Summary

In this lab, students will practice density calculations and put their calculations to test by creating their own density column.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

• calculate the density of unknown solutions given the mass and volume.
• correctly create a density column based on their calculations.

Chemistry Topics

This lesson supports students’ understanding of

• Density
• Observations
• Measurement

Time

Teacher Preparation: 30 minutes

Lesson: Two 60 minute periods

Materials

For each lab group:

• Goggles
• 250 mL beaker
• 100 mL graduated cylinder
• Balance
• 4 empty plastic cups
• 4 unknown solutions in plastic cups

For class density column:

• Nine unknowns
• 100 mL graduated cylinder (9)
• 1,000 mL graduated cylinder

Safety

• Safety goggle should always be worn when carrying out an experiment in a lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals

Teacher Notes

• One class period will be spent with students carrying out the experiment on a small scale. The second day the class will use their data to determine how to create a density column with all nine unknown liquids.
• The student with a reading disability is placed in a group with a strong leader who will assist him while reading the laboratory handout. They work well together and this arrangement has been successful in the past.
• Eight unknown solutions are prepared as follows:

• For nine lab groups, one way of distributing four unknowns to each group is as follows:

• Lab Day 1
• Launch (10-15 minutes) Teacher tells students:
  • I have a lot of differently colored solutions in the lab, but I can’t remember what they are! I need your help to determine the density of each solution.
  • During the lab you will be measuring the mass and volume of four unknown liquids. Remember to record all of your data in your data table. You will use this information to calculate the densities of each unknown solution. Once you calculate the densities, you will be testing your results by making a density column, so make sure you double check your calculations.
  • Remember to take your laboratory sheets and a pencil with you into the lab.
  • As always, read ALL instructions on your laboratory sheet before you start working.
  • You will have about 24 minutes to complete the lab. Time is short, so make sure you are working quickly and efficiently with your group to complete the data section during this period.
  • When you finish, alert your teacher to see the density column that you have made.
  • Here are some safety reminders before we get started.
  • Identify students that have not completed their laboratory safety quiz, have not returned their signed safety contract, and are not dressed appropriately and inform them that they will be completing an alternative assignment.
  • Ensure that each student has safety goggles and remind them to tie back their hair and wear their PPE (personal protective equipment) at all times.
  • Tell students to treat all chemicals as highly toxic and use caution when handling them. If they do touch a chemical, walk immediately to the sink and begin washing your hands with cold water. Have one of your lab partners alert the teacher to the situation.
  • Remind students that there is no eating or drinking in the laboratory and that they should refrain from putting their hands in their mouth to avoid ingesting dangerous chemicals. They should wash their hands thoroughly when leaving the lab, even if they don’t think that they touched any chemicals.
  • Remind students to move slowly and carefully in the lab to ensure there are no accidents.
  • You will work in pairs. When you have your partner, come see me so that I can assign your roles. The student with a learning disability knows that he always has the same lab partner who assists him in reading the instructions.
  • We are starting at (time) so you have until (time) to finish the lab.
• Activity Time (~30-40 minutes)
  • As students work in the lab, the teacher will be circulating to answer questions that students may have regarding the activity and ensure that everyone is working SAFELY.
  • Throughout the activity, there will be several questions that the teacher will want to ask groups to start them thinking about and/or discussing the phenomenon they are seeing.
  • If you have two solutions and one is more dense than the other, which sample would go on top, the one that is more or less dense? Students should say that the less dense solution would appear as a layer on top of the other solution.
  • Suppose you have two solutions with the same volume, but solution A is more dense than solution B. Which sample has more mass? Because this is one of the more difficult ideas for students to understand, the teacher should allow necessary wait time for students to think. Students should be able to use what they know about density to rationalize that the more dense solution has more mass per unit volume. If they are struggling to answer this question, the teacher can ask:
  • If I have a block of Styrofoam and a block of steel that are the same size, which one would have more mass/feel heavier? This is a real-life scenario that students can imagine and relate to, so they should be able to answer that the steel has more mass than the block of steel. I will then ask:
  • Which material has a higher density, if the same size block of steel has more mass than the Styrofoam? If they do not arrive at the answer conceptually, they should be able to use the density formula to rationalize that the steel has a higher density than the Styrofoam. They should then be able to answer the original question.
  • If two solutions have the exact same density, what would happen if you pour them together? Students should say that instead of forming two separate layers, the liquids would mix together. If they are struggling to answer this question, I will ask the first scaffolding question (above). I will then ask:
  • If there is no difference in densities, which one will form the top layer? I expect that students will struggle with this question, but they should eventually come to the conclusion that neither will be on the top or the bottom. I will press them to explain what this means. They should be able to rationalize that if neither is on the top or bottom, they must form the same layer.
  • If a group of students finishes early, the teacher should check their density column and make sure the students have cleaned up their workspace. They will then begin working on Discussion section.
• Lesson Close
  • Have students clean up their workspace and make sure that all materials are put back where they found them. Goggles should be returned.
• Day 2
  • Students will discuss the results of their laboratory experiments and work together to order ALL nine of the unknowns into a giant density column. They will have to work together and rely on their peers’ data to come to a class consensus. They will check the final answer at the end of the period by making a density column with all nine liquids.
  • Assessment:

*Adapted from a laboratory activity written by Lindsey Hubert, provided to me by Latasha Ford.

• Standards
  • S11.A.2.1.3: Use data to make inferences and predictions, or to draw conclusions, demonstrating an understanding of experimental limits.
  • S11.A.2.1.5: Communicate results of investigations using multiple representations.
  • S11.A.2.1.4: Critique the results and conclusions of scientific inquiry for consistency and logic.