INT1 Task 3
Does Hot Water Freeze Faster Than Water at Room Temperature
By Anon

Project Design Plan
Water has a fixed freezing point. While at the same altitude water will freeze at the same degrees Fahrenheit. According to the Mpemba effect, “As the liquid warms up, the hydrogen bonds stretch as the water gets less dense and the molecules move further apart.“ Condliffe, J. (2013, October 31). “Theories for the Mpemba effect have included: faster evaporation of hot water, therefore reducing the volume left to freeze; formation of a frost layer on cold water, insulating it; and different concentrations of solutes such as carbon dioxide, which is driven off when the water is heated.” Hot water freezes faster than cold - and now we know why. (2013, November 3)

Literature Review
Observing freezing times based on the liquid with various starting temperatures have been made throughout history. Aristotle, Rene Descartes, and recently Xi Xhang and his team from Mayang Technological University in Singapore have all performed experiments testing this theory. The Mphemba effect was named after a Tanzanian student who observed ice cream mixed faster when it was hot than when it was cold.

To test this theory, Nikola Bregovic placed 30 ml of room temperature water with an immersed thermistor into an empty freezer. This experiment used deionized water, the same beakers, and the same thermistor. The experimenter then tested the freezing points of various starting water temperatures. The experimenter concluded the most likely explanation was water evaporation caused the water to be less dense which is less mass to freeze. Bregovic (2013)

James Brownridge conducted a similar experiment. Brownridge froze two water samples at the same temperature and placed them in the freezer. Once frozen, he warmed one sample to room temperature and the other sample was warmed to 80 degrees Celsius and he froze both samples again. He concluded that as long as there was at least a 5 degree Celsius difference in water temperature the hotter sample always froze first when refrozen.

In his experiments, Brownridge took two water samples at the same temperature and placed them in a freezer. He found that one would usually freeze before the other, presumably because of a slightly different mix of impurities. He then removed the samples from the freezer, warmed one to room temperature and the other to 80°C and then froze them again. “The results were that if the difference in freezing point was at least 5°C, the one with the highest freezing point always froze before the other if it was heated to 80°C and then re-frozen. Edwards, L.” (2010, March 26)

Read more at: http://phys.org/news188801988.html#jCp

Experimental Design Steps
Two ice trays will be placed in the freezer, one with water at 80 degrees Fahrenheit and the other at 160 degrees Fahrenheit as follows. 1. The ice tray is completely filled with water filtered from the tap. 2. The water from the ice tray is then poured into a measuring cup. 3. The water level is marked with masking tape and pour back into the ice tray. 4. Water from the filter is poured into the measuring cup to the marked level and placed in the microwave for 2 minutes at the default setting. 5. The now hot water is poured back into the second tray. 6. The thermometers are placed in the cube trays simultaneously to avoid bias 7. Both trays are placed in the freezer at the same time 8. The water temperature and ice formation will be measured at various points in the freezing process.

Reasoning
Water freezes at 32 degrees Fahrenheit. Since hot water, in this case water at 150 degree Fahrenheit, has to cool 118 degrees; however, room temperature water, in this case 80 degrees, only has to cool 48 degrees to reach the freezing point, the room temperature water should freeze first. Measuring the temperature simultaneously using two different thermometers of the same brand and model is better than measuring them concurrently to prevent temperature variations based on the difference in time. Using the same brand and model ice tray’s and water filter will also reduce bias as the water will be pure and the trays will be identical.

Sequence of Events
The water temperature was checked at predetermined timed intervals to determine the freezing times for each tray. Once ice starts to form the ice will be measured for thickness. 1. The trays are checked for temperature and ice formation at 10 minutes 2. The trays are checked for temperature and ice formation at 30 minutes 3. The trays are checked for temperature and ice formation at 60 minutes 4. The trays are checked for temperature and ice formation at 120 minutes 5. The metal thermometer will be used to break ice in cube trays different cubes from the one used to check water temperature to prevent unintentional bias, and the thickness will be measured with a ruler. 6. The thickness of the ice is checked in millimeters 7. The temperature of the water is checked in degrees Fahrenheit

Tools and Technologies
Measuring cup (Playtex brand)
Water filter (Zero Water Brand)
1100 Watt microwave
2 ice trays
2 Food thermometers iPhone timer app (countdown)
Freezer
Variables
Independent variable: The water temperature as ice trays are placed in the freezer
Dependent variable: The temperature of water after 10 minutes, 20 minutes, 30 minutes in the freezer. The quantity of water frozen after 120 minutes in the freezer.
Controlled Variable: The amount of water added to the ice tray. The time, deration, and thermometer used to check temperature. The ruler used to check amount of ice formed.
Threat reduction to internal validity
To ensure the difference in water quality between the two sources is negligible, tap water will be filtered from the same source using a new filter. To reduce the risk of false result, the tray with hot water and the tray with cold water are both placed into the same freezer at the same time. Placing the ice trays side-by-side and testing the temperature in the cubes closest to each other will minimize any difference in airflow. Using two thermometers to check the temperatures simultaneously will reduce temperature variance during the checking process. Testing the same cube slots in the ice trays each time reduces the risk of different areas of the freezer being colder than the other. By repeating the experiment three times will verify the results as repeatable.

Hypothesis
The experiment’s hypothesis states that water at 150 degrees Fahrenheit will not freeze faster than water at 80 degrees Fahrenheit. The hypothesis was based reading about the Mpemba effect which seemed counter intuitive.

Data Collection
Contrary to the hypothesis the ice tray that started with the 150 degree Fahrenheit water froze before the tray with 80 degree Fahrenheit water. Following three tests when checked after 10 minutes, the tray with the hot water had closed the temperature gap to with 3 – 5 degrees.

At the 30 minute mark, the hot water tray temperature measured lower than the room temperature tray by two to three degrees

When checked at one hour, two of the three test runs resulted in ice forming two and three millimeters thick on the tray that started with the hot water respectfully. The third test showed ice crystallization but not solid. All three times the room temperature tray had no ice and the temperature of the water was between 34 and 37 degrees Fahrenheit.

When checked after an two hour the hot water tray had ice five to 7 millimeters thick while the room temperature tray’s ice was between one and two millimeters thick.

First run: Temperature check Initial water temp | 10 minute | 30 minute | 60 minute | 120 minute | 80 degrees F | 78 degrees | 61 degrees | 37 degree | 1 millimeter ice | 150 degrees F | 82 degrees | 59 degrees | 2 millimeter ice | 7 millimeter ice |
Second run: Temperature check Initial water temp | 10 minute | 30 minute | 30 minute | 120 minute | 80 degrees F | 77 degrees | 60 degrees | 35 degree | 1 millimeter ice | 150 degrees F | 81 degrees | 59 degrees | 3 millimeter ice | 5 millimeter ice |

Third run: Temperature check Initial water temp | 10 minute | 30 minute | 60 minute | 120 minute | 80 degrees F | 77 degrees | 60 degrees | 38 degree | 1 millimeter ice | 150 degrees F | 80 degrees | 59 degrees | 2 millimeter ice | 7 millimeter ice |

Appropriate Methods
Since the data shows that the hot water froze faster than the room temperature in all three test shows that the Mpemba effect is valid. The fact that the temperatures varied only a few degrees if at all through the three test runs indicate that the measuring time and process was fair and accurate, though more times might need to be tested to determine when each tray had completely frozen.
Results

The above graph shows that in all three test indicate that the water in the hot water tray had become colder than the room temperature tray water averaging 71.33 degree faster drop than the cold tray. The cold tray dropped an average 2.667 degrees in ten minutes while the hot tray dropped an average of 69 degrees in the same ten minute timeframe. While the rate of temperature drop decreased as the duration increased it still was dropping at a faster rate.

Conclusion
Confirmation of Hypothesis
The original hypothesis was not confirmed, instead the contradicting argument was proved. The water which was heated indeed froze faster than the room temperature water. The hot water temperature dropped rapidly in the first 10 minutes and by the 30 minute mark was in fact lower than the room temperature water shattering the initial hypothesis. The water density seems to be the more likely explanation though various scientists have different opinions.

The experiment’s design was important to limit the controlled variables to ensure test accuracy. By focusing on only one change in the experiment, in this case water temperature any difference in the results can be reasonably attributed to that changed variable.

Replication
In order to replicate this study it is vital to use the same amount of water in two identical ice trays. It is also important to keep all other variables the same including, heating the water to the same temperature for the non-room temperature water tray. The temperature should be measured using two identical thermometers the temperature of each tray simultaneously to avoid inaccurate data fluctuations.

Evaluation of Validity
With others testing this experiment it may be possible to conclude why exactly this happens. Previous tests have indicated that this effect does not always occur but is common. Which calls into question the theory; however, it has been successfully tested enough times to know that it has validity, just without a known cause. Knowing the exact reason water at higher temperatures freeze faster than cooler water can give scientists a better understanding mysterious phenomenon, and possibly give insight into a paradigm shifting discovery.
Reference List
Condliffe, J. (2013, October 31). We've Finally Figured Out Why Hot Water Freezes Faster Than Cold. Retrieved October 6, 2014.
Hot water freezes faster than cold - and now we know why. (2013, November 3). Retrieved October 6, 2014.
Bregović, N. (2013). Mpemba effect from a viewpoint of an experimental physical chemist.
Edwards, L. (2010, March 26). Mpemba effect: Why hot water can freeze faster than cold. Retrieved October 6, 2014.