Tie Dyed Milk Experiment. is amphipathic. What exactly does amphipathic mean? It means that soap

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1 Tie Dyed Milk Experiment Navdip Bhangoo Sample Experiment Brief Introduction Before we begin this experiment we need to understand the properties of soap. We have all used soap to perform a chore like washing dishes. Soap is amphipathic. What exactly does amphipathic mean? It means that soap has a non-polar hydrophobic (water fearing) end. This end does not mix with the water, but instead swallows the grease to capture it and remove it from the dishes. The other end of soap is the polar hydrophilic (water loving end). The hydrophilic (water-loving) end reacts with the water that is used to rinse the dishes. An example to better understand the concept of hydrophilic would be how salt dissolves in water. The hydrophilic (water loving) characteristics allow this to occur. An example of hydrophobic interactions would be between water and oil. When you attempt to mix these they separate because the oil is hydrophobic (water fearing) it wants to be as far away from the water as possible resulting in a visible separation. Now that we understand the characteristics of soap we can apply it to the experiment we will be performing. Milk consists of vitamins, minerals, proteins and small amounts of fat. Later on in this experiment we will

2 discover that when soap is added to milk with food coloring an extremely interesting dye pattern is created. This tie-dye pattern is caused by soap. This is because soap of the nonpolar hydrophobic and polar hydrophilic ends of a soap molecule. The characteristics of soap make the interactions between the protein and fats become weak. The polar end of soap dissolves in water and the nonpolar end binds to the fat in the milk. The result will be that the fat molecules will move in different directions. We will be able to visualize this due to the dyes we add. We will also see that more nonpolar molecules spread the dye faster. Purpose: To understand the unique characteristics of polar, nonpolar, and amphipathic molecules. Materials Q-tips (10 per student) Food coloring (one complete set of four dyes per table) Whole Milk (1/4 cup per plate) Non-Fat milk (1/4 cup per plate) Water (1/4 cup per plate) Skim Milk (1/4 cup per plate) 2% milk (1/4 cup per plate) Paper plates (5 sturdy plates per student)

3 Small Paper cups (1 per table: used to measure out soap) Dish Soap Labels Permanent markers (3 pens per table: used to write labels) Measuring cups (One for each table) Individual Containers for the whole milk, nonfat milk, water, skim milk, 2% milk (total 5 containers per table) Procedure (Repeat for non-fat milk and water) 1. Pour milk or water into a tray it does not need to be full. A quarter full should be sufficient. Label all three of the dishes: Plate 1:Whole milk Plate 2:Non-fat milk Plate 3:Water 2. Add a few drops of the first food coloring close to the center. Do the same with the rest of the colors. Try to make sure the colors do not touch. Your tray should look like Figure 1. Figure 1. Appearance of tray after adding food dye.

4 Now make sure to make a hypothesis about what is going to occur when the Q-tip touch s the water, whole milk, 2% milk, skim milk and non-fat milk. You should make a prediction or hypothesis about what is going to happen when the toothpick touches the dye and how fast it might occur in the different mediums provided. Hypotheses: 3. Carefully touch the center of the plate with a CLEAN toothpick and observe and record what happened on the lines provided. NOTE: Do NOT swirl just touch the center Water: Whole Milk:

5 Non Fat Milk: Skim Milk 2% milk 4. Place one end of the toothpick in the dish SOAP. Then carefully touch the center of the plate and observe and record what happened on the lines provided. NOTE: Do NOT swirl just touch the center Water:

6 Whole Milk: Non Fat Milk: Skim Milk 2% milk Now you can lift the toothpick and touch the center of any circle you prefer. Record what happens below. Water:

7 Whole Milk: Non Fat Milk: Skim Milk 2% milk Now repeat this after adding more soap. Record what happens. Specifically pay attention to the speed and the difference between the first time you touched the food dye and now. Water:

8 Whole Milk: Non-Fat Milk: Skim Milk 2% milk Questions Now that we have made observations and collected data we will now discuss the results of the experiment by answering the questions below. Were your hypotheses correct?

9 What did the soap interact with? Was there a difference in the rates of the tie-dye pattern appearing between the three variables (whole milk, non fat, 2% milk, skim milk and water)? Which combination had the fastest rate of spreading for the colors (whole milk, non fat, 2% milk, skim milk and water)? Which combination had the slowest rate of spreading for the colors (whole milk, non fat, 2% milk, skim milk and water)?

10 Did the color spreading occur in the water? Explain why or why not? Why do you think there was a difference between the rates of spread for the colors? (Hint it has to do with the non-polar molecules) References: Samantha House, Sample Experiment for Tie Dying