Chemistry Acetic Acid

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Determining the Molarity of Acetic Acid in Vinegar

Abstract
This experiment was done to determine the molarity of acetic acid in vinegar. The acetic acid in vinegar was titrated with a strong base sodium hydroxide to determine the equivalence point of this chemical reaction. The indicator phenolphthalein was used because the moment it changes color is on the basic side of the pH scale. To insure the experiment was done with the most accuracy, the two conductors of this experiment took three different trials to attempt to reach the best endpoint possible between the two. After punching in numbers and calculating results through a stoichiometry equation, the resultant molarity was .960M, but the actual molarity was .845M. We found that it took 9.60 mL of NaOH to neutralize 10.00 mL of acetic acid. These results left the individuals experiment with a percent error of around 13.6%. There were many places where human error could have affected the results of this experiment. If burettes are used properly, the issues should become less prominent.

Introduction and Background Information
Within vinegar, acetic acid is the second most prominent component that can be found. This experiment explores acids and bases in common everyday forms. In this conducted the individuals running the experiment will determine the concentration of acetic acid after taking a sample of vinegar and titrating the acetic acid with a strong base (sodium hydroxide). The chemical equation for the chemical reaction observed in this particular lab is shown below. HC2H2O2 (aq) +NaOH (aq) NaC2H3O2 (aq) +H2O (l)

When the starting amount of moles of H+ from the acetic acid (HC2H2O2) is completely neutralized by the exact number of OH- ions from the sodium hydroxide (NaOH), the equivalence point of the titration has been met. The equivalence point of weak-acid and strong-base titrations are for the most part basic and because of this, an indicator must be chosen that changes color in the basic region of the pH scale. The indicator used for this particular experiment was phenolphthalein which is colorless in acid and red/magenta in base. Purpose

In this experiment, the conductors of the experiment are going to determine the concentration of acetic acid in a vinegar sample by titrating the acetic acid (HC2H2O2) with the strong base that is sodium hydroxide (NaOH). Materials List

Pipets| Vinegar| Indicator (phenolphthalein)|
Sodium Hydroxide (1.00M)| 50 mL burette for NaOH| One 150 mL Erlenmeyer flask|

Procedures amd Description of Experimental Set-up
1. Obtain 10.00 mL of vinegar into the Erlenmeyer flask.
2. Record the brand of vinegar used.
3. Add 2-3 drops of indicator solution (phenolphthalein). Swirl around your flask to make sure the solution is mixed well. 4. Record Molarity of base (NaOH).
5. Drain enough sodium hydroxide into the waste bucket so the tip of the burette is filled without air bubbles. Make sure to go slowly or the amount of base may go below the meniscus. 6. Record the initial volume reading of the NaOH to the nearest .01mL. 7. Titrate first sample with good mixing to indicator endpoint. The solution should be a pale pink that is neither too light nor too dark. 8. Record final burette reading to the nearest .01mL.

9. As refilling the burette, use no more solution hydroxide than needed. 10. When completed, clean up glassware and the entire station used. Trial Number| Initial Volume| Ending Volume| Total Volume Used| 1| 50.00 mL| 40.25 mL| 9.75 mL|

2| 40.25 mL| 30.50 mL| 9.75 mL|
3| 30.50 mL| 20.90 mL| 9.60 mL|
Data
Total Volume of Vinegar| 10.00mL|
Molarity of Vinegar Sample| .960M|
Average Molarity| .875M|
Relative Standard Deviation of Class Data| .0430M|
Number of Grams contained in 10.00mL of Original Vinegar ( % concentration of vinegar)| .576g HC2H3O2| Correct Value for Molarity of Original Vinegar| .845M|
Percent Error in...
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