Looking for a commercial software that can determine refined pka constants ?
Excel should work fine. Just titrate the acid with base and plot the pH vs. the amount of added base. The resultant S shaped curve has almost linear segments at the start and end and steep linear portion in the middle. Plot the 3 straight lines. Find the midpoint between the intrertsections of the steep line with the initial and final lines. The pKa is the pH value of the midpoint.
Caso consiga modelar uma função matemática de ordem 3 para tal gráfico que o Dr.Lloyd sugeriu, poderá encontrar o ponto do pH tendo como raiz a segunda derivada de tal função a qual denomina-se "ponto de inflexão".
Dr, DE SOUZA's answer is more precise than mine. Fit pH = A*v^3 + B*v^2 + C*v + D, where v is the volume of titration solution, to the central portion of the titration curve and pKa = -B/3A. You can minimize the least squares between the cubic equation and your titration curve using the Solver Add-In to Excel to find A, B, C and D. .
Dr. Lloyd brown,
Thanks for the translation,
Can excel handle the overlapping pKa constants ?
Regards,
Raghav
My comment was not a translation but my response to reading the Google Translate of his comment. Here is the Google Translate of his comment:
"If you can model a mathematical function of order 3 for such a graph as Dr. Lloyd suggested, you can find the pH point by taking the second derivative of such a function which is called the "inflection point" as its root."
The Excel Solver can handle any equation that you can write. What you need to do is write an equation in terms of a set of parameters, subtract the calculated value from the measured value for each data point, square the difference for each point, sum the squares, and minimize the sum of squares to find the best fit of the parameters to the equation. I think you would need a fifth order equation to find three inflection points, two of which are the pKa values.
- Badges
- Science topic
- Similar topics
- Engineering
- Modeling