Researcher

Mary Ziegler

Objective

To calculate the solubility of (trans)-cinnamic acid in methanol by density method.

Procedure

-weigh proper amount of solvent / solute
-heat mixture
-transfer supernatant
-cool mixture
-transfer supernatant
-weigh supernatant


Results

Mass and Molarity calculations
The molarity of the solution of ethanol saturated with cinnamic acid was found to be:
trial 1: 1.31 M
trial 2: 1.18 M
(both trials used 2 ml volumetric flasks)

Discussion

The recorded molarity of ethanol saturated with cinnamic acid is 1.03 M. This experiment produced a recorded molarity of 1.31 M and 1.18 M, which are both significantly off (27% error and 15% error respectively). Aside from general human error in pure measurements, the solution was cooled below room temperature (19 C), which would effect the results.

Recommendations/For Future Reference

-do not cool solution below 20 C
-save and reuse solution for volumetric flasks (pour the 5ml into the 2 ml into the 1 ml)
-be prepared! (come with goggles, lab coat, markers, etc)
-rough estimate of critical values:
1 M = 1mmol/ml, so assume 1 ml, meaning 1mmol of solute (which is approximately the same as the molecular weight).
need the molecular weight in mg/ml, 1 ml too small for sample scale up to 10 ml (i.e. cinnamic acid 150 mg/ml * 10ml = 1500 mg = 1.5 g)
scale up, so approximately 2 g cinnamic acid needed
Conclusion
This experiment, while failed in the sense of the miscalculated molarity, served as a great learning experience for future ones.

Log

April 12, 2011
10:40: start experiment/general set up (fill water bath, get drabs and flasks)
10:47: weigh out approximately 2 grams of cinnamic acid (2.034 grams) into 5 dram vial (vial A)
10:50: add 8 ml of ethanol (200 proof, anhydrous)
10:55: sonicate solution, check temperature of water bath (44 C)
10:57: place mixture in bath, keeping the levels approximately the same
11:02: remove mixture, sonicate ten seconds
11:03: take picture [name the pic JCB],
11:05: transfer supernatant to vial B, sonicate ten seconds
11:06: started to cool mixture to approximately 20 C (blow air onto mixture)
11:10: check temperatue by putting thermometer into mixture (19C) [was there any precipitate at this point? JCB]
11:11: sonicate (take pictire)
11:14: transfer supernatant to vial C, take picture
11:16: weigh volumetric flasks before and after solution added
11:30: enter data into spreadsheet and start wiki page