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Driving Question: How did dish soap changed the solubility of food coloring in milk?

Purpose: The purpose of this experiment is to see what occurs when we add dish soap to milk.

Materials:

-White milk (Whole or 2%)

-Dinner plate

-Food coloring (red, yellow, green, blue).

-Dish washing soap (Dawn brand would work better)

-Cotton Swabs

Safety:

-Make sure you have an adult helping you.

-Do not drink the milk after you have put the food coloring and soap in it!

-Do this experiment near a sink so that when you are done, you don't spill milk and food coloring all over the floor.

Procedures:

-Pour enough milk in the dinner plate to completely cover the bottom to the depth of about 1/4 inch. Allow the milk to settle.

-Add one drop of each of the four colors of the food coloring - red, yellow, green, blue - to the milk. Keep the drops close together in the center of plate of milk.

-Find a clean cotton swab. Predict what will happen when you touch the tip of the cotton swab to the center of the milk. Don't stir; Just touch it with the tip of the cotton swab. Go ahead and try it. Now, did anything happened?

-Place a drop of liquid dish soap on the other end of the cotton swab. Place the soapy end of the cotton swab back in the center of the plate of milk, and hold it right there for 10-15 seconds. Just look at that color burst! It looks like the Fourth Of July!

-Add another drop of soap to the tip of the cotton swab and try it again. Experiment with placing the cotton swab at different places in the milk. Notice

Experiment Pictures:

Observations: Without liquid dish soap on the cotton swab, the food coloring did not spread. But after adding liquid dish soap on the cotton swab, with the cotton swab in the center of the dinner plate filled with milk, the colors started spreading.

Scientific Principle: The dish soap does not mix with the milk. Instead it floats on top and spreads over the surface. As it spreads, it grabs the food colouring. Soap is a "degreaser" so the molecules in it are attacking the fat in the milk, causing motion which creates the swirling of the colours. Where the colours meet, they combine and form new colours.Liquids like water and milk have a property known as surface tension, due to the cohesive forces of the liquid's molecules. If you look closely at the edge of the surface of water in a clear glass, the water appears to rise up the side of the glass because the surface tension of the water is actually pulling the water away from the glass inward toward the center of the surface. Since milk is mostly water, it has surface tension like water. Homogenized milk has gone through a process where the fat is broken up into tiny pieces of fat called globules and spread throughout the milk. When the food coloring was added to the milk, the fat globules were steady and undisturbed. Food coloring is less dense than milk, so it floats on the surface. When dish soap touches the surface of the milk, things begin to move. Dish detergent weakens the milk's bonds by attaching to its fat molecules. As the dish soap diffuses into the solution it surrounds the fat globules in the milk. When you drop the soap into the centre of the milk, it quickly spreads out toward the edges, because soap reduces the surface tension of water/milk. The active ingredient in dish soap is a class of chemicals called surfactants, which change the properties of the surface of a liquid, greatly reducing the surface tension. When the advancing surfactant ‘wave’ hits the colours, the surface tension relaxes and the drops of colour can mix MUCH faster. The stronger surface tension of the surrounding liquid then pulls the surface away from the weak, soapy region. The food colouring moves with the surface, streaming away from the dish soap. This movement sets up currents on the top and bottom of the milk and forces the food colouring under the surface of the milk. The soap reduces the surface tension of the milk by dissolving the fat molecules. The interaction between the dish detergent and the fat in the milk causes turbulence in the bowl as the soap breaks down the fat in the milk. This rapidly mixing fat and dish soap movement causes the food colouring to swirl. The swirling food colouring shows what is happening in the milk allowing us to observe the invisible activity of how the surface of the milk moves and changes in response to the soap breaking up the fat in the milk. As the soap becomes evenly mixed with the milk, the action slows down and eventually stops. With the soap removed from the surface, surface tension returns to its original strength. Adding another drop of dish soap will start the process again and the experiment can be repeated. Eventually all of the fat globules in the milk will be surrounded by soap and some soap will remain on the surface causing surface tension movement to stop.

Q: Instead of using milk, what would happen if you used type of soda, water, etc.?

A: Milk is what contains a good source of protein and fat, and the dish soap is what cuts the fat from the milk. Now, soda and water? Soda, whether it's Coke, Sprite, etc., contains 0 grams of fat, and same goes to water, which means there isn't any fat to cut off at all when dish soap is applied. So if you ever do an experiment on "Color Changing Coke" or "Color Changing Water", vice versa, I guarantee it won't work, nor will you get the exact same results as the "Color Changing Milk" experiment. You will have to use a beverage that contains A GOOD AMOUNT of fat.

Q: Do different types of milk effect the food color dispersing?

A : The food color in whole milk will disperse fastest because dish soap holds tight with the fat in the milk

Q: What is the role of soap in this experiment?

A: The weak chemical bonds that hold the proteins in the solution are manipulated

Q: How this experiment related with surface tension?

A: The drops of food coloring floating of the surface tend to stay put. Liquid soap wrecks the surface tension by breaking the cohesive bonds between water molecules and allowing the colors to zing throughout the milk