Sodium Acetate (CH3COONa) is the sodium salt of acetic acid. It has a wide range of applications. I’m going to prepare sodium acetate from vinegar (an acetic acid CH3COOH solution) and sodium bicarbonate NaHCO3. Then the extraction will be performed by crystallization, to get rid of vinegar non-volatile impurities.
I’m starting from 400g of vinegar that claims to be at 6%. Because I don’t titrate it, I don’t know the exact quantity of acetic acid in there. I’m going to proceed approximately. In 400g of 6% vinegar there are about 24 g of acetic acid (MM=60.052 g/mol) = 0.400 mol. I’ll need 0.400 mol of sodium bicarbonate (MM=84.007 g/mol) = 33.6 g.
Bicarbonate should be added slowly to avoid the “volcano effect” and prevent everything from messing up. The effervescence is caused by the forming carbon dioxide (CO2).
A basic pH indicates that the neutralization has been completed, due to sodium acetate basic hydrolysis. Now I’m going to heat the sodium acetate solution and force most of the water to evaporate, in order to obtain a saturated solution with sodium acetate (at that temperature). (I’m doing this in a well-ventilated area). When the first crystals of sodium acetate appear, the solution has reached the saturation. We add just few mL of water to re-dissolve them. Now the solution is saturated with sodium acetate at this temperature.
Cooling down the solution, the solubility of sodium acetate will drastically decrease, forming a supersaturated solution. Sodium acetate will eventually precipitate out as tri-hydrate crystals when a nucleation center is formed (chemically or mechanically).
This process is called crystallization.
After filtering off the precipitate, the remaining sodium acetate in the solution can be crystallized again, after evaporating more water, in order to obtain, again, a saturated solution. Excessive evaporation/crystallization cycles should be avoided, cause non-volatile impurities in vinegar could eventually precipitate out with the salt. Evaporating a lot of water in fact can bring the solution closer to the saturation point of some impurities, depending on their solubilities (ex. Sugar). And due to excessive heating cycles, impurities could be processed (ex. caramelization of sugar). This is an example of why preparation of sodium acetate is more efficient if started with distilled vinegar.
Sodium Acetate Tri-Hydrate melt at 57°C at normal conditions. To convert the tri-hydrate salt to the anhydrous form, a drying process is needed. Drying the salt (ex. in an oven at 150°C according to Doug's Lab*), the crystal’s water molecules are forced to evaporate off.
Due to the impurities of the white wine vinegar, which often inhibit the first crystallization of the salt, producing sodium acetate from wine vinegar is not the most efficient method. It is easier and cheaper to buy it online, or convert it from distilled acetic acid solutions. But it is an easy project to perform, in which acid-base reactions and separation processes are involved.
*Doug’s Lab “Easy Sodium Acetate Dehydration”: • Easy Sodium Acetate De...
From PubChem
Solubility of Sodium Acetate Anhydrous at 100°C = 170.15 g/100mL
Solubility of Sodium Acetate Tri-Hydrate at 20°C = 46.5 g/100mL
Solubility of Sodium Acetate Tri-Hydrate at 0°C = 36.2 g/100mL
Solubility of Sodium Acetate Tri-Hydrate at -10°C = 32.9 g/100mL
Disclaimer: The following process is shown only for demonstration and entertainment purposes. It should not be replicated without proper knowledge.
Recorded with a NIKON D7500 Digital Camera, DX SWM VR ED IF Aspherical 72 , Edited with Camtasia 9.
5 окт 2024
