1. Part A: Working Scientifically
Investigation 1 – How well does dishwashing liquid repel against fat?
Introduction
Prior to completing the activity I wrote down what I think would happen when I added
dishwashing liquid to various types of milk, these being full cream, smarter white and
skim milk.
We placed 1 drop of red food colouring on one side of the bowl and a drop of blue
food colouring on the other side of the bowl directly opposite the red colouring. Both
drops were about 5cm in from the edge of the bowl.
Predict
My prediction is that once the dishwashing liquid was added to the bowl that
contained the full cream milk, the colours would dissolve and disappear. I predicted
that this would happen to all 3 types of milk, however I believe that the colour would
not fade as much in the skim milk as they did in the full cream milk. I believe that
this would occur due to the dishwashing liquid reacting to the food colouring in the
milk.
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2. Observe
When we placed the drops of food colouring in the bowl we saw that it did not move
it just stayed as a drop in the bowl of milk. We then added the dishwashing liquid in
between the food colouring and as soon as we did this the food colouring reacted by
moving away from each other to the outer rim of the bowl.
The food colouring sank into the milk for the first part and there was a small thin
outline of the food colouring around the edge of the bowl that went for about 5cm.
We watch the bowl and we could see that nothing was happening as we continued to
watch the bowl we noticed that the colours were starting to move and react to the
dishwashing liquid.
As a group we asked ourselves “what was moving”? “What was happening”? We
noticed that the colours were swirling in the milk and we believed that there was a
reaction with the detergent and the milk. Some of the suggestions that we came up
with as to what was happening was that perhaps the milk was separating or was
curdling. We did notice that the two colours separated from each other, moving to
opposite sides of the bowl. We also considered whether the reaction was due to the
food colouring being in the milk or would it still have the same reaction if the food
colouring was not in the milk.
We completed the investigation again however this time we used the “smarter milk
which had 2% fat. We again put the drops of food colouring in the bowl followed by
the dishwashing liquid in the middle of the food colouring. This time the reaction was
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3. the same in the fact that the food colouring sank, and then began to swirl around
however the reaction was a lot slower and did not go for as long as what it did with
the full cream milk.
The third investigation was to complete it again, however this time we used skim
milk. When we put the dishwashing liquid into the milk and this time the colours
actually swirled together, but did not mix. The blue colouring sat on top of the red
colouring but they did not mix together.
Explain
We know that the reaction that we were seeing was in the dishwashing liquid
repelling against the fatty milk. It was not the food colouring that was repelling
against the milk or detergent and the colouring was there to help show how the milk
was reacting to the dishwashing liquid.
Steve Spangler explains that the reason it reacts like this is “due to the detergents
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 polar, or
hydrophilic (water-loving), end dissolves in water, and its hydrophobic (water-fearing)
end attaches to a fat globule in the milk”.
He continues on to explain that “The molecules of fat bend, roll, twist, and contort in
all directions as the soap molecules race around to join up with the fat molecules.
During all of this fat molecule gymnastics, the food coloring molecules are bumped
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4. and shoved everywhere, providing an easy way to observe all the invisible activity.
As the soap becomes evenly mixed with the milk, the action slows down and
eventually stops.
We can see from the evidence of the photo below the milk reacting to the detergent.
So we can look back at our question for completing this investigation – How well
does dishwashing liquid repel against fat? I think that we can clearly establish that it
actually repels more intensely as the milk with the higher fat content had a more
significant reaction than the milk with the lower fat content.
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5. Part B: Australian Curriculum – Science
Scenario 2 – Year 3/4
Strand
Sub- strand
Aims Learning Design (around scenarios)
An interest in science as a means of expanding their curiosity and
willingness to explore, ask questions about and speculate on the
changing world in which they live.
An understanding of the vision that science provides of the nature of
living things, of the Earth and its place in the cosmos, and of the
physical and chemical processes that explain the behaviour of all
material things
An understanding of the nature of scientific inquiry and the ability to
use a range of scientific inquiry methods, including questioning;
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6. planning and conducting experiments and investigations based on
ethical principles; collecting and analysing data; evaluating results; and
drawing critical, evidence-based conclusions
An understanding of historical and cultural contributions to science as
well as contemporary science issues and activities and an
understanding of the diversity of careers related to science
A solid foundation of knowledge of the biological, chemical. Physical,
Earth and space sciences including being able to select and integrate
the scientific knowledge and methods needed to explain and predict
phenomena, to apply that understanding to new situations and events,
and to appreciate the dynamic nature of science knowledge.
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