In order for a liquid substance to alter its form from liquid to solid, the substance must hit the freezing threshold of 32 degrees F. Conversely, to reverse this alteration in the matter’s state the temperature must rise above this same freezing point. The factor shared by–and most pertinent to–this alteration is the release of energy that drives this process. To demonstrate the inherent importance of energy, we will evaluate the cooling and warming behavior of water. To do this, in this experiment we will measure the temperature during the freezing and melting of water and subsequently graph the data provided. This will determine its energy-releasing capabilities and its importance in the debate for sustainability.
Hypothesis and Theory
We assert that once the temperature reaches the freezing point (32o F) in less than five minutes, the water will solidify continually as it drops below this point. Inversely, once the water is heated, this increase above the freezing point will then convert the water back from a solid state to a liquid state within a minute due to the glass’s excellent heat transfer potential. If you’d like a little more background on the principles surrounding the melting and freezing of water, check out Purdue University’s explanation.
Setup
You already have our material requirements listed in our experiment handout, so if you need a reminder feel free to check it out again or take a look at this video. The well-regarded Vernier Software and Technology company has provided their own walkthrough of our experiment, utilizing the same apparatus as ours:
Now to our own setup and walkthrough:
Freezing Phase
- Fill a 400 mL beaker 1/3 full with ice, then add 100 mL of water as a water bath.
- Put 50mL of water into a graduated cylinder and place it in the water bath.
- Connect the probe to the computer interface. Prepare the computer for data collection by opening the Temperature measurement program.
- When the computer is ready for measurement, click to begin data collection and then lower the graduated cylinder with probe into the ice-water bath.
- Soon after lowering the test tube, add some salt to the beaker and stir with a stirring rod. Continue to stir the ice-water bath for ten minutes.When ten minutes have gone by, stop moving the probe and allow it to freeze into the ice. Add more ice cubes to the beaker as the original ice cubes get smaller. Run the measurement for twenty minutes.
Melting Phase
- Dispose the cold water and the ice and fill a beaker with hot water.
- Place the graduated cylinder just slightly above the the hot water and begin measurement for ten minutes, after ten minutes, let the graduated cylinder be submerged but make sure that the hot water does not enter the graduated cylinder.
Results and Data Analysis
Graph 1: Freezing of Water
Graph 2: Melting of Water
As evident in our data, the behavior of the freezing and melting of water is determined once the water has reached 32 degrees F. From this point of determination, the temperature of the water drops or rises at a constant rate dependent on the change in temperature. As the temperature decreased, the water inside the graduated cylinder froze. Although it was not perfectly solid and required 481 seconds to freeze the water inside the cylinder (far longer than what we predicted in our hypothesis), it still validates our hypothesis that the water would freeze with a decrease in temperature. As a reverse validation of this hypothesis, through the heating phase of the experiment the ice melted in less than a minute- returning again to liquid form.
It is important to note that equipment limitations may have affected the general integrity of the experiment and must be considered when interpreting results. First, we used a graduated cylinder instead of a test tube because it was unavailable to us in the lab. The use of a graduated cylinder may have caused saltwater to enter the cylinder and therefore leaves the possibility for slight contamination of the water. We also had a spike in temperature due to transferring the apparatus from Raymond’s hands into Andrew’s. We did not measure the salt ultimately placed into the water which may have caused uneven dissolution. Lastly, the temperature was not properly recorded due to unavailability of a thermometer; the temperature probe was not properly calibrated before use. Because we did not have suitable clamps, Andrew had to hold the graduated cylinder in the apparatus as we conducted the melting phase of the experiment. Therefore, human errors may have played a factor in results of the melting phase of the experiment.
Further Conclusions, Final Remarks
The team aspect of this experiment certainly wasn’t forgotten. Each member-Sebastien, Isaac, Raymond, David, and AJ-contributed to their fullest capacity. I enjoyed serving as team leader because of the great work we were able to do as a result of everyone’s motivation and commitment to the project. Team chemistry can’t be overrated, especially with so many people involved in our experiment, so well rounded contributions certainly made this project what it is.
Now, if only our presentation of the experiment were as successful as our group’s test run! It was very difficult to allow the test tube to sit isolated within the beaker because we did not want anyone holding it manually. Removing our hands from the experiment would eliminate room for human error and artificially manipulating the change in temperature. We used our hands to complete the experiment initially, but it was found to skew the data so we forwent it on Wednesday April 29 for its final showing. If only we could run the experiment one more time–they same third time’s the charm, after all.
Its a good thing professor Shatz saw our experiment through previously or it would have looked quite disorienting! It reminded me of John Poindexter’s quote, “you accept failure as possible outcome of some of the experiments. If you don’t get failures, you’re not pushing hard enough on the objectives.” Although not directly relative to our experiment since it was not a failure but more of a discombobulated demonstration, it is a good reminder of the need to actualize the potential of each experiment, whether for a final project or not.
The other group’s project we viewed was quite insightful. They determined increases in energy from varying wattage in light bulbs to determine what type of wattage/bulb produces the most heat. Strangely enough, their experiment had its own major drawback: the bulb itself burned out. We first used a 43 watt bulb with no problem, but the 150 watt bulb proved too strong and make a loud snap noise as it imploded, much to our surprise of course. Because of this we were then resigned to a smaller sample size with this experiment as well, but it certainly was interesting to have a detour here too. A third group also lost its play-dough to mold just to top it all of in a funny turn of events.
All in all, though, we feel confident in our assertion that the freezing and melting of water holds great potential for sustainability. Its energy releasing characteristics can be streamlined as shown in our experiment for practical uses across all facets of contemporary society.
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch14/melting.php
http://www.vernier.com/