P H Titration of Vinegar PDF

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Okasha 1 Ossama Okasha CHEM1212 Lab Dr. Kelly March 26, 2018 pH Titration of Vinegar Introduction The purpose of this lab was to determine the extent of ionization and the Ka for a weak acid using titration. The pH of the solution was monitored when adding the strong base (NaOH) to the weak acid (acetic acid). The chemical reaction is represented by the following equation:

CH3COOH + NaOH

-

H2O+ CH3COO Na+

Acetic Acid reacted with NaOH and produced H2O where the Hydrogen from acetic acid was donated to OH, and the Acetic acid reacted with Na+ which formed salt and water, since this was a weak acid and strong base titration, in weak acid and strong base titration, the products were H2O and salt. It is an acid-base reaction when reacting with each other we get water and salt as shown in the equation above. The acid-base titration lets you determine the concentration of an acid or a base by neutralizing the acid or base with a known concentration of the acid or base. Titration is performed between two known identities of liquids, to find the unknown liquid’s concentration, the other liquids concentration should be known. The titrant is the solution with the known concentration and placed in the burette, whereas the titrand, whose concentration is unknown, is usually placed in the Erlenmeyer flask. This lets for measurable analysis of concentration the unknown acid or base solution which also neutralizes the reaction between acids and bases. Acid constants Ka and Pka are also determined from a pH titration graph. Redox titration has been used in the past. It involves an oxidation and reduction reaction between the titrant and the titrand, one of the solutions oxidizes and the other reduces. When either of the solution oxidizes, it releases electrons thus raises its oxidation number. When a solution gets

Okasha 2 reduced, it takes accepts electrons, thus reduces its oxidation number. At the end, either the titrand or the titrant produces a color. In acid-base titration a pH meter indicates the end of the titration process. The main difference between both titrations is that acid-base titrations includes an acid and a base while redox includes two redox solutions. Acid-base titration are more precise because it can be used with any acid and base whereas redox are commonly seen in the d block elements (Difference Between). Procedure A 50.00mL buret was obtained with a stand, the buret was washed several times with DI water and then rinsed with the prepared 0.112M NaOH. The Buret was filled with the prepared NaOH and the concentration was recorded. A 20.00mL pipet was obtained and washed with water then rinsed with vinegar stock solution. The pipet was used to transfer 20.00mL of vinegar stock solution into the 100mL beaker. The electrode was connected to the computer and was immersed into the vinegar solution and the initial pH was recorded. The standardized NaOH solution was added in 1mL increments, after each increment has been added the beaker was swirled and the pH of the solution was recorded along with the volume of NaOH solution added. As the equivalence point was approached, the pH changed drastically, and the increments was reduced to 0.25mL. The titration process was continued till the pH leveled off again. This acid-base titration was done with two trials. For the first trial 33.00mL was used because the stirring bar was not fully immersed along with the electrode. For this reason, the stir bar and the stir plate were not used, instead the beaker was swirled after each increment. DATA

Okasha 3 Results There wasn’t much observation, the solution stayed colorless, even when the NaOH was added to the acetic acid. The table of pH and volume of NaOH was recorded and the graph of pH Titration was also obtained along with its second derivative for the equivalence point. The pH increased drastically when it got to the end point. No indicator was used in this titration that determined the end point, it was determined by the pH reader when the pH drastically increased and leveled off again by looking at the graph while the experiment was being performed. At around 20.00mL of NaOH was being added to the 20mL of acetic acid, the pH increased drastically. This experiment showed the relation of M1V1=M2V2, when the NaOH had almost equal amount of vinegar in the solution which was the equivalence point.

Setup of titration(Titration) Trial 1 Molarity of NaOH Solution

0.112M

Volume of NaOH solution added at equivalence

32.93mL

point Volume of NaOH solution added at halfway point

16.47mL

The Ka and pKa values determined from the initial

Ka=2.52x10-4

pH and the equivalence point data The Ka and pKa values determined from the

pKa=3.59 pKa=4.72

halfway point Percent ionization

Ka=1.905x10-5 4.81%

The Percent(mass/volume) acetic acid in vinegar

6.55%(g/ml)

pKa value from literature

4.75

Percent error for pKa values

Initial: 24.42%

The percent error in acetic acid

Halfway point: 0.63% 31%

Molarity of NaOH Solution

0.112M

Volume of NaOH solution added at equivalence

19.65mL

point Volume of NaOH solution added at halfway point

9.825mL

Okasha 4 The Ka and pKa values determined from the initial

Ka=7.16x10-6

pH and the equivalence point data The Ka and pKa values determined from the

pKa=5.14 pKa=4.85

halfway point Percent ionization

Ka=1.41x10-5 0.82%

The Percent(mass/volume) acetic acid in vinegar

6.37%(g/ml)

pKa value from literature

4.75

Percent error for pKa values

Initial: 8.21%

The percent error in acetic acid

Halfway point: 2.10% 27.4%

Trial 2

Conclusion The acid-base titration technique was learned, some data were found that helped to calculate along with the volume of NaOH solution added at equivalence point, volume of NaOH solution added at halfway point. Calculated the pKa and Ka values from initial and halfway point along with the percent ionization. Percent (mass/volume) of acetic acid in vinegar was also calculated. The deference between endpoint and equivalence point was understood, learnt the chemical equations and equilibrium constants, identified the equivalence point in an acid-base titration from the pH titration curve. And identified the half-equivalence point from the pH titration curve. The pH titration curve was used when determining the value of Ka and pKa. A smaller beaker, a stir bar and a stir plate would be used for better results, the small beaker would be used so that the electrode attached to the stir bar can be immersed in the vinegar solution. Also, the when adding the NaOH increments of 1mL, it would be added slowly so it could be swirled to react with the solution in the beaker. Furthermore, do both trials with same amounts of vinegar. However, the halfway point is more precise in determining the Ka for acetic acid because at halfway point the ratio between acid and the base is 1:1. If I was working in an industry and I was verifying the purity of the vinegar I would send the vinegar back because my percent error is high compared to the actual percent, for trial one my percent error was 31% and trial 2 was 27.4%. However, the actual concentration is 5%, there is a big difference in these values.

Okasha 5

Okasha 6 Works Cited “Difference Between Acid-Base Titration and Redox Titration.” Pediaa.Com, Pediaa, 3 Dec. 2015, pediaa.com/difference-between-acid-base-titration-and-redox-titration/. “Titrations.” Chemistry102, North Carolina State University, www.webassign.net/question_assets/ncsugenchem102labv1/lab_9/manual.html....