Name: choosing oxidizing titrants in redox titration
Uploaded: 2024-12-05T18:31:57.000Z
Duration: 1 min 26 s
Channel: JoVE

بالإضافة إلى اليود، يمكن استخدام العديد من العوامل المؤكسدة أو المختزلة الأخرى كمعايرة بالتحليل الحجمي في معايرة الأكسدة والاختزال.
برمنجنات البوتاسيوم هو مادة معايرة مؤكسدة قوية تقلل من المنغنيز (VII) إلى المنغنيز (II) في محلول شديد الحموضة.
هنا ، يعمل البرمنجنات الأرجواني كمؤشر ذاتي لأن المنغنيز (II) عديم اللون.
يمكن أيضا معايرة التحليلات المختزلة باستخدام محاليل السيريوم الحمضية (IV) أثناء استخدام مؤشرات الأكسدة والاختزال للكشف عن نقطة النهاية. في المعايرة بالتحليل الحجمي ، يتأكسد التحليل بينما ينخفض السيريوم (IV) إلى السيريوم (III).
ثنائي كرومات البوتاسيوم هو مادة معايرة مؤكسدة قوية إلى حد ما تقلل من الكروم (VI) إلى الكروم (III) في المحاليل الحمضية. لوحظت نقطة نهاية ثنائي الكرومات باستخدام مؤشر الأكسدة والاختزال.
في المقابل ، تتأكسد معظم مواد المعايرة بالتحليل الكيميائي المختزلة بواسطة الأكسجين الجوي ، لذلك نادرا ما تستخدم للمعايرة بالتحليل الحجمي المباشر للتحليلات المؤكسدة.
على سبيل المثال، يستخدم ثيوسلفات بشكل غير مباشر كمحلول معايرة بالتحليل الكيميائي المختزل النموذجي لمعايرة اليودومتر.
ومع ذلك ، يمكن استخدام محلول الحديد المحمض (II) لمعايرة بعض التحليلات المؤكسدة القوية ، مثل السيريوم (IV) والكروم (VI) والفاناديوم (V).

المعايرة بالأكسدة والاختزال: عوامل مؤكسدة ومختزلة أخرى

Redox Titration: Other Oxidizing and Reducing Agents

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بالإضافة إلى اليود، يمكن لعوامل مؤكسدة أو مختزلة أخرى أن تعمل كمُعايرات في المعايرة بالأكسدة والاختزال. تشمل المُعايرات المؤكسدة الشائعة KMnO_4، والسيريوم (IV)، وK_2Cr_2O_7. يعتمد اختيار المُعايرات المؤكسدة على عوامل مثل الاستقرار والتكلفة وقوة المحلل ومعدل التفاعل بين المحلل والمُعاير. KMnO_4 هو معاير مؤكسد قوي يُختزل من Mn(VII) إلى Mn(II) في محلول شديد الحموضة، ويؤكسد المحلل في نفس الوقت إلى حالة أكسدة أعلى. في هذه الحالة، يعمل KMnO_4 كمؤشر ذاتي، ويتحول إلى عديم اللون عند اكتمال التفاعل.

يمكن أيضًا معايرة المحللات المختزلة باستخدام محاليل السيريوم (IV) الحمضية، مع استخدام مؤشرات الأكسدة والاختزال للكشف عن نقطة النهاية. يتأكسد المحلل أثناء المعايرة بينما يُختزل Ce(IV) إلى Ce(III). يختزل ثنائي كرومات البوتاسيوم (K_2Cr_2O_7)، وهو معاير مؤكسد قوي إلى حد ما، إلى Cr^3+ في المحاليل الحمضية. تتم ملاحظة نقطة نهاية ثنائي الكرومات باستخدام مؤشر الأكسدة والاختزال.

وعلى النقيض من ذلك، تتأكسد معظم المعايرات المختزلة بواسطة الأكسجين الجوي، مما يجعلها غير مناسبة للمعايرة المباشرة للمحللات المؤكسدة. على سبيل المثال، يتم استخدام الثيوكبريتات بشكل غير مباشر كمعاير مختزل نموذجي للمعايرة اليودية. ومع ذلك، يمكن استخدام محلول الحديد (II) المحمض لمعايرة بعض المحللات المؤكسدة القوية، مثل السيريوم (IV) والكروم (VI) والفاناديوم (V).
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إلى جانب اليود، يمكن أن تعمل العوامل المؤكسدة أو المختزلة الأخرى كمعايرة بالتحليل الحجمي في معايرة الأكسدة والاختزال. تشمل مواد المعايرة المؤكسدة الشائعة KMnO4 والسيريوم (IV) و ...

redox-titration-other-oxidizing-and-reducing-agents

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

choosing oxidizing titrants in redox titration

Redox titrations can use oxidizing titrants other than iodine. Common choices include potassium permanganate (KMnO4), cerium(IV), and potassium dichromate (K2Cr2O7). The best titrant depends on stability, cost, analyte strength, and the reaction rate between the analyte and the titrant.

Potassium permanganate is a strong oxidizing titrant in highly acidic solution. It reduces from Mn(VII) to Mn(II) while it oxidizes the analyte to a higher oxidation state. KMnO4 also works as a self-indicator, so the solution turns colorless when the reaction is complete.

Cerium(IV) solutions can titrate reducing analytes in acidic conditions. During the reaction, the analyte is oxidized and Ce(IV) is reduced to Ce(III). A redox indicator is used to detect the endpoint.

Potassium dichromate is a moderately strong oxidizing titrant. In acidic solution, dichromate reduces to Cr3+, and a redox indicator is again used to spot the endpoint. Most reducing titrants are oxidized by atmospheric oxygen, so they are not suitable for direct titration of oxidizing analytes.

Thiosulfate is a common reducing titrant used indirectly in iodometric titrations. An acidified iron(II) solution can also titrate some strong oxidizing analytes, including cerium(IV), chromium(VI), and vanadium(V).

Choosing Oxidizing Titrants in Redox Titration

choosing-oxidizing-titrants-in-redox-titration

electrochemistry: overview

Electrochemistry and Redox Reactions

Electrochemistry connects electrical measurements with chemical reactions, especially oxidation and reduction. It focuses on how electron movement helps explain reaction behavior. Oxidation is the loss of electrons from a substance, and reduction is the gain of electrons. A species with strong electron affinity is an oxidizing agent, or oxidant. A species that donates electrons is a reducing agent, or reductant. These redox steps are often described with half-reactions. When electrons move...

electrodes: overview

Types of Electrodes in Electrochemistry

Electrodes are conductive materials in an electrochemical cell. They allow electron transfer reactions to happen at their surfaces. Electrochemical measurements use them to control and measure current and potential. The working electrode, also called the indicator electrode, is the main sensing electrode. Its potential changes with the analyte concentration and with the activity of the electroactive species. Common indicator electrodes include inert platinum electrodes, silver electrodes that...

interfacial electrochemical methods: overview

interfacial-electrochemical-methods-overview

Static and Dynamic Electrochemical Methods

Static and dynamic electrochemical methods study what happens at the boundary between an electrode and a solution. These interfacial methods focus on the electrode-solution interface rather than the overall properties of the liquid. They are useful in electroanalytical chemistry because they can detect very small changes in analyte concentration. These methods are grouped by whether a nonzero current flows through the cell. Static methods, such as potentiometry, measure the cell potential...

potentiometry: overview

Potentiometry and Electrochemical Cell Potential

Potentiometry measures the potential difference between two electrodes in an electrochemical cell. It does this without drawing significant current, so the solution’s composition is not altered. The method uses an indicator electrode, which exchanges electrons with the analyte solution, and a reference electrode, which keeps a constant potential. Each electrode is placed in a solution that makes up a half-cell. In a common setup, the reference electrode is the anode, or left-hand electrode,...

potentiometry: types of electrodes

Reference and Indicator Electrodes in Potentiometry

Potentiometric measurements use reference electrodes and indicator electrodes to track changes in a solution. A reference electrode gives a stable baseline, while indicator and working electrodes respond to changes in the solution’s composition. The Standard Hydrogen Electrode, or SHE, is a common reference electrode. It keeps a zero potential at all temperatures. However, it needs a continuous supply of hydrogen gas, so it is not practical for routine use. The Saturated Calomel Electrode, or...

potentiometry: membrane electrodes

Membrane Electrodes in Ion Sensing

Membrane electrodes measure ions by using a selective membrane that creates a potential difference across it. This membrane potential is called the asymmetry potential, and it can remain nonzero even when analyte concentrations are the same on both sides of the membrane. The signal usually depends on all ions in the sample that can interact with the membrane, not just one analyte. Selectivity is described by a selectivity coefficient. This value compares the response to an interferent with the...

redox titration: overview

Redox Titration Endpoints and Indicators

Redox titration uses electron transfer in a redox, or reduction-oxidation, reaction to find the concentration of an unknown solution. The titrant has a known concentration, and it is added gradually to the analyte, which is the solution being tested. The endpoint shows when the reaction between the two substances is complete. Before a redox titration begins, the analyte should be in a single oxidation state. If needed, this is done by pre-oxidizing or pre-reducing the sample with an auxiliary...

redox titration: iodimetry and iodometry

Using Iodine to Find Unknown Concentrations

Iodometry and iodimetry use iodine to measure unknown concentrations in redox titrations. These methods help determine the amount of an oxidizing or reducing agent in a sample. The key idea is that iodine changes color and reacts in a known stoichiometric ratio with the analyte. In iodometric titrations, the sample usually contains an oxidizing agent. The solution is acidified and then treated with an excess of iodide ions, which releases an equivalent amount of iodine in equilibrium with...

redox titration: other oxidizing and reducing agents

Redox titrations can use oxidizing titrants other than iodine. Common choices include potassium permanganate (KMnO4), cerium(IV), and potassium dichromate (K2Cr2O7). The best titrant depends on stability, cost, analyte strength, and the reaction rate between the analyte and the titrant. Potassium permanganate is a strong oxidizing titrant in highly acidic solution. It reduces from Mn(VII) to Mn(II) while it oxidizes the analyte to a higher oxidation state. KMnO4 also works as a self-indicator,...

potentiometric titration: overview

Endpoint Detection in Potentiometric Titration

Potentiometric titration is a quantitative analytical method used to find the concentration of an analyte by measuring the potential difference between two electrodes in a solution. The endpoint is the point where this potential changes sharply. It usually appears when the stoichiometric reaction between the analyte and the titrant is complete. To find the endpoint, the measured potential difference is plotted against the volume of titrant added. This graph is called a titration curve. A...

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Gran Plot for Titration Endpoint Prediction

A Gran plot helps predict the endpoint of a potentiometric or acid-base titration before the endpoint is reached. It uses titration data collected only up to a point that is still below the equivalence volume. The data are then transformed into a straight-line format. To build the plot, the line is extended to the x-axis. That x-intercept shows the titrant volume needed to reach the equivalence point. In potentiometric titration, the Gran plot uses the volume-corrected base-10 antilogarithm of...

electrogravimetric analysis: overview

Electrode Weighing in Electrogravimetric Analysis

Electrogravimetric analysis measures an analyte by weighing the material that deposits on an electrode. A pre-weighed working electrode is placed in solution, and a potential is applied. The target substance then deposits by reduction at the cathode or by oxidation at the anode. After electrolysis, the electrode is weighed again. The mass increase gives the weight of the analyte in the solution. To check that deposition is complete, the fresh electrode surface is exposed to the solution while...

coulometry: overview

Coulometry and Electrical Charge Analysis

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controlled-potential coulometry: electrolytic methods

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Measuring Analyte Charge by Potentiostatic Coulometry

Controlled-potential coulometry measures analyte amount by carefully controlling electrode potential during electrolysis. It is also called potentiostatic coulometry. A potentiostat keeps the working electrode at a set potential in a three-electrode system. The working electrode choice depends on the potential range. Platinum working electrodes are used for positive potentials. Mercury pool electrodes are preferred for very negative potentials. The platinum counter electrode is kept away from...

controlled-current coulometry: overview

Controlled-Current Coulometry in Redox Analysis

Controlled current coulometry is an electrochemical method used to measure the amount of a substance by passing a steady current through a cell. It is also called amperostatic coulometry. The analyte, or substance being analyzed, reacts at the electrode surface as charge moves through the system. The amount of analyte is found by measuring how long it takes for a known charge to pass. This calculation follows Faraday’s laws of electrolysis. A typical setup includes a galvanostat, a...

controlled-current coulometry: coulometric titration

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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...

voltammetry: overview

Voltammetry for Detecting Redox Species

Voltammetry measures current in an electrochemical cell as the applied potential changes. It is an electroanalytical method used to study redox-active species. The current response is shown on a graph called a voltammogram. A voltammetric cell uses three electrodes: a working electrode, a reference electrode, and an auxiliary electrode. Redox reactions happen at the working electrode, and a potentiostat controls its potential. The reference electrode, such as a saturated calomel electrode or a...

voltammetry: factors affecting measurements

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Voltammetry and Faradaic Current

Voltammetry measures faradaic current, which is the current created by redox reactions of an analyte at the working and auxiliary electrodes. The current from reduction is called cathodic current and carries a positive charge. The current from oxidation is called anodic current and has a negative charge. The applied potential at the working electrode controls the flow of faradaic current. The size of that current depends on how fast the oxidation or reduction reaction occurs at the electrode...

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Voltammogram Shapes and Redox Analysis

Voltammograms are current plots made against applied potential. They help show how an electrochemical system behaves during a redox reaction. The shape of the plot depends on how the current is measured and on whether convection, or fluid movement, is present. When convection is present, as in hydrodynamic voltammetry, the voltammogram usually has a sigmoid shape. In this case, the current rises from a residual current to a limiting current at the analyte’s oxidation or reduction potential.

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Polarography and Voltammetry with Mercury Drops

Polarography and hydrodynamic voltammetry are voltammetric techniques used to study electrochemical reactions. They track the current that flows as the electrode potential changes. In polarography, the key working electrode is a dropping mercury electrode, or DME. A DME uses a capillary tube filled with mercury. A tiny mercury droplet forms at the tip and then drops away. This gives a fresh electrode surface for each measurement. During the test, the potential applied to the DME changes...

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Pulse Voltage Methods for Electrochemistry

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voltammetric-techniques-cyclic-voltammetry

Reading Redox Peaks with Cyclic Voltammetry

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Trace Analysis by Stripping Voltammetry

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Measuring Analytes with Amperometric Sensors

Amperometry measures specific analytes in a solution by tracking the electric current from an electrochemical reaction. A constant potential is applied between a working electrode and a reference electrode. The current that results is proportional to the analyte concentration. The Clark oxygen electrode is a common example of amperometry. It uses a cathode and an anode sealed inside a gas-permeable membrane. The cathode is typically platinum or gold, and the anode is silver. When a potential...

key terms and concepts

Explore how KMnO4, cerium(IV), and dichromate are used in redox titrations, how endpoints are detected, and why some reducing titrants are used indirectly.

Choosing Oxidizing Titrants in Redox Titration | JoVE K12

analytical chemistry

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Choosing Oxidizing Titrants in Redox Titration

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