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€

[deleted-71447]

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.

[deleted-71447]

"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/pha ... tsoln.html

This page has a better phase diagram, but less explanation.
http://www.ucalgary.ca/~kmuldrew/cryo_c ... ap6_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

[bradleyshanrock-solberg]

I'm also reading Louise's information, as it's been about 20 years since I studied the H2O crystal structure. Water is quite unusual in how it behaves compared to other materials.

I've got nothing to add at this time, beyond encouraging you to keep going.

[Louise]

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

Yes, this is complicated! If you don't understand something, please ask us questions. This is a really nice project because it demonstrates several effects clearly, and there is a lot of data out there that you can reference. Some of the material is written at a pretty advanced level (like the page on the different types of ice), and you probably don't need to understand every detail, but it is very interesting to think about all the different types of ice that can be made. ("I'd like my pepsi served with ice-eleven, please." )

If you have trouble understanding how to read the 'phase diagrams' please let me know. These diagrams help you predict exactly what material you have in your mixture at certain conditions.

Water is really interesting, because even pure water forms many different kinds of ice depending on the temperature and the pressure. Even liquid water is very complicated, and many research groups still study plain water so they can understand hydrogen bonds and how they change with time.


Louise

[deleted-71447]

Hi Micheal,
In addition to Louise's excellent info and advice, make sure to follow up on Paul Descarli's suggestion in the other thread to read about the freezing of sea water. That info should be relatively simple to understand, and the processes are very relevant to your experimental results. For example, as saline water freezes, it fractionates so that the initial ice formed has a lower salt content than the surrounding water. You should be able to find many references to this online. Also, solid ice expands at different rates depending on the salt concentration. These coefficients of expansion are also available online.

There may be other factors aside from salinity that could affect your results. For example, did both types of ice (saline and fresh water) appear equally cloudy? If it is cloudy, do you see tiny bubbles in the ice? Formation of air bubbles in freezing water affects the final volume of ice, and you might see some differences in air content between the saline versus fresh water ice, or in the different layers of ice in the saline trials.

Great experiment! Keep up the good work.

[Michael]

Hello. Hope everyone is doing well especially with the holidays quickly approaching.

I've been reviewing the suggested material from Louise and feel I have a much better understanding. As a result, I need to correct
my prior trial results that were done at -70 degrees celsius. When I took the cans out of the freezer, they were actually "supercooled". They actually froze out of the freezer. I didn't completely understand what was happening. I believe they ended up freezing when they reached the appropriate temperature.

I decided to contact the local lab in my neighborhood and got permission to do another trial using their scientific freezer but this time at -20 degree celsius.

I took Chris' advice and conducted the test this time using balloons.
The fresh water balloon definitely expanded more than the salt water balloon. But, what I found interesting was that the salt water was a cloudy color whereas the fresh water was almost crystal clear. In addition, when I observed the salt water I found that the water ice crystals formed in one area, but in the total opposite area of the ice crystals were clusters of salt. You could also see small air bubbles in the fresh water and the ice was completely smooth.

I learned that my hypothesis was correct.

The more "salt" in water, the lower its freezing point. Basically, salt "disrupts" the bonding between the Hydrogen atoms and Oxygen atom. As a result of the disruption between the Hydrogen and Oxygen atoms, the salt water solution freezes at a lower temperature and expands less.

Please let me know your thoughts and any other suggestions.

Best regards....MICHAEL

[deleted-71588]

There are some other possibilities that you need to think about. The solubility of a given salt in water is often a function of temperature and typically decreases with temperature (hot water will typically allow more salt to disolve than cold water).

Since you observed clumps of salt crystals in some samples, what might have occurred is that salt precipitated out of solution as the temperature was lowered but before it froze. Similar techniques are often used to seperate out various protiens in biochemistry applications. I maybe wrong, but I seem to recall that "freeze drying" was utilized as a step in commercial separation of insulin from pancreatic cells before people figured out how to DNA splice bacteria to produce insulin.

Ice from pure distilled water is a crystal structure that has a very regular pattern so its optical properties are uniform which translates into transparency.

Frozen salt water has an irregular structure so its optical properties are not uniform which translates into optical scattering which is translates into translucent behavior (cloudy appearance).

[bradleyshanrock-solberg]

Yes...the salt solution will likely have examples of all of the following

1. essentially pure ice
2. essentially pure salt
3. frozen salt/water solution

The phase diagrams referenced in early links show that if you heat it up and then cool it down (at certain concentrations of salt) you would expect to get all 3 states.

These will be visually different. How much you get of each may well depend on how fast you cool it. The -70 degree freezer will give a different mix than a -20 degree freezer, assuming the samples go in at room temperature.

This technique is used in a lot of metallurgy - steel for example is a mix of iron and carbon, carefully heated and cooled to cause a precise mix of different combinations of iron and steel (crystal structures) in the final product which gives it a desired mix of hardness and toughness. You get a very different result if you heat up your carbon/iron mixture and suddenly cool it in water versus letting it cool down slowly in the air.

You're doing kind of the same thing by using different refrigerator temperatures. The water will go from liquid to solid state faster in the cooler freezer, and that will change the percentage of the three materials you see (probably less pure ice and salt, more mixed salt/ice if you cool quickly vs cool slowly - depends on the phase diagram and the amount of salt in the solution)

[Louise]

Hello. Hope everyone is doing well especially with the holidays quickly approaching.

I've been reviewing the suggested material from Louise and feel I have a much better understanding. As a result, I need to correct
my prior trial results that were done at -70 degrees celsius. When I took the cans out of the freezer, they were actually "supercooled". They actually froze out of the freezer. I didn't completely understand what was happening. I believe they ended up freezing when they reached the appropriate temperature.

I decided to contact the local lab in my neighborhood and got permission to do another trial using their scientific freezer but this time at -20 degree celsius.

I took Chris' advice and conducted the test this time using balloons.
The fresh water balloon definitely expanded more than the salt water balloon. But, what I found interesting was that the salt water was a cloudy color whereas the fresh water was almost crystal clear. In addition, when I observed the salt water I found that the water ice crystals formed in one area, but in the total opposite area of the ice crystals were clusters of salt. You could also see small air bubbles in the fresh water and the ice was completely smooth.

I learned that my hypothesis was correct.

The more "salt" in water, the lower its freezing point. Basically, salt "disrupts" the bonding between the Hydrogen atoms and Oxygen atom. As a result of the disruption between the Hydrogen and Oxygen atoms, the salt water solution freezes at a lower temperature and expands less.

Please let me know your thoughts and any other suggestions.

Best regards....MICHAEL

Michael,
I'm glad to see that things are going well with your experiment. The results with supercooling is really neat! Did you see the control (pure water) do the same thing? (And why didn't you mention this observation before?? This is an important observation!). I hope your experiments with the -20 freezer work well! Looking at the phase diagram though:
http://www.ucalgary.ca/~kmuldrew/cryo_c ... ap6_1.html

I think you not be able to freeze all samples. If you look at the 0-40% salt part of the phase diagram, it looks like -20 is very near a phase transition between getting a solid of [H2O ice and NaCl*H2O2] and having a mixture of solid (either pure H2O ice or the NaCl hydrate solid) and brine. You should determine the temperature of the freezer very carefully because a few degrees cooler than -20 is a very different result from a few degrees warmer.

I think you need to be careful about how you word your last paragraph. Not all ice that forms is 'disrupted' ice. As the phase diagrams show, some of the ice forms the regular 'pure' water ice, with the normal density and structure. In terms of conclusions, I would probably rely more on the phase diagrams. Hydrogen bonds are important- and they do dictate the type of ice structure you get as well as the properties of the liquids and solutions, but you don't directly observe them. The colligative properties can be understood with out knowing the details of the molecular interaction- you can understand freezing point depression without knowing that a particular solvent does or does not form hydrogen bonds. I would recommend you look at this site again:
http://en.wikipedia.org/wiki/Freezing-point_depression

I would also recommend taking photographs of the different types of ice if possible. This would look really cool on your poster board, and would help illustrate the complexity of the ice/water/salt behavoir.

Good luck with the rest of your experiments.

Louise

[Michael]

Louise had confirmed the following:

"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."


Please clarify if "chlorine ions" in the above quote should read "chloride ions".

Thank you.

Michael

[Louise]

Louise had confirmed the following:

"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."


Please clarify if "chlorine ions" in the above quote should read "chloride ions".

Thank you.

Michael

I don't think I 'confirmed this'; I actually think this is not the best description of what happens. I think you should write in terms of 'colligative properties', which is why I included a link to colligative properties this quote. Please see my early post to you today.

Chlorine is the element. Chloride is the negatively charged chlorine (-1). Chloride is technically correct, and you should use it. 'chlorine ion' would probably be understood by a chemist to mean chloride (which I am), but is not technically correct. So, if you choose to keep this paragaph in your paper, you should use chloride.

Again, I would recommend re-reading my last post and reviewing colligative properties.

Good luck with your paper!
Louise

[Michael]

Hello!

I'm trying to think of a good title for my display board that will catch people's attention.

Any ideas will be greatly appreciated.

Thank you... Michael

[Michael]

Hello again.

Can anyone think of a good title for this experiment?

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

I'm starting to put my information together..... Everyone has been so helpful. I couldn't have done this experiment without your direction.

THANK YOU!!!!! MICHAEL

[bradleyshanrock-solberg]

You might just try something a bit more general.

"Phase changes and effects on volume in saline solutions at different cooling rates"

Really what you're doing is exploring the phase diagram for salt and water at the liquid/solid boundary. You're doing it in a fun way, showing pressure exerted by volume change in a dramatic fashion, but the meat of your results is in the combination of pure ice, saline ice and salt that emerge from the different treatments.

[Louise]

You might just try something a bit more general.

"Phase changes and effects on volume in saline solutions at different cooling rates"

Really what you're doing is exploring the phase diagram for salt and water at the liquid/solid boundary. You're doing it in a fun way, showing pressure exerted by volume change in a dramatic fashion, but the meat of your results is in the combination of pure ice, saline ice and salt that emerge from the different treatments.

I really like this suggestion. I haven't posted back about a title, becuase I haven't had any good ideas!

I think this is a really good title, and the different cooling rates parts allows you to mention both the -20 and -70 data.

Louise

[Michael]

Hi, Everyone.

I've been sick with the flu / strep throat. What a time to get sick? With the holidays coming and the project being due on January 10th, I'm trying to finalize my project so that I can focus on the actual presentation. Of course, I value your input and look forward to your comments.

I spent alot of time reading the research material that was recommended especially the Solid-Liquid Phase Diagrams suggested by Louise. I feel it finally clicked in and am able to explain it. In brief, when freezing a salt water solution nothing happens until you get down to the eutectic temperature (the temperature which the mixture of salt and water freezes -21.1 degrees C) and it is at that point, that both ice crystals and salt crystals start forming. The end product is that you're left with ice crystals and salt crystals. They're no longer in the solution, they're separate.

So that I'm clearly answering the purpose of my experiment Does the increase in salinity affect the water's ability to expand when it freezes inside an aluminum can, I feel I need to include the following points in very simple terms so that my classmates (8th graders) understand and can follow what I'm saying:

Fresh Water:
When water freezes, it expands because of hydrogen bonding. The water molecules rearrange themselves to form a crystal that takes up more space than of the liquid molecular arrangement. The crystal consitsts of molecules in a very precise, repeating array, hexagonal (6 sided) structure like a snowflake. (Will include a great picture of this)

Salt Water:
When salt water freezes, the expansion is less because: As you add salt to water, the salt slows down the molecules from expanding and freezing. The salt interferes with the bonding between the hydrogen and oxygen atoms found in water making it difficult for them to bond. Salt water form cubic crystals (with 4 sides) whereas ice (fresh water) is hexagonal (with 6 sides).

After conducting the experiment, I concluded that my hypothesis was correct! As the salinity of water increases, the expansion decreases.

This is specifically shown in my experiment when the can with 0g of salt expanded 2 cm (in diameter), the can with 5g of salt expanded 1 ½ cm (in diameter) and the can with 10g of salt expanded 1 cm (in diameter) .

I learned that the reason for this is because the salt (NaCl) in the water interferes with the bonding between the Hydrogen and Oxygen atoms when freezing, causing the ice to expand less and freeze at a slower pace. As the water freezes, the dissolved salt lowers the freezing point of the water to less than 0°C.

Taken together, my experiment proves that the increase in salinity does affect and decrease the expansion of the water when frozen.


This project can apply to real life in helping to determine the causes of erosion:

 The expansion of ice is responsible for much of the erosion that makes our soil. During the winter, water that has found its way into cracks in rocks freezes. As the water freezes, it expands, and the cracks are forced open and enlarged by the ice. This turns big rocks into little rocks and makes mountains into molehills.

 Erosion can occur when water freezes and glaciers are eroding the surface of the earth.


Appreciate your thoughts of any changes or if I can go forward with the above.

All the best....Michael

[Louise]

Hi, Everyone.

I've been sick with the flu / strep throat. What a time to get sick? With the holidays coming and the project being due on January 10th, I'm trying to finalize my project so that I can focus on the actual presentation. Of course, I value your input and look forward to your comments.

I spent alot of time reading the research material that was recommended especially the Solid-Liquid Phase Diagrams suggested by Louise. I feel it finally clicked in and am able to explain it. In brief, when freezing a salt water solution nothing happens until you get down to the eutectic temperature (the temperature which the mixture of salt and water freezes -21.1 degrees C) and it is at that point, that both ice crystals and salt crystals start forming. The end product is that you're left with ice crystals and salt crystals. They're no longer in the solution, they're separate.

So that I'm clearly answering the purpose of my experiment Does the increase in salinity affect the water's ability to expand when it freezes inside an aluminum can, I feel I need to include the following points in very simple terms so that my classmates (8th graders) understand and can follow what I'm saying:

Fresh Water:
When water freezes, it expands because of hydrogen bonding. The water molecules rearrange themselves to form a crystal that takes up more space than of the liquid molecular arrangement. The crystal consitsts of molecules in a very precise, repeating array, hexagonal (6 sided) structure like a snowflake. (Will include a great picture of this)

Salt Water:
When salt water freezes, the expansion is less because: As you add salt to water, the salt slows down the molecules from expanding and freezing. The salt interferes with the bonding between the hydrogen and oxygen atoms found in water making it difficult for them to bond. Salt water form cubic crystals (with 4 sides) whereas ice (fresh water) is hexagonal (with 6 sides).

After conducting the experiment, I concluded that my hypothesis was correct! As the salinity of water increases, the expansion decreases.

This is specifically shown in my experiment when the can with 0g of salt expanded 2 cm (in diameter), the can with 5g of salt expanded 1 ½ cm (in diameter) and the can with 10g of salt expanded 1 cm (in diameter) .

I learned that the reason for this is because the salt (NaCl) in the water interferes with the bonding between the Hydrogen and Oxygen atoms when freezing, causing the ice to expand less and freeze at a slower pace. As the water freezes, the dissolved salt lowers the freezing point of the water to less than 0°C.

Taken together, my experiment proves that the increase in salinity does affect and decrease the expansion of the water when frozen.


This project can apply to real life in helping to determine the causes of erosion:

 The expansion of ice is responsible for much of the erosion that makes our soil. During the winter, water that has found its way into cracks in rocks freezes. As the water freezes, it expands, and the cracks are forced open and enlarged by the ice. This turns big rocks into little rocks and makes mountains into molehills.

 Erosion can occur when water freezes and glaciers are eroding the surface of the earth.


Appreciate your thoughts of any changes or if I can go forward with the above.

All the best....Michael

Sorry to hear that you were sick. I'm glad the phase diagrams "clicked"! I think your explanation of the phase diagram can also be included in your report and perhaps a copy of it included in your display with either dots or lines representing your experimental trials (show what part of the phase diagrams you studied). Remember too, your report and presentation are not just for your classmates, but also teachers and judges. I don't think you should simplify too much just because your classmates are in the 8th grade; your classmates can learn a lot from what you present.

I like your paragraph about erosion. It is nice that you are thinking about the larger picture.

Lastly, did you see the different types of crystals? Could you tell that you were forming cubic rather than hexagonal? I'm not sure you could see specific structures by eye, but did you see differences in the surfaces or shapes? (I know some looked cloudy, but that is for a different reason.)

One last, tiny detail... It is usual to put a space between the number and the unit. Thus '5 g' and not '5g'.

Louise