Experiments

Experiment 1:

Rate Ice Melts With & Without Salt 

Our first experiment was to put 1 ice cube into a cup with 1 tablespoon of rock salt and another ice cube in a cup without rock salt.

We left the ice cubes in the cups for 1 hour to observe which one would melt the fastest.

Our results:

1. At ½ hour we removed 2.5 tablespoons of water from the salt & ice cup, and1 tablespoon of water from the cup with only ice.

Neither ice cube was completely melted.

2. At one hour: We removed 3.3 tablespoons of water from the salt & ice cup, and 1.75 tablespoons of water from the cup with only ice.

The ice cube in the cup with salt was completely melted.

The ice cube in the cup with no salt was still approximately 1/3 frozen.

    What we learned:

That the salt melts the ice at a much faster rate - approximately twice as fast - than when ice melts at room temperature alone.

Why: 

Salt water freezes at a lower temperature than fresh water.  Because salt freezes at a lower temperature, it will remain liquid when fresh water will stay frozen.

Therefore, the salt on the ice cube makes the ice melt.

The melted liquid is actually colder than 0 degrees, the temperature at which fresh water freezes.

   Experiment 2:

Making Ice Cream Without A Freezer

Our second experiment is using salt and ice to make ice cream without the use of a freezer. 

Using the information we understand from Experiment 1, we add salt and ice to a container. The salt and ice create a very cold solution, cold enough to freeze the ingredients for ice cream, which are in a cylinder inside the salt and ice container.

Our results:

1. Our first attempt at making ice cream was unsuccessful.

We did not have enough ice to fill the chamber completely, and therefore the ice cream stayed liquid.

2. Our second attempt was half successful; the ice cream in the middle was completely runny but the ice cream touching the metal surface of the chamber was perfect ice cream because the ice had been closest to that part. We also learned that if you use chocolate chips they sink to the bottom and freeze in a clump.

3. Our third attempt was successful.  There was enough ice in the chamber to fully freeze the ice cream ingredients.  We scraped the sides so the whole surface of the inner chamber could come into contact with the freezing solution.  There was nothing too hard or heavy in the ice cream ingredients.

The results were delicious!

  What We Learned:

1. From our first attempt we learned that you have to have the exact right amount of ice cubes for the ice and salt solution get cold enough and allow the whole surface of the inner chamber to become frozen.

2. From our second attempt we learned that if you add chocolate chips they sink to the bottom and freeze together.

We also learned that you have to scrape the sides of the ice cream chamber half way through the process. 

Why:

The reason for scraping the sides of the cylinder is to make sure that all of the surface of the chamber is cooled so that the cream and sugar mixture gets frozen.  If the sides are not scraped down then only a thin layer of ice cream forms on the inside of the chamber and the rest of the ingredients do not get cold enough to freeze.   

The low temperature reached by the interaction of ice and salt makes it possible to freeze the ice cream.