Name: using iodine to find unknown concentrations
Uploaded: 2024-12-05T18:31:57.000Z
Duration: 1 min 23 s
Channel: JoVE

요오도메트리(Iodometry)와 요오드측정법(iodimetry)은 각각 샘플에 존재하는 산화제 또는 환원제의 양을 분석하는 데 사용되는 적정법입니다.
요오드 적정에서 산화 분석물 용액은 일반적으로 산성화되고 과도한 요오드 이온으로 처리되어 트리요오드화물과 평형 상태에서 동일한 양의 요오드를 생성합니다. 그런 다음 유리된 요오드를 표준화된 환원제에 대해 적정합니다.
갓 준비된 전분 용액을 종말점 근처에 첨가하여 매우 진한 파란색 전분-요오드 복합체를 형성합니다. 그런 다음 파란색이 사라질 때까지 적정이 계속됩니다.
산화 분석물과 환원 적정제 사이의 요오드를 통한 화학량론적 관계를 통해 분석물의 농도를 측정할 수 있습니다.
대조적으로, 요오드 적정은 용액이 짙은 파란색으로 변할 때까지 표준 요오드 용액에 대해 전분이 있는 상태에서 환원 분석물을 직접 적정하여 모든 분석물이 산화되고 전분-요오드 복합체가 형성되고 있음을 보여줍니다.
반응 화학량론과 소비된 적정제의 부피를 알면 분석물의 농도를 측정할 수 있습니다.

산화환원적정: 요오드 측정법과 요오드 측정법

Redox Titration: Iodimetry and Iodometry

요오드 측정법과 요오드 측정법은 요오드를 사용하여 산화제 또는 환원제의 농도를 결정하는 데 사용되는 분석 방법입니다. 요오드 측정법 적정에서 산화 분석물 용액은 일반적으로 산성화되고 과잉의 요오드 이온으로 처리되어 삼요오드와 평형을 이루는 동일한 양의 요오드가 생성됩니다. 방출된 요오드는 이후 표준화된 환원제에 대해 직접 적정됩니다. 희석된 요오드 색상이 옅은 노란색이 되면 새로 준비한 전분 용액 몇 방울을 첨가하여 진한 진한 파란색 전분-요오드 복합체를 만듭니다. 적정은 파란색이 사라질 때까지 계속되어 요오드, 산화 분석물 및 환원 적정제 간의 화학양론적 관계를 통해 분석물의 농도를 결정할 수 있습니다. 정확한 결과를 얻으려면 적정을 빠르고 강하게 교반하면서 수행해야 합니다.

요오드 적정에서 환원 분석물은 전분이 있는 표준 요오드 용액에 대해 직접 적정됩니다. 전분은 지시약 역할을 하며 요오드가 과도할 때 진한 파란색 전분-요오드 복합체를 형성합니다. 적정이 진행됨에 따라 환원 분석물은 요오드와 반응하여 요오드 농도가 감소합니다. 모든 환원 분석물이 반응하고 완전히 산화되면 추가된 요오드는 환원되지 않아 진한 파란색 전분-요오드 복합체가 형성됩니다. 이 색상 변화는 적정의 종말점을 나타냅니다.

분석물의 농도를 결정하기 위해 반응의 화학양론(균형 화학 방정식으로 표현)과 적정 중에 사용된 표준 요오드 용액의 부피를 고려합니다. 분석물과 반응한 요오드의 양과 요오드와 분석물 간의 화학양론적 관계를 알면 원래 샘플에서 환원 분석물의 농도를 정확하게 결정할 수 있습니다.

요오드 측정 및 요오드 측정은 요오드를 사용하여 산화제 또는 환원제의 농도를 결정하는 데 사용되는 분석 방법입니다. 요오드 적정에서, ...

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

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 triiodide. The iodine is then titrated against a standardized reducing agent.

As the iodine solution becomes pale yellow, a few drops of freshly prepared starch solution are added. Starch forms a dark blue starch-iodine complex. The titration continues until the blue color disappears. The sample should be stirred vigorously and the titration should be done quickly for accurate results.

In iodimetric titrations, the process is reversed. A reducing analyte is titrated directly with a standard iodine solution in the presence of starch. As the reducing analyte reacts with iodine, the iodine level drops. When all of the reducing analyte has reacted, extra iodine remains and the dark blue starch-iodine complex appears. That color change marks the endpoint.

For both methods, the concentration of the analyte is calculated from the balanced chemical equation and the volume of iodine solution or titrant used. The stoichiometric relationship between iodine and the analyte shows how much of the sample reacted. This makes iodometry and iodimetry useful analytical tools for measuring unknown redox concentrations.

Using Iodine to Find Unknown Concentrations

using-iodine-to-find-unknown-concentrations

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...

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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,...

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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...

redox titration: iodimetry and iodometry

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

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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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...

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controlled-current-coulometry-coulometric-titration

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

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voltammetry: factors affecting measurements

voltammetry-factors-affecting-measurements

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

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

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voltammetric techniques: pulse voltammetry

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Pulse Voltage Methods for Electrochemistry

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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

Learn how iodometry and iodimetry use iodine, iodide, and starch to measure unknown oxidizing or reducing agents in redox titrations.

Using Iodine to Find Unknown Concentrations | JoVE K12

analytical chemistry

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.

Using Iodine to Find Unknown Concentrations

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