Ice Cream Lab Write-up 6h3u51

Name_______________________________________________Period_________Date_____________________________ Making Ice Cream History of Ice Cream Once upon a time, 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 disfavor 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. This story is just one of many of the fascinating tales which surround the evolution of our country's most popular dessert, ice cream. It is likely that ice cream was not invented, but rather came to be over years of similar efforts. Indeed, the Roman Emperor Nero Claudius Caesar is said to have sent slaves to the mountains to bring snow and ice to cool and freeze the fruit drinks he was so fond of. Centuries later, the Italian Marco Polo returned from his famous journey to the Far East with a recipe for making water ices resembling modern day sherbets. In 1774, a caterer named Phillip Lenzi announced in a New York newspaper that he had just arrived from London and would be offering for sale various confections, including ice cream. Dolly Madison, wife of U.S. President James Madison, served ice cream at her husband's Inaugural Ball in 1813. Mr. Jacob Fussell, now known as the father of the American ice cream industry, began commercial production in North America in Baltimore, Maryland, 1851. http://www.foodsci.uoguelph.ca/dairyedu/ichist.html The traditional method of ice cream making, using ice and rock salt to freeze a milk and sugar mixture, involves the application of several chemistry principles: Colligative Properties: Physical properties determined by the concentration of dissolved particles in a mixture, and not affected by the type of dissolved particles. Osmotic pressure (tendency of water to flow from high water concentration to low water concentration as seen when applying salt to a slug), boiling point elevation and, most importantly in this activity, freezing point depression are examples of colligative properties. When 1 mole of NaCl dissolves in a liter of water it dissociates into 1 mole of sodium ions and 1 mole of chloride ions, or a total of 2 moles of particles per liter of mixture (a 2M concentration). When 1 mole of sugar dissolves in a liter of water there are just 1 mole of sugar molecules per liter (a 1M concentration). The greater the particle concentration, the stronger the colligative effect. 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 rock salt to ice produces a melting ice and saltwater mixture with a depressed freezing point in which the ice cream can be frozen. Heat of Fusion: Melting a solid to form a liquid is an endothermic process. The heat of fusion of a substance is the amount of energy needed to change 1 gram of solid to liquid. The heat of fusion of water is 334 joules/gram. 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! Materials 1 quart Zip Lock Bag 1 gallon Zip Lock Bag ~2 tablespoons of sugar

~1/2 cup of milk Vanilla or other flavoring Ice

~ 2 tablespoons of salt

Procedure for Milk Mix Dissolve 2 tablespoons of sugar in 1/2 cup of milk, and then add a few drops of vanilla for flavor. Note just in case you want to do this at home: Milk mixture can be made in larger batches in a blender, but freezing is best done in small batches of 3/4 cup or so. Experiment by using a blender to mix in strawberries, cookie pieces, etc.

Procedure to freeze the ice cream Pour milk mixture in a zip-close sandwich bag and close securely. Half fill a 1-gallon zip-close freezer bag with ice cubes, and then add about 2 tablespoons of rock salt. Place the sandwich bag into the freezer bag and securely close the freezer bag. Gently massage the bags together to keep the inner bag mixing without heating it with your hands, so use a towel to insulate. Take care not to cause the inter bag to open. After 25 minutes or so, the ice cream should be ready to scoop into a cup and enjoy. Larger batches will take significantly longer. Lab Questions What is a colligative property?

What phase changes in the ice did you observe after the salt was added?

List two ways adding rock salt helped to freeze the ice cream.

Why should larger crystals of NaCl be used instead of smaller ones?

If you did not add sugar would the ice cream have frozen faster? Why?

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

Why must you continuously mix the ice cream as it freezes?

Why did the outside of the 1-gallon bag get wet?

Tell if the kinetic energy of the water in the gallon-sized bag increases, decreases, or remains the same in each of these situations during the lab. a. When the temperature is changing after the salt is added to the ice. b. When the temperature remains constant during the experiment. c. When the temperature begins to rise near the end of the experiment.

Salt is often place on icy roads and sidewalks in parts of the country. Based on what you observed in this lab, explain why this is done.

List any problems you encountered as you made the ice cream.

What would you change if you were to repeat this activity?