Michael wrote:Thanks Louise - You're the Best!!!!!!!!
I will include some great pictures that I took of the different type of crystals - you can really tell best by the shape.
I will incorporate your other suggestions. But I just want to make sure, you're okay with the information / conclusion layout above.
Thank you again.
Michael wrote:-As you add salt to water, there are fewer water molecules in the liquid because some of the water has been replaced by the salt.
-Salt is a soluble material that separaes into ions with positive or negative charges when they dissolve.
-Since these positive and negative salt ions take up some of the positive and negative sides of the water molecules making it more difficult for them to bond and form into the hexagonal (6 sides) crystalline structure of ice. It forms an irregular structure of cubic crystals with 4 sides.
- For this reason, salt water requires a lower temperature to freeze. Here's what happens.
1. Tiny platelets and needles of ice form over the surface of the liquid.
2. The ice crystals incorporate water, but leave salt behind.
4. Crystals of ice and salt both start to form at the eutectic temperature (the temperature which the mixture of salt and water freezes -21.1 Degrees Celsius).
5. At -21.1 Degrees Celsius, the water freezes pushing the salot out of the solution. The salt begins to crystallize out of the solution.
6. You're left with ice crystals and salt crystals. They're no longer in the solution, they're separate.
Let me know if I should run with this..
Michael wrote:Hi, Louise.
I'm feeling alot better today and will take your valuable input and finalize my display board. I've definitely learned alot from this project but your guidance was most valuable and am eternally grateful. I've included an acknowledgement of science buddies and a special thanks to you on my display board. I also shared this wonderful experience with my teacher and classmates.
Thank you for being there for me.
I want to wish you and everyone at Science Buddies a Happy New Year 2008!
Michael wrote:Hello and Happy New Year to Everyone.
Would you recommend including the phase diagram of salt water solution (chart) on the display board?
The question came up while practicing my presentation that I did a good job on explaining why salt water and fresh water freeze at a lower temperature but I did not fully explain why salt water expands less. I thought I was clear with my layout, but the feedback I'm getting is saying I'm not. It was my understanding that salt water expands less when frozen due to hydrogen bonding as illustrated below. Appreciate if you could clarify again. THANK YOU!!! MICHAEL
When water freezes, it expands because it takes up more space due to “hydrogen bonding”.
Water is a “polar” molecule. Polar means that there is a charge difference throughout the molecule – that is the oxygen atom has a negative electrical charge while the two hydrogen atoms are positive. This is important because it means that the charged ends of a water molecule are attracted to oppositely charged portions of other molecules it encounters. This attractive force is called hydrogen bonding.
As the water freezes, the molecules start holding on to each other tightly. They rearrange themselves to form a crystal that takes up more space than of the liquid water molecular arrangement. The crystal consists of molecules in a very precise, repeating arrangement, hexagonal (6-sided) structure like a snowflake.
When salt water freezes, the expansion is less because:
As you add salt to water, the salt (NaCl) “disrupts” the bonding between the hydrogen molecules found in water (H2O) making it more difficult for the water molecules to bond and form ice. As you add salt to water, there are fewer water molecules in the solution because some of the water has been replaced by the salt.
Salt is a soluble material that separates into ions with positive or negative charges when they dissolve. Since these positive and negative salt ions take up some of the positive and negative sides of the water molecules making it more difficult for them to bond and form into the hexagonal (6 sides) crystalline structure of ice. It forms a different type of structure with cubic crystals (4 sides). For this reason, salt water requires a lower temperature to freeze.
Michael wrote:After reading all of the research material, I believe salt water expands less than fresh water when frozen because the salt influences the crystal structure of solid ice in such a way that bonds take up less space then if there were no salt.
Any other thoughts?
What's the difference in volume between a bunch four-sided crystals and a bunch of six-sided crystals, if both bunches have the same mass?
Salt crystals also have a cubic structure, so I wonder if the cubic water and the cubic salt can fit together well. Think of stacking blocks again. How well can you pack hexagonal with cubic? Having the same structure makes it easier. However, at some conditions you have hydrated salt- not sure what the structure (or density) of that is. I'll look tomorrow when I am at school. I can't find out with normal search engines, so I'll try the university library.
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