I want my synthesis to be performed at a particular reaction temperature say between 60-95 degrees. I am adopting Co-precipitation process and have two initial precursors. My general doubt is, if I am using a hot plate on a magnetic stirrer and set it to a particular temperature, first the plate will get hot then the beaker and finally the solution. Generally it will take larger time as a result for the solution to reach at that temperature, if the final reaction mixture consist of say 300-400 ml solution (this much amount because of large amount of base being added), which includes initial precursors and base (or say for 200-300ml solution too). In many papers they say/claim their synthesis reaction temperature is this "x" much amount, so do they measure the temperature of hot plate or the solution is what my concern is mainly because it is the solution temperature which must be measured!!
The way I was thinking is that before mixing the two things, I preheat them at that particular temperature and mix them and then I add the base? Is this correct or not?
Dear Anshul Sharma ,
Normally, in order to avoid any temperature differences between the reaction bulk and the hot plate, different set-ups can be used, such as:
1) There are some hot plates that normally have a "rounded" shape, in which the rounded-flask fits into, and heats it uniformly.
2) Since the former might be quite expensive, normally thermal baths are used, which can be water, oil, or high-temperature liquid silicones. What you normally do is heating up the bath, in which your flask is submerged.
Since your volumes are quite big, your approach of pre-heating reactants is a good option. Nevertheless, strong agitation (such as magnetic stirring) should be considered within the bulk reaction, to collaborate to the uniform distribution of temperature, and reactants as well.
Finally, if a thermometer can be introduced in your reactive solution, that would be a good option as you mention, for you to measure the exact temperature in your system. Remember that this should always be accompanied by stirring (I suggest magnetic) to have homogeneity mainly. To do so, normally three-necked round bottom flasks are employed.
Hope this helps!
One other thing to keep in mind is that adding the base to the mixture may cause a temperature increase, either due to an acid-base reaction or simply due to heat of dilution. You may want to test for this issue in a separate experiment. Since the enthalpy of both the acid-base reaction and the mixture of aqueous solutions is a weak function of temperature, you don't need to try hard to hit the exact temperature in this initial experiment - the important data is the size of the temperature excursion.
If you don't want to use a regular thermometer or a thermocouple because of concerns about interference with nucleation, you can measure the temperature with an IR thermometer. This tends to be less accurate so it may be desirable to verify accuracy in a separate experiment.
Finally, note that working close to the boiling point of water will cause significant evaporation, which may affect both concentrations and temperature inside the vessel.
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