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Ice Cream 20091205 (student preso)

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student presentation …

student presentation
general physics
5 dec 2009


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Transcript

  • 1. The Physics of Ice-cream
    Napat
    Peerada
  • 2. How to make ice-cream?
    Put syrup and water into the small cup/bag
    Put ice and salt into the big cup/bag
    Put the smaller bag into the bigger bag
    Shake until the ingredients in the smaller bag freezes
  • 3. Water
    At 0 °C, melting point of ice and freezing point of water
    The ice molecules are constantly escaping to water, and the water molecules are captured at the surface of ice.
    This equilibrium will be maintained as long as the temperature is kept at 0°C and there is no external interruption
  • 4. Salt
    Salt decreases the freezing point
    Salt molecules disrupt the equilibrium
    Even though salt molecules are dissolved in water, they do not easily attached to the ice.
    This means that the number of water molecules able to captured by ice goes down, so the rate of freezing goes down as well
    At the same time, the rate of melting of ice is unchanged, so melting occur faster than freezing
  • 5. Salt
    To return to equilibrium, the temperature must be lower to make the water molecules slow down and attached to the ice more.
    The higher the concentration of salt, the lower the freezing point drops.
  • 6.
  • 7. What about sugar in the syrup?
    Temperature of the larger container has decreased: the inside decreases as well
    Sugar does not disperse into ice, only in water
    As water freezes out, the remaining sugar solution become more concentrated, making it harder for water to crystallize in its pure form.
    The temperature is further lowered, the equilibrium shifted and the freezing point has decreased
  • 8. Ice-cream freezing curve
    Not all of the water is frozen!
    The rest remain as very concentrated sugar solution
  • 9. Freezing-Point Depression
    ΔTf = Kfcm
    Kf : freezing point depression constant
    Cm : molar concentration
  • 10.
  • 11. Task
    Peerada
    Introduction
    Salt and water
    Napat
    Sugar and water
    Freezing point depression
    Conclusion
  • 12. References
    http://books.google.co.th/books?id=bKZ1oICZWywC&dq=the+science+of+ice+cream&printsec=frontcover&source=bl&ots=BOF8B945rQ&sig=cdjqNFX_zUvCdIpGvRr7Yjw3_r0&hl=en&ei=4UEXS_jaNNGHkAWUl-HkAw&sa=X&oi=book_result&ct=result&resnum=6&ved=0CCIQ6AEwBQ#v=onepage&q=&f=false
    http://www.worsleyschool.net/science/files/saltandfreezing/ofwater.html
    ://www.foodsci.uoguelph.ca/dairyedu/icstructure.html
    http://hyperphysics.phy-astr.gsu.edu/hbasees/Chemical/meltpt.html
    http://www.chemguide.co.uk/physical/phaseeqia/raoultnonvol.html