Jennifer Tuch- Investigating Liquids: Color Changing Milk

Title: Investigating Liquids: Color Changing Milk

YouTube Reference: (MCExperiments)— “Fun With Magic Milk & Food Coloring! (Home experiment)”

Principle(s) Investigated:

Weak chemical bonds that hold the proteins in milk are altered when dish soap is added. The molecules of fat and proteins bend, roll, and twist in all directions causing the food coloring to react and look like exploding fireworks.

Standards:

Physical Science-Matter- 2.2.1.2.1-physical properties of materials can be changed, but not all materials respond the same way to what is done to them.

Materials:

Milk (whole or 2%), dinner plate, food coloring (red, yellow, green, blue), dish-washing soap (Dawn brand works well), Q-tips. All items can be obtained at any market.

Procedure:

1) Poor enough milk in the dinner plate to completely cover the bottom and allow it to settle.

2) Add a couple drops of each of the four colors of food coloring- red, yellow, blue, and green in random places in the milk.

3) Predict what will happen before you squeeze a few drops of soap in random places in milk.

4) What what happens.

Student prior knowledge:

Understand how to work in groups. Understand the observation/inquiry process in regards to lab work. Possess fundamental knowledge of chemical bonds and surface tension.

Explanation:

Milk is mostly water but it also contains, vitamins, minerals, proteins, and droplets of fat suspended in solution. Fats and proteins are sensitive to changes in the surrounding solution (the milk).

When you add soap, the weak chemical bonds that hold the proteins in solution are altered. The molecules of protein and fat bend, roll, twist, and contort in all directions. The food color molecules are bumped and shoved everywhere, providing an easy way to observe all the invisible activity. At the same time, soap molecules combine to form a micelle, or cluster of soap molecules. These micelles distribute the fat in the milk.

This rapidly mixing fat and soap causes swirling and churning where a micelle meets a fat droplet. When there are micelles and fat droplets everywhere the motion stops.

Another reason the colors explode the way they do is—milk is mostly water, it has surface tension like water. The drops of food coloring floating on 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.

Questions & Answers:

1) Q: The proteins in milk are held together by chemical bonds. How do chemical

bonds work?

A: A chemical bond is an attraction between atoms that allows the formation of

chemical substances that contain two or more atoms. The bond is caused by

the electromagnetic force attraction between opposite charges, either between

electron and nuclei, or as the result of dipole attraction. In this case, milk has

a weak chemical bond so would most likely be characterized as a “dipole”

attraction. Dipole-dipole interactions are caused by a large difference in

electronegativity between to bonded atoms. This will cause a permanent

charge separation, or dipole, in a molecule or ion. The bonding electrons in a

molecule or ion will, on average, be closer to the more electronegative atom

more frequently than the less electronegative one, causing partial charges on

each atom, hence resulting in a “weak” chemical bond.

2) Q: The weak chemical bonds in milk are altered when the dish soap is added.

Why does the dish soap alter the chemical bonds in the milk?

A: Dish soap, because of its bipolar characteristics (nonpolar on one end and

polar on the other), weakens the chemical bonds that hold the proteins and

fats in solution. The soap’s nonpolar, or hydrophilic (water-loving), end

dissolves in water, and its hydrophobic (water-fearing) end attaches to a fat

globule in the milk.

3) Q: Milk has surface tension like water. This is why the food coloring stays in

place until the dish soap is added which breaks the surface tension by

breaking the cohesive bonds between water molecules. What is surface

tension?

A: Surface tension is a property of the surface of liquid that allows it to resist

an external force. For example, surface tension is evident through the

floating of some objects (insects, reptiles) on the surface of water, even

though they are denser than water. This property is caused by cohesion of

like molecules, and is responsible for many of the behaviors of liquid.

Applications to Everyday Life: (Examples of the breaking of chemical bonds)

1) When you heat a solid, such as ice, you transfer energy to the molecules, allowing them to break the chemical bonds that hold them in a solid state. This could take place on a warm day, sitting outside with some ice in water.

2) An egg is made up of individual proteins floating in water, the proteins consisting of long-chain molecules twisted and held in a roughly spherical shape by chemical bonds. As an egg is heated in a pan, these bonds break and the molecules unravel, bonding with other molecules to form a network that traps the water and turns the egg solid.

3) In the process of digestion, chewing which uses saliva bathes the broken down bread and peanut butter with the first digestive enzyme, salivary amylase. Amylase breaks the chemical bonds between the carbohydrate molecules, changing them into smaller sugar molecules. These molecules are now free to be broken down even further to complete the process of digestion.