pH Titration Curves

Acid solutions are often analyzed by titration with a solution of a strong base of known concentration; similarly, solutions of bases are analyzed by titration with a strong acid. In either case, the measured pH is plotted as a function of the titrant volume. Calculation of a pH titration curve is a particularly good introduction to acid-base equilibrium calculations since a variety of calculations are involved.

Example

Compute the pH vs. volume curve for the titration of 10.0 mL of 0.25 M HCl with 0.10 M NaOH.

Since HCl and NaOH are completely dissociated in dilute solutions, and the reaction goes to completion, this is really a simple stoichiometry problem in which we convert the H₃O⁺ concentration to pH. If the initial number of millimoles of HCl is

then, before complete neutralization [H₃O⁺] after the addition of V mL of NaOH solution is

We set up a table for several volumes of NaOH added:

When we add exactly 25.00 mL of NaOH, all the H₃O⁺ from the HCl has been consumed—the equivalence point. The solution then contains NaCl, and, since Na⁺ and Cl^- are neither acidic or basic, the H₃O⁺ concentration is due to water ionization alone and pH = 7.00. Beyond the equivalence point, the solution will contain excess OH^-, the concentration of which is

and the pH is computed as pH = 14.00 - log[OH^-]. Continuing the table for two more points:

These points (and a few more) are plotted in Figure 1.1.

Figure 1.1. pH titration curve for titration of 10 mL of 0.25 M HCl with 0.10 M NaOH.

مواضيع ذات صلة

الشكل الوضعي للسكريات الأحادية configuration of monosaccharides

نظام استخلاص الجزئيات البسيطة

اختيار الطور الجديد وعدد مرات الاستخلاص

ميكانيكية الاستخلاص

طبيعة الصنف المستخلص

الاستخلاص بالمذيب

امتصاص الشعاع الكهرومغناطيسي وطيف الامتصاص

الطرق الكيميائية الطيفية في التحليل.

طبيعة الكيمياء التحليلية

التحليل بالحقن الجرياني المتقطع Batch flow injection analysis

الحقن الجرياني متعدد التخفيف Multi-commutation in FIA

التحليل بالحقن المتعاقب Sequential Injection Analysis