Droplets Behaving Strangely! Polarity in Liquids

Submitting Organization: Community Resources for Science

Grade Levels: 5th Grade

Subject Area: Science

Standards Alignment: Next Generation Science Standards

Physical Science: 5. Structure and Properties of Matter 5-PS1-3. Make observations and measurements to identify materials based on their properties

Description of the Activity: Students use notebook to note predictions and results of each step.

  1. On a piece of wax paper with edges folded up, students place one drop of water and closely observe the drop.
  2. Next, students place a drop of oil on the wax paper, and observe and note differences and similarities. Tilt the paper until the drops touch. What happens?
  3. Predict what will happen if a drop of soap is added? What will happen to the water drop? The oil drop?
  4. After noting prediction, place drop of soap onto wax paper, bring into contact with oil and with water.
  5. What happens? Why? Draw or describe results.

Discussion Questions: Using their notes, students share their sketches, describing results and observations for each step of the activity.   

  • Describe the water droplet and the oil droplet?
  • Are they the same or different?
  • Why are oil and water drops shaped that way? (Because water is polar; water molecules are attracted to each other. Oil isn’t.)
  • Why don’t oil and water mix? (Because water is polar; water molecules are attracted to each other. Oil isn’t.)
  • Why does soap flatten the water bubble? (The “tail” of the soap droplet is hydrophobic, while the “head” is hydrophilic — they react in opposite ways to the water and to the oil.)

Resources Needed:

  • Wax paper, 5 inch square (approx), 1 per student
  • Droppers (one per table group)
  • Small cup water, small cup oil, small cup dish soap (1 each per table group, 1-2 oz per liquid)

Link to further resources: http://www.crscience.org/lessonplans/5_Bowring_ChemistryofSoap_1011.pdf