Help with a Science Fair Project

[Michael]

I would like to do my experiment on "Does increase in salinity affect the force that water exerts on an aluminum can?" Below is the Experminetal Design, Can I have some feedback on it? Does the problem make sense- as well as the procedure?

Also, Does anybody have some "interesting" ideas on how this project applies to real-life? I had come up with a couple ones, Like how when Ice Freezes it causes erosion.

Looking foward to all feedback- Thanks, Michael

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Problem: Does the increase in salinity affect the water’s ability to expand inside an aluminum
can?

Hypothesis: I think that as the salinity increases, the aluminum can will expand less than a can with
a smaller level of salinity.

Materials: To complete my experiment I will use the following materials:

• Veneer Calibers- To measure thickness of each can
• 15g. of Sea Salt- To increase the amount of salinity in the ice/water
• A minimum of 3 Aluminum cans (Same “Brandâ€

[staryl13]

Hi Michael!
This sounds like a really interesting project. Your experimental methods seem to be great so far. You might want to check out this link for some background info:
http://antoine.frostburg.edu/chem/senes ... lume.shtml
As for real-world applications, it might be cool to talk about freezing point depression with the increase in salinity as an extension of your project. You can discuss the differences in density and talk about examples such as the use of salt on icy roads. These are not directly related to your project, but they might be ideas for discussion. Good luck!

[bradleyshanrock-solberg]

Also, Does anybody have some "interesting" ideas on how this project applies to real-life? I had come up with a couple ones, Like how when Ice Freezes it causes erosion.

If you think about what you are doing, without the aluminum can involved, you're measuring the volume of ice created with normal water vs salt water. Ie, is the ice bigger or smaller with more salt in it.

If it is larger, it will exert more force on the can when it freezes. If smaller, less force.

Some real world applications might involve thinking about how a boat being caught in a freshwater lake that freezes over might differ from a boat caught in arctic water that freezes. Or whether salt water that is absorbed into something like concrete or waterlogged wood that then freezes and thaws would be harder on those materials than freshwater. Or how pipes whose water freezes might be more or less affected by salt content.

[bradleyshanrock-solberg]

Note that salt can also affect freezing point of water, which is not what your current experiment is measuring. You'll need to pick a cold enough temperature to freeze all your water samples, not just those with less salt.

[Michael]

Does the increase in salinity affect the water’s ability to expand while freezing inside an aluminum can?
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I'm thinking about doing this in a closed (sealed) aluminum can, vs. an opened aluminum can. By using a nail to create 2 small holes on the top & bottom of the can. Then, by "blowing" through one of the holes to dispose the liquid. After that, I would be sucking in (As if it were a straw) the salt water.

Any other ideas on how I can do it in a closed (Sealed) aluminum can?

[bradleyshanrock-solberg]

I'm not sure I am visualizing what you are trying to do correctly.

Can you break it down, step by step?

(ie, here is how I might go about what you're describing. it might not be better or worse, it's just a way to do it)

1. start with soda can (diet preferred, no worries about sugar content)
2. pop top, empty the can of soda
3. rinse out the can thoroughly
3. fill can with water (fresh water or measured water+salt solution)
4. pull up tab somehow (or maybe do not fill can all the way)
5. label can, so you know what you filled it with later
6. stick can in freezer, wait till it is frozen solid
7. measure deformation of can

)

[bradleyshanrock-solberg]

Hm...I just noticed step 7 of your proposed procedure, a few posts up.

What kind of thermometer are you using? Is it really designed to be placed in a liquid and frozen? (the pressures might crush a typical glass/mercury thermometer, of the sort you would measure fever with, but it could work ok for an electronic thermomiter, where you just stick a metal wire into the water)

[Michael]

I'm doing my science experiment: "Does the increase in salinity affect the water's ability to expand while freezing inside an aluminum can?"

I need your advise as to whether it would be best to use a soda can with an opening or a sealed soda can. Appreciate your expertise and how I should go about doing it.

I thought it would be more challenging to do it in a sealed aluminum can. I would use a nail to make a hole in the can and remove the liquid and then re-fill one can with fresh water and the others with the salt water combination. I would use an aluminum sealer to close the cans. I would measure the volume based on the shape of the can. I could fill a pitcher of water to the very top. Take the can and push it in. Collect the water that comes out. Measure it. The volume that can displaces is the volume of the can. Please comment and make suggestions.

Thank you...Michael

[bradleyshanrock-solberg]

To answer in reverse order....

The volume displacement method is an excellent way of measuring the change in the aluminum can size before and after testing. That is much better than your original idea of measuring the can dimensions with a caliper. You will also want to measure the can this way before freezing the water inside, so you can know what the change was.

I don't think that poking a hole in the can and filling it, then sealing it, is very different from using a pop-top can, filling it, and pulling up the tab somehow and doing your best to seal that.

Either way, the sealant may prove a weak spot and burst, leaving you with the same result as just pulling up the tab as best you can but leaving it open a little bit. Sealing the can has some advantages with respect to not spilling any water and ensuring the same amount of water is freezing in all tests.

My instinct would be to not introduce a weakness into the can along the side or bottom. (if you must punch more holes than the tab, to it on the top). Soda cans are designed to be under pressure and their geometry tends to encourage the "fizz" to escape out the top rather than have the can explode. You'd change that if you poke a hole in the main body.

I'm not actually sure how likely it is that the can will rupture if you freeze the water inside. My recommendation would be to do a couple tests of your process. First fill a can with the tab open, freeze it, see what happens. Then try another one with the tab pulled up and sealed. In both cases you probably need to be careful of the other contents of the freezer in case the can bursts or the contents push out of the top during the process. Put the can in a tupperware or similar plastic bowl, to capture any liquid etc that might escape.

You may find that the easiest approach is to not fill the can all the way, but to mark the level at which you filled it, then do the volume test to that measure on the can. When the water freezes, immerse the can+ice. This requires a bit of correction for the parts of the can not filled when you begin, the volume of the aluminum. You can correct for that by getting a volume measure of the empty can, and subtracting the amount of water added to fill it up to the line.

So that's a lot of ideas tossed out with the main thought being "try it both ways and see for yourself". (This can be a useful experimental approach if it isn't too expensive in the real world. This is however an "engineering" trick rather than "science". Building lab apparatus to do experiments though often tends to need some "cut and try" to make do with the materials you have and still test your hypothesis)

Whatever you decide, the first time you do it, as a safety thing, you need to protect the contents of the freezer from your potentially explosive can. There are a lot of possible failure modes for a sealed aluminum can (it might rupture along the side, the top might be pushed off, it might burst along your sealing or it might just deform like you are expecting. It's also possible the can may prove so sturdy that you can't measure any volume change, but that is probably unlikely). If it gives way while there is liquid in the can, the can might spill all over the freezer, then turn to ice.

The easy way is to stick the can in a bowl big enough to hold the can and its contents, and stick the bowl+can into the freezer.

[Michael]

Thank you so much for all the information you provided. I am so grateful for all your help. I'm getting really excited about the project. I'm taking your suggestions and working on doing some freezing samples using my home freezer just as a pre-trial. I thought about sealing the opening of the can with duct tape and special aluminum glue that I found at a hardware store.

I plan to conduct the actual experiment on Tuesday. I've contacted a local laboratory in my neighborhood that will allow me to use their freezer that goes to a -70 freezing point. I think I will see better results.

I have one more question on the data I should be collecting/recording. I will:

1. Measure Starting Volume
2. After water is frozen in can, Fill a pitcher with water to the very top
2. Place the frozen can and push it in the pitcher of water. Collect the water that comes out. Measure it. The volume that can displaces is the volume of the can.
3. Data Collected would be:
Final Volume minus Starting Volume = Change in Volume
Change in Volume Minus Starting Volume = Fractional Change in Volume (based on substance itself)

Do you think I should include other measurements every half hour as its freezing? Appreciate your thoughts on how I best display my results so that it makes sense.

Thank you again...Michael




I would like to show my data/results in a line graph. Do you suggest I

[ChrisG]

Michael, I'm glad to see that you are excited about this project and that things are moving ahead. To follow up on comments the other experts have made, I have some suggestions about your experimental design for you to think about before you run your experiments.

It seems to me that using an aluminum can adds unneeded complexity to your experiment. It will be difficult to remove 100% of air and bubbles from an aluminum can. If there is air left in the can, the ice will compress this gas, creating the false appearance that the can is containing the ice. If there is no air in the can, it will probably rupture, which will make your experiment messy and error-prone. I agree with previous comments that your cans are likely to leak or explode. Domestic plumbing is much thicker than an aluminum can (and stronger than a can sealed with tape and epoxy), and domestic plumbing will often rupture when filled with ice.

As a starting point, why not leave out the can? To answer the question of how salinity affects the volume of frozen water, I believe you will get better results by putting the water in an open container, or an expandable container like a balloon. I expect you would get the same results with an improved ability to make reliable measurements. Then, if you want to follow up with additional experiments that study the effects of pressure or the integrity of sealed containers, you could use aluminum cans, metal pipes, plastic pipes, etc.

I hope that helps. Good luck on tuesday!

[bradleyshanrock-solberg]

Chris has a very good point. If the focus is the water and not the effect on the container, then what you might want to do something like this:

1. Measure the water carefully and put it in an open container. (you know how much water you measured). Pick something where the ice won't be difficult to remove from the container - a flexible bowl is pretty good, or maybe something like a plastic freezer bag or baloon where you could just peel it off.

2. Freeze the water in the container

3. Drop the frozen ice into your displacement-measure apparatus, making sure it jut barely submerged. It will start to melt, but not before you get your water displacement.

Again, you will want to experiment a bit with the container to see what will release the ice easily without breaking it up or forcing you to hack it out. What I suggested is kind of like a flexible rubber ice-cube tray, where you flex it to remove the ice, but other approaches may work.

[Michael]

Chris and Brad,

Thanks for all your input. I had originally chosen the aluminum can because I thought it would be more of a challenging project. Based on your comments, I think I have to replace the can. At this point, do you suggest I use a balloon or a clear plastic bottle that I can put a top on. I would like to do an impressive project. Please feel free to make other suggestions. I'm going all over the place with this project. I really have to get it together by Tuesday as the local lab is allowing me to use their -70 degree freezer.

Again - I'm sincerely grateful for all your help.
Michael

[bradleyshanrock-solberg]

A plastic bottle might also rupture, but if it does not it might be better than the balloon. With the bottle you'd have to be careful to get all the air out before putting the lid on, or the air will just compress and your bottle size will not change.

If it was me, I'd test it both ways in the home freezer (with precautions taken in case either bursts) before using the -70 degree freezer. You want to be sure of your technique before using the big iron lab machinery.

[Michael]

I was able to do some testing with the cans in my home freezer to get an idea of the outcome. I will try your balloon idea tomorrow. In the meantime, I was successful in sealing the top opening of the an aluminum (seltzer) can and observed that the fresh water did expand outward and cracked the can. The salted water can did not crack yet, but that's because it freezes at a lower temperature. On Tuesday, I will have an opportunity to drop off my samples in a local lab that will allow me to use a -70 degree freezer.

Would you pursue testing the aluminum can in the -70 degree freezer now that we know what is likely to happen? Or do you think I should drop the can idea and simply use the balloons that you suggested.

I would like to make a really good impression with this project. Which way would you go?