Question

Question 3 (20pts): 20 mL of an unknown weak acid is titrated using 0.02 M NaOH. pH is monitored with a pH-meter and the data below collected (see back of this sheet). A) Create a plot of this titration using the data below. Label the approximate position of the equivalence point on the plot. B) Create a Gran plot using this data. Include the equation of the line that you fit to the data as well as the R2 value. C) Use the linear fit of the data to determine the equivalence volume. D) What is the initial concentration of the unknown weak acid sample? E) Estimate the pKb of the conjugate base.

Answer 1

12 4-4- 10 8- Equivalence point 6 pH pka 4 Half way point 7.82 0 4 6 8 10 12 14 16 18 20 22 24 26 2 Volume of NaOH added (ml) Hd

We know that: At half of the equivalence point pH pka From graph pka 4.64 We know pka pkb 14 pkb 14 -4.64 = 9.36

y a bx Equation 12 No Weighting Weight 33.20776 Residual Sum of Squares 0.93241 Pearson's r Adj. R-Square 0.86371 Standard Error Value 10 Intercept 2.30382 0.46101 B Slope 0.3888 0.03142 8.42 8 Equivalence point 6 pH pka Half way point 7.88 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Volume of NaOH added (ml) Hd

We know that: At half of the equivalence point pH pka From graph pka 5.29 We know pka pkb 14 pkb 14-5.29= 8.71