Compare dishwashing liquids for their ability to clean oils.

Introduction: (Initial Observation)

Almost all manufacturers of detergents claim that their products can clean better. What is the fact? Which one really cleans best? Some buyers compare the price and simply buy the more expensive one assuming that there must be a good reason for price difference. Those who are more price conscious may choose the cheapest one assuming that they are all the same.

In this project you will compare three (or more) different detergents for their ability to remove organic stain. Here we focus on organic stain because organic stain is the most common form of stain. Organic stains are stains from plants or animal sources such as stains from foods and fruits.

Information Gathering:

For each dishwashing liquid you choose to test see if there is a home-page on the web and find any information the producer provides about that specific product. Also search the web for the term “detergents” and related terms to gain useful information about detergents.

Visit your local library and find books about soaps and detergents. Get an idea of what material is used in making detergents.

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.

The purpose of this project is to find out which dishwashing liquid is more effective on dissolving oil.

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.

The independent variable is the brand of the dishwashing liquid.

The dependent variable is the the amount of oil that can be dissolved by each unit of the detergent. This is the same as the ratio of oil to detergent.

Controlled variables are:

• Concentration of detergent (ratio of detergent to water)
• Temperature

Constants are:

• method, procedures and water
• Original form of detergent (liquid, powder)
• Oil type

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.

In your hypothesis you will state which dishwashing liquids you have selected for comparison and which of them you think is most effective in dissolving oil. The hypothesis may be based on your intuition or past experiences with detergents.

This is a sample hypothesis:

I hypothesize that among the three detergents I am comparing (Dawn, Ajax, Palmolive), the Ajax will be more effective in removing oils.

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.”

Materials Needed are:

1. Samples of 3 different dishwashing liquids
2. 4 test tubes 16x150mm or similar size
3. 5 pipettes
4. water
5. Test tube rack
6. Metric ruler

Procedure:

1. Label each test tube with the name of one of the dishwashing liquids. Label one test tube as “Control”.
2. Label each pipette with the name of one of the dishwashing liquids you compare. Also label one pipette “water” and the last pipette “oil”.
3. Use the pipettes to add 2 ml dishwashing liquid to each test tube. Make sure you use same-name test tubes and pipette for each detergent in order to prevent cross contamination.
4. Use the “water” pipette to add 10 ml water to each dishwashing test tube. Add 12 ml water to the “control” test tube.
5. Use the “oil” pipette to add 5ml oil to each of the test tubes.
6. Shake each tube vigorously for 30 seconds and then put them in the test tube rack.
7. After 1 hour, the material will separate in 3 layers. The lowest layer will be the emulsion. Above that you will have a layer of oil. Finally you will have some foam over the oil. Measure and record the height of emulsion, oil and foam in each test tube. The test tube with the highest emulsion and the highest foam and the lowest oil contain the detergent that is the most effective in dissolving oil.

Your results table may look like this:

The above data table can be analyzed and processed to get a more understandable results table. We really want to know what ratio of oil was dissolved by 2 ml detergent. If you deduct the height of oil column in each experimental test tube from the height of the oil column in the control test tube, and then divide the results by the height of oil column in the control test tube, you will gat the ratio of oil that is dissolved.

Multiply the ratio by 5 ml (initial amount of oil) to calculate the amount of dissolved oil in milliliters.

Divide the dissolved oil amount by the detergent amount to get the dissolved oil per ml of detergent.

You can then right that in your results table like this:

Make a graph:

Use a bar graph to visually present your experiment results. Make one vertical bar for each of the dishwashing liquids you test. Write the name of dishwashing liquids under the bars. The height of each bar represents the amount of oil dissolved by one ml of each dish washing liquid.

Results of Experiment (Observation):

The data could be presented in written form or a bar graph would be an excellent visual method of displaying the final results. Each brand tested should have its own bar. The length of the bars would be proportional to the percent of stain removed or percent of stain that remained.

Calculations:

Calculate the ratio of dissolved oil:

Deduct the height of oil column in each experimental test tube from the height of the oil column in the control test tube, and then divide the results by the height of oil column in the control test tube, you will gat the ratio of oil that is dissolved.

Example:

Height of oil in the experimental test tube is 21mm

Height of oil in the control test tube is 36

The ratio of dissolved oil is: (36 – 21) / 36 = 0.416

Calculate dissolved oil

Multiply the ratio by 5 ml (initial amount of oil) to calculate the amount of dissolved oil in milliliters.

Dissolved oil = 0.416 x 5 = 2.08ml

Divide the dissolved oil amount by the detergent amount to get the dissolved oil per ml of detergent.

dissolved oil per ml of detergent = 2.08 / 2 = 1.04

This means that each 1 ml of the detergent can dissolve 1.04 ml of the oil

All the numbers in the above examples are fictional. Real values may be very different.

Summary of Results:

All measurements should be recorded in the project book and may be presented in the final project report either as numerical data or shown as a bar graph. For each brand of detergent tested, the length of the bar should show the percentage of stain removed.

Conclusion:

The conclusion to the report will state the ranking of the various detergents, and decide if the original hypothesis was proved or disproved. The conclusions might also state any relationships you have noted between the popularity of a given detergent and its effectiveness or its price.

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.

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:

Your references are this website and the books that you will find in your local library about detergents. You can also include the websites of detergent manufacturers and some of the following:

http://www.epa.gov/grtlakes/seahome/housewaste/house/deterg.htm

http://www.sdahq.org/sdalatest/html/soapproducts1.htm

http://cecalaveras.ucdavis.edu/soaps.htm