Snow Day Activity: Freezing Temp

It’s cold enough outside to freeze water, so why not do a freezing experiment! We tested the effects of 3 different solvents reactions to the outdoor freezing temps (it was 25°F outside when we tested) and compared it one plain water sample. The purpose of this experiment is to test the freezing temperature of each solvent.  Food coloring was added for differentiation but had no impact on the freezing effect.

Materials:
4 cups
1/2 tbsp. of sugar, salt, and baking soda
Food coloring (option)
Thermometer

Sample 1: water + salt w/ blue dye
Sample 2: water + sugar w/ green dye
Sample 3: water + baking soda w/ orange dye
Sample 4: water only w/ red dye

Procedures
Mix a half a tablespoon of either salt, sugar and baking soda into 3 separate cups and add one inch of tap water in each. Then add food coloring (for fun) and place cups outside in the freezing cold air. After 30 min to an hour, check on the cups to see which ones have already started to freeze. The red solution and green solution will probably have a thin frozen layer on top. Place a thermometer directly into each cup and recorded each temperature.

Our Results
Sample 1: -1.2°C/ frozen top layer
Sample 2: -.2°C/ frozen and slushy layer
Sample 3: -.9°C/ slushy layer
Sample 4: 0 °C/ completely liquid

What Is Happening?
It is known that water freezes at approximately 0°C/ 32°F. The water froze the quickest, followed by the sugar sample (with respective temperatures at 0°C and -2°C) which both produced a frozen layer, followed by the baking soda sample at -.9°C with a slushy layer and finally the salt sample ( -1.2°C) which remained in its original liquid state. What is most observable is that sugar froze the water quicker than the salt froze the water. This can be simply explained by the principle that the freezing point (the temperature at which solution will freeze) of sugar water is lower than the freezing point of salt water. Sugar (sucrose) interacts with water using similar forces (dipole-dipole) and attracts the water molecules, where as salt forms a dissociating interaction (ion- dipole)- so it has to be a much colder temperature to freeze the salt water . Thus concluding the stronger the intermolecular force, the lower the freezing point and the quicker the water freezes as you’ll discover after doing this experiment!!!!