Freezing Salt Water Experiment


by Edward1
Tags: experiment, freezing, salt, water
Edward1
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#1
Jan15-13, 09:21 AM
P: 1
I'm in a bit of a time crunch for science fair, and there are still a few questions about my experiment that are unanswered. What I'm dong is trying to accelerate the freezing of salt water by adding electrodes to the bottom of my container (attached to a battery). If the ions of the salt are attracted to the positive and negative electrodes, that should increase the salinity of the water near the bottom of the container, and decrease the salinity of the water near the top. I'll put my samples in the freezer, and periodically check on them to measure the thickness of ice formed.

Since I don't want electrolysis to occur, will insulating the electrodes work? As well, if I'm insulating the electrodes, will there be electrical charge to attract the ions?

Someone suggest to me instead of connecting electrodes the the battery, just build a small capacitator in the water. I think that this would be less bulky than wires from a battery. Any details on how this might work?

Also does anyone have a general time scale for how long it takes ice to freeze from water and salt water?

Thanks
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Borek
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Jan15-13, 09:32 AM
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Have you checked the numbers? How much ions will concentrate around electrodes and how large the concentration change will be?

Even if you were using kilovolts, concentration changes would be almost undetectable, especially as they will be present only on the electrode surface (google for double layer), not in the bulk of the solution.
pm5
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#3
Jan15-13, 03:29 PM
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This science experiment will not work. The concentration of salt particles to water in seawater (pretty salty) is 35000/million, or 35g/L (http://en.wikipedia.org/wiki/Saline_water). If you were try to saturate your water with salt, to maximize the salinity (and thus, the ions), you would max out at around 26% salinity. Additionally, by adding salt to water, you are actually lowering the freezing point (i.e., making it harder for the solution to freeze (The freezing point is −21.12 C for 23.31 wt% of salt from http://en.wikipedia.org/wiki/Sodium_chloride)). Essentially, a normal amount of salt and you will have a very negligible % of ionized solution even POSSIBLE to be drawn towards the electrodes, and too much salt and you've brought the freezing point down to −21.12 C, probably much colder than your freezer goes.

Also, the time water takes to freeze is variable based on the surface area of the structure holding the water, ambient temperature of the water, and temperature/structure of the freezer (is it windy in your freezer? if so, things will freeze faster. no wind? slower).

This is a bad science project idea, you should try something else.


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