It is a wonderful real-world application to the concepts we've been studying - reactions, and the amounts of chemicals involved. If the proportions are incorrect, things go BOOM!! (or you get lousy ice cream).
It's incredibly easy to do, and fits nicely into one class period:
Into a quart-sized resealable bag combine:
* 1 cup milk
* 2 tablespoons sugar
* 1/8 teaspoon vanilla
Half fill a gallon-sized resealable bag with ice and toss in a generous handful of rock salt.
Seal the smaller bag & place it into the larger bag. Seal the larger bag, and then shake the entire thing for about 15-20 minutes. The more you agitate the bag, the quicker the concoction will solidify. It is ready when it's about the consistency of soft-serve ice cream. Pour into bowls & enjoy!
Tips:
- You really do want a quart-sized bag instead of a regular sandwich bag. Sandwich bags are thinner and are more likely to develop holes from all the shaking. Nobody wants salt-flavored ice cream!!
- If you are feeling particularly nice, have towels (or old spit-up washcloths & cloth diapers) on hand for the students to use as insulation for their poor, dainty hands. (did you catch the sarcasm there? *groan*) In all seriousness, though, it is very cold, and if you are not as prone to wearing thick sweatshirts like my students are, you will need something for your hands.
- If too much rock salt is added, the ice will melt before the ice cream is ready. Just add more ice & salt.
- Collect all the ice in one sink - rock salt is a pain to clean up.
- Don't want plain vanilla?? Add whatever flavor you want to the sandwich bag. This last time, my TA (who's also one of my AP students) & I decided to make chocolate ice cream. Dumped a bunch of Hershey's syrup into the milk mixture & smooshed it around before putting the bag into the ice bag. Very tasty!!
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