Use the following experimental titration data to calculate the unknown concentra

Question

Use the following experimental titration data to calculate the unknown concentration and pH of the acid. The initial solution of acetic acid is clear and colorless. A few drops of phenolphthalein indicator are added to each sample. A dilute solution of potassium hydroxide is used as the titrant. As the mixture reaches the endpoint, flashes of pink color are seen and the titrant is added drop by drop. The endpoint is reached when one drop of titrant turns the mixture a pale pink color that does not fade.

Explanation / Answer

Trial 1

Volume of KOH added = 25.30mL

N1V1= N2V2

25.3 x 3 x 10-4 mol/L = N2 x 10

N2 = 7.6 x 10-4 mol/L is the acetic acid concentration

Trial 2

Volume of KOH added = 50.51-25.30 = 25.21mL

N1V1= N2V2

25.21 x 3 x 10-4 mol/L = N2 x 10

N2 = 7.56 x 10-4 mol/L is the acetic acid concentration

Trial 3

Volume of KOH added = 75.89-50.51 = 25.38mL

N1V1= N2V2

25.38 x 3 x 10-4 mol/L = N2 x 10

N2 = 7.61 x 10-4 mol/L is the acetic acid concentration

Average acetic acid concentration is 7.61 + 7.56 + 7.61/3 = 7.59 x 10-4 mol/L

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