instructables
Are We Drinking Plastic?!
by lamabuolayan
Dhahran Ahliyya Schools Science Fair
Project name: The E ect of the pH of Acetic Acid on the Solubility of the Casein Protein Found in Milk Molecules
Class 9A diploma
Project done by: Lama Buolayan, Sara AlSheddi, Nouf Alkhereiji
https://www.youtube.com/watch?v=eRFtbXb7T_s
Step 1: Define the Problem
How does the solubility of the casein protein depend on the pH of the acetic acid added into it?
Step 2: Background Information
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Milk contains a protein called casein. Casein is a protein
chain that contains special carbon and oxygen atom
chains, forming a molecule. Casein and other proteins
found in milk are composed of amino acids that may
both have positive and negative charges. The isoelectric
point of a protein is the point of pH where all of the
charged groups have an overall net neutral charge.
Proteins are less soluble at a pH level at their isoelectric
point and more soluble at a pH level below or above
their isoelectric point. In order to be able to form plastic
out of the casein protein found in milk, the pH of the
vinegar added to it will have to lower the pH level of milk
to become at the isoelectric point of the casein protein.
This is because if the pH level of the milk was higher or
lower than the casein protein, the protein will be more
soluble in it and will not be able to form a dough with
the casein protein and eventually create casein plastic
because the casein will dissolve into the liquid. For
example, milk has a pH of 6.8 and the isoelectric point of
the casein protein is 4.6, because the pH of the milk is
higher than the isoelectric point of the casein protein
the protein is more soluble therefore dissolving in the
milk and not forming a dough.
Step 3: Hypothesis
If the amount of pH in the acetic acid lowers the pH of the milk to a pH level that is near the isoelectric point of the casein
protein, then the casein protein will form a dough and eventually become a solid piece of plastic, because proteins are
less soluble at a pH level at their isoelectric point and more soluble at a pH level below or above their isoelectric point.
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Step 4: Variables
Independent variable: pH in vinegar, we will be manipulating the pH in vinegar using a pH meter to
measure the amount of pH that will going into the warm milk.
Dependent variable: solubility of the casein protein, we will be collecting data on the solubility of the
casein protein according to the amount of casein protein plastic produced (by weighing it in grams)
when the acetic acid (vinegar) is added to it. Each beaker of milk will have a di erent amount of acetic
acid (vinegar) according to the pH of each one, starting with the pH of 1, adding 0.2 – 0.3 level of pH in
each cup of warm milk (1, 1.3, 1.5, 1.7, 2, 2.5).
Control variables: the amount of milk used (in order to have the same pH), the temperature of the milk,
the type of milk used, the type of vinegar used, and the duration of leaving the casein protein to harden.
we will be measuring the amount of milk going into each cup using a beaker (250ml) and will be using
the same kind of milk in order for the milk to have the same pH (6.8), and we will be making sure that the
milk in each cup is in a warm temperature (49 degrees Celsius) using a thermometer, as well as choose
the same kind of vinegar (white vinegar 5% acidity) for all small beakers. we will also leave all of the casein
protein balls to harden for the same amount of time (48 hours).
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Step 5: Materials
1.5 liters of whole milk
105 ml of Distilled white vinegar (our acetic acid)
6 normal size beakers
6 small beakers
1 thermometer
1 pH meter
Heating tool (stove top)
6 spoonsPaper towels
6 Labels
1 Pen/Pencil
1 Paper
1 Ruler
1 Sift
1 Plastic plate
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Step 6: Procedures
1. Use the pH meter and spoons to measure out the vinegar into small paper cups that have: 1, 1.3, 1.5, 1.7,
2, and 2.5 levels of pH in each one of them.
2. Measure out 1.5 liters of whole milk by using the measurements in each beaker and heat it using the pot
on the stove top.
3. Use the thermometer to make sure the whole milk is 49 degrees Celsius.
4. Add the vinegar with 1 pH in into one of the normal size beakers that contains 250ml of warm whole milk.
5. Add the vinegar with 1.3 pH in into one of the normal size beakers that contains 250ml of warm whole
milk.
6. Add the vinegar with 1.5 pH in into one of the normal size beakers that contains 250ml of warm whole
milk.
7. Add the vinegar with 1.7 pH in into one of the normal size beakers that contains 250ml of warm whole
milk.
8. Add the vinegar with 2 pH in into one of the normal size beakers that contains 250ml of warm whole milk.
9. Add the vinegar with 2.5 pH in into one of the normal size beakers that contains 250ml of warm whole
milk.
10. Label each glass cup with the pH level of vinegar added into it.
11. Mix the whole milk and vinegar in each glass cup using the spoon.
12. Strain the casein protein from the milk.
13. Layer the paper towels to get ready for the casein protein dough.
14. Use the spoon to gather up the casein protein curds and place it on the paper towels.
15. Stack paper towels over the casein protein curds and press down on them to absorb the excess liquid
from casein protein curds.
16. Use your hands to form a ball from the casein protein curds.
17. Repeat steps 12-16 with all of the vinegar/milk solutions.
18. After all of the casein protein balls are ready, put them on a plastic plate.
19. Leave the casein protein balls to dry for 48 hours.
20. Weigh each of the casein protein balls to test the solubility of them and collect data using a table drawn
in the paper.
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1
1
1. Use the pH meter and spoons to measure out the vinegar into small
paper cups that have: 1, 1.3, 1.5, 1.7, 2, and 2.5 levels of pH in each
one of them.
1. Use the thermometer to make sure the whole milk is 49 degrees
Celsius.
1
1
1. Label each glass cup with the pH level of vinegar added into it.
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1. Weigh each of the casein protein balls to test the
solubility of them and collect data using a table
drawn in the paper.
1
1. Leave the casein protein balls to dry for 48 hours.
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https://www.instructables.com/ORIG/F4P/AZP3/KMYW1A95/F4PAZP3KMYW1A95.mp4
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Step 7: Raw Data Table
This data shows the solubility of the casein protein from the amount of casein protein plastic it has
produced when exposed to di erent levels of pH in acetic acid.
We can see that we have used whole milk with di erent amounts of acetic acid according to the pH level
to test our theory, adding one more level in each solution.
We can see di erent patterns in our data, but one pattern that has shown in all tests is that the solubility
of the casein protein has decreased when exposed to acetic acid of pH that decreased the pH of the
whole milk to most closest to the isoelectric point of the casein protein.
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Step 8: Patterns
All of the beakers with whole milk in them started with
the same temperature (49 degrees Celsius) and solubility
of the casein protein. The casein protein was soluble in
whole milk because of the following: whole milk has a
pH level of 6.8 whilst the isoelectric point of the casein
protein is 4.5. As mentioned before, proteins are less
soluble at a pH level close to their isoelectric point and
more soluble at a pH level below or above their
isoelectric point.
Acetic acid (vinegar), is used to lower the pH of the milk,
making it closer to the isoelectric point of the casein
protein, which makes the casein protein less soluble.
When the casein protein is less soluble, it produces
casein protein curds that will later dry and become
plastic. The plastic is measured by grams to test the
solubility of the casein protein (the heavier the casein
protein plastic is, the less soluble it is). From the results
we have collected, we can see that the acetic acid with
the pH level of 2 has produced the most casein protein
plastic. That is because the 2-pH level of the acetic acid
has decreased the pH of the milk to 4.8 (6.8 – 2 = 4.8),
which is the closest to the isoelectric point of the casein
protein.
The pattern that has been seen here is that although
casein protein plastic has been produced in all of the
tests, the largest amount of casein protein was produced
when the pH of the vinegar lowered the milk to the pH
closest to the isoelectric point of the casein protein. So,
there has been a neutral relationship between the
independent variable (the pH of acetic acid) and the
dependent variable (the solubility of the casein protein)
in which when the pH of the acetic acid made lowered
the milk to equal the isoelectric point of the casein
protein, the solubility of the casein protein decreased
and the most casein protein plastic was produced.
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Step 9: Results
According to the data we have collected, the casein
protein was least soluble when exposed to a level of pH
closes to its isoelectric point. As mentioned before, the
pH of the whole milk used in the experiment was 6.8.
This level of pH is much higher than the 4.6 isoelectric
point of the casein protein. So, when adding di erent
levels of pH from acetic acid to the whole milk with the
pH of 6.8, the pH of the whole milk decreased. As the
amount of pH in the acetic acid increased, the same
amount of pH decreased from the whole milk. This has
caused the level of pH of the milk to slowly get closer
and closer to the isoelectric point of the casein protein.
So, when acetic acid with the pH of 2 was added in the
whole milk, it decreased the pH of the whole milk to a
level very close to the isoelectric point of the casein
protein (4.8). This has allowed the casein protein to
become insoluble and has produced the largest amount
of casein protein plastic with the weight of 13 grams. So,
the when the pH of the acetic acid decreased the pH of
the milk to a level close to the isoelectric point of the
casein protein, the casein protein was the most insoluble
and produced the largest amount of casein protein
plastic.
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Step 10: Conclusion
According to the results, our hypothesis is proven to be
correct, yes, if the amount of pH in the acetic acid lowers
the pH of the milk to a pH level that is near the isoelectric
point of the casein protein, then the casein protein will
form a dough and eventually become a solid piece of
plastic.
But for the beaker with 2 pH of acetic acid added into it,
lowering the pH of the whole milk to 4.8, has made the
casein protein the most insoluble because of its
closeness to the isoelectric point of the casein protein
(which is 4.6), producing the largest amount of casein
protein plastic, 13 grams.
All tests have started with the beaker containing 250 ml
of whole milk with the temperature of 49 degrees
Celsius, but each has produced a di erent amount of
casein protein plastic depending on the pH of the acetic
acid that has been added into the whole milk. For
example, the beaker that has had 1 pH of acetic acid
added into it, lowering the pH of the whole milk to 5.8,
has made the casein protein insoluble by only a little,
making it produce only 1 gram of casein protein plastic.
From this data, we can clearly see the drastic change and
increase in the amount of casein protein plastic
produced as the pH of the acetic acid added into the
whole milk has gotten the whole milk’s pH closer to the
isoelectric point of the casein protein. The data we have
collected proves that the solubility of the casein protein
does depend on the pH of the acetic acid added into the
whole milk.
Step 11: Evaluating the Method
Strengths
We have measured all of our variables correctly and precisely in order for our experiment to be successful.
We have followed the experiment procedure exactly and got a result we were expecting meaning our
theory is correct.
Weaknesses
Not being able to get the exact materials needed for the experiment like the scale. We have used a scale
to measure the size of the casein protein plastic in order to get the results of the solubility of the casein
protein when exposed to a pH near its isoelectric point, but the scale did not measure less that 1 gram,
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meaning that the results would have been more precise if we had used a scale that measured less than 1
gram.
Step 12: Improving the Experiment
If we test this theory and apply this experiment again, we will make sure to get the exact materials we
need in order to get more precise results.
We would also like to test the solubility of the casein protein when exposed to levels of pH near its
isoelectric point but using di erent types of liquids like lemon juice and apple cider vinegar to cure our
curiosity and compare between the amounts of casein protein plastic each has produced.
Step 13: Applications
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What is the importance of this research to humans?
This research explores the change in pH of di erent liquids and the solubility of proteins in these liquids, all of which may
be constantly entering the human body. This research has been done to study the e ects of mixing liquids to change the
pH of one, which has resulted in insolubility. This helps the community learn more about the human body and what
substances are harmful to it. From this research, we have learned that acetic acid lowers the pH of milk from a 6.8 down
to nearly a 4. Liquids that have a pH of less than a rounding of 7 are considered acidic, Liquids that have a pH of more
than a rounding of 7 are considered alkaline, 7 is neutral. When the human body consumes too many acids, health
problems and conditions can occur. This research is important to humans because it shows the e ect of acidic acid when
added to milk(lowers pH under 7), which helps humans make smarter choices in order to keep their bodies healthy.
How can it be applied in practice?
After much research and study about the topic of pH change in liquids, humans in our community learn to make sure not
to have large amounts acetic acid and milk together because of the danger it exposes their bodies to. They learn that in
order to have the nutrients from the milk they need keep it in a neutral pH level and when adding acetic acid, the pH of
the milk decreases making it acidic instead of neutral and harmful. By reading this study and learning about this
research, humans apply their knowledge in practice by making smarter choices in order to keep their bodies healthy.
What did you learn from this research?
From this research, we have learned about many di erent topics. First, we have learned about the inner workings of a
protein and its solubility. We now know that proteins found in milk are composed of amino acids. One protein of those is
called the casein protein that contains special carbon and oxygen molecules. The solubility of proteins depends on the
level of the pH that is surrounding them compared to their isoelectric point. If the pH is higher or lower than their
isoelectric point, then the protein is soluble, but if the pH is at the isoelectric point of the protein, then the protein
becomes insoluble. We have also learned that adding acidic acid or vinegar lowers the pH of milk, which then causes
harm to the human body when consumed because the acids can cause health problems and in order for the body to be
healthy, more alkaline-forming foods (higher than 7 pH) should be consumed instead.
Step 14: Services As Action
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This project can be used as a Service as action project because of its stages.
Investigating: Brainstorming topics and choosing our selected topic after much research about the basic
information. Forming the scienti c question and writing background information.
Planning: Forming the hypothesis with use of the variables including the independent, dependent, and
control variables. Planning out the materials that will be used and the steps of the procedure of the
experiment.
Solving: Applying the knowledge learned from investigating and planning and doing the experiment
according to the procedures written before. Recording videos and pictures and collecting data.
Re ecting: Analyzing data to reason with the results of the experiment to prove if the original hypothesis
was correct or not and writing the conclusion. Finding strengths and weaknesses and improvements.
Making a poster and a tiktok to raise awareness.
This experiment has given results that will help the community improve and maintain health amongst themselves
making this research a service as action for our community.
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Step 15: ATL Skills Reflection
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Research skills:Whilst working on my project, we have used my research skills in various situations. First,
we have used our research skills when we were brainstorming and choosing a topic for my project.
Second, we have used our research skills in order to nd more about our chosen project and write down
our background information. We have also used research skills whilst collecting and analyzing data and
making conclusions in which we were conducting our own primary research in order to nd our
solutions.
Self-Management skills:We used our self-management skills to divide the work among me and my
classmates to 12 weeks in order to make sure that we are done on time and ready to present and submit
by the due date.
Thinking skills:I have used my thinking skills in order to brainstorm ideas for my project and choose my
current one after considering the elements of the experiments. I have also used my thinking skills to
analyze the data I have collected from my experiments and realize the wrong in my theories and the right
in them in order to create strengths, weaknesses, and improvements for myself during this project.
Communication and social skills:This project has been conducted as a group project in three classmates
have worked together to complete this project. We have researched and brainstormed together to
choose one idea we all agree on. We have divided the materials of the experiments between us and then
have met together in the school lab and conducted our experiment together and have collected the data
together.
Thanks for sharing!
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