Question

PN ml NaOH PH 302 3.OR 3:35 CI 12.88 15.83 15.3 17.45 19.95 3.15 17.45 19.95 20.98 22.43 23.78 24.45 22.43 22.43 23.78 21.78 24.45 24.45 5.65 24,77 5.73 24.77 24.77 25.13 25.131 25.82 26.03 27.01 27.38 10.55 27 38 27.38 28.25 10.82 28.98 10.95 28.98 11.18 30.IR 11.05 29.051 11.26 31.5 11.15 11.21 198.56 29.12 10.95 29.85 11.65 30.58 11.76 31.25 11.84 574.06 + 201.63 C74.915 543.84 + =643.12 32.431 11.45 574.74 214.38 = 631.93 pal Find-pkal pkal kal Kal - kal Average Kal - Standard Deviation pkaz . - pra2 - pka2 Kq2 koz. ka2 A verace Kaz Standard deviation

Answer 1

We know that pH = pKa1 + log([A-]/[HA]),
which follows the curve y = mx + c as in Regression analysis.

Using the Analysis ToolPak and Data Analysis Tool in the Data Tab, we get Intercept pKa as

Intercept	2.389807
X Variable	0.212665

Intercept	2.382928
X Variable	0.244474

Intercept	2.31832
X Variable	0.226043

pKa1 = -log10Ka1

Hence, the values are 4.08 X 10-3, 4.14 X 10-3, 4.80 X 10-3, respectively.

Mean	St Dev
4.34E-03	4.04E-04

using the function average() and stdev() in excel

Since, I do not know which acid it is and how it has hydrolysed in NaOH. Most of the polyprotic acids (having multiple protons or Hydrogen ions for exchange) are considered weak, generally, because their Ka2 values are extremely small. It will be difficult to calculate Ka2 value from error because Ka2 values are around 3 orders of magnitude smaller than Ka1, unless it is sulphuric acid, which does not seem from this data set.