After seeing the teacher compare the weight of equal volumes of water and corn syrup, students compare the weight of equal volumes of water and vegetable oil to investigate the question: Is vegetable oil more or less dense than water?

Objective

Students will be able to explain that the density of a liquid has to do with how heavy it is for the sample size. Students will also be able to explain that if a liquid is more dense than water, it will sink when added to water, and if it is less dense than water, it will float.

Key Concepts

• A liquid, just like a solid, has its own characteristic density.
• The density of a liquid is a measure of how heavy it is for the amount measured. If you weigh equal amounts or volumes of two different liquids, the liquid that weighs more is more dense.
• If a liquid that is less dense than water is gently added to the surface of the water, it will float on the water. If a liquid that is more dense than water is added to the surface of the water, it will sink.

Note: We are purposely using the terms “size” and “amount” instead of “volume” in this lesson about density. We are also using “heavy”, “light”, and “weight” instead of “mass”. If your students have already learned the meanings of volume and mass, you can easily use those terms to define density (Density = mass/volume), and then use those terms in this lesson.

NGSS Alignment

• NGSS 5-PS1-3: Make observations and measurements to identify materials based on their properties.

Summary

In the previous lesson, students learned that density has to do with how heavy an object or substance is relative to its size, and that density determines whether an object sinks or floats. Students also observed that you can compare the density of a substance to the density of water by comparing the weights of equal amounts of the substance and water using a balance.

In this lesson:

• As a demonstration, the teacher will compare the weight of an equal amount or volume of water and corn syrup so students can observe that corn syrup is more dense than water and sinks.
• Students will compare the weight of an equal amount or volume of water and vegetable oil and see that vegetable oil is less dense than water and floats.
• Students add corn syrup to layered oil and water and see the corn syrup sinks below both the oil and water.

Evaluation

Download the student activity sheet (PDF) and distribute one per student when specified in the activity. The activity sheet will serve as the Evaluate component of the 5-E lesson plan.

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