6-14: Study of Acid-Base Titrations-Polyprotic Acids (Virtual ChemLab) OVERVIEW:

Question

6-14: Study of Acid-Base Titrations-Polyprotic Acids (Virtual ChemLab)

OVERVIEW:

The buret will be filled with NaOH, and 25.00 mL of H2SO3 will be in the beaker with the thymol blue as an indicator. At this point, I opened the stopcock and let the volume reach 40mL.

(the beaker contains 0.2556 M H2SO3 and the buret contains 0.3106 M NaOH.)

QUESTION:

What would cause the changes in the level of conductivity throughout the experiment?

Below is the data collected throughout the experiment.

Volume pH Conductivity 0 1.3 23.29 0.05 1.3 23.19 0.15 1.31 23.01 0.54 1.35 22.37 1.04 1.38 21.24 1.43 1.41 20.58 1.83 1.43 19.95 2.24 1.47 19.39 2.54 1.5 18.98 3.05 1.54 18.48 3.36 1.55 18.05 3.85 1.59 17.57 4.24 1.62 17.23 4.54 1.64 16.98 4.93 1.67 16.69 5.43 1.71 16.36 5.83 1.75 16.13 6.12 1.77 15.98 6.63 1.8 15.72 7.13 1.86 15.49 7.53 1.87 15.34 7.93 1.91 15.21 8.33 1.94 15.08 8.84 1.99 14.94 9.14 2.02 14.87 9.63 2.05 14.76 10.02 2.1 14.68 10.42 2.14 14.61 10.82 2.17 14.55 11.21 2.22 14.49 11.31 2.22 14.47 11.71 2.27 14.42 12.11 2.33 14.39 12.32 2.34 14.37 12.51 2.37 14.34 12.77 2.41 14.32 12.83 2.43 14.32 12.88 2.42 14.32 12.93 2.44 14.32 12.99 2.45 14.3 13.04 2.45 14.32 13.28 2.5 14.3 13.48 2.53 14.29 13.63 2.54 14.28 13.88 2.59 14.26 14.08 2.63 14.24 14.44 2.71 14.22 14.84 2.81 14.21 15.25 2.95 14.19 15.64 3.15 14.2 16.04 3.44 14.18 16.44 4.33 14.23 16.94 5.3 14.67 17.34 5.56 15.04 17.74 5.74 15.4 18.15 5.87 15.75 18.56 5.98 16.07 18.96 6.06 16.39 19.26 6.12 16.6 19.75 6.19 16.94 20.14 6.27 17.22 20.54 6.31 17.48 21.05 6.39 17.78 21.44 6.44 17.96 21.84 6.48 18.19 22.24 6.52 18.48 22.64 6.57 18.68 22.94 6.59 18.83 23.44 6.65 19.08 23.83 6.69 19.27 24.23 6.74 19.45 24.63 6.78 19.63 25.13 6.82 19.83 25.53 6.85 19.99 25.93 6.9 20.15 26.33 6.95 20.3 26.73 7 20.44 27.12 7.04 20.56 27.52 7.08 20.71 27.93 7.12 20.82 28.31 7.17 20.92 28.71 7.22 21.06 29.1 7.28 21.14 29.5 7.34 21.27 30 7.42 21.41 30.39 7.5 21.46 30.78 7.58 21.59 31.18 7.67 21.66 31.57 7.8 21.74 31.98 7.97 21.82 32.38 8.24 21.89 32.79 8.94 21.96 33.19 11.09 22.17 33.49 11.38 22.57 33.89 11.59 22.96 34.38 11.76 23.39 34.77 11.86 23.75 35.17 11.94 24.11 35.48 12 24.37 35.98 12.06 24.79 36.38 12.12 25.1 36.78 12.16 25.43 37.07 12.18 25.66 37.57 12.23 25.97 37.96 12.26 26.33 38.36 12.29 26.64 38.77 12.32 26.93 39.06 12.34 27.14 39.56 12.36 27.48 39.82 12.38 27.66 39.87 12.38 27.69 40.22 12.4 27.95

Explanation / Answer

Since the titration is between an acid and an base initially the presence of H+ and SO3-2 Shows certain higher conductivity as titration proceeds there will be neutralisation of H+ ions followed by salt formation hence conductivity decreases continously upto a volume of 15.25 ml of NaOH added.

From 15.25 to 15.64 conductivitry remains constant and at 15.64 there is again increase in conductivity due formation of OH- ions in the solution now the solution starts showing alkaline conditions as the acid taken is completly neutralised. since the titration is of weak acid and strong base there is a gradual change in conductivity.

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