Name: electrically generated reagents in titration
Uploaded: 2024-12-05T18:31:57.000Z
Duration: 1 min 18 s
Channel: JoVE

يقيس المعايرة بالتحليل الحجمي كمية المادة المراد تحليلها في المحلول باستخدام كاشف قياسي يتفاعل مع المادة المراد تحليلها ويتولد كهربائيا بواسطة تيار ثابت.
يوفر الجلفانوستات التيار المنظم ، وسلائف الكاشف القياسية زائدة ، مما يضمن كفاءة التيار بنسبة 100٪.
في خلية المعايرة بالتحليل الحجمي النموذجية، يولد القطب الكهربائي العامل الكاشف داخل محلول الاختبار، والذي يتفاعل بعد ذلك مع المادة التحليلية.
يظل القطب الإضافي أو المضاد ، الذي يكمل الدائرة الكهربائية ، معزولا عن المحلول السائب لمنع التداخل من منتجات التفاعل الخاصة به.
في بعض الحالات، بدلا من عزل القطب المضاد، يتم إنتاج الكاشف خارجيا في خلية تولي معزولة قبل إضافته إلى خلية المعايرة بالتحليل الحجمي.
في المعايرة بالتحليل الحجمي ، تتدفق الكهرباء في البداية عبر الخلية لفترات طويلة ، وتتناقص تدريجيا مع اقترابها من التكافؤ الكيميائي ، مثل توزيع كمية أقل وأقل من السوائل من السحاحة.
يتم تحديد نقطة النهاية بواسطة الكاشف الذي يتفاعل مع دائرة الكاشف ، ويتم حساب كمية المادة المراد تحليلها باستخدام التيار والوقت المطلوبين لإكمال المعايرة بالتحليل الحجمي.

القياس الكولومتري بالتيار المتحكم فيه_المعايرة الكولومترية

Controlled-Current Coulometry: Coulometric Titration

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المعايرة الكولومترية هي شكل من أشكال التحليل بالمعايرة حيث يتم توليد الكاشف كهربائيًا، ويتم تقييم كميته بناءً على التيار ووقت التوليد. يعمل الإلكترون ككاشف قياسي. الإجراء مشابه للمعايرة التقليدية، مثل الكشف عن نقطة النهاية.

المتطلبات الأساسية للمعايرة الكولومترية هي (1) كفاءة 100% في تفاعل القطب المولد للكاشف و(2) تفاعل متكافئ ويفضل أن يكون سريعًا بين الكاشف الناتج والمادة المحددة. يمكن توليد الكاشف مباشرة داخل محلول الاختبار أو خارجيًا في محلول منفصل.

تقدم المعايرة الكولومترية العديد من المزايا، بما في ذلك الحساسية العالية بسبب القياس الدقيق لكميات صغيرة من الكهرباء. علاوة على ذلك، لا تتطلب محاليل قياسية، ويمكنها استخدام الكواشف غير المستقرة، وتسمح بتوليد كميات صغيرة من المحاليل، وتتجنب تخفيف العينة، وتوفر نتائج أكثر دقة من خلال المعايرة المسبقة، وقابلة للتكيف مع التحكم عن بعد والتلقائي.

تتطلب المعايرات الكولومترية مصدر تيار ثابت ومكامل لقياس ناتج التيار والوقت. تتكون خلية المعايرة عادةً من دورق ومولد ومساعد وأقطاب مؤشر.

تتضمن الإجراءات العامة للمعايرة الكولومترية إعداد خلية التحليل الكهربائي بأقطاب المولد والمؤشر، وشحن الخلية بمحلول الاختبار، وضبط التيار، والسماح للتفاعل بالمضي قدمًا. يتم تقييم نقطة نهاية المعايرة بناءً على تغير التيار أثناء المعايرة. يظل القطب المساعد أو المضاد، الذي يكمل الدائرة الكهربائية، معزولًا عن المحلول السائب لمنع التلوث. يتم أحيانًا توليد الكاشف خارجيًا قبل إضافته إلى وعاء المعايرة.

يمكن اكتشاف نقاط النهاية في المعايرة الكولومترية باستخدام المؤشرات الكيميائية أو الملاحظات الجهدية أو الإجراءات الأمبيرومترية. تعتمد هذه الطرق على تحديد الظروف التي تسبب تفاعل المادة التي يتم تحديدها أو المعاير للتفاعل عند قطب مؤشر، مما ينتج تيارًا متناسبًا مع تركيز المادة الفعالة كهربائيًا.

تتضمن قيود المعايرة الكولومترية مع التوليد الداخلي للمعايير وجود مواد قد تتفاعل عند أقطاب المولد وصعوبة تحديد نقطة التكافؤ بالطرق الأمبيرومترية للعينات الكبيرة الحجم. يمكن التغلب على هذه القيود عن طريق توليد الكاشف خارجيًا بتيار ثابت بكفاءة 100٪ في خلية مولد خارجية، والتي يتم تسليمها بعد ذلك إلى خلية المعايرة. على الرغم من عيبها البسيط المتمثل في تخفيف محتويات خلية المعايرة، فإن هذا الإجراء مناسب تمامًا للتحكم التلقائي وتحديد المواد الموجودة بكميات صغيرة.
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المعايرة بالتحليل الحجمي هي شكل من أشكال تحليل المعايرة بالتحليل الحجمي حيث يتم توليد الكاشف كهربائيا ، ويتم تقييم مقداره بناء على التيار و ...

controlled-current-coulometry-coulometric-titration

Education

JoVE Core

Analytical Chemistry

الكيمياء التحليلية

Unit 1

الوحدة الأولى

Electrochemical Analyses and Redox Titration

التحليلات الكهروكيميائية والمعايرة بالأكسدة والاختزال

electrochemical-analyses-and-redox-titration

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

electrically generated reagents in titration

Coulometric titrations use an electrically generated reagent to measure the amount of a substance in a sample. The electron acts as the standard reagent, and the result depends on the current and the time used to generate it. The method follows the same basic idea as a regular titration, including endpoint detection.

Two conditions are essential for this type of titration. First, the electrode reaction that makes the reagent must be 100% efficient. Second, the generated reagent must react quickly and in a stoichiometric way, meaning it reacts in the correct ratio, with the substance being tested. The reagent may be formed directly in the test solution or made in a separate solution first.

Coulometric titrimetry has several practical advantages. It is very sensitive because it measures small amounts of electricity with high accuracy. It does not require standard solutions, and it can use unstable reagents. It also allows very small amounts of titrant to be made, avoids sample dilution, improves accuracy through pre-titration, and can be adapted for remote or automatic control.

A coulometric titrator needs a constant current source and an integrator to measure current over time. The titration cell usually includes a beaker, generator electrodes, an auxiliary or counter electrode, and an indicator electrode. The general procedure is to set up the electrolysis cell, add the test solution, adjust the current, and let the reaction proceed. The endpoint is found from the change in current during titration. The counter electrode completes the circuit but stays isolated from the bulk solution to prevent contamination.

Endpoints can be detected with chemical indicators, potentiometric measurements, or amperometric methods. These approaches depend on making either the analyte or the titrant react at an indicator electrode so that a current is produced. That current is proportional to the concentration of the electro-active substance.

There are limits to internal reagent generation. Substances in the sample may react at the generator electrodes, and amperometric methods can make it difficult to locate the equivalence point in macro-scale samples. These problems can be reduced by generating the reagent externally at a constant current with 100% efficiency and then delivering it to the titration cell. This method slightly dilutes the contents of the cell, but it is useful for automatic control and for measuring substances present in small amounts.

Electrically Generated Reagents in Titration

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key terms and concepts

Learn how coulometric titrations use electrically generated reagents, constant current, and endpoint detection to measure small amounts of a substance.

Electrically Generated Reagents in Titration | JoVE K12

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JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Electrically Generated Reagents in Titration

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