Acidity Value Lab Report

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Discussion:
Acidity number or acid value is defined as the mass of sodium hydroxide expressed in milligram used to neutralize one gram of acidic substance. This measurement is very important in order to understand the substance’s long term stability and corrosiveness in order to compare the quality of the oil. Fats are converted into fatty acid and glycerol during rancidification and increasing acidity of the sample. More sodium hydroxide is needed to neutralize the acid, and hence acidity number increases. (Peter.J.W, 2007) Therefore, the smaller the acidity number, the higher the quality of the oil. Free fatty acids concentration affects oil recovery and it determines the grade and price of the oil. Rancidification lowers nutritional value …show more content…

As the sodium hydroxide is added to the oil sample, the free fatty acids will undergone neutralization to form sodium carboxylate and water. Purple color can be observed due to alkaline and must last for 10 seconds to resemble as an endpoint of the titration.



Based on the Table 2, the A4 oil sample has the highest free fatty acids among all the six oil samples, followed by A2, A1, A3, A6 and A5. Therefore, A5 oil sample can be said that it has the highest quality. By comparing the results given, we have found some possible oil for our oil samples, A3 and A4. According to Peter J.W (2007), the possible oil for A3 and A4 are refined olive oil and soybean oil respectively.



According to Frank D.G (1994), acid value could be determined by the potentiometric method. Potentiometric titration uses an electrode to detect the change of electric potential instead of phenolphthalein. This is a more accurate and common method for highly colored oil or fats. The free fatty acids are in non-aqueous medium, titrating with a solution of potassium hydroxide in isopropanol. There are other numerous methods to determine acid value, such as Thermometric titration, measurement of metal-fatty acid complexes, enzymatic methods, methods using a fatty acid binding protein and spectroscopic methods (Cyberlipid, n.d). Chemical titration is suitable for this experiment because it is low in cost, simple oil samples

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