August 08, 2022, 02:33:22 AM
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Topic: Would like professional opinions on possible improvements to this procedure  (Read 4245 times)

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Offline gebraroest

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I have designed a lab for our chemistry grade 12 project.
The lab is based around the colligative properties of different organisms.
I would have to demonstrate this lab in class, so any room for improvements is appreciated.

It is determined our school has access to Citrate and Glycine. We would need to find Threonine on our own, or provide a plausible substitute
Colligative Properties:
Investigating Antifreeze Proteins
and Their Effects on Freezing Points

The plasma of the blood, in several species, contains (among a large concentration of water) many molecules and ions which exhibit considerable colligative properties in order to allow such organisms as plants, fish and insects to survive in lower temperatures; such proteins as the antifreeze proteins found in most cold-blooded animals and plants help to considerably enhance their ability to retain heat. It is known that, in mass, 90.0% of the plasma is water, approximately 1.0% is inorganic ions, approximately 1.0% is organic compounds, and 8.0% are proteins. Inorganic ions and organic compounds are abundant in many forms of life; salts and sugars (monosaccharides) occupy the body of any organism being investigated in this lab, whether it be plants, fish or insects. Seeing as all of them contain these compounds, they will be used in order to exhibit their own colligative properties.
Most importantly, however, are the compounds that are unique to the particular organism. The amino acid Glycine is a prominent component of Dehydrin, which is a plant antifreeze protein. Its presence in a water solution will have an effect on the solution at hand, as it would in the actual plant itself. Likewise, Citrate exhibits colligative properties in the bodies of insects, and it can also be put in a water solution to view its effect on the freezing point. Compounds such as disaccharides and the amino acids Alanine and Threonine operate similarly in the bodies of fish, and thus examining their presence in solution will offer similar results.
Known quantities of the contents of several antifreeze proteins (such as those of fish, plants, and insects), will be tested in a salt-sugar-water solution of specific concentrations in order to determine how the presence of these substances affect the freezing points of the water solution, which should theoretically be 0°C (273K). In culmination, this will allow one to explain how colligative properties exist in the proteins of several living species, and it will allow one to dictate which of these proteins are more successful in terms of changing the freezing point of the solution than others (in other words, which exhibit higher colligative properties than others). By calculating the time it takes for each substance to crystallize, one can also draw a parallel between colligative properties and how they affect rates of reaction.

50-mL graduated cylinder
Four test tubes (~40mL)
Ice cooler
Four thermometers
Plastic container
Distilled water
NaCl (table salt), 2.00g
Sugar (Glucose), 2.00g
Threonine [an amino acid that is a  prominent component of Fish Antifreeze Glycoproteins], 1.600g
Glycine [an amino acid that is a prominent component of Dehydrin, a Plant Protein], 1.600g
Citrate [primary exhibitor of collig. Properties in Insect Proteins], 1.600g

1. Label the four test tubes: a) Control b) Fish c) Plant d) Insect
2. Add 18.0mL of water to each of the four test tubes.
3. For all four test tubes, add 0.200g of NaCl and 0.200g of sucrose. Add nothing more to the first test tube (this is the control group). For the subsequent three, add 1.600g of the respective organic compound (Alanine to the cylinder labelled “Fish”, Glycine to the cylinder labelled “Plant”, Citrate to the cylinder labelled “Insect”). These values are based upon the known concentrations found in the plasma.
4. Each solution will be placed in the same ice cooler for up to 25 minutes with a thermometer (if the weather outside is cold enough, one could use the freezing temperatures outside as another option). Measure the initial temperatures. When the water inside of the test tube begins to crystallize, that particular test tube will be finished. The process will continue until all four test tubes have reached a freezing point.
5. Record the temperatures at which each substance froze on the data table. Fill in the temperature change table to determine how much of a change was required in order to freeze each substance.
6. Relate the results obtained to the species involved (this will only be done for test tubes 2-4 as they are specific to certain species; 1 is all-inclusive) and observe the trend in the proteins and the organism in question.

Offline Borek

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I think you will have much better chances of getting some feedback if you post this question to CHEMED-L mailing list (easily googlable).
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