FAQ for Investigating the 'Mpemba Effect'

Questions about "Investigating the 'Mpemba Effect': Can Hot Water Freeze Faster than Cold Water?" project and kit. (http://www.sciencebuddies.org/science-f ... l?from=AAE)

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FAQ for Investigating the 'Mpemba Effect'

Postby amyc » Wed Dec 28, 2011 12:02 pm

The following FAQ contains frequently asked questions and answers about the Investigating the 'Mpemba Effect' project. If you are having trouble with the procedure, you may find assistance in the answers below.

Q: What if my metal plate is getting red on the stove?
A: That means that the plate is reaching around 1000°F, which is extremely hot! If you see the metal plate getting red, turn down the stove to a lower temperature. You won't need that much heat to warm up the water, and even though it will take a little longer to raise the water temperature while maintaining a low stove temperature, a lower stove temperature is a lot safer.

Q: Do you need to cover the beaker?
A: You can use a plastic wrap to cover your beaker during the heating, although the heat can make it become very soft, and it could potentially fall off or into the beaker. One thing to note is that if you are covering the beaker with plastic wrap, you will prevent evaporation, so the water vapor will collect underneath the wrap. That being said, the project idea doesn't explicitly call for covering the beaker, and it would probably be easier to work with open containers (make sure your hypothesis is appropriate). If you are using a sealed container (e.g. covered with plastic wrap), you'll have to make sure that all of your samples have the same pressure, volume, and temperature of the gas to begin with, which can be difficult.

Q: Can I use a meat thermometer instead?
A: Yes, you'll just need to make sure that every time you measure the water temperature, you immerse the meat thermometer in the same amount of water. Many meat thermometers are very sensitive to how far into the meat they are inserted, and typically you should insert it about half way.

Q: Should I weigh the beaker and water before or after heating?
A: The Project Idea says to quickly weigh the beaker and the water after heating, but if you are weighing the beaker and water before heating, you might want to conduct a separate side experiment to check if the mass difference between weighing the samples before or after heating is statistically significant. If there is a statistically significant difference, it could be due to loss of water mass or other reasons. Feel free to think of other possible reasons for different masses!

Q: How am I supposed to keep the freezer shut as much as possible if I have to open it every 5 minutes to check on the temperature?
A: Try to keep the freezer shut as much as possible. You can try things like not opening the door all the way whenever you measure the water temperature, and measuring as fast as possible without losing accuracy. Another idea is to use an electronic thermometer with a remote temperature probe so you don't have to open the freezer at all! However, it should be perfectly fine to use normal thermometers as long as you try your best to be as quick and efficient as possible.

Q: Are there any safety precautions we should follow when using dry ice, carbon dioxide, and acetone?
A: When using such materials, the best bet is to check out the Material Safety Data Sheets (MSDS) for the specific materials you are using. Such MSDS info can be found online, typically on supplier websites. For instance, dry ice can cause frostbite if it comes into contact with bare skin, and it should also not be contained in a sealed container, as the container could explode as it sublimes and produces gas. Carbon dioxide should be used and stored in an area with proper ventilation. Acetone is flammable, so it should be kept away from flames. It can also be mildly toxic, so it should not come into contact with your skin. If you're unsure, consult the MSDS information and always be sure to have an adult supervise you while you're doing your project!

Q: Should I measure the time that it takes for the water to reach 0°C or for all of it to freeze?
A: The Project Idea says to measure the time at which the water reaches 0°C. As it is difficult to pinpoint at what time freezing occurs (you'd have to look for tiny crystals of ice forming in random places in the water!), the most simple and accurate way is to measure at what time the water hits 0°C. In order to be very accurate, make sure that your thermometer/measuring device is kept in the SAME place in the water at all times!

Q: Why am I not seeing the Mpemba Effect?
A: There are many reasons why you might not be seeing the Mpemba Effect, and to be perfectly honest, no one really knows the true reason behind the Mpemba Effect. The fact of the matter is that sometimes it works, and sometimes it doesn't. The phenomenon certainly exists for certain conditions, but no one really knows why it doesn't exist for other conditions. The best advice we have is to try to carefully control your experiments as much as possible. If it doesn't work on the first try, vary your conditions slightly and see if another set of conditions will allow you to see the Mpemba Effect. For instance, you should carefully control your freezer conditions, as different freezer conditions can alter the different types of heat transfer (conduction, convection, evaporation, and radiation) and consequently produce changes in the freezing rate of the water.

Q: What if my results do not match my hypothesis? What if I really can't see the Mpemba Effect?
A: If your results don't match your hypothesis, that's perfectly okay! The beauty of science can sometimes be found in its unpredictability, and you certainly shouldn't change your hypothesis to change your results should you find a discrepancy. Changing your hypothesis to match your results is actually an example of scientific dishonesty. If you really can't see the Mpemba Effect, don't fret, as we mentioned before, it's anyone's guess as to why certain conditions allow for the effect to be observed, while other conditions don't show the effect. Remember, science is about repeating trials and reproducing results, so we encourage you to keep trying and have fun with the project!


If you have other questions about the procedure or need assistance troubleshooting your project or the Experimental Procedure, please post your question in the forum for this kit at Ask an Expert: http://www.sciencebuddies.org/science-fair-projects/phpBB3/viewforum.php?f=62. Our team of volunteer Experts is available to assist. We attempt to reply to questions within 24 hours. Please note that you will need a free Ask an Expert account in order to post questions.
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