Prep: 15-20 mins | Activity: 30-45 mins
In this activity, students gather evidence of molecular interactions and reactions from a mixture of oil and water like that in a lava light. Students must reconcile their observations with the molecular shapes of oil and water, building toward the concept of intermolecular forces generally and molecular polarity specifically.
This is a picture of the Gulf of Mexico taken from a NASA satellite in 2006. The white area is sun glint, where sunlight is being reflected off the ocean surface and scattered. Notice the dark streaks within the box. Dr. Chuanmin Hu, an optical oceanographer, identified these streaks as oil seeps, oil that bubbles up naturally from the ocean floor. How can the surface streaks be explained? Share your ideas with your lab partners.
How does molecular structure influence the strength of electrical forces between molecules?
PE HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at a bulk scale to infer the strength of electrical forces between particles.
Planning and Carrying Out Investigations
PS1.A: Structure and Properties of Matter
Patterns
No PPE is required for the activity.
Collect the lava lamp mixture in a waste container and dispose of the container in accordance with your school and state requirements. Do not pour it down the drain.
Did the oil and water mix? Did the oil and water react? What evidence do you have to support your claim?
The oil and water did not mix—2 distinct layers were formed. The oil and water did not react—no evidence of a new product formed.
Describe what is happening at the boundary of the oil and water.
Small oil droplets are being surrounded by water molecules.
Sketch what is happening at the boundary of the oil and water on the particle level.
Check student work to ensure they have drawn a “blending” of oil and water at the boundary and not a hard separation of oil and water.
Which substance is more reactive, oil or water? What evidence supports your claim?
Water is more reactive. The antacid did not react with the oil but did react with the water.
Based on the molecular structures of oil and water below and your observations, which substance appears to have larger intermolecular forces? Justify your claim.
Water is a bent molecule with a negatively charged oxygen on one side and positively charged hydrogens on the other, making it polar. The polarity of water and its hydrogen bonding gives the molecule strong intermolecular forces between it and other polar compounds which affects its ability to be a solvent and its reactivity. (Students may also realize that the polarity of water increases its boiling point, contributes to surface tension and capillary rise. Water molecules attract other water molecules.)
Oil is a large, nonpolar molecule, so there are no attractive intermolecular forces between oil and water. Water is not attracted to the oil, so oil molecules cannot be permanently surrounded by water or dissolved. The same is true for the antacid tablet. Oil is not attracted to the ions making up the tablet, so it is not dissolved in the oil and does not react with it. Water is attracted to the metallic carbonate ions, the ions dissociate, and then the carbonate ion decomposes to form carbon dioxide gas.
*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, these products.
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