This experiment is to test the theory that the temperature of water affects the duration of time it takes to water to reach freezing? Hot water freezing faster than cold has been observed for many centuries. The earliest known reference to this effect is by Aristotle, who wrote: “The fact that water has previously been warmed contributes to its freezing quickly; for so it cools sooner. Hence many people, when they want to cool hot water quickly, begin by putting it in the sun. . .” (Jeng)
1. According to a study of the Mpemba effect by Monwhea Jeng Many factors impact water as it cools and eventually freezes, evaporation can contribute to a loss of mass, Hot water can hold less dissolved gas than cold water and large amounts of dissolved gas escape upon boiling, convection currents and non-uniform temperature distribution happen as water cools, the environmental of the hot sample also impacts the environment around it. Super cooling may also have an important role in the effect, super cooling occours when water freezes not at 0c but at some lower temperature. (Jeng, The Mpemba effect: When can hot water freeze faster than cold? , 2006)
2. In 1963 a student named Erasto B Mpemba noticed that placing recently a recently boiled mixture of milk and sugar into the refrigerator it froze into ice-cream faster than another students mixture that was not heated. He asked his physics instructor why this had happened and his physics instructor informed him “you are confused, that cannot happen” this response highlights the need for objectivity in scientific studies. After repeatedly asking various instructors to explain his observations Mpemba took two 50ml beakers and filled one with water from the tap and one from hot water from a boiler and put them into a freezer, after an hour he discovered that their was in fact more ice formation in the sample from the boiler. Dr Osborne visited the school where Mpemba studied and Mpemeba asked him to explain the effect, he could not but unlike previous instructors and peers Dr. Osborne conducted experiments and did infact repeat Mpemba’s discovery (Osborne)
The Dependent variable is the starting temperature of the water being placed into the freezer. The Independent variable time elapsed until each sample freezes The Controlled variables are temperature of the freezer, the volume of the water samples and the sample containers.
My hypothesis is that the hot water will freeze in a shorter elapsed time than the cold water due to a combination of loss of volume during the heating/cooling process; I arrived at this hypothesis through researching the Mpemba effect and reviewing the results of other experiments. Experimental design
After reading multiple possible ways to conduct experiments on the Mpemba effect I chose this design plan because the experiment could be conducted with supplies I had on hand and should be easily reproducible. I will measure the temperature with a common digital kitchen thermometer every fifteen minutes until the water sample has frozen solid enough that the thermometer cannot penetrate the ice to take measurements. The tools I will be using are 1 Plastic measuring cup,1 Thermometer, Two .30 l plastic storage containers,1 Kitchen timer, 1 Clock, 1 Range cook top, 1 Sauce pan.
Threat Reduction to Internal Validity
To reduce the threats to internal validity I will use the same procedure’s to objectively measure the variables of temperature and volume in my experiment. Each temperature reading will be taken using the same thermometer; each volume measurement will be taken using the same measuring cup. Identical storage containers will be used to store the water samples and they will be placed at the same time into the same freezer on the same bare shelf. Experimental procedure.
Step 1 Draw two samples of tap water 250ml each and record initial temperature Step 2 pour one sample into sauce pan heat to boiling; pour other sample into .30 l plastic storage container Step 3 pour boiling sample into measuring cup and note any loss of volume
Step 4 return samples to .30l plastic storage container
Step 5 measure temperatures of boiled sample and room temperature sample
Step 6 place both .30l plastic storage container into freezer
Step 7 measure temperature of both samples every 15 min logging results until both samples are held at or below zero degrees Celsius long enough that the thermometers temperature probe cannot pierce the surface of the sample. .
Step 8 Allow both samples to thaw at room temperature and measure for any loss of volume
In my investigation the boiled sample of water did in fact freeze faster than the colder tap water sample the greatest temperature differential during my experiment arrived in the first 15 minutes of the boiled sample being introduced to the freezer, the boiled sample entered the freezer at 99.6C and 15 minutes later the temperature was 18.1c this represents a reduction of 81.5 degrees. No notable change of temperature to the environment was recorded. The cold sample also experienced the greatest reduction in temperature in the first 15 minutes of my experiment with a starting temperature of 14.3c and 15 minutes later the temperature was 2 degrees Celsius
The hot sample continued to lose heat faster than the cold sample until 120 min into my experiment where both samples reached -0.6c and were too solidly frozen to continue measurements.
After both samples were too solid to continue measurements I removed both samples from the freezer and allowed them to thaw once both samples were thawed I measured the remaining water volume the hot sample lost 30% of its volume whereas the cold sample had only lost 10%
This experiment has proven my hypothesis the hot water sample did in fact freeze in a shorter elapsed time than the cold water. The hot sample also lost 30% of its volume. The experimental design was a key factor in proving my hypothesis as it controlled many of the variables that could impact the outcome of my investigation. To replicate my experiment you will need a thermometer 500ml of water, two identical storage containers and a freezer with a constant temperature of 18 degrees Celsius . I replicated my experiment using the same experimental procedure and achieved the same results with a slight variation in the loss of volume in the hot sample, in my second attempt the hot sample lost 35% of its volume. Because I achieved similar results using the same experimental design I believe my observations are valid.
Jeng, M. (n.d.). Retrieved from http://math.ucr.edu/home/baez/physics/General/hot_water.html#History Jeng, M. (2006). The Mpemba effect: When can hot water freeze faster than cold? . American Journal of Physics, 514. Kurtus, R. (n.d.). Retrieved from http://www.school-for-champions.com/science/mpemba.htm Osborne, E. M. (n.d.). Retrieved from