Unit+15++-++Day+01-02

Instructions **__
 * Ice Cream Lab **__**
 * // Make a new page on your wiki titled "Ice cream lab" //
 * // Give your best guess to the answers for ALL questions & analysis in the lab below. //
 * // You can use the book (ch 15) to help make your guesses educated. //
 * // After you do the lab, go back and change your answers if they were wrong. //

__** Lab **__ Who knew chemistry could be so tasty! Today we will be investigating colligative properties and how they affect freezing points, and some yummy results of energy changes.

__Pre-Lab reading__ Ice cream, a mixture of milk, sugar and vanilla, is really an aqueous mixture with many particles in each liter. Because of this the freezing point of ice cream is lower that that of water, so to freeze ice cream, or to keep it frozen, you must keep its temperature significantly below 0 degrees Celsius. Adding salt to ice produces a melting ice and saltwater mixture with a depressed freezing point in which the ice cream can be frozen. Since the room temperature and the milk mixture are both warmer than the freezing point of the ice mixture, energy will be transferred into the ice mixture on all sides. This energy will be used in melting the ice (334 joules per gram melted) and the temperature of the ice mixture will stay at its freezing point as long as there is still ice to melt. This process will effectively draw energy out of the milk mixture, lowering its temperature and, eventually, freezing it! One story of how ice cream came about was……, hundreds of years ago, Charles I of England hosted a sumptuous state banquet for many of his friends and family. The meal, consisting of many delicacies of the day, had been simply superb but the "coup de grace" was yet to come. After much preparation, the King's French chef had concocted an apparently new dish. It was cold and resembled fresh-fallen snow but was much creamier and sweeter than any other after-dinner dessert. The guests were delighted, as was Charles, who summoned the cook and asked him not to divulge the recipe for his frozen cream. The King wanted the delicacy to be served only at the Royal table and offered the cook 500 pounds a year to keep it that way. Sometime later, however, poor Charles fell into disfavour with his people and was beheaded in 1649. But by that time, the secret of the frozen cream remained a secret no more. The cook, named DeMirco, had not kept his promise. Another story of how ice cream came about was…… that the Roman emperor, Nero, discovered ice cream. Runners brought snow from the mountains to make the first ice cream. In 1846, Nancy Johnson invented the hand-cranked ice cream churn and ice cream surged in popularity. Then, in 1904, ice cream cones were invented at the St. Louis World Exposition. An ice cream vendor ran out of dishes and improvised by rolling up some waffles.
 * Hess' Law and Enthalpy Change**: The energy absorbed by the ice mixture is transferred from the room and the milk mixture so DH ice = DH milk mix + DH room. This is an application of Hess' Law.


 * __PRE-LAB QUESTIONS__**

-Is the freezing point of ice cream lower or higher than the freezing point of water?

-To freeze ice cream, what temperature must it be?

-What does adding salt to ice do?

-How is the energy transferred and why?

-How many joules per gram should melt?

-The ice mixture will stay at its freezing point until when?

-Is this an endothermic reaction or exothermic reaction?

-Out of (ice, milk, salt, vanilla, sugar) Which of the 5 ingredients do you want IN the ice cream?

-Which of the 5 ingredients should NOT be in?

-Why are there 2 bags?


 * __MATERIALS__**

1/2 cup milk 1/2 teaspoon vanilla 1 tablespoon sugar 4 tablespoons salt 2 quart size Zip-loc bags 1 gallon size Zip-loc freezer bag

What state of matter was the milk when you began?
 * Analysis**:

What state of matter was the milk when you were done?

In order to change the phase of the milk, what had to be removed?

What happened to the heat energy that left the milk?

Why was salt added to the ice?

If you did not add sugar, would the ice cream freeze faster or slower? Why? Explain, using your knowledge of chemistry.

Why did the outside of the bag get wet? (assume that your bag did not spring a leak.)

Describe the transfer of energy that occurred in this lab.

How could you improve your recipe?