Michael wrote: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
Michael wrote: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.
Michael wrote: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".
bradleyshanrock-solberg wrote: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.
Michael wrote: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:
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)
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 Â½ 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 0Â°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:
ï‚§ 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.
ï‚§ 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
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