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Exploring Density

Investigation 3 – Lab

Back to Investigation 3

BE PREPARED

Supplies and Equipment:

Class Materials:

10 400 ml beakers
10 100 ml beakers
550 ml vegetable oil
550 ml rubbing alcohol
1 roll of masking tape
1 marker

Group Materials:

1 100 ml beaker
1 400 ml beaker
2 100 ml graduated cylinders
1 triple beam balance
several paper towels
1 calculator

Individual Materials:

1 Student Data Record

Teacher Preparation:

1. Fill five 100 ml beakers with 30 ml of rubbing alcohol. Label “rubbing alcohol.”

2. Fill five 100 ml beakers with 30 ml of vegetable oil. Label “vegetable oil.”

3. Label five 400 ml beakers “rubbing alcohol” and number from 1 – 5.

4. Label five 400 ml beakers “vegetable oil” and number from 1 – 5.

5. Prepare the 400 ml beakers with one sample of each liquid for each group. To do this, follow the table below:

6. Assemble materials at a distribution point.

7. Divide class into five cooperative groups and assign each group a number from 1 to 5.

Instruction:

1. Assign each student group a number (1 to 5) for this Investigation. Assign the samples as follows:

2. Direct each student group to obtain the following necessary materials from the distribution point: one (1) empty 100 ml beaker, one (1) empty 400 ml beaker, two (2) 100 ml graduated cylinders, one (1) 100 ml beaker that contains 30 ml of rubbing alcohol, one (1) 100 ml beaker that contains 30 ml of vegetable oil, two (2) numbered 400 ml beakers corresponding to their group number, one (1) triple beam balance, one (1) calculator and several paper towels.

GET FOCUSED

Investigation Three gives students more practice performing density calculations.

INVESTIGATE

Trials 1 and 2

During these Trials, students will continue their exploration of density by investigating a 30 ml sample of rubbing alcohol and a second sample of rubbing alcohol that is assigned to them as shown on the following chart:

2. Trial 1 will give students an opportunity to explore the density of rubbing alcohol. Students will use a triple beam balance to measure the mass of a 30 ml sample of rubbing alcohol. They will then use the values for volume and mass to calculate the density of rubbing alcohol.

Trial 2 will guide students to perform the same procedure with either a 50 ml or 100 ml sample of rubbing alcohol. By performing these Trials, students will find that the density of rubbing alcohol is a constant. That is, it does not change as the sample size changes. From these Trials, students should be able to conclude that, like water, in order to calculate the density of rubbing alcohol, the volume and mass must first be measured.

Students should also conclude that the density of rubbing alcohol is different than that of water. This would indicate that 30 ml of rubbing alcohol has a different amount of particles than 30 ml of water. Trials 1 and 2 are designed to encourage students to answer the questions:

Will different volumes of rubbing alcohol have different densities?

Is the density of rubbing alcohol different from the density of water?

Does the density of rubbing alcohol depend on the volume and mass of the sample?

Is the density of rubbing alcohol a constant value?

Encourage students to Predict whether changing the volume of rubbing alcohol will change the density of rubbing alcohol. Students should record their predictions in Problem 4a of their Student Data Record.

Trials 3 and 4

During these trials, students will calculate the density of a second liquid: vegetable oil. To do this, students will measure the volume and mass of a 30 ml sample of vegetable oil and a second sample of vegetable oil that is assigned to them as shown on the following chart:

4. Trial 3 will give students an opportunity to explore the density of vegetable oil. Students will use a triple beam balance to measure the mass of a 30 ml sample of vegetable oil. They will then use the values for volume and mass to calculate the density of vegetable oil.

Trial 4 will guide students to perform the same procedure with either a 50 ml or 100 ml sample of vegetable oil. By performing these trials, students will find that the density of vegetable oil is a constant. That is, it does not change as the sample size changes. From these trials, students should be able to conclude that, like water and rubbing alcohol, in order to calculate the density of vegetable oil, the volume and mass must first be measured.

Students should also conclude that the density of vegetable oil is different than that of water and rubbing alcohol. This would indicate that 30 ml of vegetable oil has a different amount of particles than 30 ml of water and 30 ml of rubbing alcohol.

These trials are designed to encourage students to answer the questions:

Will different volumes of vegetable oil have different densities?

Is the density of vegetable oil different from the density of water?

Does the density of vegetable oil depend on the volume and mass of the sample?

Is the density of vegetable oil a constant value?

Encourage students to Predict whether changing the volume of vegetable oil will change the density of vegetable oil. Students should record their predictions in Problem 6a of their Student Data Record.