Complexation Equilibria

Metal ions such as Cu2+ are Lewis acids that combine with Lewis bases such as H₂O to form complex ions, e.g.,Cu(OH₂)₄²⁺. The number of ligands, the coordination number, varies from one metal ion to another; the most common coordination numbers are 4 and 6, but 2, 3, 5, 7, and 8 are also known. In the presence of another Lewis base such as NH₃, the H₂O ligands can be replaced in stepwise equilibria:

K₁ = 1.6 × 104, K₂ = 3.2 × 103, K₂ = 9.5 × 102, K₄ = 1.3 × 102. Since ΔH° is nearly the same for each step, -23 kJ/mol, the decrease of Kn with increasing NH₃ substitution is an entropy effect which can be partly explained by statistics. In the first step, any one of four H₂O ligands can be replaced in the forward reaction but only one NH₃ can be replaced in the reverse reaction, contributing a factor of 4 to K₁. In the fourth step, the statistics are reversed, one H₂O can be replaced in the forward reaction but any of four NH₃ ligands can be replaced in the reverse step, contributing a factor of 1/4 to K₄. We sometimes can use the overall formation constant corresponding to the sum of the four steps,

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