Starch in Liquids
Lesson 2 of 11
Objective: SWBAT identify liquids that contain starch using a scientific investigation.
Prior to the lab, I create a liquid test bag for each group of four students. The bag contains five liquid samples (water, corn oil, corn starch, milk, and corn syrup) in dropper containers, a numbered test tray, and a bottle of diluted iodine (test solution). The student groups can use the liquid test bag during all labs throughout the unit.
Because this is my students' first experience testing liquids in our study of food chemistry, I model the test procedures using the document camera. I show students how to use the numbered test tray to keep liquids separated and how to add liquid to the test tray using the dropper containers. When I model the lab procedures, I use only water so as not to reveal any test results. This also presents me with the opportunity to discuss how water is used as a control during the tests. Modeling is important because it shows students how to correctly use the test materials and avoid contamination.
I then provide each student with a copy of the starch and liquids recording sheet. I review the procedures that the students just saw me model, stressing the importance of using the correct liquid in each section of the test tray. I also share with my students how they can record their test results. As students work on the lab, I circulate around the classroom providing feedback and guidance to student groups, as needed.
To close the lesson, I discuss with students the importance of sharing test results with peers. I create a test chart to record and display student data for all of the tests throughout the unit.. After students have completed the lab, I ask each student group to share their test results and record them on the chart. Where test results are ambiguous (as is the case with corn oil), there exists an opportunity to discuss the observational data each group used to make their decision. Sharing test results also allows us to discuss any outlier data.
A photo of my class' completed chart can be found here (pleae note that I teach three science classes and each class' test results are recorded in a different color). The classes I teach had different results for two tests. We recorded the class results and then discussed the need to conduct further tests to obtain clearer results.