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Solubility book (3rd Edn)
Investigating the effects of temperature on the solubility of vanillin in ethanol and methanol (experiment repeat)
This is a repeat of experiment JennyHale 4 with some changes and additions to try and answer the queries given by JCB. Therefore this experiment compares inversion and vortexing solutions. There has also been a change to screw cap vials as they were sealing better than the current stock of eppendorfs in the lab.
12 Eppendorfs were taken and labelled with their planned contents and weighed. These eppendorfs would be used to evaporate the saturated solutions. 6 Screwcap eppendorfs were taken and labelled with their planned contents as were 6, 2 ml screw cap vials. (
change to screw cap vessels as normal eppendorfs were not sealing well
). Two heat blocks were set to 30 and 40°C and the lab temperature measured as being 23°C again (by holding the thermometer in the air)
750 µL of ethanol and methanol were added to the vials accordingly and the vials either added to heat blocks or kept at room temperature.
Vanillin was added to each vial. Screw cap eppendorfs were inverted to dissolve as shown in video 1 here
(Also on youtube at
) whilst 2 mL vials were vortexed, also shown in video 2 here
. (Also on youtube at
Both were either shaken or vortexed in 10 second intervals. More vanillin was added and dissolved until the solutions became saturated (usually requiring an average of 20, 10 second inversions/vortexes).
(Are you saying that the solutions were vortexed for a total of 200 seconds? Are you defining saturation as vortexing for 10 seconds and still seeing solid present? JCB)
(The solutions were either initially vortexed or inverted for 10 seconds. On many occasions this fully solubilised the solid so more solid was added and vortexing/inverting done in 10 second intervals either until the solid all dissolved or nothing was happening after at least three 10 second intervals of shaking/vortexing. JH)
Between inversions/vortexes, the solutions at 30 and 40°C were put back in the heat block to maintain the temperature.
(It isn't clear how long the solutions were allowed to equilibrate at the different temperatures JCB)
(I didn't keep a track of the time. Usually whilst the solution equilibrated in the heat block, I would be adding solid and dissolving another sample so at least 1 minute would have elapsed before it's removal from the heat block. JH)
This gave 12 saturated solutions: vanillin in ethanol at 23, 30 and 40°C made by inversion; vanillin in ethanol at 23, 30 and 40°C made by vortexing; vanillin in methanol at 23, 30 and 40°C made by inversion; and vanillin in methanol at 23, 30 and 40°C made by vortexing.
The solutions were centrifuged at room temperature for 1 minute at 13,200 rpm/16,100 g. 500 µL of supernatant from each solution was added to its respective eppendorf and the solutions dried in the speedvac at room temperature (no known g, just on/off) initially for 3 hours. The samples were weighed after 3 hours and then replaced in the speedvac for further drying. The samples were dried for a further hour and then re-weighed. A number of samples had gained in mass and these have been indicated in red on the spreadsheet. The samples were placed back in the speedvac for further drying for 30-45 minutes, before final weight measurements were taken.
The results can be found in this spreadsheet here
After the second drying period a number of the samples had gained in mass. By the time I had finished weighing the samples all the last samples to be weighed had gained in mass. My thought therefore is that it was my fault for not shutting the leds the moment the samples were removed from the speedvac. I suspect that the samples were dried but picked up moisture from the atmosphere during standing. If this is the case, then those mass gains should be lost after putting back on the speedvac and re-weighing.
After a further 30-45 minutes on the speedvac, some of the weights had decreased whilst others had stabilised. the increased masses had begun to lose mass again so I think it may have been as I predicted. I have taken the molarities based on the final figures, but may try drying the samples that had apparently gained mass tomorrow.
I have produced a graph of solubility and temperature, but there is no obvious trend, so perhaps temperature does not make a significant difference. The vortexing and inversion methods seem to have very little difference in solubility either.
(At first glance it looks like there is no temperature effect for vanillin in methanol -assuming you left them to equilibrate long enough - but there it does appear that the vortexed samples are significantly higher than the inversion method if you take the three values as a group and get a standard deviation that may bear it out. Note that you vortexed for 10 seconds to assess saturation while we did it for 30 seconds in
and got a value of 4.19M. To settle the issue I think we need to vortex for a much longer period - say 5 or 10 minutes JCB.)
I will set up an experiment where samples are vortexed for a longer period of time. JH
I have also updated this spreadsheet to include a standard deviation. However, I'm not sure that I did it correctly so I will probably need more guidance.
I didn't see the standard deviation numbers - you can do that in Google Spreadsheets by going on a blank cell and typing =stdev and selecting the cells JCB
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