numbering the students goes quickly and adds to the suspense.

I ask my #1s to stand, come to the lab station where I am standing with the ob-scertainers (which I call "black boxes"), and introduce themselves to each other.  Then I hand them a black box, without giving them instructions.

I then proceed to have the remaining groups go through the same process, until all of the black boxes have been distributed.  By this point, students are shaking the boxes and noticing that they make noise.  Some are still confused, but they are curious and without realizing it, are already starting to investigate.

I explain to students that inside of their black boxes is one steel ball that can roll around inside.  I tell them that there may or may not be "walls" on the inside impeding the balls movement.  I remind students of the toys they may have had when they were younger that had balls on the inside and there was a maze they needed to navigate, like pictured here: 

Then I tell students that they will be working with their group to determine what is on the inside of their assigned black box.

Individual Group Investigation

5 minutes

I give students 5 minutes to work together to see if they can figure out what some possible shapes (or lack thereof) inside of the black box might be.  On the white board I have written 17 circles and numbered them 1-17.  I write the due time on the board (5 minutes from the current time) and explain that students need to come to a decision within their group as to what they believe the inside of their black box looks like.  One person from the group needs to take a dry erase marker and draw the inside on their numbered circle on the board before time is up.


While students are investigating, I walk around and listen to their conversations.  If groups are not actively investigating the black box by tilting it and listening to the ball, I ask them what they have found.  Usually, students stop investigating because they do not know what else to do.  In those cases, I ask students to "swirl" the black box (or I model that motion myself).  I ask if they hear the ball crashing into any walls or not.  Students will usually respond with "oh, I get it now."

Here is one class period's predictions of what is inside of the black boxes:

Comparing Between Groups

15 minutes

Once students have drawn what they believe might be what the inside of the black box looks like, I tell them that the next part of the investigation is to find their match.  I explain that another group's black box might be the same as theirs and that they should be able to find each other.  Each group should find a match or convince themselves that they have no match.

My set of ob-scertainers has a set of four that match (have the same interior structure), 5 pairs that match, and 3 singles with no match.  Even with a different set of ob-scertainers, instructing students to find a match OR convince themselves that they have no match allows for variation.

Students should be actively walking around the room, mingling with other groups and investigating each other's black boxes.  I walk around, as an outside observer, available for questions if students need help, but most of my answers are indirect and reflected back to them.  When students ask, "Are these a match?"  I answer, "Do you think they match?"  and regardless of their answer, I ask them why do they think what they do.  The purpose of this activity is not to be right, it is to draw conclusions based on evidence.

Whole Class Discussion

10 minutes

Once students have really investigated and compared all of the other black boxes in the room to theirs, I ask students to take a seat in their desks so that we can discuss our findings.  I ask each group to tell me if they had found a pair.  As I go through the numbers chronologically, and pairs come up, I ask the "pair" groups to compare their initial drawings of the black box insides.  Questions each pair has to answer are:

  • Do your prediction drawings match?
  • If yes, how did you come to make that prediction?
  • If no, which group do you think is closer to the truth?  Why?

If groups didn't find a match, I ask them to explain how they know theirs was different.  Every answer that students give without evidence or justification, I ask a follow-up question like "How did you know?" or "What observation did you make to indicate that?"

Students will want to know if they were right or not, and I do not want the focus to be on right versus wrong.  I truly want to keep the focus on the process.  When students ask to open them up, or if they were right, I tell them that sometimes we just do not get to know the answer.  I then follow-up with a promise to open them at a later date, and I record their predictions by taking a picture of the board.

Student Reflection

5 minutes

In student's Warm-Up/Reflection Books, students should spend about 3-5 minutes writing a response to the day's reflection prompt.  Prompts are designed to either help students focus on key learning goals from the day's lesson or to prompt deeper thinking.  The responses also allow me to see if there are any students who are missing the mark in terms of understanding.  The collection of responses in the composition books can also show a progression (or lack thereof) for individual students.  (For more information about how I use Warm Up and Reflection Books, please see the attached resource.)

Today's Reflection Prompt:  "What did you learn about making "blind" observations?"

Desired student responses should indicate that:

  • Using other methods of observing can be helpful instead of just vision
  • Sometimes we cannot know if our predictions are correct

Sample student work: