Question about Mpemba Effect Experiment

[deleted-513326]

Hello. my name is Hannah.
I am in 8th grade and have to do a science fair experiment for school this year.
I have decided to test the mpemba effect with different liquids to see if certain liquids (water, milk, juice) freeze faster when they are hot then when they are cold.
My question is how to keep the variables to a minimum, especially with a freezer.
How can I properly test the temperatures of the liquids when I have to open the freezer every few minutes?
How many minutes should I be waiting in between checking the temperatures?
What kind of thermometer should I be using?
Can I leave the thermometer in the liquid for the whole time so that when I do open the freezer I can quickly read it and then close the door, or would that change the results of the experiment?
I probably have more questions that I cannot think of at the moment haha.
Thank you so much,
Hannah

[norman40]

Hi Hannah,

I’m assuming that you’re working on the project described here:

https://www.sciencebuddies.org/science- ... p032.shtml

As you've pointed out it might be a bit tricky to get good data when you open the freezer door every few minutes to check the temperatures of your samples. You might try placing the beakers toward the back of the freezer. That way the effects of outside air entering when the freezer door is opened would minimized. Also, you might try leaving the thermometers in the liquids while in the freezer. Doing so would allow you to quickly read the temperatures as you've noted in your post. And, you'll want to minimize how often you open the freezer door during your tests.

How often you check the temperatures depends on how fast the temperatures are changing, and how big the differences in freezing times are for your samples. For example, if the freezing times for hot and cold water are 5 minutes apart and you check temperatures every 10 minutes you would not be able to observe the freezing time difference. My suggestion is to try a preliminary experiment to figure out how often you should check the temperatures. Try putting room temperature water in the same beaker you'll use in your testing. Put the beaker in the freezer and check the temperature every two minutes. When you're doing this, try to work out your best practices for placing the beaker and making your temperature readings. Continue making readings until the water reaches 0 deg. C. How long did it take for the water to get to freezing temperature? You want to check your temperatures more often than this amount of time. For example if your total time was 20 minutes, you might try temperature checks every 4 minutes during your tests.

Here's a thermometer that is similar to the one supplied in the kit for this project:

https://www.carolina.com/lab-thermomete ... ?question=

Any similar thermometer that covers the temperature range you will test should work fine.

I hope this helps and good luck with your project. Please post again if you have more questions.

A. Norman

[deleted-513326]

Hello again.
Thank you for the helpful information!
I was doing background research and came across a fundamental issue in my experiment.
If I am going to be testing water, milk, juice, and soda and comparing them, I need to have them at their accurate freezing points. Going into this, I thought that milk, juice, and soda would have the same freezing point as water, but when I did additional research I found that all three have slightly lower freezing points than water. However, their freezing points can vary because of the different types of consistency in milk and juice especially. I feel like the best approach to this problem is to do a preliminary experiment to see exactly what the freezing points of these liquids are, but I don't know how to test that. Any advice is much appreciated.
Thanks, Hannah

[norman40]

Hi Hannah,

The freezing point of a solution is usually lower than that of pure water. So you would expect that milk, juice or soda would have a lower freezing point than water. A preliminary test to find the freezing points of the liquids you want to use is a great idea.

Keep in mind that the freezing point and melting point are the same. And the temperature of a melting (or freezing) liquid is at the melting/freezing point until all the material is melted/frozen. It's a bit easier to test the melting point. To do this you freeze a sample of liquid, then allow the frozen material to partially melt. Next stir the slush while measuring the temperature. Record the temperature when you see the last of the frozen material melt. Here's a link with more details on the melting point procedure:

https://sciencing.com/measure-freezing- ... 36072.html

I hope this helps and good luck with your project. Please post again if you have more questions.

A. Norman

[deleted-513326]

Thanks for the help. I will definitely post in the future if I need more advice.
Hannah

[deleted-513326]

Hello.
I have a question about thermometers.
Are there any thermometers that you can set to beep when they hit a certain temperature?
I was thinking about how just checking after so many minutes might be a bad idea because there could be a very small temperature difference between the samples that I could miss by only checking every few minutes.
However, I cannot just leave the freezer door open, because that is a huge variable (obviously).
Thermometers with remote probes are extremely expensive, and aren't a good option.
So my next idea is to find a thermometer that you can program to beep when it hits a certain temperature.
I wouldn't have to open the freezer door at all, completely eliminating that variable, and could get an exact time for when the liquid hits freezing point.
Plus I think it might be less expensive than one with remote probes, and could actually be useful for other things.
If anyone happens to know of any that do this and where to get them, that would be great.
I tried searching for this on google, but I didn't find anything.
thanks.
Hannah

[deleted-513326]

http://www.thermoworks.com/ChefAlarm
would something like this work?

[norman40]

Hello Hannah,

It is possible to make the experiment work by repeatedly opening the freezer to check a standard thermometer. In fact, this is one of the techniques used to produce the results described in the project background section.

That said, it's probably easier to have a temperature sensor in the freezer and a display outside so that you can monitor the temperature without opening the freezer. The “Chef Alarm” thermometer you found looks like it could work. It appears that you could put the probe in the freezer and run the cable out between the freezer door seals. That way, you could read the temperature from outside the freezer at any time.

I hope this helps. Please post again if you have more questions.

A. Norman

[LeungWilley]

Hi Hannah,
In addition to A. Norman's comment, I would also like to add that according to the specs of the chef alarm, it only have an operating range of 0 to 50C (32 to 122F). Unfortunately, i don't think that will work all that well in you experiment.

Here's a couple of alternative that may work for you:
http://www.labdepotinc.com/p-60591-min- ... .php?c=830
http://www.daigger.com/digital-lab-ther ... -i-ctl4142

Good Luck and please let us know if there's anything else we can do to help.
Willey