Liquid Freezing Time Experiment

Over Fall Break my daughters and I completed several science experiments.  In one experiment we took several liquids and tested to see which froze first.  Our chosen liquids were:

Orange Juice
Skim Milk
Water
Apple Cider

Physics tells us that the rate at which something changes temperature is dependent on the specific heat capacity of a substance.  If we link this directly to the phase change from liquid to solid, we should be able to predict which freezes first.

We put exactly one tablespoon of liquid in a same sized ice cube section.  This allowed us to be consistent with both volume and depth.  The tray was placed in the freezer and we waited, checking every few minutes for changes.  

What should we expect?  Water has a specific heat capacity of 4.18 kJ/kg*C.  This means that it takes 4.18 kJ of energy to raise or lower the temperature of water 1 degree Celsius for each kg of water.  Objects with a greater heat capacity take longer to increase/decrease temperature and objects with a lower heat capacity take less time to increase/decrease temperature.  Therefore, the liquid with the lowest specific heat capacity should freeze first, everything else being equal.  So what are the specific heat capacities of these four liquids?

Water = 4.18 kJ/kg*C

Orange Juice = 3.73 kJ/kg*C

Milk = 3.94 kJ/kg*C

Apple Cider = 3.65 kJ/kg*C

This means the apple cider should freeze first with the water last.  In reality, it was difficult to tell.  We did notice the apple cider turning a bit slushy early on and a crust of orange juice ice forming early, so that is expected given those two have the lowest specific heat capacities.  The water and milk did take a bit longer to show any signs of freezing, as expected.  Using a specific heat capacity to predict is a bit simple, as the latent heat needed for a phase changes is also necessary.  Regardless, we did have some predictions that matched our results.  Another result was the milk cube.  It wasn't white, it was much more clear!