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Analytical Chemistry4

الكلية كلية العلوم للبنات     القسم قسم الكيمياء     المرحلة 1
أستاذ المادة محمد حامد سعيد الدهيمي       21/01/2017 04:22:27
LECTURE 4
Indicator Range
At a low pH, a weak acid indicator is almost entirely in the HIn form, the colour of which predominates. As the pH increases - the intensity of the colour of HIn decreases and the equilibrium is pushed to the right Therefore the intensity of the colour of In- increases. An indicator is most effective if the colour change is distinct and over a low pH range. For most indicators the range is within ±1 of the pKln value
A Universal Indicator is a mixture of indicators which give a gradual change in colour over a wide pH range - the pH of a solution can be approximately identified when a few drops of universal indicator are mixed with the solution.
Indicators are used in titration solutions to signal the completion of the acid-base reaction
An indicator is a substance which show characteristic change in its colour when comes in contact with acid or base and thus it is used to determine dicators the degree of acidity or basicity of any solution. For example litmus solution or litmus paper.
Role of indicators in chemistry is very important. They are used are also used to find out the end point in a titration.
In acid-base titrations, organic substances (weak acids or weak bases) are generally used as indicators.
Indicators change their colour within a certain pH range.
There are two theories which explain the change of colour indicators with change in pH.

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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 .