Buffer Solutions

In Figure above, we see that the pH changes most slowly in the vicinity of the half-equivalence point, the buffer region. Small additions of base (or acid) to a solution containing comparable amounts of an acid and its conjugate base change the pH only slightly; the solution is said to be buffered against pH changes. Consider 100 mL of a solution containing 0.1 M CH₃COOH and 0.1 M CH₃CO₂^-, pH = 4.75. Addition of 10^-3 mol of HCl would change the ratio [CH₃CO₂^-]/[CH₃COOH] from 0.1/0.1 to 0.09/0.11 and the pH would change from 4.75 to 4.66. We could, of course, prepare 100 mL of a pH 4.75 solution by diluting HCL to 1.78 × 10^-5 M. However, addition of 10^-3 mol of HCl would reduce the pH to 2.0, a much bigger change than for the buffer solution.

Example

How many moles of NaH₂PO₄ and Na₂HPO₄ should be used to prepare 250 mL of a solution with a total phosphate concentration of 0.10 M and pH = 7.00?

The relevant equilibrium is the second proton transfer step for phosphoric acid,

مواضيع ذات صلة

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

التحليل بالجريان المتقطع Segment Flow Analysis