Determination of the Relative Viscosities of Liquids.

Introduction: (Initial Observation)

For many products such as shampoos, liquid detergents, paints, glues and lotions manufacturers try to maintain the consistency of their product. Variations in shades of color and different thickness or viscosity, are usually the signs of an unreliable and low quality product. Factories have a quality control laboratory that test samples of each product from each production batch to ensure consistency. Viscosity of liquid products is one of such factors that is being tested on a daily basis.

This project includes two different experiments you may choose from. In the first experiment you compare the viscosity of different liquids. In the second experiment you compare the viscosity of one liquid in different temperatures.

Information Gathering:

Find out about what you want to investigate. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from. Following are samples of information you may find.

What is viscosity?

The viscosity of a fluid is an important property in the analysis of liquid behavior and fluid motion near solid boundaries.

The viscosity is the fluid resistance to shear or flow and is a measure of the adhesive/cohesive or frictional fluid property. The resistance is caused by intermolecular friction exerted when layers of fluids attempts to slide by an other.

Viscosity is a measure of a fluid’s resistance to flow.

The knowledge of viscosity is needed for proper storage, pumping or injection of fluids.

What is a Lubricating Oil?

Lubricating oil is a mixture of straight and branched chain hydrocarbons derived from the fractional distillation of crude oil. The fraction is collected above 300°C and contains hydrocarbons with from 18 to 22 carbon atoms. The higher viscosity oil has longer chains with a higher total number of electrons. This means that the dispersion forces are greater. In the experiment 2, the students should see the direct relationship of viscosity to the strength of the attractive forces. The oil mixtures usually consist of both straight chain and branched chain hydrocarbons.

Lubricating oil behaves as a “Newtonian liquid”. In his book Principia (1687), Newton discussed “lack of slipperiness” or resistance to flow as being “proportional to the velocity with which the parts of a liquid are separated from one another” (Whitten and Galley). This resistance to flow or fluid friction is referred to as viscosity.

In 1941, the concept of equilibrium was introduced into the theory of liquids. Liquids were described as structures with “holes” and the flow of the liquid was dependent on the transfer of molecules by way of these holes. For example, with two layers of molecules sliding past each other, the motion of the one layer with reference to the other involves the passage of a molecule from one position to another in the same layer. Scientists have a special interest in the measurement of the variation of viscosity with temperature (Blair).

Grades of Lubricating Motor Oil:

Motor oil is generally labeled with an S.A.E. number. If only one number is stated (for example, an S.A.E. 20), this means that the oil was tested at only high temperatures (above 100°C). Most oils are multigrade and have two ratings (for example, S.A.E. l0W30). The lower rating was tested at -18°C and the higher at 100°C.  Read more …

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Question 1: Compare the viscosity of common liquids?

Question 2: How does the temperature affect the viscosity of motor oil? (You may try corn oil or any other vegetable oil instead of motor oil.)

Other Possible questions:

1. Effect of natural polymers on the viscosity of water?
2. Compare the viscosity of different motor oils?
3. Effect of starch on the Viscosity of water?
5. Effect of temperature on the viscosity of starch solutions.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

For Question 1:

Independent variable (also known as manipulated variable) is the type or name of the liquid you test.

Dependent variable (also known as responding variable) is the flow time or the travel time of a ball inside the liquid.

Constants are the experiment method and instruments including any ball or funnel that may be used.

Controlled variable is the temperature. We try to run all experiment trials in the same place and at the same time so they will be under the same temperature conditions.

For Question 2:

Independent variable (also known as manipulated variable) is the temperature.

Dependent variable ( also known as responding variable) is the flow time or the travel time of a ball inside the liquid.

Constants are the experiment method and instruments including any ball or funnel that may be used.

Controlled variables are None (not needed).

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Sample hypothesis for question 1:

Among the liquids I compare their viscosity (Water, Milk, Mineral Oil, Sugar solution), Mineral Oil has the highest viscosity. (You must include at least 3 different liquids in your study. Other liquids may include Shampoo, Corn Oil, Baby Oil, paint, Ketchup, Maple Syrup, … )

Sample hypothesis for question 2:

The viscosity of oil reduces as the temperature increases.

Possible Hypotheses for other questions:

1. Among natural polymers starch, gelatin, agar, and alginate, Agar will increase the viscosity of water the most.
3. Among liquids A, B, C and D, liquid C has the highest viscosity.
4. Starch will increase the viscosity of water. More starch will result a higher viscosity.
5. The viscosity of a starch solution increases as the temperature decreases.

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Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.

Experiment 1: Simple Method

Introduction: In this experiment we will drop a ball in each liquid and record the time it takes for the ball to sink to the bottom, or travel a certain distance. The liquid that has a higher viscosity, will create more resistance against the movement of the ball, so it will take more time for the ball to travel to the bottom.

This method works only if the liquids have the same or almost the same density (specific gravity). For example this method is good for testing different oils or different water based solutions.

Materials:

• 3 small Aluminum or rubber balls
• 3 clear, tall bottles with cap
• Stopwatch
• Samples of different liquids you want to test
• Safety Goggles

Procedure:

1. Drop one ball in each bottle.
2. Fill up each bottle with one of the liquids you want to test (all the way to the top).
3. Place and tighten the caps of the bottles.
4. Label each bottle with the name of liquid it contains.
5. Invert each bottle and observe the ball dropping through liquid.
6. With the stopwatch try to measure the time it takes for the ball to travel from top to the bottom.
7. Repeat this five times for each bottle and record the results in a table like this:

Preparation and substitution:

For best results you need bottles that are tall and narrow with straight sides. Right size bottles are hard to find and the other problem with the bottle is that you need a lot of liquid to fill it up. For these reasons many students prefer to make their own bottles using a clear tube of glass or plastic. The diameter of tube must be more than the diameter of the ball you use.

The ends of a tube can be sealed or plugged using a rubber stopper or a cork. It all depends on your own creativity. You may find the right size bottle at a local glass recycling drop off place or in a local store. A perfect bottle or tube must be more than 10 inches (25 cm) tall, but 2 feet (60 cm) tall is preferred.

What size or material ball do I need?

The type of ball depends on the density of liquids. For most water based liquids and oils, a rubber ball or an aluminum ball works fine. If the ball is too heavy (like steel or brass balls), then it will fall too fast. Some students use a very small glass bottle instead of the ball. You can fill up the small glass bottle with different amounts of sand or small nails to adjust its weight for slow fall. The glass bottle you may use must be sealed with a cap so the liquid cannot enter the bottle.

Make a Bar Graph

You can make a bar graph to visually present your results. Make one vertical bar for each of the liquids you test. The height of each bar is the average time it takes for the ball to drop through the liquid. Call your graph “Relative Viscosity”.

Experiment 2: More advanced method

Introduction:

In this experiment the viscosities of a sample oil will be tested at room temperature and a higher temperature.

Materials:

Obtain one 10″ long, 1.5″ internal diameter PVC pipes; one rubber stoppers; a 12″ glass tube; one table tennis balls; a stop watch; a thermometer; and 250 mL of any motor oil or vegetable oil you want to test.

1. Stand the PVC pipe, which have stoppers in the bottom, on a tray and clamp into position with a utility clamp attached to a ring stand.
2. Place your oil sample in refrigerator for 2 hours before your experiment.
3. Record the temperature of the cold oil before it is carefully poured into the PVC pipe. Shove a table tennis ball into the oil, submerse it and force it to the bottom of the pipe with the 12″ glass tube. Start the timing as soon as you quickly release the submersed ball. Stop the watch as soon as the ball reaches the surface and record the time.
4. Repeat step 3 two more times for statistical purposes and then record the average.
5. Pour the oil from the pipe back into your beaker.
6. Leave the beaker out of the refrigerator in the room for a few hours so it gets to room temperature and becomes ready for step 7 (or you may have another 250 ml of the same oil already at room temperature and use that for step 7).
7. Record the temperature of the room temperature oil and pour it into the pipe and perform the experiment in the same manner as for the cold temperature oil.
8. Repeat step 7 two more times for statistical purposes and then record the average.
9. Pour the oil from the pipe back into your beaker.
10. PERFORM THE FOLLOWING PROCEDURE UNDER THE FUME HOOD. Place the beaker of oil on a hot plate. Slowly heat the oil in the beaker to 60°C.
11. Carefully and quickly pour the hot oil into the pipe and perform the experiment in the same manner as for the room temperature oil. Measure the temperature of the oil before and after the experiment. Perform three trials.
12. Return the oil to the container under the fume hood. Invert the beakers on a tray covered with newspaper to drain.
13. Compute the average time for the ball to rise to the top of each temperature.
14. Compare the average times for the cold, room temperature and hot oils. Using your data, formulate a statement which will show the relationship between the temperature and viscosity for the specific oil you tested.
15. Try to relate the differences in viscosity to the differences in attractive forces
16. Recycle the oil and keep the PVC pipe for use in this experiment only. Carefully wipe off the table tennis balls for reuse.

Extreme care is required when handling hot oil. The hot oil may fume and must be kept under the hood. Oil at 100°C may melt the table tennis balls. Oil should not be poured into the sink since it will clog the drain. Goggles must be worn throughout the experiment.

Experiment 3: Optional

Introduction:

The viscosities of two grades of oil will be tested at room temperature and a higher temperature in order to study the relative meaning of the S.A.E. numbers. The experiment is intended for almost any level chemistry class and works especially well with a general level class. The activity can also be part of the study of matter by a first-year college-prep class. Variations may be utilized with a more advanced group or extensions of the experiment may be suggested as a research project for an ambitious student. Two lab periods are needed to test viscosity at more than one temperature.

Materials:

Obtain two 10″ long, 1.5″ internal diameter PVC pipes; 2 rubber stoppers; a 12″ glass tube; two table tennis balls; a stop watch; a thermometer; and 250 mL of each grade of motor oil.

1. Stand the PVC pipes, which have stoppers in the bottom, on a tray and clamp into position with a utility clamp attached to a ring stand.
2. Record the temperature of the lower viscosity oil before it is carefully poured into the PVC pipe. Shove a table tennis ball into the oil, submerse it and force it to the bottom of the pipe with the 12″ glass tube. Start the timing as soon as you quickly release the submersed ball. Stop the watch as soon as the ball reaches the surface and record the time. Notice the surface phenomena as the ball approaches the top.
3. Repeat step 3 two more times for statistical purposes.
4. Pour the oil from the pipe back into your beaker.
5. PERFORM THE FOLLOWING PROCEDURE UNDER THE FUME HOOD. Place the beaker of oil on a hot plate. Slowly heat the oil in the beaker to 60°C.
6. Carefully and quickly pour the hot oil into the pipe and perform the experiment in the same manner as for the room temperature oil. Measure the temperature of the oil before and after the experiment. Perform three trials.
7. Using the second PVC pipe and a new table tennis ball, repeat the same procedure for the higher viscosity oil. Perform three trials at room temperature and three trials for a higher temperature.
8. Return both grades of oil to the containers provided under the fume hood. Invert the beakers on a tray covered with newspaper to drain.
9. Compute the average time for the ball to rise to the top of each grade of oil at each temperature.
10. Compare the average times for the room temperature oils. Using your data, formulate a statement which will show the relationship between the SAE number and the viscosity (The higher the SAE number of an oil, the ……….)
11. Compare the average times for the hot oils with the average times for the room temperature oils. From your data, formulate a statement which describes how temperature affects viscosity. (The hotter the oil, the……..)
12. Which oil has the greatest change in viscosity per degree change in temperature?
13. Try to relate the differences in viscosity to the differences in attractive forces
14. List the possible reasons for the variations in each of your data sets.
15. Recycle the oil and keep the PVC pipe for use in this experiment only. Carefully wipe off the table tennis balls for reuse.

Extreme care is required when handling hot oil. The hot oil may fume and must be kept under the hood. Oil at 100°C may melt the table tennis balls. Oil should not be poured into the sink since it will clog the drain. Goggles must be worn throughout the experiment.

Materials and Equipment:

Chemicals:

• SAE 30 motor oil
• gear oil
• Corn Oil

Equipment:

• table tennis balls
• PVC pipe (1.5 inch internal diameter)
• rubber stoppers to fit PVC pipe
• thermometers
• stopwatches or watch with a timer function
• Bunsen burners or hot plates
• wire gauze
• utility clamps
• 250-mL beakers
• beaker tongs
• glass tubing about 12″ long or piece of metal rod for pushing table tennis balls to bottom of PVC tube
• cafeteria trays
• Aluminum ball or rubber ball

This list is provided as a sample. Your list of materials may be different from this list.

1. All of the materials, with the exception of the stopwatch, can be purchased at a rather low cost. It is possible that many of the supplies can be borrowed or procured by donation.
2. Have an adult shop technician cut the PVC pipe. Label pipes for high and low viscosity. For future years, store pipes in newspaper and/or plastic bags after draining.
3. The viscosity will fall with a rise in temperature. The experiment will work best when there are extreme differences in the grades of the oils. SAE 30 (a normal lawn mower oil) and SAE 90 (a gear oil) were used with much success.
4. If stopwatches are not available, the timer/stopwatch function on digital watches can be used.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

You will calculate the average for multiple trials of each experiment.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

1. Further research is suggested in the following areas:
2. Comparisons of multigrade oils with standard oils.
3. Comparisons of average times to known viscosities.
4. Literature research studies on the methods used to determine the viscosities of Newtonian liquids.
5. Testing a series of oils and plotting the SAE number versus the time.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and find books in chemical physics with some content or discussion about viscosity. Include such books in your list of references.

Whitten, K.W. and Galley, K.D. General Chemistry, Saunders College Publishing, Philadelphia, PA, 1984, p. 864. — This work discusses Newtonian fluids and viscosity and its relationship to molecular structure.

Blair, Scott G. W., Elementary Rheology, Academic Press, New York, 1969. p. 24.