In this lesson students will determine how temperature affects viscosity and relate the data to the structure of motor oil and the optimal functioning of a car.
This lesson plan will help prepare your students to meet the performance expectations in the following standards:
- HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
- Scientific and Engineering Practices:
- Analyzing and Interpreting Data
- Constructing Explanations and Designing Solutions
- Engaging in Argument from Evidence
AP Chemistry Curriculum Framework
This lesson supports the following unit, topics and learning objectives:
- Unit 3: Intermolecular Forces and Properties
- Topic 3.1: Intermolecular Forces
- SAP-5.A: Explain the relationship between the chemical structures of molecules and the relative strength of their intermolecular forces when: a. The molecules are of the same chemical species. b. The molecules are of two different chemical species.
- Topic 3.3: Solids, Liquids and Gases
- SAP-6.A: Represent the differences between solid, liquid, and gas phases using a particulate-level model.
- Topic 3.1: Intermolecular Forces
By the end of this lesson, students should be able to
- Plan and conduct an investigation.
- Gather evidence to infer carbon chain length based upon viscosity.
- Identify an unknown oil using viscosity data.
- Explain the relationship between temperature and viscosity.
- Identify patterns in motor oil structure and function.
- Make a claim supported by scientific evidence.
This lesson supports students’ understanding of
- Physical Properties (viscosity, freezing point, melting point)
- Intermolecular forces
- Molecular Structure
- Organic chemistry
Teacher Preparation: 45-60 minutes
- Engage: 10-15 minutes
- Explore: 2 -2.5 hours
- Explain: 45 minutes
- Elaborate: 75 minutes
- Evaluate: N/A; done outside of class as homework
- 3 to 4 different motor oils. See below for suggestions.
- Ice and hot water baths for cooling and heating oil.
- Test tubes, beakers, thermometers, timers
- Marbles or heavy bearings
- Slanted surface (smooth and non-absorbent: glass, cookie sheet, plastic tray)
- Students should wear eye protection in all lab work.
- Oils should not be near a flame at any time.
- Disposal of oils should follow local laws.
- This resource could be used as a post-AP Chemistry exam activity.
- The this lesson can serve as an introduction to learning more about bonding OR serve as an application of what students already know about bonding.
- If this lesson is an introduction to bonding or physical properties, focus on the following:
- Atoms bond to form compounds.
- There are different types of chemical bonds.
- Melting and boiling points and viscosity are physical properties.
- The energy and spacing of atoms is dependent on temperature.
- Cars use oil.
- If this lesson is an application of what is already known about intermolecular forces and bonding, focus on the following:
- Factors that affect intermolecular forces.
- Relative bond strengths
- Essential Questions for this lesson include:
- What is the function of motor oil in a car?
- How is the structure of motor oil suited for its function?
- How does chemical structure affect physical properties?
Engage: Show Penzoil Race Car Video (one minute) and use the following questions for discussion. Familiarize students with these questions (also found on student handout “Assignment 1”) prior to video.
- What does oil have to do with speed?
- What does the speaker mean when he says the oil is designed so they can run faster, hotter, harder”?
Students should see that racers are particular about which motor oil they use. This should help raise questions in students minds about the nature of oil...it is not all the same. Also, students should see that the requirements of racing vehicles are different from family vehicles. The race cars get hot from high speeds. Students should start to question what these temperatures have to do with motor oil and its function in the engine.
Explore: This portion of the lesson is subdivided into 4 tasks, and is outlined for the student under the subheading Assignment 2. Students may not have any idea how motor oil is used in cars. This is critical to this lesson, so it should be known. Students should find that oil is a lubricant and reduces wear. They should also learn where in the car this is important and begin to hypothesize about how car/engine temperature affects it. Thus, they should focus on viscosity and the freezing and boiling points of oils. Students who live in hot and cold climates should think about how different seasons affect the oil. Let the students research this information and share what they learned with the class. Students who know about cars could examine the types of wear that vehicles experience and get pictures of this. Students interested in race cars can research car temperature and the types of oils that are designed for these cars. The resources section has many good sites for students to visit for this research. The purpose is to explore. Students should learn and raise new questions for further study. In the resources section, many excellent and readable sites are listed. In addition, in the resources section, is a quick summary of pertinent information about motor oil that is useful to know before starting this lesson.
The suggested timing breakdown for this portion of the lesson is: 45 minutes for research, 15 minutes to share information, 15 minutes to plan the test, 60 minutes for lab work.
You will need to obtain oils of various viscosities. You might want to get three or four different oils. Make sure that they are not synthetics (these are formulated differently and have many additives). For example, you might want a 5W, 10W, 30W and 50W. Do not show the students the labels at first. They will test the viscosities, rank them, and then compare to the actual rankings.
It is fairly important for teachers to know what the label on the motor oil means! Become familiar with the codes on the containers. The way the numbers are obtained by the Society of Automotive Engineers (SAE) is actually quite complex. For the purposes of this lesson the following should be understood:
- The “W” stands for winter, not weight.
- It is useful to think of the numbers as a viscosity ratings or rankings.
- The lower number, the lower the viscosity.
- The first number ranks the viscosity at cold temperatures. So, 5W is less viscous than 30W at the same temperature.
- Since viscosity changes with temperature, a second number ranks the viscosity at higher temperatures.
- Follow this link for a helpful viscosity chart to see the SAE ratings and operating temperatures.
During the lab investigation allow students to devise their own plan for determining viscosity. There are many ways to do this and lab teams should be allowed to come up with their own plan. The most simple is to put a drop of the oil on a slanted surface and measure the rate at which it flows. Another way is to drop a bead or marble into the liquid and measure the rate at which it drops. Of course, students should be reminded to control variables and keep the amount of oil, temperature of the oil, angle of slant, and timing the same. If they are dropping a sphere (marble, bearing), the same variables need to be controlled. Class data should be discussed and sources of error analyzed. It is valuable to discuss how different results may have been found using different tests. After the lab, show the students the actual oil “weights” and explain how the number on the bottle refers to viscosity. Have them evaluate the accuracy of their tests. Does their data agree with the labeled viscosity ratings? If not, explain using sources of error.
For identifying the unknown oil, you can use one of the same oil samples that the students already tested (labeled as unknown), or provide a new oil weight as a challenge to see where it fits in the data trend. Another option for advanced students is to provide them with a used motor oil sample to see if they can determine how it fits into the data.
Summary of tasks for students (Assignment 2 on student handout):
- Present 3 different weights of oils for students to look at in test tubes. How are they similar and different? Why might a car need one oil type and not another? Why might race cars have different oil needs than a normal passenger car?
- How is oil used in cars? What physical properties of oil are important for its use? Students will research this online and summarize what they learn.
- How can you test the viscosity of motor oil? The teacher will provide 3-4 motor oil samples that are not labeled. Students will devise a plan to test the viscosity of each oil and rank the oils accordingly. After finishing, they will be shown the sample “weights’ and evaluate the accuracy of their data.
- Can you identify an unknown oil based on its viscosity? Students will receive an unknown oil, test its viscosity, and identify it based on data from prior tests.
*SAFE USE OF OIL: all students should wear eye protection when using oil. No flames should be used in any of the activities. Do not ingest motor oil.
*DISPOSAL OF OIL: please follow your state or county guidelines for disposal of motor oil. In the lab, very little oil is needed for the tests. Minimize amounts as much as possible. Oil used in the viscosity tests can be used in the temperature tests as well.
Explain: Depending on the prior background of the student, some may need an introduction to intermolecular forces and bonding. Others may need to review this. Students who are not in chemistry (possibly 9th grade students being introduced to bonding) might benefit from simple explanations such as this: More bonds=less able to freely move=more viscosity and higher boiling point. This simple relationship is shown on the slide show that is listed below. The emphasis here is on the crosscutting concepts: patterns and structure/function. Higher chain length means more bonds and greater intermolecular forces. The information can be obtained through individual research, using a text, teacher lecture, etc. the questions presented in the “Assignment 3” section of the student handout aligns with this section of the lesson.
The sites below provide this information in a student-friendly manner.
- Slideshow on intermolecular forces and viscosity: While this is a comprehensive presentation, slides 37-38 focus on viscosity. For students who need a review of intermolecular forces, the introductory slides are excellent due to the clarity of explanations and good graphics.
Carbon chain length data for petroleum distillates: This site lists the carbon chain lengths for typical motor oils.
Download the Teacher's Guide to view the rest of this lesson.