Ravi Prapharsavat IB chemistry SL2 September 16, 2010 Determine the acetic acid in commercial vinegarIntroduction: The research being conducted in the lab is to prove that commercial vinegar contains fivepercent of acetic acid, by titration method. As acetic acid is an organic compound, it reacts with basessuch as NaOH to form salt and water.CH3COOH+ NaOH NaCH3COO+ H2O Equation: 1 The balanced chemical equation for neutralization of acetic acid with NaOH, and theequivalence point of this neutralization reaction can be determine using a chemical indicator to signalthe end point such as Phenolphthalein. The titration method is that a drop of a solution (substance, in this case NaOH and vinegar) toanother solution (substance, in this case Vinegar and NaOH with indicator) to determined theconcentration. The drops continue until the titration meets the End Point, which is the sudden changein a physical property, such as the indicator color (in this caseit turns pink). The standardization is thenuse, whereby the concentration of a reagent is determine by reaction with a known quantity of a secondreagent. Therefore, according to the theory of titration and acetic acid reacting with NaOH, thestandardization should give a percentage of how much acetic acid is in the commercial vinegar.Design:Research Question: Prove that commercial vinegar contained 5% of acetic acid.Control Variables: NaOH (constant amount), Vinegar (constant amount), and phenolphthalein (constantdrops)Dependent Variables: the amount used by the NaOH and vinegar solution in the burretIndependent Variable: the constant amount and concentration of the solutions (NaOH, Phenolphthalein,and vinegar)Equipment: 125 mL Erlenmeyer flasks, 50 mL beret, beret stand and clampChemical: o.5 M. of NaOH, Phenolphthalein (chemical indicator), and commercial vinegar claiming tocontain 5% acetic acidProcedure: Pour 20mL of vinegar into the 125 mL Erlenmeyer flask
Fill the burret with 50 mL of NaOH solution Add 4 drops of the chemical indicator to the vinegar solution in the Erlenmeyer flask Perform the titration until the vinegar and indicator solution turns and remains light pink Record the final volume of NaOH solution inside of the burret Perform this experimentation another two times. When finish the trials, repeat it again three times but is time with vinegar in the burret Using the volume and the molarities of NaOH, and the volume and density of vinegar, the percentage of acetic acid will be calculatedData Collection and Processing: NaOH ReadingTrials Initial volume of NaOH Final volume of NaOH Volume of NaOH used in Burret (mL) ±0.05 in Burret (mL) ±0.6 (initial volume-Final volume) (mL) ± 0.61 50.0 13.5 36.52 50.0 14.5 35.53 50.0 15.8 34.2 Average 14.6 35.4Table 1: indicate the NaOH solution as it comes to the end point, where the solution used in theErlenmeyer flask. Vinegar ReadingTrials Initial volume of Final volume of Vinegar Volume of Vinegar Vinegar in Burret (mL) in Burret (mL) ±1 used (initial volume- ±0.05 Final volume) (mL) ± 11 50.0 28.1 31.12 50.0 29.0 33.23 50.0 30.2 32.1 Average 29.1 32.1Table 2: indicate the vinegar solution as it comes to the end point, where the solution used in theErlenmeyer flask.
Density of Vinegar = 1.01 g/mLMolarity of Vinegar= 0.5 MTrue value of CH3COOH= 5.00 %Sample Calculation:Uncertainties:Example:Calculation of the percentage of acetic acid in commercial vinegar:
Conclusion and Evaluation: The commercial vinegar does not contained 5% of acetic acid as it is stated in the bottle,however it is possible. The percentage of CH3COOH in the sample vinegar is found to be 3.3%, however,the label indicate that its 5.00%, which gives the deviation of the experimental value from the true valueto be 1.7. By using the true value, a percentage error was calculated to be 4.5%; the experimentalpercentage of CH3COOH in the vinegar sample is lower than the true value. There are two weaknesses that have been encounter in this experimentation. One possible errorthat might be taken to an account is how the titration could past the true equivalence point of thereaction. By being accurate in the color change will result in a less NaOH or vinegar value used in theburret. Another weakness that is encountered in the experimentation is: the solution is sometimesmixed with water, and therefore causes the acetic acid as well as NaOH to be less concentrated;resulting in reacting slower (turning pink slower). The solutions, such as the vinegar and NaOH, are leftopen on the table. Therefore the molecule evaporate, leacing it with mostly water, which the acetic acidand NaOH will become less concentrated. If the NaOH and the vinegar are new and the lids are close,the result might indicate a smaller volume of NaOH used, which increase the percentage of the aceticacid.