The Dependence of Distribution Coefficient Upon pH Case Study Sample

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Introduction to The Dependence of Distribution Coefficient Upon pH - A Case Study Sample

Acid Benzoic is an acid (organic) that, because of its weak nature, can be found in everyday products such as pharmaceuticals, food products and many industrial processes. This behavior followed by its effective partitioning efficiency between phases of aqueous/organic are of general importance when considering its bioavailability and the distribution of the substance in the biological as well as environmental systems. “In this laboratory experiment, the spectrophotometric analysis of acid benzoic and the acid benzoic distribution between aqueous and ethyl acetate buffer solution prepared in this experiment at different pH values will be determined.

In the first part, the calibration curve was prepared with solutions that are standard of acid benzoic solubilized in acetate of ethyl. UV-V was used by this spectrophotometry for the determination of the 270 nm absorbance, and the molar coefficient of absorption was determined through the Beer-Lambert Law formula usage. This coefficient is used later in other experiments for the concentration determination of acid benzoic.

Second part and part 3 was to determine the DDD at pH values of 7.0 and 6.0. For the determination of the amount of acid benzoic have equilibrated, both solutions of acid benzoic in acetate ethyl were equilibrated with the buffer solutions that is aqueous at the indicated values of pH and the acid benzoic concentration which remained inside ethyl acetate layer estimated previously through the spectrophotometry usage. The concentration related to aqueous phase was determined based on the concentration that is initial, and the depletion measurement in the phase of organic was also investigated (Kochetkova et al. 2023).

Finally, in the last section of the experiment, coefficient of partition (DpH6.0, DpH7.0) were calculated as the concentration of benzoic acid in the organic phase over the concentration of benzoic acid in the aqueous phase. The outcome confirmed pH influence on benzoic acid’s distribution, an attribute of ionization and solubility tested under different conditions.

Aim: For the determination of the molar coefficient of absorption of acid benzoic and analyze its behavior regarding phase distribution in ethyl acetate and aqueous buffers of 6.0 pH, and 7.0 pH.

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Methods

In the first section, the benzoic acid standard solution was prepared by weighing 0.244 grams and dissolving it in ethyl acetate to a concentration of up to 1 dm3. As shown on the following page, the five standard solutions were prepared by aliquoting 2.5 microliters of the stock solution into five separate tubes and adding an increasing volume of ethyl acetate. Each solution's absorbance was accurately transferred to a spectrophotometer cuvette, where it was measured at 270 nm. The calibration curve, which was generated by plotting absorbance against concentration, was used to accomplish this. The flask's contents were allowed to separate for some time before the stirrer was turned off, resulting in two distinct phases. Using a pipette, the videos of the upper layer were carefully transferred, and the ethyl acetate layer's absorbance at 270 nm was recorded. The diffused benzoic acid concentration in ethyl acetate solution was chosen based on the first part of the molar coefficient of absorption (Karimova et al.). 2023). After partitioning with ethyl acetate, the difference between the initial concentration and the concentration in the layer of aqueous buffer was used to determine the concentration of benzoic acid. Each compound's equilibrium concentration in the ethyl acetate phase was divided by its equilibrium concentration in the aqueous phase to calculate the packet apparent coefficient of distribution (DDD) for each pH.

Materials

Results

Part 1.

Figure 2: Calibration plot

The Dependence of Distribution Coefficient Upon pH Case Study Sample

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R2 = 0.1543 and y = -0.0159x + 0.0868 are the Excel equations. The Lambert-Beer equation shows that the relationship between the substance's UV absorbance and concentration is A = εcl

There, the length of the path is 1 cm. Consequently, = 0.0159 M-1.cm-1 (mol. dm-3 cm-1) The calibration plot was created in order to obtain the appropriate coefficient of molar absorption () of benzoic acid in the appropriate ethyl acetate. A stock solution of benzoic acid was made, and one was diluted to make five different concentrations. The dilution solution formula was used to determine the concentration parameter. A spectrophotometer was used to measure each solution's absorbance at 270 nm to document these effects (Mishra 2021). Excel estimated the equation as y = -0.0159 x + 0.0868, and the value of R2 was determined to be 0.1543.

Part 2.

As a result, the effective partition at pH 7.0 yields a density of 0.0286 mol. dm3 for benzoic acid in ethyl acetate phase. The partitioning of the benzoic acid at a neutral pH of 7 was also determined by the experiment (Mishra 2021). The absorbance was 0.455 at 270 nm. According to the Beer-Lambert law, 0.0286 mol.dm3 of benzoic acid was present in the ethyl acetate solution (Chandni et al. 2023). Additionally, this result demonstrates that the organic layer contains a lower concentration of benzoic acid than when the extraction was performed at pH 6.0. At the conclusion of the second titration, more benzoic acid was present in the aqueous layer (Mishra, 2021). The effect of pH on partitioning is supported by this change in solubility.

Part 3.

There is only a footnote stating that the benzoic acid partitioning measurement was done at pH 7.0. Fifty milliliters of the prepared fifty millimolar phosphate–bicarbonate buffer was mixed with fifty milliliters of the 0.1 M benzoic acid stock solution and effectively stirred for ten minutes. The two layers were observed to have different densities hence the mixture was left to stand for a while so as to ensure valid separation (Karimova et al. 2023).

Part 4.

= 0.0013 mol. dm^-3

D_{pH 7} = ( 0.0286/ 0.0528 ) = 0.541

The aqueous buffer's concentration was determined to be 0.0013 mol.dm3. As a result, the D value at pH 6.0 AA was 61.62 (Ahn et al. 2024). At pH 7.0, the correct partitioning revealed a concentration of 0.0286 mol.dm3 in ethyl acetate. At pH 7.0, this was found to be the case with the D of 0.541. In particular, it has been discovered that benzoic acid prefers the aqueous layer at a pH of 7.0 and partitions more efficiently in ethyl acetate at a pH of 6.0. This demonstrates that a significantly higher concentration of benzoic acid molecules releases the ions that make it less soluble in the organic phase at a higher pH.

Discussion

The absorbance was measured to be 1.273 at the pH of 6.0 Thus, concentration of benzoic acid in ethyl acetate was calculated to be 0.0801 mol.dm⁻³. Before the partitioning, the concentration was 0.0814 mol.dm⁻³. This means that only 0.0013 mol.dm⁻³ of benzoic acid dissolved into the aqueous phase. The D at pH 6.0 was as low as 0.61562, meaning that the compound had a high preference towards the organic phase.

For a benzoic acid concentration of mol.dm3 in ethyl acetate, the absorbance was read at 7.0 and found to be 0.455. The findings also show that the partition coefficient decreases as the pH value rises steadily. This is because benzoic acid is a weak acid. At lower pHs, a greater number of molecules are non-ionized and more soluble in ethyl acetate, whereas at higher pHs, most molecules are ionized and more soluble in the aqueous phase (Mishra, 2021). Errors could come from improper pipette handling, improper phase separation, or inaccurate absorbance readings, among other things. Repeating the measurements to increase accuracy and possibly better separating the layers of solutions prior to measuring their absorbance could be future improvements (Salas et al. 2025).

Overall, the experiment correctly determined the partitioning properties of benzoic acid based on various pH levels. These results supported the pH activity of a variety of weak acids in both phases, which is important for its technical application in drug formulation and chemical extraction isolation.

Conclusion

This experiment sought to identify the distribution preference of the specific benzoic acid among ethyl acetate and the aqueous solution of pH 6.0 and pH 7.0. The values of partition coefficient factor (D) were obtained for the two pH values by using the spectrophotometric method at λ max and based on the law of Beer-Lambert. Benzoic acid at pH 6.0 was found to be partitioned mainly in the organic phase and the parameter D was found to be 61.62. At pH 7.0, there is a change of distribution in which more of benzoic acid was in the phase which is aqueous and D is 0.541. This shows that the effective solubility of benzoic acid is lesser at a greater pH so it reacts more with ethyl acetate solubility”. The observation obtained from the study can prove the effect of pH in partitioning and solubility of weak acids.

This test is very useful in pharmaceutical and chemical applications. It is a well understood fact that coefficients of partitions are used to determine the absorption, distribution and the efficiency of a particular drug sensor. The substances having an ionizable functional group are to be soluble in an aqueous solution, while the substances which do not contain an ionizable functional group are to be soluble in an organic solution.

The entire experiment was seen to be successful, and the outcome fitted the expected theory well. The study also agreed and confirmed that pH is a crucial role in the chemical partitioning studies, the drug preparation process, the extraction technology and environmental sample analysis.

Reference List

Journals

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