Extraction of Propionic Acid from Aqueous Solution


This laboratory investigation is purposed at familiarizing with the solvent extraction method of separation as a way of separating different components of the mixture as well as extracting the organic compound from the aqueous media. The experiment will also enable comparison of both single and multiple propanoic acid extractions from a solution that is aqueous into an organic phase and determining the propanoic acid concentration of the two phases after the removal.  Physical extraction comprises isolation of a solute into inert and non-reactive hydrocarbons as well as substituted hydrocarbons which are reasonably free of complexities. Different diluents exert different levels of dissolution which is dictated by two key factors. The first aspect is partial dissociation of an acid in an aqueous solution while the second factor is dimerization in a hydrocarbon phase. Also, the carbon-oxygen donor liquids in water of hydration serve as an essential parameter in extraction.

Theory of solvent extraction

Sometimes it is necessary to isolate organic substances from aqueous solution using the extraction method.  This technic involves shaking the mixture with another solvent that is immiscible in a separator. If the correct organic compound is chosen, a more substantial fraction of the organic compound will be easily transferred from the aqueous phase into a water-immiscible organic phase. The compound is the collected via separating the two layers as well as well as evaporating off an organic solvent.

The chemical extraction technique utilizes extracting chemical which varies according to the substance under extraction, kind of equipment used and its mode of operation. This particular experiment is limited to solvent extraction where an organic solvent is utilized as an extractant. The technique is only limited to substances that have low molecular weight because it is least useful for organic compounds with very high molecular weight and highly hydrophilic. This process is augmented with other techniques including crystallization and sublimation. The distribution/partition coefficient plays a vital role in this method of extraction. A solution is poured into a separating funnel and thoroughly shaken together with an immiscible solvent. The compound being extracted dissolves in part in the two layers. The compound distributes or partitions themselves between the two layers. The partition coefficient is, therefore, established when equilibrium is achieved, and the concentration ratio of every segment is constant for every system.

Partition coefficient, K = (Molarity in organic phase/Molarity in the aqueous phase)

In this case, the partition coefficient is a ratio between the concentration of a compound in the organic layer and the aqueous layer. This value is easily approximated by using solubility data although actual values of K are experimental.

The solvent for extraction

A good solution needs to have very minimal solubility in water, and it should be volatile for easy evaporation from a substance it is extracted. The organic content needs to have high solubility in an extracting solvent compared to solubility in water, and it should be unreactive when in water and the material being extracted. In this experiment, diethyl ether will be used as an extracting solvent because it is known to be inert, easily removed from the mixtures, and dissolves many organic compounds. Care should, however, be taken because ether is a flammable substance.

The extraction process is demonstrated by the following dissociation:

CH3CH2COO2 + Na+ + CL + H3O+               CH3CH2COOH + Na+ + Cl + Water


Fifteen grams of CH3CH2COONa+ was weighed and placed in a 250ml beaker and dissolved in 65ml tap water. A volume of 30ml 6M HCl was added followed by stirring with the stirring rod. Twelve grams solid NaCl was added to a solution and the mixture stirred for 2 minutes which facilitated “salting out.” The aqueous solution was then transferred into the separating funnel from the beaker and the aqueous solution extracted using diethyl ether.

  CH3CH2COONa+ Hydrochloric acid Propionic acid Sodium Chloride
Molecular Weight 96.1g/mol 36.5mol/mol 74.1g/mol 58.5g/mol
No. of moles 0.1561     0.2041
Grams 15     12
Density   1.19g/ml    


In the calculation of the % yield, the moles of the product obtained after distillation needs to be calculated followed by calculation of the number of moles expected to be extracted from the weight of sodium propionate that was started.

The chemicals used include:

Name Amount/Volume
CH3CH2COONa+ 15g
NaCl 12g
H2O 65ml
HCl 30ml


The chemical equation for the reaction is:

  CH3CH2COONa+ Hydrochloric acid CH3CH2COOH Sodium Chloride
Molecular Weight 96.1g/mol 36.5 g/mol 74.1g/mol 58.5g/mol
Grams 15g   10.90g 12g
Moles 0.1561   0.1471  


Theoretical yield:

No. of moles = M/ MW

CH3CH2COONa+ = 15g / 96.1 g/mol

= 0.1561 moles

Recovery yield:

No. of moles = mass/ MW

=10.90g / 74.1

= 0.1471 moles


The yield = (0.1471) / (0.1561 x 96.1) x 100

= 72.67%

The percentage yield:

= (0.1471) / (0.1561) x 100

= 94.23 %




The experimental investigation above reveals that propionic acid was successfully recovered from the aqueous solution into the organic solvent (ether). This particular solvent can be regenerated to produce pure acid and therefore extractive separation, as well as the recovery process, usually constitutes two steps including solvent regeneration and extraction. Propionic acid is an oily colorless liquid but the color observed was bright yellow indicating the presence of impurities in the distillate. Anhydrous MgSO4 effectively removed water since no droplets were detected in the ether solution meaning the aqueous solution was removed entirely after distillation.

MgSO4 + n H2O —–> MgSO4 n H2O (S)

If you are not sure about which among the two layers in the separating funnel is aqueous during extraction of an aqueous phase with the use of a non-polar solvent, drops of water can be used for identfication. Add s drop of H2O and examine whether it mixes with the topmost layer or it remains undissolved as a droplet within this layer. If the water droplet homogenously distributes itself, then it can be concluded that the top layer is an aqueous component. But if a droplet is formed, then it can be concluded that the top layer is organic. Sometimes it is difficult to trace where water droplets go and therefore it is important to check the volumes of the two layers. The layer that increases when water is added is the aqueous layer while the other layer is organic. An alternative to this method is consideration of relative volumes of organic and aqueous solvents concerning the quantities utilized in the laboratory.


Water and diethyl ether are immiscible solvents and therefore sodium propionate distributed between the aqueous and organic phase due to a difference in the distribution coefficient of the two liquids. HCl acid was used to break the sodium propionate compound into its corresponding ions to allow for extraction using diethyl ether.

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