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Milk Rainbow Experiment
8
Milk Rainbow Experiment
Ages 7-8
Aim
Children will be able to observe the chemical reaction of a surfactant (dish washing liquid)
with lipids. Food colouring makes the reaction visible to children.
Context for Children
Dish washing liquid is used on greasy and oily dishes because it breaks the bonds in the fats allowing them to separate to clean the dishes.
Science
Milk contains fat, the fat is all connected with bonds.The food colouring floats to the top of the fat. When you add the dish washing liquid to the milk it bonds to the fat.The molecules in the soap are racing around joining up with fat molecules. It keeps going until the soap becomes evenly mixed in the milk.
> Context
Science behind the experiment
Hypothesis
As the dish washing liquid reduces the surface tension of
the milk and reacts with the fat, the particles in the milk move around and
create swirls of colour.
The different fat content in the three different types of milk used will result in different speed of pattern formation.
> Hypothesis
Total fat content per 100ml of milk:
- Full cream: 3.4g
- Skim: 0.3g
- Almond: 1.7g
Method
> Experiment
1.
Pour whole milk in the shallow dish and add a drop of each colour of the food colouring.
2. Dip a cotton tip in the dishwashing liquid and place it in the middle of the triangle.
3. Watch the reaction and record it in the lab book.
4. Repeat with skim milk and almond milk and compare the results.
Skim Milk
Almond Milk
Whole Milk
Further investigations
> Further Investigations
Colour investigation - mixing primary colours and creating secondary colours within the experiment and creating patterns.
Testing different substances instead of dish washing liquid.
Extending on the experiment
Colour Mixing
Reducing the surface tension by a paper clip placed on the surface of the liquid.
Float or Sink?
Results and Conclusion
Findings:
When droplets of food coloring are placed onto the milk’s surface, the food colouring stays suspended on the surface in a small area.
How does the dish washing liquid interact with the components of the milk?
When you touch a cotton tip soaked in soap to the milk, the colouurs spread throughout the milk creating visually pleasing result - colourful swirls children will enjoy.
> Conclusion
The fat in milk has proven sensitive to changes and food colouring makes the chemical reaction, which occurs when the dishwashing liquid is added, visible. The dish washing liquid and fat take time to join together, which causes the movement in the dish.
The higher the fat content of the milk, the longer the movement or 'dance of fat molecules' lasted (see graph on the right).
Resource List
Consumables
- Whole Milk
- Skim Milk
- Organic Almond Milk
- Dish washing liquid
- Food Colouring
- Red
- Yellow
- Blue
- Cotton tips
> Resources
Equipment
- Shallow dish