Name: voltammogram shapes and redox analysis
Uploaded: 2024-12-05T18:31:57.000Z
Duration: 1 min 16 s
Channel: JoVE

&#160;A voltammogram is a graph generated experimentally, plotting current on the y-axis and applied potential on the x-axis.
Their shape depends on the method of measuring the current and the presence or absence of convection, which is the heat transfer by the macroscopic movement of a fluid.
In the presence of convection, the plot shows a sigmoid growth from the residual to the limiting current at a potential equal to the oxidation or reduction potential of the analyte.
Here, the limiting current suggests a constant value for the diffusion layer thickness, achieved by stirring the solution as observed in hydrodynamic voltammetry.
Without convection, the diffusion layer thickness is enhanced with time, leading to a peak current.
When the change in current is monitored against the potential, the peak current characterizes the plot.
The limiting current can be used to estimate the analyte concentration in the bulk solution, as it is directly proportional to the analyte concentration.
In addition, peak potentials determined from voltammograms can be applied to determine the standard state potentials of redox reactions by using the Nernst equation.

voltammogrammen: overzicht

Voltammograms: Overview

Voltammogrammen zijn stroomdiagrammen als functie van het toegepaste potentieel, die inzicht bieden in elektrochemische systemen. De vorm van een voltammogram hangt af van hoe de stroom wordt gemeten en of convectie (warmteoverdracht door vloeistofbeweging) aanwezig of afwezig is.

Vormen van voltammogrammen

De vorm van een voltammogram weerspiegelt het gedrag van de analyt tijdens het redoxproces. In aanwezigheid van convectie, zoals roeren in hydrodynamische voltammetrie, vormt het diagram een sigmoïde vorm, waarbij de stroom toeneemt van een reststroom tot een grensstroom bij het oxidatie- of reductiepotentiaal van de analyt. Deze grensstroom treedt op omdat de dikte van de diffusielaag, die de massaoverdracht naar de elektrode regelt, constant blijft vanwege de vloeistofbeweging.

De diffusielaag groeit in de loop van de tijd zonder convectie, wat leidt tot een piekvormig voltammogram. De piekstroom vertegenwoordigt het punt waarop de reductie- of oxidatiesnelheid van de analyt een maximum bereikt voordat deze afneemt vanwege de uitdijende diffusielaag. Deze twee verschillende vormen, sigmoïde en piek, zijn essentieel voor het begrijpen van het massatransport en de reactiekinetiek van elektrochemische systemen.

Kwantitatieve toepassingen

Voltammogrammen hebben ook belangrijke kwantitatieve toepassingen. De grensstroom is recht evenredig met de analytconcentratie in de oplossing. Deze relatie wordt gebruikt in analytische technieken zoals hydrodynamische voltammetrie om analytconcentraties te berekenen. Door de grensstroom te meten, kunnen chemici nauwkeurig de hoeveelheid van een stof in een oplossing bepalen, wat cruciaal is voor toepassingen in milieuanalyse, farmaceutica en industriële monitoring.

Kwalitatieve toepassingen: standaardtoestandspotentialen

Naast concentratiemetingen leveren voltammogrammen kwalitatieve gegevens door de standaardtoestandspotentialen van redoxreacties te bepalen. Het piekpotentiaal in een voltammogram kan worden gebruikt met de Nernst-vergelijking om het redoxpotentiaal van een analyt te berekenen. Dit potentieel geeft inzicht in de waarschijnlijkheid dat een stof onder standaardomstandigheden wordt geoxideerd of gereduceerd.

Voltammetrie helpt ook om onderscheid te maken tussen omkeerbare en onomkeerbare reacties op basis van de symmetrie en vorm van het voltammogram. Omkeerbare reacties vertonen symmetrische pieken, terwijl onomkeerbare processen meer asymmetrie vertonen.

Voltammogrammen dienen als essentiële hulpmiddelen voor kwalitatieve en kwantitatieve elektrochemische analyse. Hun vormen, sigmoïd of piek, bieden inzicht in de aard van de elektrochemische reactie, terwijl hun stroom-potentiaalrelaties de nauwkeurige bepaling van analytconcentraties en redoxpotentialen mogelijk maken. Dit maakt voltammetrie een veelzijdige techniek voor het bestuderen van elektrochemische systemen.

Voltammogrammen: Overzicht

Voltammograms are current plots as a function of applied potential, offering insights into electrochemical systems. The shape of a voltammogram depends on ...

Education

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Analytical Chemistry

Analytische chemie

Unit 1

Electrochemical Analyses and Redox Titration

Elektrochemische analyses en redox-titratie

electrochemical-analyses-and-redox-titration

KEY TERMS AND CONCEPTS

KERNTERMEN EN CONCEPTEN

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. The limiting current appears because the diffusion layer thickness stays constant when the liquid is moving.

Without convection, the diffusion layer grows over time. This often produces a peak-shaped voltammogram instead of a sigmoid one. The peak current marks the point where analyte oxidation or reduction is fastest before the rate drops as the diffusion layer expands. These two shapes, sigmoid and peak, help explain mass transport and reaction kinetics in electrochemical systems.

Voltammograms are also useful for quantitative work. The limiting current is directly proportional to the analyte concentration in solution. Chemists use this relationship in hydrodynamic voltammetry to measure how much of a substance is present, which is important in environmental analysis, pharmaceuticals, and industrial monitoring.

They also provide qualitative information about redox reactions. The peak potential can be used with the Nernst equation to find the standard state potential of an analyte. Voltammograms can also help distinguish reversible reactions from irreversible ones, since reversible reactions show symmetric peaks and irreversible processes appear more asymmetric. These current-potential plots are therefore useful for both concentration measurements and redox potential analysis.

Voltammogram Shapes and Redox Analysis

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...

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Static and Dynamic Electrochemical Methods

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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...

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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,...

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Endpoint Detection in Potentiometric Titration

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Measuring Analyte Charge by Potentiostatic Coulometry

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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...

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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...

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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...

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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...

voltammograms: overview

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.

voltammetric techniques: linear-scan (e vs time)

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Polarography and Voltammetry with Mercury Drops

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Pulse Voltage Methods for Electrochemistry

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Reading Redox Peaks with Cyclic Voltammetry

Cyclic voltammetry measures how current changes as the potential at an electrode is varied. It is used to study the redox properties of a chemical species, meaning how easily it is oxidized or reduced. The setup uses three electrodes in an electrolyte solution. The working electrode is where the redox reaction of interest takes place. The reference electrode provides a stable potential, and the counter electrode completes the circuit for current flow. The process starts at a chosen initial...

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Trace Analysis by Stripping Voltammetry

Stripping voltammetry is an electrochemical method used to detect trace amounts of analytes in solution. It works by applying a potential to an electrode and measuring the current that results. The current is then used to estimate the analyte concentration. Anodic Stripping Voltammetry, or ASV, is used for metals and metalloids at very low levels. It has two main steps: deposition and stripping. First, a negative potential reduces analyte ions and deposits them on the working electrode surface.

amperometry: overview

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 voltammogram shapes reveal redox behavior, limiting current, analyte concentration, and standard state potentials in electrochemistry.

Voltammogram Shapes and Redox Analysis | JoVE K12

analytical chemistry

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Voltammogram Shapes and Redox Analysis

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