Chemistry Lab Practical - Mystery Liquids

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Objective

SWBAT conduct a variety of chemistry related tests in order to determine which of four samples is water.

Big Idea

Use this lesson to gauge your students' understanding of chemistry concepts including physical and chemical changes, solubility and pH.

Background

The premise of the activity is that the students are traveling in outer space when they become stranded on an alien planet.  Mission control knows that the crew has crashed, but help will not arrive before the crew runs out of water.  The crew must examine and conduct tests on four different samples of liquids in order to determine which sample is water. 

I place the students in groups and give each group a kit with basic supplies to use to test the samples.  The aliens are also willing to help the students by trading them materials for the answers to questions.  For this portion of the activity I write various tasks on alien cutouts and if the students can accomplish the task, they earn equipment.  For instance, if students can balance an equation they are given pH paper.  They soon realize that the pH paper does not do them much good without the color key, so they must balance another equation to earn the key. 

Students also draw Bohr diagrams, list various products and reactants in equations, and answer questions about material we reviewed in class.  This serves as a great review of the information from the unit and helps prepare the students for the unit test. I hide the clues around the room and add to the challenge by telling students that if their table is left completely unattended, their materials may be taken back by the aliens.  Between day one and day two I add new clues based on student suggestions.  I also move clues to new locations and take some clues away.  Students are also required to re-earn items they used the day before.  Phase changes can also be included in the experimentation process, but I did not include them in this activity.

This lab practical meets NGSS: MS-PS1 Matter and Its Interactions, specifically Disciplinary Core Ideas: PS1.A: Structure and Properties of Matter and PS1.B: Chemical Reactions.  The lab practical also addresses NGSS Science and Engineering Practices: Asking Questions and Defining Problems, Planning and Carrying Out Investigations, Analyzing and Interpreting Data as the students are required to design and conduct their own experiments.

Before the Activity:

In the days prior to the activity, I collect the materials, which are listed here in the resources. I also build student anticipation by discussing the upcoming activity.  I also used Blabberize to create a newscast about the students being stranded (see it in the next section!). I set up one lab kit for each group and prepared the colorless liquids by numbering them and making a teacher’s key.  Clues and aliens were also prepared in advance and placed around the lab.

Engage

5 minutes

To begin class, I play a recording I created using Blabberize.  The Newscast video helps to set up the background for the activity the students will be completing.  I have spoken with the students before about the lab practical and they received a study guide a week in advance, but the video helps to set the stage for the activity and build student enthusiasm.

Explain

5 minutes

I hand out hard copies of the chemistry lab practical.  Generally the students complete laboratory activities using Chromebooks, but for this lab I do not want them using the internet as a resource.  I review the laboratory guidelines with the students and remind them that it will be very beneficial to look for the aliens using clues hidden around the lab.  

I also remind them to be careful and not all leave their lab station at once because if their supplies are left unattended, the aliens may take them.  I use this as a technique to encourage team work as two students typically stay at the lab table while two students look for aliens.  This task can be difficult to complete in only two days, so the students will need to think strategically in order arrive at accurate results. 

Explore

60 minutes

The students begin working on the lab practical.  As they work, I circulate through the room with a lab scoring sheet.  During this time, the students are able to work on the questions posed by the aliens. The students then bring their answers to me in order to earn lab equipment.

In this water characteristics video, you can see students are working on listing the characteristics of water and begin to have difficulty determining the pH of water.  I remind the students that they are able to review their notes, even though just before they open their notes, one of the group members recalled the answers.

In this video, students are making their initial observations video of the four liquids.  The students try to rely only on smell during this lab, but I tell them that liquids smell differently on a different planet.  I also emphasize the importance of being completely sure of themselves when they are determining which liquid is water and remind them that they must have more than one type of evidence to prove their idea regarding which liquid is water.

In this lab example, the student answer for part three did not include the characteristics of water. Ideally, students will list the characteristics of water that they have observed, such as color, scent, and viscosity.

Wrap up

10 minutes

Once the students have completed the labs and I have graded them, I return the labs to the students and we review them.  I tell them the liquids that were used in the lab.  I then review with them the equipment that was in their lab kits and we discuss the types of tests that they could have completed.  We also talk about the equipment that was available for the students to earn and how that equipment could be used to determine which liquid was water.