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Viscosities of Motor Oils

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This laboratory exercise is to acquaint you with a very crude way of measuring viscosity - actually RELATIVE viscosities. Furthermore, you will perhaps gain an understanding of why motor oils come in various viscosities. For example, a dealer will sell 5W, 10W, 30W, 40W, or blends like 10W-40. What is this really all about? And finally, it will teach you to think ahead about safety concerns.

Starting materials

• Use NEW oils: Buy a quart of a blend of motor oil with the two numbers as far apart as possible.
• A quart of motor oil with strictly the lower of the two numbers on the first container.
• A quart of motor oil with only the upper number.
• A sauce pan
• An ice bath
• A hotplate But not an open flame! Unless, that is, you want to have the fire department come to put out the smelliest, smokiest, sootiest fire you have ever seen!
• A thermometer that with a range of 0 to 150°c or higher.
• A stopwatch
• A GLASS bead of some strongly contrasting color. Do not use plastic beads as they will melt in the hot oil.
• A liter pyrex or heat-resistant GLASS beaker. Unless you want a dangerously hot, huge mess, do NOT use ordinary glass containers such as a large bottle. It must read pyrex or give some other indication of heat resistance. "Soft" ordinary glass will most surely break in this experiment! Likewise do NOT use a plastic container which will melt - again a huge, dangerously hot mess!
• Two large [disposable] roasting pans.
• Safety goggles
• Hot pads or mitts

DIRECTIONS

1. Place all three containers of oil in the ice-bath in a refrigerator overnight.
2. Put on your safety glasses!
3. Then, one oil at a time, do the following cluster of steps:
   1. Empty one of them into the beaker
   2. Note the height of the oil in the container
   3. Measure the temperature of the oil.
   4. Start the stopwatch when the bead is dropped into the oil
   5. Stop the stopwatch when the bead hits the bottom of the beaker.
   6. Record the type of oil, its temperature and the time it took the bead to sink to the bottom.

4. Place the hot plate in the center of a roasting pan (to catch spills), pour an oil into the sauce pan and heat to about 30°C with constant stirring.
5. Place the beaker in the middle of the other roasting pan (to catch the oil in event the beaker breaks!) and do the above cluster of steps (a-f).
6. Do this for all oils and for other temperatures so that you have data for approximately these temperatures: 0°C, 30°C, 60°C (use hot pads or mitts), 100°C (use hot pads or mitts).
7. Continue, for further study:
   1. Make a 50-50 mixture of the two "single-weight" oils used above.
   2. Repeat the cluster of steps through the various temperatures.

8. Now graph your data using different colors for the different oils.
9. Discuss what the meaning of the various "weights" is.
10. Was the graph of the blend identical to that of the mix you made? What does this mean? Does the blend contain something more than just your mix? Can you now figure out what is meant by RELATIVE viscosity? (Hint: "This hot oil is only half as viscous as it was when it was cold.")
11. CLEAN-UP! After the oils have cooled, pour them into labelled bottles for storage until the next class does this exercise. All pans and glassware should be wiped well with DRY paper towels. Later, hot water and detergent will wash them clean.
12. List all the safety concerns in this exercise, and state why they were done.

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