ICE CREAM
THERMODYNAMICS LAB
LAB OBJECTIVES:
To use both the laws of
thermodynamics and properties of
solutions to aid in freezing an ice
cream mixture.
STATE THE QUESTION: How can you
lower the freezing point of water in
order to freeze an ice cream
mixture?
GATHER INFORMATION
It’s 35˚ C in the shade and to cool
off, you are eating an ice cream
cone. As you sit there you wonder
just how ice cream is made. One
area of chemistry that helps to
explain the making of ice cream is
thermodynamics. There are
3 laws of Thermodynamics –
copy in notebook!
1. The total amount of energy in
the universe is constant.
Law of Conservation!
Everything Cycles
2. The entropy (which is a
measure of disorder) of the
universe is always increasing.
Constant changing by
conduction, convection or radiation
3. Absolute Zero 0˚ K energy can
not be reached YET.. An Atoms Electrons
spin cause’s frictional heat so has KE and a
temperature is the average KE of a substance.
In making ice cream you remove about 1000
calories of heat from the milk/sugar (chocolate
milk) mixture and transfer it to the salt/ice
mixture. Energy is conserved and the first law is
satisfied. Heat is always transferred from a hot
object to a cooler one. Imagine your surprise if
you had a glass of water and the water froze
and the glass got hot. The glass pulled heat out
of water.
The 2nd law determines the direction of heat
transfer and states heat always moves from a
hot object to a cooler one. Entropy -chaos
trying to reach evenness.
Another aspect of chemistry involved is the
properties of solutions as compared to pure
solvents. The presence of solute (the thing
being dissolved) particles in a solution will raise
the boiling point and lower the freezing point
of the solvent (the dissolver). Therefore,
because the ice cream mixture is mainly a
solution of sugar and water, its freezing point
is depressed below 0˚ C.
Before refrigerators were invented,
ice cream was made using ice. In this
method, the “hot” ice cream
mixture has to lose energy to the
“cold” ice. Since ordinary ice is only
0˚ C, this is the lowest temperature
that the ice cream could become.
The ice cream mixture would still be
a liquid.
To freeze the ice cream mixture, it
is necessary to use “colder” ice.
Again, properties of solutions
provide the answers. A salt-ice
mixture has a lower freezing point
than pure ice, so it acts as “colder”
ice. The more salt added to the ice,
the lower the freezing point. The ice
cream mixture can then lose more
energy to the salt-ice mixture and
freeze. Big bag
Gather Info of individual variables:
Temp of Milk _____
Temp of ice ________
Temp. Of ice & rock salt __
CONDUCT THE EXPERIMENT
MATERIALS:
ICE CREAM MIXTURE:
 Quart size Ziploc bag (smaller bag)
 1 cup of chocolate milk
MAKING THE ICE CREAM MATERIALS:
 Gallon size Ziploc bag (bigger bag)
 Ice
 Rock salt
 Thermometer
PROCEDURE:
PART 1:
1. Add 1 cup of chocolate milk to smaller size
Ziploc bag.
2. Seal the bag well. Try to make sure all of
the air is out of the bag.
3. Mix the ingredients until they are blended.
4. Take the initial mass of the milk mixture
and record in your data table.
5. Take the initial temperature of the milk
mixture by wrapping the baggie around the
thermometer. Do not put the thermometer
directly into the mixture as then it would not
be safe to eat.
PART 2:
6. Fill the gallon-sized Ziploc bag about half to
three-fourths full with ice.
7. Add rock salt so that it is lightly coating the
ice cubes, 2 tsp. is good.
8. Take the initial temperature of the ice/ salt
mixture by wrapping the baggie around the
thermometer. Record on data table.
9. Put the Ziploc sandwich bag with the ice
cream mixture in it (keep it sealed!) into the
gallon sized Ziploc bag.
10. Seal the gallon sized bag with as much of
the air out as possible.
11. Wrap it in newspaper (insulator) and shake
for 5 minutes really fast. it will be COLD!
12. You can put into a white can to shake if you
wish.
PART 3:
13. Once your mixture is the correct
consistency, use the thermometer to find the
final temperature of the milk mixture (ice
cream) and the rock salt/ice/water mixture.
Record on data sheet!
14. Once you have read the temperature, pour
the contents of the gallon sized bag in the sink.
15. Take the final mass of the milk/ ice cream
mixture.
16. Get a plastic spoon, and enjoy your tasty
thermal treat.
17. Make sure your lab station is clean and all
used bags are in the trash before you leave.
ANALYZE YOUR DATA
DISCUSSION:
When you took the temperature of the rock
salt/ice/water mixture, it should have been
lower than 0 oC.
How is it possible to have ice water colder
than the freezing point of water? Well, here’s
an explanation…
When ice is at 0 oC, essentially water
molecules are going from the solid
phase to the liquid phase as fast as
they are going from the liquid phase
to the solid phase. (This is called a
dynamic equilibrium.) This means
that at 0 oC, neither freezing nor
melting are occurring.
When rock salt is added to water,
the Ca+2 and Cl-1 ions slows the rate
at which water molecules go from
the liquid phase to the solid phase.
There is more flow of solid liquid.
In other words, we see the ice melt.
But, how is the temperature lower
than the freezing point of water?
Water molecules in ice are held
together by strong intermolecular
forces (like hydrogen bonding).
When the ice melts, the forces
holding the ice particles together
must be overcome (broken).
Well, it takes energy to overcome
these intermolecular forces. Where
does this energy come from?
The ice particles use thermal energy
(heat) from the surrounding liquid in
order to overcome (break) the
forces holding them together.
Water’s heat
So, the liquid water is losing heat
(getting colder), and the ice is using
that heat to overcome break the
intermolecular forces that hold the
ice particles together. The
temperature of the rock salt + water
is colder because it lost heat to
break hydrogen bonds.
Name : ___________________
ICE CREAM THERMODYNAMICS LAB
Problem: How can you lower the freezing point of water in order to freeze an ice cream mixture?
Gather Info of individual variables:
Temp of Milk ____________ Temp of ice ______________
Temp. Of ice & rock salt _______
FORM A HYPOTHESIS
If _____________________________________________________________________________________,
then ____________________________________________________________________________________.
COLLECT YOUR DATA
INITIAL READINGS
Initial Mass of Milk Mixture
FINAL READINGS
Final Mass of Milk Mixture
=
Initial Temp of Milk Mixture
Final Temp of Milk Mixture (Ice Cream)
=
Initial Temp of Ice/ Salt
Final Temp of Ice/ Salt
=
DIFFERENCE
QUESTIONS:
Discussion:
1. How would you define the second law of thermodynamics?
2. How does adding salt to ice make ice “colder”?
3. Why is the salt-ice mixture needed to freeze the ice cream mixture?
Re-read the explanation!
_______________________________________________________________Answer on Back_____________________
4. Discuss the reason for the heat transfer that occurs as the ice melts and the ice cream mixture freezes. Draw a
diagram of the baggie-ice cream freezer. Use arrows to indicate the direction of the heat transfer.
Label the energy transfer of conduction and convection in the process!
5. How could you speed up the freezing of the ice cream mixture?
6. Graph the relationship of the temperature of the milk before shaking and after shaking it in rock salt freezer..
DRAW YOUR CONCLUSIONS
Write a DETAILED paragraph that includes the following:
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Restate your scientific question and your hypothesis.
Tell whether your hypothesis was ACCEPTED or REJECTED by the data. Use actual data (qualitative and
quantitative ##’s data) from your experiment to back it up.
Tell if you had anything go wrong/ unexpected in your experiment or if it went as you expected AND WHY.
How did that affect your results?
How could you extend this experiment? How could you make it better, what would you change next time?