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Analytical Chemistry 4

الكلية كلية العلوم للبنات     القسم قسم الكيمياء     المرحلة 1
أستاذ المادة محمد حامد سعيد الدهيمي       04/01/2013 16:28:37
Analytical Chemistry
Lecture No. 4 Date :16 /12/ 2012
Dr. Mohammed Hamed
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Buffers solutions: - buffers are solutions that resist changing pH when small amounts of acid or base are added they resist changing pH by neutralizing added acid or base

The components of a buffer solution :- It is a mixture of weak acid and its salt:- CH3COOH is weak acid , CH3COONa is Salt of weak acid
The Mechanisms of buffer solution to remain stable:
- If base is added (OH-):
It will be buffered by the following reaction
CH3COOH + OH- --------- CH3COO- + H2O
So the pH will not change. the weak acid present in the buffer mixture can neutralize added base.
- If acid (H+) is added:
it will be buffered by the following reaction,
CH3COO- + H+ ------------ CH3COOH
The pH will not alter significantly because the CH3COOH formed is a weak acid.
Two important characteristics of a buffer include:

1. pH Range
• The pH range is the range of pH values over which a buffer system works
effectively.
• The pH range of an acid or base can be seen as the region of little pH change vs. volume of base/acid added on a titration curve
• It is best to choose an acid with a pKa close to the desired pH.
2. Buffering Capacity
• The buffering capacity of a buffered solution represents the amount of acid or base that can be absorbed by the solution without a significant change in pH.
• A buffer with a large capacity contains large concentrations of buffering components. Therefore the capacity of a buffered solution is determined by the
magnitudes of [HA] and [A-].
For more information open pdf file

المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .