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Chemistry Background Information
I scream you scream we all scream for ice cream! We have all had a craving for some chocolate chip cookie dough sometime in our life, what many people don't know is they have the ability to make ice cream at home. Ice, sugar, some heavy cream, vanilla flavoring, Ziploc bags some strong arms and you are half way there to creating a delicious batch of homemade ice cream. There is some simple chemistry behind the creation of ice cream.

When the rock salt is added to the ice, it in turn lowers the freezing point. Freezing point depression as it is most often called, is one of the colligative properties, which are the properties of a solution that depend on the amount of solute particles not their identity. Some other colligative properties include osmotic pressure, boiling point elevation and vapor pressure depression. All of these involve the amount of the particles. When the freezing point is lowered it makes it more difficult for the ice to melt. The change is freezing point was lowered from 0oC to -9.5oC . Using the freezing point depression equation.

ΔTf= (Kf)(m)(i)
ΔTf = change in freezing point
Kf = freezing point of water
i = Van't Hoff factor

ΔTf= (1.86oC kg/mol)(2.55 mol/kg)(2)
ΔTf= 9.5oC

Since the freezing point of milk is -0.505oC and the solution surrounding is -9.5oC then the milk mixture is able to freeze into ice cream!

Another way that to create ice cream is using liquid nitrogen. The ice cream is made with just a few ingredients cream, sugar, flavoring, and liquid nitrogen. The coldness of the liquid nitrogen causes the milk solution become ice cream. Liquid nitrogen exists at -320oF. Colder than Pluto!
The process that is occurring with the nitrogen is a phase change from a liquid to a gas, or better known as vaporization. There are many different types of phase changes that can occur, some including solid to a liquid, solid to gas or liquid to gas ar just a few examples. More specifically a latent heat exchange, which is the amount of energy absorbed or released. The equation to solve for latent heat is
Q=mLv

Q= is the amount of heat added or removedphase_change.jpg
m= mass
Lv= specific latent heat

m=3.2332 kg
Lv= 200 kJ/kg

Q= (3.2332)(200)
Q= 646.64 kJ

646.64 kJ is the amount of energy released when phase change from a liquid to a gas occurs.

Additional Resources:


References/Useful Links:
http://www.safety.seas.harvard.edu/services/nitrogen.html
http://classes.ansci.uiuc.edu/ansc438/Milkcompsynth/milkcompfreezing.html
http://webs.wichita.edu/facsme/nitro/cream.htm
http://crafts.kaboose.com/ice-cream-in-a-bag.html
http://chemistry.about.com/od/solutionsmixtures/a/afreezingpointde.-Nxc.htm
http://www.uigi.com/n2_conv.html
http://rowan.edu/colleges/lasold/physicandastronomy/LabManual/labs/SpecificAndLatentHeats.pdf
http://en.wikipedia.orgwiki/Latent_heat
http://www.alterniawhatif.com/HPS%20Project/Phase%20Changes_files/phase_change.jpg
http://classshares.student.usp.ac.fj/CH203/VincentBowry/Lecture_pdfs/L2_Colligatives.ppt.pdf


vanilla_ice_cream.jpgice_creammm.jpg doubleinsulate.jpg
ice_cream_salt.jpg liquid_nitrogen.jpg