Co-Authored by Hannah Nandor and Stephanie Coyle

Science is often assessed with a typical paper and pencil test. However, science is an action and should be treated (and therefore tested) as such. Scientists are often required to know how to carry out a lab, take data, determine results, and then justify their results. This assessment gives students the opportunity to test in a laboratory setting.

The lab described is used as both a learning opportunity and summative assessment. During the instructional portion of the unit, students complete the lab with hexane, water, and isopropanol to learn the lab procedure, techniques, and analysis process. For the assessment, students repeat the lab procedure but use acetone, ethanol, heptane, and water. Independently, students analyze their data to demonstrate their understanding of covalent bonding and intermolecular forces. For both labs, students gather data on miscibility, evaporation rate, and surface tension. Students test the miscibility of each liquid by mixing small amounts of two liquids in a well plate. The water, acetone, ethanol, and isopropanol are colored with either water-based or ethanol-based dyes. This makes it easier for students to see the different layers and if the liquids are miscible. To gather data on evaporation, students use a cotton swab to swipe each liquid across the top of the lab table and time the rate of evaporation. Finally, students add drops of each liquid to a penny and record the number of drops that can fit on the penny before the surface tension is broken. Lastly, students draw Lewis structures for the molecules provided a skeletal structure. 

For the conclusion, students write a CER classifying each liquid as polar or nonpolar and justify their answers using their results. Some students will classify liquids as “intermediate polarity” or will rank them as more polar to less polar. 

Materials

*Acetone, Ethanol, Water, and Isopropanol were dyed using alcohol-based dyes to make it easier to see if the liquids mixed.

**Well plate MUST be ceramic or else the acetone will eat away at it. Instead of well plates, students can use Pyrex test tubes.

Background

Procedure

See the Supporting Information for access to the in-depth procedure and data tables for the practice formative assessment lab and summative assessment. Readers must log into their account to access. Not a member? Register for free!

1. Determine miscibility of each liquid in other liquids.

2. Run Q-Tip on the lab table with a liquid on it and time how long liquid takes to evaporate.

3. Count drops of the liquid that can be added to a penny before surface tension breaks.

4. Complete Lewis structure from skeleton structure.

5. Write CER justifying whether each liquid is polar or nonpolar.

SAFETY: Acetone and ethanol are both flammable and volatile liquids. Students and teachers must use appropriate safety protection (goggles). Students and teachers may opt to use nitrile gloves to protect hands. For extra protection, 70% acetone and ethanol can be used instead of the laboratory grade that is around 90%. Room needs to be adequately ventilated. In order to minimize amounts of acetone and ethanol exposed, dropper bottles should be used as well. All liquids should be disposed of using appropriate safety precautions.

Questions

Concepts

Time Required

Class Time Required – 90 minute class period (45 minutes for testing and 45 minutes for discussion and writing)

Teacher Preparation & Time Required –  20 minutes. 

Preparation

Before class, the teacher should add dye to acetone, ethanol, isopropanol and water. We adjust the colors based on the needs of our students (ie color blindness). 

Teacher should add liquids to each dropper bottle. 

Attribution

Thank you to Kelsey Mescher for collaborating on the development of the lab and assessment. Thank you to Gary Wright for helping review the writing.

Credits