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# Ice Cream 20091205 (student preso)

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general physics
5 dec 2009

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### Ice Cream 20091205 (student preso)

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