Researcher

Sozit Kurtu

Objective

To isolate error in the density method of solubility determination due to differences in flask sizes and types. The additivity of volumes is an assumption and the density of the solid is obtained from ChemSpider prediction.

Procedure

Results

Measurements
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Discussion

  1. Larger flasks appear to result in values more precise and accurate (literature value of 0.791 at 20C), omitting outlying data points, as apparent by the standard deviation charts; this makes the assumption that there are several outlying data points within the 10-mL flask measurements, as once the standard deviation for the 10-mL flasks are removed, there is a definite downwards trend. However, it must be noted that there were less iterations of the 25mL and 10mL flasks than 5mL, 2mL, or 1mL. This may be due to the proportionally more significant consequences of a small error in measurement with the smaller flasks in comparison with the larger flasks.
  2. The difference in values between capped and uncapped samples was on the order of 10^-4. It should be noted, though, that all uncapped samples were measured immediately upon being placed on the scale, as evaporation skewed weight immediately. Also, because it would be prohibitively difficult to standardize caps, measurements will most likely be taken uncapped in the future.

Conclusion

Despite the above results, the are sufficiently precise despite flask size or type, and the density method of solubility should not be discarded due to any small error resulting from the volumetric flask. If feasible, however, larger flasks should be used, because standard deviation appears to decrease as flask size increases.

Log

2010-09-24

12:00 - Took lab temperature, found to be 22C.
12:10 - Weighed flask 25A (dry).
12:11 - Added methanol; weighed.
12:12 - Cleaned and dried using compressed air.
12:15 - Second methanol run.
12:16 - Cleaned and dried.
12:17 - Third methanol run.
12:19 - Continued above pattern for samples 25B-10B.
12:48 - Weighed sample 10C with cap (dry).
12:49 - Added methanol and cap; weighed.
12:50 - Cleaned and dried.
12:52 - Second methanol run with cap; also, without cap (recorded first number before evaporation and continued this process below).
12:53 - Cleaned and dried.
12:54 - Third methanol run same as second.
12:56 - Cleaned and dried.
12:37 - Continued above pattern for samples 5A-1C.