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

전기량 적정은 분석물과 상호 작용하고 일정한 전류에 의해 전기분해 방식으로 생성되는 표준 시약을 사용하여 용액 내 분석물의 양을 측정합니다.
갈바노스타트는 조절된 전류를 제공하고 표준 시약의 전구체가 초과되어 100% 전류 효율을 보장합니다.
일반적인 적정 셀에서 작동 전극은 테스트 용액 내에서 시약을 생성한 다음 분석물과 반응합니다.
전기 회로를 완성하는 보조 또는 상대 전극은 반응 생성물의 간섭을 방지하기 위해 벌크 용액과 격리된 상태로 유지됩니다.
어떤 경우에는 상대 전극을 분리하는 대신 시약이 적정 셀에 추가되기 전에 격리된 생성 셀에서 외부에서 생산됩니다.
전기량 적정에서 전기는 처음에는 셀을 통해 장기간 흐르다가 뷰렛에서 점점 더 적은 유체를 분배하는 것과 같이 화학적 동등성에 가까워짐에 따라 점차 감소합니다.
종말점은 검출기 회로와 반응하는 시약에 의해 식별되며, 적정을 완료하는 데 필요한 전류와 시간을 사용하여 분석물의 양이 계산됩니다.

제어 전류 전량법_전량법 적정

Controlled-Current Coulometry: Coulometric Titration

전량법 적정은 시약을 전기적으로 생성하고 전류와 생성 시간을 기준으로 양을 평가하는 적정 분석의 한 형태입니다. 전자는 표준 시약 역할을 합니다. 이 절차는 종말점 검출과 같은 기존 적정과 유사합니다.

전량법 적정의 기본 요건은 (1) 시약 생성 전극 반응에서 100% 효율, (2) 생성된 시약과 결정된 물질 간의 화학양론적이고 바람직하게는 빠른 반응입니다. 시약은 시험 용액 내에서 직접 생성하거나 별도의 용액에서 외부에서 생성할 수 있습니다.

전량법 적정은 소량의 전기를 정확하게 측정하여 높은 감도를 포함하여 여러 가지 장점을 제공합니다. 또한 표준 용액이 필요하지 않고 불안정한 시약을 활용할 수 있으며 소량의 적정제를 생성할 수 있고 표본 희석을 피하고 사전 적정을 통해 더 정확한 결과를 제공하며 원격 및 자동 제어에 적응할 수 있습니다.

전기 적정기는 전류와 시간의 곱을 측정하기 위해 일정한 전류원과 적분기가 필요합니다. 적정 셀은 일반적으로 비커, 발전기, 보조 전극 및 지시 전극으로 구성됩니다.

전기 적정의 일반적인 절차에는 발전기와 지시 전극으로 전기 분해 셀을 설정하고, 셀에 시험 용액을 충전하고, 전류를 조정하고, 반응을 진행시키는 것이 포함됩니다. 적정의 종말점은 적정 중 전류 변화에 따라 평가됩니다. 전기 회로를 완성하는 보조 전극 또는 상대 전극은 오염을 방지하기 위해 벌크 용액과 분리되어 있습니다. 시약은 때때로 적정 용기에 추가되기 전에 외부에서 생성됩니다.

전기 적정의 종말점은 화학 지표, 전위차 관찰 또는 전류 측정 절차를 사용하여 감지할 수 있습니다. 이러한 방법은 측정되는 물질 또는 적정제가 지시 전극에서 반응하여 전기 활성 물질의 농도에 비례하는 전류를 생성하는 조건을 설정하는 데 의존합니다.

적정제의 내부 생성을 통한 전기량 적정의 한계에는 생성 전극에서 반응할 수 있는 물질의 존재와 거시적 표본에 대한 암페로메트릭 방법으로 당량점을 찾는 데 어려움이 포함됩니다. 이러한 한계는 외부 생성 셀에서 100% 효율로 일정한 전류로 시약을 외부에서 생성한 다음 적정 셀로 전달하여 극복할 수 있습니다. 적정 셀 내용물을 희석한다는 사소한 단점에도 불구하고 이 절차는 소량으로 존재하는 물질의 자동 제어 및 결정에 적합합니다.

전기량 적정은 시약이 전기적으로 생성되고 그 양이 전류 및 ...

controlled-current-coulometry-coulometric-titration

Education

교육

JoVE Core

Analytical Chemistry

분석 화학

Unit 1

제1단원

Electrochemical Analyses and Redox Titration

전기화학적 분석 및 산화-환원 적정

electrochemical-analyses-and-redox-titration

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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

electrically-generated-reagents-in-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...

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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...

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Potentiometry and Electrochemical Cell Potential

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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...

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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...

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

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,...

potentiometric titration: overview

Endpoint Detection in Potentiometric Titration

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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...

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Electrode Weighing in Electrogravimetric Analysis

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coulometry: overview

Coulometry and Electrical Charge Analysis

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Measuring Analyte Charge by Potentiostatic Coulometry

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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

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

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voltammetry: factors affecting measurements

voltammetry-factors-affecting-measurements

Voltammetry and Faradaic Current

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Voltammogram Shapes and Redox Analysis

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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

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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