My experiment is based on Chemistry of Ice-Cream Making: Lowering the Freezing Point of Water.
Question: Will the solute be greater when sucrose is dissolved in water or when sodium chloride is dissolved in water?
Hypothesis: The solute molecules will be greater when sucrose is dissolved in water than when sodium cholide is dissolved in water.
I am doing the first solution of NaCl and it was been going for over 10 minutes. I have disturbed the test tube, but thats only to keep the ice to a temperature of -10 degrees. Should I wait longer or start over?
Solute Molecules
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pinkspacehippo
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pinkspacehippo
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Re: Solute Molecules
I am using 20mL of the solution in a 500mL beaker filled with ice and salt.
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agm
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Re: Solute Molecules
Hi pinkspacehippo,
For others' reference, the project mentioned is here:
https://www.sciencebuddies.org/mentorin ... p023.shtml
It sounds like the problem you're having is that your solution of NaCl is not freezing. Is that correct?
The project design implies that the concentrations it specifies should freeze at or above -10 degrees C. Did you use the ratios of water to salt recommended -- that is, 100 m of water plus either 5.8, 4.35, or 2.9 g of NaCl -- or did you add one of those amounts to 20 mL of water? If so, you may have depressed the freezing point below the temperature of your ice bath. It is also possible that your ice bath is warmed than -10 deg C. Have you measured its temperature by rinsing off the thermometer and placing it directly in the ice bath?
About your question and hypothesis: I'm not sure I understand what you're asking. What do you mean by a "solute" being "greater"? A larger amount of solute? If so, by mass or by number of molecules? Either way, that's something that depends on the solutions that you mix up, and not really something that you're going to measure in the experiment. The experiment will show you the effect of adding given amounts of sucrose and NaCl to a constant amount of water. One of the finer points it makes it that freezing-point depression depends on the number of molecules in solution; even though a sucrose molecule is much heavier, it stays whole when placed into water, while NaCl breaks into Na+ and Cl-.
If you read the "Variations" section, that might give you an idea for a hypothesis to compare the effects of sucrose and NaCl. A place to start for more info about that equation is here:
http://en.wikipedia.org/wiki/Freezing_point_depression
Amanda
For others' reference, the project mentioned is here:
https://www.sciencebuddies.org/mentorin ... p023.shtml
It sounds like the problem you're having is that your solution of NaCl is not freezing. Is that correct?
The project design implies that the concentrations it specifies should freeze at or above -10 degrees C. Did you use the ratios of water to salt recommended -- that is, 100 m of water plus either 5.8, 4.35, or 2.9 g of NaCl -- or did you add one of those amounts to 20 mL of water? If so, you may have depressed the freezing point below the temperature of your ice bath. It is also possible that your ice bath is warmed than -10 deg C. Have you measured its temperature by rinsing off the thermometer and placing it directly in the ice bath?
About your question and hypothesis: I'm not sure I understand what you're asking. What do you mean by a "solute" being "greater"? A larger amount of solute? If so, by mass or by number of molecules? Either way, that's something that depends on the solutions that you mix up, and not really something that you're going to measure in the experiment. The experiment will show you the effect of adding given amounts of sucrose and NaCl to a constant amount of water. One of the finer points it makes it that freezing-point depression depends on the number of molecules in solution; even though a sucrose molecule is much heavier, it stays whole when placed into water, while NaCl breaks into Na+ and Cl-.
If you read the "Variations" section, that might give you an idea for a hypothesis to compare the effects of sucrose and NaCl. A place to start for more info about that equation is here:
http://en.wikipedia.org/wiki/Freezing_point_depression
Amanda
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agm
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Re: Solute Molecules
*warmeR than 10 deg C, sorry.