THE MAKING OF ICE CREAM – A FREEZING POINT DEPRESSION LAB
PROCEDURE:
1. Place a generous amount of ice in a large Ziploc bag. Record the temperature of the ice: ______
2. Put ½ cup milk, ¼ teaspoon vanilla, and 1 tablespoon sugar into the small Ziploc bag.
3. Place the sealed small bag that contains the milk mixture into the larger bag that contains the ice. BE SURE THAT THE INNER BAG IS SECURELY SEALED!
4. Add cup of salt to the ice in the outer bag. Close securely.
5. Knead the ice bag by shifting it from side to side and squeezing it until the milk mixture becomes hard.
6. After about 8 minutes, observe the appearance. Also take the temperature of the salt-water mixture: ______
7. Enjoy your dessert.
8. Read the following:
The dissolved sugar, by getting in the way of the molecules that bond together to form ice crystals, lowers the freezing point of the cream from about 0˚C to –3˚C. This is why the cream solution will not freeze at a temperature of 0˚C which is the temperature that water freezes. When the temperature of the cream gets to around –3˚C, then the water molecules have slowed down enough that their mutual attraction becomes stronger than the disruptive influence of the sugar. How was it possible for the temperature of the cream to get as low as–3˚C? As they crystallize, the water molecules are removed from the solution which means the remaining solution gets more concentrated with sugar so its freezing point is even lowered further. It is clear from this trend that the liquid phase of ice cream will never freeze completely though the lower the temperature, the less liquid remains…thus the harder the ice cream. Ice cream at -6˚C (22˚F) is the typical temperature of soft ice cream (because it contains more water). At the temperature of soft ice cram there is 50% liquid. At -18˚C (0˚F) there is only 20% liquid.
When freezing ice cream, salt must be added to the water in the bag in order for the ice cream to freeze. Salt reduces the freezing point of water. Thus when salt is added to ice the ice melts.
H2O(s) + heat → H2O(l). When this heat is absorbed by the melting ice, the resulting water gets colder because heat is removed from it.
The churning prevents the growth of large crystals in the ice cream and puts in some air. In 1946, the average person ate 20 quarts per year. This year was the highest consumption year recorded. Since that time, ice milk, sherbet, and water ices have taken a bite out of the market. (Just a little trivia that I thought you might be interested in).
Chemical Freezing Point DepressionsName______
And Boiling Point Elevations
Date______
- Find the freezing point depression and the boiling point elevation of each of the following NON-ELECTROLYTES in solution:
- 10.0 g urea (CH4N2O) in 125 g water
- 27.6 g glucose (C6H12O6) in 200. g water
- What are the newfreezing points and boiling points of the solutions in a - b question #1?
- Find the freezing point depression and the boiling point elevation of each of the following ELECTROLYTES in solution.
- 18.0 g Mg Cl2 in 250. g water
- 80.0 NH4 Br in 100. g water
- 56.8 g Ba(NO3)2 in 1200. g water
4. What are the new freezing points and boiling points of the solutions in a – c in question #3?