Help with a Science Fair Project

[Michael]

Today I continued my experiment with freezing salt water and fresh water in a balloon. The fresh water balloon expanded almost double in size than the salt-water balloon.

Based on my preliminary results with the aluminum can and the balloon, I thought the aluminum can was more impressive and would like to continue using it. As you know, I will be dropping off my water samples at a local lab on Tuesday. They are allowing me to use their -70 degree freezer. I think I will see better results with their freezer.

Please let me know your thoughts and if you would make any modifications to my plan design below.

Your assistance is eternally appreciated. Thank you!! Michael

Science Fair 2007/2008
EXPERIMENTAL DESIGN


Problem: Does the increase in salinity affect the water’s ability to expand when it freezes 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:

• 30g. of Sea Salt- To increase the amount of salinity in the ice/water
• A minimum of 3 Aluminum cans (Same “Brandâ€

[ChrisG]

Hi Michael,
Nice job writing up your experimental plan. It is very thorough and clear. I do have some questions and comments.

Why is the aluminum can more impressive than a balloon? Is it easier to use than a balloon? Does it cause less error in your measurements than using a balloon? Does it tell you something that you would not know if you used a balloon?

How will the thermometers be inserted into a sealed can (and will they survive the freezing process to -70)?

When your cans burst in the previous trials, did you lose any liquid?

The last line of your procedure says that cans will be used to test the amount of pressure exerted. How are you going to test the amount of pressure?

To include the effects of pressure, one possibility would be to freeze the same liquid in a balloon and in a can and see if the amount of expansion differs between the balloon (which will exert very little pressure) and the can (which might exert some greater, but unknown amount of pressure during freezing).

To compare changes in volume, I would suggest using the change in volume divided by (not minus) the starting volume, or some similar ratio.

The more trials you can do, the better.

Good luck!

[Michael]

Chris,

The aluminum can is more impressive than a balloon because I was able to fill it up with water and successfully seal it using an object similar to a quarter and special glue. Also, I thought the crack in the can is a good way to illustrate expansion.

As for the thermometer, I will just test the temperature of the water before sealing the cans to make sure its the same. The freezer I'm using on Tuesday is set at -70 degrees so I already know that temperature.

In my previous trial, each of the cans was put in a zip loc bag and the fresh water can that expanded did not lose water.

Appreciate any additional input or thoughts before I drop off my samples at the lab.

Thank you.

[ChrisG]

"The aluminum can is more impressive than a balloon because I was able to fill it up with water and successfully seal it using an object similar to a quarter and special glue. Also, I thought the crack in the can is a good way to illustrate expansion."

I agree that the the technique of using a sealed can is more impressive as a technical achievement, not to mention that destroying something always adds a bit of a thrill. I also agree that the burst can makes a great demonstration of the pressure exerted by the expanding water & ice. That sort of demonstration will be an excellent way to grab the attention of judges and teachers. On the other hand, when it comes time for them to evaluate the scientific merit of your project, I expect you will get better scores if you use the simplest and least error-prone methods to collect your data. Currently, your only experimental variable is the change in volume of the freezing fluid, and for this topic, it is not clear why the can is important to the scientific question or as a method of collecting data. This doesn't mean that you wouldn't use the cans - you could still use the cans as a very nice demonstration, and then you could use simpler methods such as balloons or bags for collecting the data.

Better yet, you could use both methods (cans and balloons/bags) to introduce pressure as an experimental variable. You mentioned pressure in your write-up, but pressure is not currently measured or included as an experimental variable. By using balloons/bags in addition to cans, you would have a basis to compare expansion under "high" and "low" pressure.

That's the last I'll say about the can versus balloon/bag dilemma, because I can tell that I'm repeating myself and probably becoming annoying. Good luck!

[Michael]

I got to do the 1st trial of freezing my water and salt water samples in an aluminum can. As the amounts of salinity increased, the expansion of the aluminum can was less. I took some wonderful pictures of the sealed cans and how they expanded - evident by the size of the cracks.

I am doing another trial tomorrow and also doing the same test using a balloon.

In the meantime, can you comment on my research to back up my hypothesis: I think that as the salinity increases, the aluminum can will expand than a can with a smaller level of salinity".

Research to Back Up Hypothesis
When a liquid (like water) is frozen, all of the molecules start sticking to each other on very tightly. When the molecules get closer together, they take up less space, so the frozen solid ends up being smaller than the unfrozen liquid.

Water, however, is a bit weird. When the water molecules start holding on to each other really tightly, they make a pattern that actually takes up / more / space than they did when they weren’t stuck together. This pattern is what you see if you look at ice crystals. So, when water freezes, the molecules take up more space and the ice ends up being even / bigger / than the water was.

As water approaches freezing (below 3.98 degree Celsius), the bonds between its hydrogen atoms become more rigid, which causes the molecule to expand, take up more space and become less dense. As water freezes, its molecules bonded in a crystalline structure to form the mineral, ice. The crystals point in definite directions over long ranges.

When you dissolve salt in water, the freezing point of the solution will be lower than the water alone. The reason for this is that salt, actually sodium and chloride ions in solution, “gets in the wayâ€

[Louise]

[quote="Michael"]I got to do the 1st trial of freezing my water and salt water samples in an aluminum can. As the amounts of salinity increased, the expansion of the aluminum can was less. I took some wonderful pictures of the sealed cans and how they expanded - evident by the size of the cracks.

I am doing another trial tomorrow and also doing the same test using a balloon.

In the meantime, can you comment on my research to back up my hypothesis: I think that as the salinity increases, the aluminum can will expand than a can with a smaller level of salinity".

Research to Back Up Hypothesis
When a liquid (like water) is frozen, all of the molecules start sticking to each other on very tightly. When the molecules get closer together, they take up less space, so the frozen solid ends up being smaller than the unfrozen liquid.

Water, however, is a bit weird. When the water molecules start holding on to each other really tightly, they make a pattern that actually takes up / more / space than they did when they weren’t stuck together. This pattern is what you see if you look at ice crystals. So, when water freezes, the molecules take up more space and the ice ends up being even / bigger / than the water was.

As water approaches freezing (below 3.98 degree Celsius), the bonds between its hydrogen atoms become more rigid, which causes the molecule to expand, take up more space and become less dense. As water freezes, its molecules bonded in a crystalline structure to form the mineral, ice. The crystals point in definite directions over long ranges.

When you dissolve salt in water, the freezing point of the solution will be lower than the water alone. The reason for this is that salt, actually sodium and chloride ions in solution, “gets in the wayâ€

[Michael]

[b]Hypothesis:[/b] I think that as the salinity of the water increases, the water will expand less.

I clarified and shortened the Research to back up my Hypothesis. I hope that it is more clearer than the first draft. Appreciate all comments made on it.

[b]Research to Back Up Hypothesis[/b]

* When adding salt to water and freezing the salt water solution, the salt in the water slows down the molecules from expanding and even freezing.

* As you add salt to water, the density of the water increases. This is part of the reason why we need such low temperatures to freeze salt water.

*When water freezes, it is "unusual". Unusual in the sense that it expands when frozen. Usually, when a liquid is frozen all of the molecules start sticking together, very tightly. When the molecules get closer together, they take up less space, so the frozen liquid ends up being smaller than the liquid at first. But, Water, however is a bit weird. The molecules start holding on to each other tightly. This creates a pattern that actually takes up more space than when they were a liquid. This pattern forms a hexagonal structure, like a snowflake. This allows air space in the structure and creates space in the structure and the air makes the ice light. So, when water freezes, the molecules take up more space causing the ice to expand larger than the water was.

*Now, for salt water: Tiny platelets and needles of ice form over the surface of the liquid. The ice crystals incorporate water, but tend to leave the salt behind. So, the solution becomes saltier and saltier as the freezing process continues.

[bradleyshanrock-solberg]

I apologize for the slow response, I was away from all internet for the last week due to holidays and a family vacation.

I would have recommended doing the balloon test as well.

As you have managed to capture all the water (ensuring your volume measurements are valid) it is quite dramatic to use the ruptured can experiments. I'd use the balloon test as more of a control (show that the volumes end up the same, that the ice isn't being compressed somehow in the can before it ruptures...and if they don't end up the same discuss that fact)

I like your comment about how the solution gets saltier as some of it freezes. I don't have a lot to add to the other responses at this point, but keep us posted on your progress - this is a very interesting project.

[Michael]

Bradley,

No need to apologize - I am sincerely grateful for your response. I appreciate everyone's input as I'm proceeding with this experiment. Since my parents can't help, I rely on this website for help and direction. The 1st thing I do everyday is check the website.

In the meantime, I want to make sure the research to backup my hypothesis is clear and that I'm supporting it. Maybe, Louise and Chris G. can comment further on the revised information above.

I'm dropping off my balloons to the local lab this afternoon and will let you know how I make out.

Hope you're having a great day! THANK YOU.....
Michael
8th Grade Student

[Louise]

Bradley,

No need to apologize - I am sincerely grateful for your response. I appreciate everyone's input as I'm proceeding with this experiment. Since my parents can't help, I rely on this website for help and direction. The 1st thing I do everyday is check the website.

In the meantime, I want to make sure the research to backup my hypothesis is clear and that I'm supporting it. Maybe, Louise and Chris G. can comment further on the revised information above.

I'm dropping off my balloons to the local lab this afternoon and will let you know how I make out.

Hope you're having a great day! THANK YOU.....
Michael
8th Grade Student

Michael,
I noticed you started a new thread with your background/hypothesis. Which one is the current one (I'm guessing the new thread)? I also like the additional discussion of the types of ice (cubic vs. hexagonal) and the increased salinity as you freeze. Again, I recommend you 'peel open' one of your frozen balloons and see if you can see these different types of ice or chunks of salt. I'll comment in more detail after you let me know which one is current.

Thanks,
Louise


Louise

[Michael]

Thanks Louise. I started a new thread by error. I will try to delete it. I copied it below so that you can reply. I thought it would be best to display it in bullets so that I don't confuse anyone. I'm trying to make it simple and clear so that everyone can follow what I'm saying. I want to hit all the key points so that I am supporting my Hypothesis.

I'm so excited about this project - I look forward to your comments and recommendations. AGAIN, I AM SO GRATEFUL FOR ALL YOUR HELP!!

MICHAEL

Hypothesis: "My prediction is as the amount of salinity increases in the water, the water will expand less."

Research to Back Up Hypothesis:

- As your add salt to water, the salt slows down the molecules from expanding and freezing.

- As you add salt to water, the density of the water increases. A lower temperature is required to freeze the salt water.

- When water freezes, the molecules start holding on to each other tightly. This creates a pattern that actually takes up more space than when they were a liquid. This pattern forms a hexagonal structure like a snowflake. This allows air space in the structure and creates space in the structure and the air make the ice light. So, when water freezes, the molecules take up more space causing the ice to expand larger than the water was.

- When salt water freezes, tiny platelets and needles of ice form over the surface of the liquid. The ice crystals incorporate water, but tend to leave the salt behind. So, the solution becomes saltier and saltier as the freezing process continues. The salt is excluded because salt has a different crystalline structure. It forms cubic crystals (with 4 sides) whereas ice is hexegaonal )with 6 sides.

- The 6 sided ice crystals build one on another to form sheets of ice. When salt (sodium chloride) is mixed into the water, chlorine ions grab the hydrogen atoms in H2O that interferes with the ice crystal building. It's difficult then for the ice crystals to connect and so they move slower to freeze.

[Louise]

Thanks Louise. I started a new thread by error. I will try to delete it. I copied it below so that you can reply. I thought it would be best to display it in bullets so that I don't confuse anyone. I'm trying to make it simple and clear so that everyone can follow what I'm saying. I want to hit all the key points so that I am supporting my Hypothesis.

This is the part that is going on your poster board then? I do agree with the expert who replied on the other thread who said the research paper should be more complete.

You took out all the stuff on hydrogen bonds! Hydrogen bonds are key!

- As your add salt to water, the salt slows down the molecules from expanding and freezing.

The salt disrupts the hydrogen bonds. I don't know that is 'slows down' the molecules from expanding, because I don't really understand what that means. The structure of water (and maybe ice) is different with and without salt. This is actually pretty complicated, and I would probably delete it and focus on the colligative properties (see below)

- As you add salt to water, the density of the water increases. A lower temperature is required to freeze the salt water.

The density of the _solution_ increases. Water always has the same density.

- When water freezes, the molecules start holding on to each other tightly. This creates a pattern that actually takes up more space than when they were a liquid. This pattern forms a hexagonal structure like a snowflake.

This is good. But is the hexagonal always formed or is that just when it is frozen at 0 degrees? At -70, you might get a different type of ice. ( I think the answer is that for pure water you always get hexagonal ice at normal pressures, but you should check this for yourself. I found this cool (a joke- it is cool because it is all about ice!) website : http://www.lsbu.ac.uk/water/phase.html)

This allows air space in the structure and creates space in the structure and the air make the ice light. So, when water freezes, the molecules take up more space causing the ice to expand larger than the water was.

Okay, the second part is okay. The water network takes up more space because of hydrogen bonds. But air? No! It isn't lighter because there is more air, it is less dense because the hexagonal structure takes up more room.

- When salt water freezes, tiny platelets and needles of ice form over the surface of the liquid. The ice crystals incorporate water, but tend to leave the salt behind. So, the solution becomes saltier and saltier as the freezing process continues. The salt is excluded because salt has a different crystalline structure. It forms cubic crystals (with 4 sides) whereas ice is hexegaonal )with 6 sides.

Okay. But you don't necessarily have crystals of salt in there, do you? You have salt ions?

- The 6 sided ice crystals build one on another to form sheets of ice. When salt (sodium chloride) is mixed into the water, chlorine ions grab the hydrogen atoms in H2O that interferes with the ice crystal building. It's difficult then for the ice crystals to connect and so they move slower to freeze.

Addition of any material causes freezing point depression. This is an example of a colligative property. See:
http://en.wikipedia.org/wiki/Freezing-point_depression

Anyway, I want to give you one last link. This mostly deals with the colligative properties of the salt/water mixture. I think if you can understand this page, you will understand your project very well!

http://www.chemguide.co.uk/physical/phaseeqia/saltsoln.html

This page has a better phase diagram, but less explanation.
http://www.ucalgary.ca/~kmuldrew/cryo_course/cryo_chap6_1.html

Here are some definitions to help you with the second page.
brine= salt water (salt dissolved in water)
ice= pure hexagonal water ice
NaCl*H20, another form of salt where the crystal is formed from both salt and water molecules. This is called a "hydrated crystal" since the salt crystal contains water.


This is a LOT of information, I know. Please ask questions about ANYTHING I posted. A lot of this stuff is pretty complex, but it is really cool!


Louise

[Michael]

I continued with my experiment today by testing various salt water samples in a ballon. The expansion results were similar to the can with the exception that the ballons did not crack, as the cans did.

I also took Louise's advice and opened the balloons to observe the frozen sample. It was interesting to see that the salt accumulated in one area and it appeared that the water seperated from the salt, and froze ontop of it. I think this is because of the different density levels of the salt and water. The salt probably went to the bottom because it has a higher level of density than water!

This was really amazing to see and I will incorporate in my presentation. I have some awesome pictures as well. I did not expect to see some of these results but this is a wonderful learning experience.

I also am anxious to hear what you think about the research to back up my hypothesis above.

THANK YOU - I am very grateful MICHAEL :D

[Louise]

[quote="Michael"]I continued with my experiment today by testing various salt water samples in a ballon. The expansion results were similar to the can with the exception that the ballons did not crack, as the cans did.

I also took Louise's advice and opened the balloons to observe the frozen sample. It was interesting to see that the salt accumulated in one area and it appeared that the water seperated from the salt, and froze ontop of it. I think this is because of the different density levels of the salt and water. The salt probably went to the bottom because it has a higher level of density than water!
[quote]

Cool! I wrote some comments about your report in the post before this. I think you are on the right track for explaining the salt. The links I provided in the previous post may help too.


Louise

[Michael]

I am reviewing the information suggested by Louise. Wow - this is really complex material.

Any other suggestions - please let me know.

Thank you again.....Michael