Title: Determination of Acidity Number in Fatty Acid
determine the acidity ac idity number in fatty acid. Objective: To determine Introduction:
A fatty acid is a carboxylic acid with a long aliphatic tail, which is either saturated or unsaturated. It is also a large group of monobasic acids that found in animal and vegetable fats and oils. Fatty acids have the general formula
C n H 2 n+1 COOH
. Fatty acids are usually
derived from triglycerides or phospholipids. It is a important source of fuel because when metabolied, it yield large !uantities of AT". In chemistry, acid number is the mass of potassium hydroxide # $%& ' in milligrams that is re!uired to neutralie one gram of chemical substance. The acid number is a measure of the amount of carboxylic acid groups in a chemical compound, such as fatty acid or in a mixture of compound. As fats rancidify, triglycerides are converted into fat ty acids and glycerol, causing an increase in acid number. Therefore, the smaller the acid value, the higher the !uantity of oil. Reagents:
(. )tandard )tandard potassium potassium or sodium sodium hydroxi hydroxide, de, *.*+N *.*+N for for refined refined oils oils +. "henol "henolpht phthale halein in indic indicato atorr soluti solution on . Isop sopropanol Apparatus:
(. -urette, -urette, +m/ +m/ with graduation graduation in *.*m/ *.*m/ divisions divisions +. 0rlen 0rlenme meye yerr flas1 flas1,, +* +*m/ m/ . 2easuri 2easuring ng cylin cylinder der,, *m/ *m/ and (**m (**m/ / 3. -ea1 -ea1er er,, *m *m/ / and and (** (**m/ m/ . &ot plate plate with with tempera temperatur turee contr control ol 4. Anal Analy ytica ticall bala balanc ncee 5. Funnel 6. Thermo rmometer ter 7. 8etort sta stand (*. Droppe Dropper r Procedure:
(. The oil sample A was weighed for +.* g in an 0rle nmeyer flas1. +. *ml of the neutralised solvent #isopropanol' was added into the sample . . The flas1 was heated and regulated on the hot plate to temperature of 3*9:. 3. A few drops of "henolphthalein were then added into the flas1. f las1. . The 0rlenmeyer flas1 was titrated with sodium hydroxide until the colour of solution changed to a first permanent pin1 that stayed for (* seconds. 4. The volume used for titration were recorded down for observation. 5. )tep ( to 4 were repeated by changing the oil sample to - and :.
Results:
Type of oil sample A :
;eight of oil sample#g' + + +
Calculation: 25.6 x N x V
FFA = as palmitic acid >
W
;here N> normality of Na%& solution <> volume of Na%& solution used in m/ ;> weight of sample
For oil sample A? 25.6 x 0.02 x 2.40
FFA = as palmitic acid >
2
> *.4(33=
For oil sample -? 25.6 x 0.02 x 6.65
FFA = as palmitic acid >
2
> (.5*+3=
For oil sample :? 25.6 x 0.02 x 1.05
FFA = as palmitic acid >
2
> *.+466=
Discussion
In determination of acidity number in fatty acid, a !uantity of potassium hydroxide act as a base is re!uired to neutralie the acidic constituents in (g of sample. Acidity number is used to describe the amount of acid present in an oil #fatty acid'. The acidic value is also the mass of sodium hydroxide needed to neutralie one gram of chemical substance, in this case which is the fatty acid. In the beginning of the experiment, the oil samples is added with isopropanol as a solvent. It helps in simplifying the titration without the need of using violent sha1ing for the reaction to be happened. During the titration, an indicator is added into the solution which is phenolphthalein. "henolphthalein has two form in different condition, when it is in acidic form, it is colourless, yet it turn to pin1ish white when &@ ion is removed and the solution is turning base form. Therefore, phenolphthalein act as the indicator for this experiment. )odium hydroxide is being titrated slowly into the solution until the indicator changed its colour. The Na%& solution has the reaction of? &%@#a!' @ %&#a!' B &+%#l' If the &%@ is still remaining in the solution of 0rlenmeyer flas1, the phenolphthalein will remain colourless, when there is enough Na%& solution titrated into the solution, reaction is complete, colour changed. The volume of Na%& used to titrate can help us to calculate the acidity of fatty acid. The FFA we obtain from our calculation are the result of bro1en down oil. FFA = is used to describe the free fatty acid contents of oil, while acidity number only describe the FFA content of completed biodiesel. FFA = is calculated by the weight to weight ratio of FFA found in the content with the formula of FFA= > +.4 x N x < C w. To calculate this value, we need the volume of Na%& solution used in ml, normality of Na%& and the weight of the sample. All of this result can be obtained in our table. &ence, we can calculate the FFA percentage of all sample and conclude with a trend.
In this experiment, oil sample : has the lowest FFA= as palmitic acid which is only *.+466=. Thus, it has greater stability in triglycerides form. 2eanwhile, for oil sample -, it has the greatest FFA= as palmitic acid which is (.5*+3=. Therefore, its triglycerides are more readily to convert into fatty acid and glycerol. During the experiment, there are a few matters that has to be concerned of to get the best result. First of all, when weighing the oil sample, the mass of flas1 must be minus out from the overall mass. Next, the accuracy of it must not more or less than *.* g to ensure best result. 2oreover, during titration, the sodium hydroxide solution must be added drop by drop to ensure precise result for titration. If the sample in the flas1 changed its colour to pin1,e turn off the burette so that no excess of sodium hydroxide is lea1ed out of the burette. Furthermore, the colour of sample must stay at least for (* seconds to ensure that the titration is complete. /ast but not least, after the experiment, all the flas1s must be cleaned with soap as it is oily. Conclusion:
%il sample : has the lowest FFA= as palmitic acid which is only *.+466=. Therefore, it has greater resistance towards rancidification.
