Mineral oil and water — they are alike in many ways. But their differences may tell us more about the nature of Earth's materials. In this investigation, students explore some differences between oil and water as they make their way toward an understanding of density.

First students compare some properties of oil and water by sight, then they measure volumes of oil and water at three different weights. They find a relationship between the weights and volumes and consider whether the relationship holds true for all weights of these materials.

By the end of this investigation students will understand that oil will always have more volume than water when their weights are equal. With this they have the beginnings of an understanding of density as the amount of space a material takes up per unit of weight.

Learning Goals

• Observe some differences between oil and water
• Compare the amount of space a gram of water and oil take up
• The volume of one gram of a particular liquid is a property of that material

Sequence of experiences
1. Ask the question	All Class	10 Mins
2. Explore oil and water	Small Groups	10 Mins
3. Share weight and volume data	All Class	15 Mins
4. Make meaning	Discussion	10 Mins

Materials and Preparation

For the class:

• Post the investigation question in a place where all students can see it.
• Make an overhead transparency of the notebook page titled "Observations about oil, water, weight, and volume," or copy it onto a class chart for everyone to see (optional).
• 1 classroom weight line (see kit for instructions)
• Blue food coloring

For each tray:
Different groups work with different-sized samples; you will prepare 3 sets of trays, one with 20g of oil, another with 40g, and a third with 80g.

• 1 index card labeled "20 grams" or "40 grams" or "80 grams"
• 1 capped 150cc container with exactly 20 or 40 or 80 grams of mineral oil *
• 1 empty 150cc covered container *
• 1 20oz cup approximately half filled with blue-tinted water
• 2 paper towels
• 1 pipette
• 1 digital scale
• 1 fine tip permanent marker

* The containers with 40g of mineral oil were used in Investigation 2.4; the others are new. All containers should have a vertical strip of masking tape applied to the outside for marking volumes.