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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:
A – (1.00 g/mL) Colored green water (add two drops of green food coloring)
B – (1.37 g/mL) 100% Maple syrup C – (1.06 g/mL) Blue dish soap D – (0.83 g/mL) Baby oil (add one drop of yellow, one drop of red food coloring) E – (0.92 g/mL) Vegetable oil F – (1.42 g/mL) Honey G – (1.33 g/mL) Light corn syrup (add one drop of red food coloring) H – (0.79 g/mL) Rubbing alcohol (add two drops of blue food coloring) |
- For nine lab groups, one way of distributing four unknowns to each group is as follows:
Group 1: A C E G | Group 4: B D G H | Group 8: C D F G |
Group 2: A B D F | Group 5: C E F G | Group 9: A B E H |
Group 3: B C F H | Group 6: A B F E | |
Group 7: A E G H |
- 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:
Objective |
When Assessed |
How Assessed |
Students will be able to calculate the density of unknown solutions given the mass and volume. |
In the results/ |
I expect students to be able to calculate the density of each unknown solution by correctly measuring both the mass and volume. They should also have their data table filled out correctly so that I can quickly see where students made mistakes in their calculations and address them during the whole-class discussion. |
Working in pairs, students will be able to correctly create a density column based on their calculations. |
In the analysis section of the laboratory handout as well as the density column. |
I expect students to have correctly calculated the densities of all four unknown solutions. They should use this data to determine the order from most to least dense, described in the Analysis section. When students “test” their rankings by making a density column and four distinct layers appear, the students have correctly calculated the density for each unknown solution. The answer key above also shows whether students determined this order correctly. |
*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.
For the Student
Lesson
Materials
- four unknown solutions (labeled)
- 100-mL graduated cylinder
- 250-mL graduated cylinder
- balance
Procedure
- Using a balance, find the mass of an empty 100-mL graduated cylinder. Record this mass.
- Using the graduated cylinder, measure a certain amount (between 30 and 60 mL) of one unknown solution. This will be the volume measured for every unknown solution. Record this volume in the data section.
- Remass the graduated cylinder. Record this mass in the data section.
- Calculate the mass of the unknown solution. Record this mass in the data section.
- Pour the solution back into its plastic cup.
- Calculate the density of this unknown solution and record this in the data section.
- Repeat steps 2–6 for the rest of your unknown solutions.
Results/Calculations
Unknown solutions |
Volume (mL) |
Mass of empty graduated cylinder (g) |
Mass of graduated cylinder with solution (g) |
Mass of solution (g) |
Density of solution (g/mL) |
Analysis
Rank your unknowns in order from most dense to least dense.
- Take your most dense solution and slowly pour it into the 250 mL graduated cylinder.
- Continue adding each solution from most dense to least.
Conclusion
Do you see all 4 unknown solutions in the graduated cylinder? If not, which ones mixed? Why do you think they mixed?