2. Following the Procedure of this experiment, a student titrated 0.653 g of an

Question

2. Following the Procedure of this experiment, a student titrated 0.653 g of an unknown weak, monoprotic acid with 0.100M NaOH and monitored the titration with a pH meter. Her titration data were: volume of volume of NaOH solution added, mL NaOH solution added, mL pH pH 22.00 5.74 24.00 5.88 6.00 6.03 28.00 6.24 30.00 6.57 31.00 6.89 32.00 8.99 33.00 11.08 34.00 11.38 36.00 11.67 38.00 11.83 0.00 4.22 4.55 4.76 4.92 5.06 5.18 5.29 5.40 5.51 5.62 4.00 6.00 8.00 10.00 12.00 16.00 18.00 20.00 (a) Prepare a titration curve of this student data using the Logger Pro software as instructed on pages 7-9 of this experiment. Determine the ml of NaOH solution used at the equivalence point? Attach the pH curve and 1st derivative plots to this pre-lab assignment.

Explanation / Answer

From the given titration data for a weak acid versus a strong base

(a) Drawn below is the titration plot

(b) number of equivalents of NaOH required to reach equivalence point = 1

(c) number of equivalents of acid titrated = 1

(d) equivalent mass of unknown acid = 0.653 g/0.1 M x 0.032 l = 204.0625 Eq

(d) pKa of unknown acid = 6.89

(f) pKa = -log[Ka]

Ka of unknown acid = 1.3 x 10^-7

(g) Identity of unknown acid = NaH2PO4

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