How Sweet It Is
Chemistry you can eat!
Clarendon High School chemistry students recently learned about colligative properties of solutions, and got to enjoy a special treat in the process. Solutions freeze at lower temperatures than pure solvents and boil at higher temperatures than pure solvents. That’s why antifreeze used for your car’s radiator in the winter is the same compound found in radiator coolant used in summer. The compound lowers the freezing point and raises the boiling point of water at the same time. “Sidewalk salt” is placed on frozen roads or sidewalks to melt the ice, and it does so because it lowers the freezing point of the ice. Those are two great uses of the concept, but the most pleasant use of this phenomenon is in making homemade ice cream.
Ice cream freezers have been around since 1843, long before people had an actual freezer in their home that cools air with refrigerant, fan motor, and compressor. In homemade ice cream freezers rock salt is placed on some ice surrounding a can containing milk, cream, and sugar that spins to speed up cooling rate, and since the rock salt lowers the freezing point the ice and salt around the can will drop to 14 °C below zero. This temperature is cold enough to freeze the mixture and make ice cream.
In chemistry lab students made a solution and froze it using a “homemade ice cream technique”. They found the freezing point of the solution then used a formula to find the identity of an unknown chemical while their teacher made them some homemade ice cream. They learned some valuable lessons and enjoyed a great treat at the same time. How sweet it is.