Showing posts with label Redox titration. Show all posts
Showing posts with label Redox titration. Show all posts

Monday, February 6, 2023

Redox indicator: Theory, Mechanism, Types, Use, Example, List

Learn about the characteristics, mechanism, examples, and types of redox indicators that are used to detect the endpoint of redox reactions by different ways such as self indicators, redox indicators, external indicators, and instrumental techniques, etc.

Titration, also known as titration, is a volumetric analysis used to determine the concentration of an analyte in a sample solution in the presence of an indicator. Based on the reaction and the goals there are four types of titration: acid-base, complexometric, redox, and precipitation.

A solute is titrated by placing a burette containing a titrant with a known concentration over a conical flask or beaker containing the solute. Titrant is added until the reaction is complete; typically, an indicator indicates an endpoint or an equivalence point of the reaction.

What is redox titration?

Redox titration is a method used in the laboratory to determine the concentration of an analyte by carrying out a redox reaction between the analyte and the titrant. Redox titration depends on the oxidation-reduction reaction that occurs between the analyte and the titrant.

In order to evaluating the redox titrations, it is necessary to obtain the shape of the titration curve that corresponds. In this type of titration, it is much easier to monitoring the concentration of the reaction potential rather than the concentration of the reacting species.

Depending on the titrant used, there are different types of redox titration, such as bromatometry, cerimetry, permanganometry, iodometry or iodimetry, dichrometry, etc., and depending on the method it is classified as direct titration, and back titration.

What is redox indicator in chemistry?

An indicator that exhibits a definite color change at a specific electrode potential is referred to as a redox indicator. Due to the need for a rapid and reversible change in color, the oxidation-reduction equilibrium of an indicator redox system needs to be established very rapidly.

Redox indicators are organic molecules can be either oxidized or reduced, and their oxidized and reduced forms exhibit different colors.

In ox + ne ↔ In red

Example of redox indicator:

A good example of a redox indicator is 2, 2’-bipyridine, it is an organic compound with the formula C10H8N2 that changes color from pale blue to red when in solution at an electrode potential of 0.97 V.

Types of redox indicators:

There are two common types of redox indicators that are used in chemistry are metal complexes of phenanthroline and bipyridine, and organic redox systems.
  • In the systems of metal complexes of phenanthroline and bipyridine the metal changes oxidation state.
  • In the systems of organic redox (methylene blue) systems a proton participate in the redox reaction. Consequently, redox indicators can also be classified into groups of pH-independent or pH-dependent.
Some commonly used redox indicators are methylene blue, diphenylamine, Ferroin (1, 10- phenanthroline iron (II) sulphate, and nitro ferroin, etc.

Redox indicator

Characteristics of redox indicators:

The following are the general characteristics of good redox indicators.
  • In a redox titration, a redox indicator should show that the oxidation potential changes rapidly near the equivalence point.
  • In a redox titration, a redox indicator should characterize the rapid change in oxidation potential near the equivalence point.
  • The ideal redox indicator has an oxidation intermediate midway among the solution titrating and the titrant that need to be produce a sharp, easily noticeable color change.
  • When we carry out the redox reaction, both the oxidation and reduction processes need to be quick and reversible.
  • When operating a specific potential range, each redox indicator will change color.
  • The indicator's standard potential must be at least 0.15V different from the redox system's for a sharp color change at the endpoint.

Mechanism of redox indicator:

Diphenylamine was one of the first redox indicators that were commonly used in titrimetric analysis. Since this molecule is not readily soluble in water and tungstate ion and mercury (II) chloride interfere with its activity, the barium or sodium salt of diphenylamine sulfonic acid is utilized more frequently. 

This indicator is available in both reduced and oxidized forms, with the latter having a dark violet color. Using diphenylamine as an example, it has been shown that the mechanism underlying the color shift is as follows:

The diphenylamine solution in concentrated sulphuric acid (H2SO4) is colorless. It is used while titrating Fe (II) in a solution of potassium dichromate (K2Cr2O7). It is initially converted to colorless diphenyl benzidine by an oxidizing agent. This is then further reversibly oxidized to produce diphenyl benzidine violet.

If diphenyl benzidine violet is let to in an excess of dichromate solution, it will oxidize further. The subsequent oxidation is irreversible, and red or yellow compounds of unknown composition are formed.

List of redox indicators:


pH dependent pH independent
Sodium 2,6-Dibromophenol-indophenol (+0.64 V/+0.22 V) 2,2'-Bipyridine (+1.33 V)
Sodium o-Cresol indophenol (+0.62 V/+0.19 V) Nitrophenanthroline (+1.25 V)
Thionine (+0.56 V/+0.06 V) n- Phenylanthranilic acid (+1.08 V)
Methylene blue (+0.53 V/+0.01 V) 1,10-Phenanthroline (+1.06 V)
Indigotetrasulfonic acid (+0.37 V/-0.05 V) n- Ethoxychrysoidine (+1.00 V)
Indigotrisulfonic acid (+0.33 V/-0.08 V) 2,2`-Bipyridine (+0.97 V)
Indigocarmine ( +0.29 V/-0.13 V) 5,6-Dimethylphenanthroline (+0.97 V)
Indigomono sulfonic acid (+0.26 V/-0.16 V) o- Dianisidine (+0.85 V)
Phenosafranin (+0.28 V/-0.25 V) Sodium diphenylamine sulfonate (+0.84 V)
Safranin T (+0.24 V/-0.29 V) Diphenylbenzidine (+0.76 V)
Neutral red (+0.24 V/-0.33 V) Diphenylamine (+0.76 V)


References:
  • ‘What Is a Redox Indicator in Chemistry?’ ThoughtCo, Available Here: 
  • ‘Redox Indicator’. Wikipedia, 8 Apr. 2022. Wikipedia, Available Here:
  • Redox Indicator - Wikidoc, Available Here
  • Sabnis, Ram W., et al. ‘Indicator Reagents’. Ullmann’s Encyclopedia of Industrial Chemistry, edited by Wiley-VCH Verlag GmbH & Co. KGaA, Wiley-VCH Verlag GmbH & Co. KGaA, 2009, p. a14_127.pub2. DOI.org (Crossref), Available Here:

Keywords:
Examples, internal, work, pharmaceutical analysis


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Friday, January 13, 2023

Applications of redox titration

Titration is a common laboratory technique for quantitative chemical analysis, to determine the concentration of a specific analyte/solute by comparing it with the known concentration of a solution in the presence of an indicator. 

Titration is classified into four different types based on goals and processes such as acid-base titration, redox titration, precipitation titration, and complexometric titration.

What is redox titration?

Redox titration is an analytical method to determine the concentration of sample analyte, redox reactions are oxidation-reduction chemical reactions in which the oxidation states of the reactants change. In which a redox indicator solution or potentiometer is used to determine the endpoint.

There are different types of redox titration depending on the titrant used, such as permanganometry, iodometry, bromatometry, iodimetry, cerimetry, and dichrometry, and based on the method are direct titration and back titration.

The reactions involved in redox titration are redox reactions in which electrons are transferred and oxidation states are changed. As a result, redox titrations are a useful way to learn more about the substances we come into contact with.

Concept of oxidation and reduction:

Oxidation:
It could be described as the loss of electrons to an oxidizing agent to produce a more positive or higher oxidation state.

Reduction:
It could be described as gain electrons from a reducing agent to produce a more negative or lower oxidation state.

Applications of redox titration:

Redox titrations have numerous applications in chemistry, industrial analyses, food industries, pharmaceutical preparations, agriculture, environmental analysis, and other fields. Its common example is the titration of sulfite in wine using iodine, as well as that of alcohol, which can be determined based on its oxidation by potassium dichromate (K2Cr2O7).
  • Industrial applications of redox titration:
Evaluation of chlorination of public water sources is one of the most important industrial applications of redox titration. As well as to determine the purity or content analysis of raw materials, oxidation-reduction reactions are also used.
  • Pharmaceutical applications of redox titration:
Redox titration is used in pharmaceutical analysis to measure the concentration of active pharmaceutical ingredients (concentration of iron) in pharmaceutical goods, such as tablets, capsules, and other medicinal products.
  • Applications of redox titration in chemistry:
Redox reaction is most commonly used to identify elements with medium and high concentrations. Many inorganic analytes can be analyzed using redox titrimetry. In inorganic analysis, it is used to determine the water content in a non-aqueous solvent using Karl Fischer reagent as a titrant. As well as dissolved oxygen can be a determination by this method.
  • Applications of redox titration in food:
The food industry makes broad use of an analytical method that enables it to estimate how much of a reactant is present in a sample. Redox titration can be used to measure the concentration of salt, sugar content as well as vitamin C, and E content present in a food product.

Some of the real-life applications and common applications of redox reactions are as follows.
  • It is used to purify metals.
  • It is used in environmental analysis for the determination of dissolved oxygen.
  • Redox reactions are used to manufacture a wide variety of chemicals, including chlorine and caustic soda.
  • Redox Reaction is used in combustion
  • Redox Reaction is used in electrochemistry
  • Redox Reaction is used in photosynthesis applications
  • Redox Reaction is used in photographic Films
  • Redox reactions are used in the electroplating process
  • Oxidation-reduction reactions are used to sanitize water and bleach materials.

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Class 11 ncert pdf, medicine,  photosynthesis, pharmacy, potential, electrochemistry, everyday life, chemistry, dentistry, food, metallurgy, public health and environmental analyses.
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Thursday, July 7, 2022

What is redox titration in chemistry?

Titration (also known as titrimetry and volumetric analysis) is the most common quantitative and volumetric lab technique for determining the unknown concentration of an analyte by comparing it with the known concentration of a solution in the presence of an indicator.

Depending on the goals and process, there are different types of titrations, such as acid-base titrations, redox titrations, complexometric titrations, and precipitation titrations.

What is redox titration?

Redox titration is a method used in the laboratory to find out the concentration of the analyte by carrying out a redox reaction between the analyte and the titrant.

This titrimetric method is mostly based on the change in oxidation number or the transfer of electrons between the reactants. This means that these reactions are mostly based on oxidation-reduction reactions.

In the oxidation-reduction titration, a reducing substance is titrated with a standard solution of an oxidizing agent (For example - ceric ammonium sulphate (NH4)4Ce (SO4)4), or an oxidizing substance is titrated with the standard solution of the reducing agent(e.g., titanous chloride- TiCl3).

For redox titration evaluation, it is significant to obtain the shape of the titration curve that corresponds. In redox titration, it is much easier to monitor the concentration of the reaction potential rather than the concentration of the reacting species.

What is the principle of redox titration?

The principle behind the oxidation-reduction (Redox) titration is that during the oxidation process, electrons are lost, whereas, during the reduction process, electrons are gained.

Oxidant + ne ↔ Reductant

redox titration

How will we be able to detect the oxidation of a substance?

The substance has experienced oxidation if even one of the scenarios listed below occurs.

If hydrogen is removed from the given substance, if the substance loses electrons, if the oxidation state exhibited by the substance increases, and if oxygen is added to the substance.

How will we be able to detect the reduction of a substance?

If even one of the possibilities listed below is true, we can conclude that the substance has undergone reduction. 

If hydrogen is added to the substance, if the oxidation state exhibited by the substance decreases, if the substance gains electrons and if oxygen is removed from the given substance.

So, you can conclude that there is a transfer of electrons between the analyte and the titrant during redox titrations.

What is the example of redox titration?

An example of redox titration is when an iodine (I2 )solution is treated with a reducing agent such as thiosulfate (Na2S2O3 ) to produce iodide using a starch indicator to detect the endpoint, also referred to as iodometric titration. Another example is the titration of potassium permanganate with oxalic acid.

What are the types of redox titration?

Depending on the titrant used, there are several forms of redox titrations, such as iodometry which uses iodine, dichrometry which uses potassium dichromate, cerimetry which uses cerium(IV) salts, permanganometry which uses potassium permanganate, and bromatometry which uses a bromine (Br2) titrant, etc., and depending on the method, direct titrations, and back titration.


Frequently Asked Question (FAQ):


What is redox titration used for?

Redox titrations are used to determine the concentration of an unknown substance in a solution. The equivalence point is found when the titrant and analyte have reacted stoichiometrically by transferring electrons.

Which indicator is used in redox titration?

A redox indicator is an indicator that changes color change at a specific electrode potential. There are two common classes of redox indicators used in the redox reaction: pH independent (e.g. Diphenylamine, Nitrophenanthroline) and pH dependent (e.g. Methylene blue, Indigo carmine)

What is the role of phosphoric acid in redox titration?

Phosphoric acid is added to reduce the electrode potential for the Fe3+ → Fe2+ by stabilizing the ferric ion. This ensures that the ferric product, Fe3+, remains in its colorless form.

Which is the factor that affects redox titration?

pH is the only factor that influences redox titration. Potassium permanganate (KMnO4) is a good example because it has the maximum oxidizing effect in an acidic condition and the lowest in an alkaline medium.

What are self-indicators?

A self-indicator is a chemical molecule that, in addition to self-participating in the reaction, can also serve as an indicator when the analyte and titrant have finished reacting (Endpoint/equivalence point). An example of a self-indicator is KMnO4.

What is a back titration in chemistry?

A back titration is a technique for estimating the concentration of an analyte by reacting it with an excess of a known reagent. The remaining excess reagent is then titrated with another, second reagent.


Key terms used in redox titrations:

  • Redox titration/oxidation-reduction titration:
A kind of titration in which the analyte and titrant undergo a redox reaction
  • Burette:
A graduated glass tube having a tap at one end is used for titration to administer known volumes of liquid.
  • Analyte:
A substance whose quantity/concentration is to be determined.
  • Titrant:
A solution with a known concentration is filled in the burette that is added to another solution to find out the concentration of a second chemical species.
  • Oxidation:
Oxidation is a chemical process that happens when an atom, molecule, or ion loses one or more electrons. Oxidation increases the oxidation state of a chemical species.
  • Reduction:
A chemical reaction between two substances in which one of the atoms in the reaction gains an electron.
  • Reducing agent:
A reactant gets oxidized to produce electrons in the reaction.
  • Oxidizing agent:
A reactant that undergoes a reduction reaction to gain electrons.


People also ask
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  • Titrant used in redox titration
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  • Acid base and redox titration

References:
  • GH Jeffery, J Bassett, J Mendham, RD Denney, Vogel's Textbook of Quantitative Chemical Analysis, 5th ed, 1989, Wiley, NY.
  • Wikipedia contributors. "Redox titration." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 4 Feb. 2022. 
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Sunday, July 3, 2022

When we titrate oxalic acid with a KMnO4 solution, it gets pink with the first drop of KMnO4 from the burette, why is that?

When we add the first drop of potassium permanganate (KMnO4) to a solution of oxalic acid (C2H2O4), the reaction happens, without a catalyst. So, you can see that the color is slowly disappearing.

Unless you shake it, the pink color gradually fades away if you shake the solution. Furthermore, once we add a few drops, the rate of disappearance accelerates, and as soon as we add a drop of KMnO4 the decolorization happens.

The reason for why it happens is given below.

When we add the first drop of potassium permanganate to a solution of oxalic acid (C2H2O4), the reaction happens automatically, i.e., uncatalyzed. So, we can observe that the color is slowly disappearing. 

After a few drops have been introduced, the formation of Mn2+ ion makes the reaction autocatalytic. KMnO4 droplets are now decolorized more rapidly than before.


What happens in the reaction between potassium permanganate and potassium oxalate?

In which a redox reaction is involved. Oxalic acid is oxidized to CO2 by KMnO4, which itself gets reduced to MnSO4. The reaction takes place in a medium that is acidic (sulphuric acid-H2SO4) and occurs between 60-70 °C.
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Why does a temporary color appear in KMnO4 titration with oxalic acid?

The titration of potassium permanganate (KMnO4) against oxalic acid (C2H2O4) is a redox titration.

As the reaction intensifies, the color of the solution will fade. It will start out dark purple, as the acid is added and the reaction is heated (at room temperature, it is quite slow), the permanganate ions will be converted to manganese 2+ cations in solution.

These are almost colorless (a very pale pink) while oxalic acid (C2H2O4) is converted to carbon dioxide (CO2) and water (H2O). For complete oxidation to occur, the reaction must occur in an acidic solution, which is usually accomplished by adding dilute sulfuric acid (H2SO4) to the process. 

Throughout the reaction, if the solution becomes neutral, some brown manganese (IV) oxide MnO2 will also form (which will precipitate out).


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Saturday, July 2, 2022

Why does oxalic acid decolorize potassium permanganate?

KMnO4 is a potent oxidizer, and as a result, oxalic acid is oxidized to carbon dioxide (CO2). Therefore, its deep purple color disappears and Mn²⁺ ions are formed. These give a very light pink color to the aqueous solution, while bubbling can be seen.

In the redox titration of potassium permanganate (KMnO4) against the standard solution of oxalic acid (C2H2O4), potassium permanganate is a strong oxidizing agent and becomes even more potent when sulfuric acid (H2SO4), is present.

The following equation represents the oxidizing ability of KMnO4 in an acidic medium.
MnO4– + 8H+ + 5e– → Mn2+ + 4H2O

When permanganate solution is introduced to a solution containing a reducing agent, the permanganate solution is decolorized because the solution containing MnO4- ions is purple while the solution containing Mn2+ ions is colorless. At the moment when KMnO4 is present in excess, the solution turns purple. Consequently, KMnO4 acts as a self-indicator in acidic solutions.



Frequently Asked Question (FAQ):

Explain in short why adding oxalic acid to KMnO4's solution in an acidic medium causes the color to disappear.

Potassium permanganate oxidizes oxalic acid to CO2 and itself turns into Mn2+ ions which are colorless.

What color change occurs at the endpoint of the permanganate oxalate reaction?

As permanganate is added to the oxalate solution, it turns purple and then the permanganate is consumed, and the purple color disappears. As more permanganate is added and eventually all oxalates are oxidized, and the endpoint is indicated by the appearance of a faint purple color, due to the presence of excess permanganate.

Why in the titration of oxalic acid with KMnO4 pink colour disappears slowly at the beginning but rapidly afterwards?

Because of the formation of Mn2+ ions which act as auto-catalysts for the reaction, the pink colour disappears slowly at the beginning but rapidly afterwards.




People also ask:
  • Why does KMnO4 disappear when oxalic acid?
  • Does oxalic acid decolorize potassium permanganate?
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  • Why the purple colour of permanganate disappears by adding it to the aqueous solution of oxalic acid?
  • Why in the titration of oxalic acid with KMnO4 pink colour disappears slowly at the beginning but rapidly afterwards?
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Friday, July 1, 2022

Why is it necessary to heat the oxalic acid solution?

Oxalic acid (C2H2O4) solution required to be warmed along with diluted sulphuric acid (H2SO4) before being titrated against potassium permanganate (KMnO4). This is important because the reaction takes place at a higher temperature.

Throughout the titration, first manganous sulphate (MnSO4) is formed; this compound acts as a catalyst for the reduction of KMnO4 by C2H2O4. Consequently, the initial reaction rate is slow, and as the reaction progresses, the reaction rate increases.

Why do you need to heat the solution before titrating it against permanganate?

By oxidizing oxalic acid in a solution of potassium permanganate, carbon dioxide is produced. To remove the CO2 gas produced in the preceding reaction, the reaction mixture must be maintained hot which is conducive to the further reaction. Therefore, before beginning the titration, the reaction mixture is warmed to 60–70 °C.

Why is oxalic acid heated and not boiled while titrating against KMnO4?

Oxalic acid (C2H2O4) is an organic compound that decomposes when heating to excessive. Also, note that we add a stoichiometric amount of concentrated sulfuric acid (H2SO4) to the titration.  

Now, H2SO4 is an exceptional dehydrating agent, its converts the C2H2O4 into carbon dioxide (CO2), carbon monoxide (CO), and water (H2O). High temperatures cause this reaction to accelerate. So, we heat slowly until the vapor starts to form instead of just boiling.

Why is Mohr’s salt not heated during titration?

Mohr's salt is a very powerful reducing agent. At room temperature, it reduces the (Mn+2) cation from KMnO4. Because of this, it is not heated.



Frequently Asked Question (FAQ):
  • What happens if the reaction mixture is heated above 70 degrees in the titration of oxalic acid and KMnO4 (Redox  titation)?
  • Why do we heat the solution before titration?
  • Why is a titrate heated to nearly 60°C during the titration of KMnO4 vs. oxalic acid?
  • Why is heating done for oxalic acid, and KMnO4 titration?
  • Why is it necessary to heat oxalic acid and dilute H2SO4 before titration in permanganometric titration?
  • Why do we heat oxalic acid solution containing sulphuric acid?
  • Why oxalic acid solution is needed to be warmed between 50- 60°C before it is titrated with permanganate solution?
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Thursday, June 30, 2022

Endpoint in KMnO4 titration

In the titration of KMnO4 and C2H2O, the oxalic acid is the analyte, and potassium permanganate is the titrant. The oxidizing and reducing agents are potassium permanganate and oxalic acid, respectively.

Because the permanganate ion in an acidic medium is a very potent oxidizing agent, the reaction between potassium permanganate and oxalic acid is conducted in an acidic medium.

By introducing weak H2SO4, the acidic condition is maintained. No other indicator is required to determine the endpoint, as KMnO4 acts as an self-indicator.


What is the endpoint potassium permanganate titration?

In redox titration such as potassium permanganate (KMnO4) with oxalic acid (C2H2O4), the solution of oxalic acid is in a conical flask and the solution of potassium permanganate is filled in the burette.

When we perform titration, on reaction with oxalic acid, permanganate solution discharged its violet color. The endpoint is indicated by the appearance of a pale pink color. Potassium permanganate acts as a self-indicator in these titration.

Why is the color of KMnO4 purple before the titration and after the endpoint it is pink?

The answer to this question is found in the experiment. During the titration, the Mn oxidation number is +7 before the reaction and after the reaction, it forms mostly +2. As a result of this transition, the color evolved to be pink which is why we see pink at the endpoint.

Why is the endpoint in permanganate titration not permanent?

The excess permanganate ion slowly reacts with the relatively large concentration of manganese (II) ions at the endpoint, this is the reason that the color of KMnO4 at the end point of titration may disappear after some time.

Why is the endpoint in the titration of KMnO4 and H2C2O4 pink?

The reaction between potassium permanganate and oxalic acid and H2C2O4 is a redox reaction in which MnO4- is reduced to Mn2+ while (C2O4)2- is oxidized to form CO2. The color of Mn2+ is very pale pink, and in low concentrations, it is almost completely colorless.

The pink color that you observe at the titration's end point is caused by the one additional drop of MnO4-, which does not decolorize because there isn't any further (C2O4)2- present to react with it. 

The contents of the flask dilute the excessively purple droplet, making it appear pink. This deep purple color drop is diluted with the contents of the flask and therefore appears pink.

Why do we add dilute H2SO4 in the titration of KmNO4 with oxalic acid?

Because KMnO4 acts as an oxidizing agent only in acidic environments, to create an acidic environment, diluted sulphuric acid is introduced.

What is the color change of KMnO4 in the acidic, alkaline, and neutral medium in titration?

  • Due to Mn (2+, it turns from purple to a faint permanent pink color in an acidic medium.
  • The color of the MnO2 precipitates changes in neutral media, going from purple to reddish brown.
  • Mn(VI)O4(2-), 1-electron turns from purple to green in strongly alkaline media.


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  • What is the endpoint of a titration of oxalic acid and KMnO4 solution?
  • What is the indicator used in permanganometric titration what is its endpoint?
  • The colour of end point in KMnO4 oxalic acid titration is…..
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Why is an indicator not needed in titration with KMnO4?

It’s because KMnO4 acts as a self-indicator, the indicator is not required in the titration of permanganometry. A self-indicator is a chemical compound that itself indicates the endpoint of the titration.

KMnO4 is an oxidizing agent that turns purple in solution and becomes colorless when reduced to Mn2+ ions. Potassium permanganate is used in redox titrations as a titrant against a solution or analyte that contains Fe2+ ions. 

It is a deep purple color in an environment with a basic pH level. When introduced to an acidic medium, KMnO4 turns colorless. This is due to the reduction of KMnO4 and the transition of Mn (VII) to an Mn (II) state. For this reason, we don't need to use an indicator.

Its primary purpose is to provide a visual signal for the viewer so that they can determine when the reaction is complete. Additionally, potassium permanganate is a very potent indicator. 

Particularly if we perform the titration in reverse (Example: the acid in the burette and permanganate in the conical flask) such that the permanganate changes from pink to colorless, it's very simple to detect the color change.

For example, when KMnO4 is in slight excess, a solution of sodium oxalate (Na2C2O4) and potassium permanganate (KMnO4) turns from colorless to pink.
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Wednesday, June 29, 2022

Why KMnO4 is a self indicator

Potassium permanganate (KMnO4) is a versatile and powerful oxidant. It can be used direct or indirect to classify many different substances. The unique property of potassium permanganate is that it acts as a self-indicator in redox titrations.

KMnO4 is intense purple, when used in redox titration it is reduced to brown Mn2+ ion (in acidic conditions) at the endpoint, and the color transition at the endpoint can be quickly observed. The titration of potassium permanganate against oxalic acid is an example of redox titration.

Why KMnO4 is a self indicator?

KMnO4 is always in a stable form. In an acidic condition, KMnO4 undergoes reduction from Mn2 +. As a result, the color of the solution changes from pink to brown. Once KMnO4 starts to react in a chemical reaction, no separate indicator for permanganate titration is required. Due to color changes, we will observe the indication. Therefore, KMnO4 is a self-indicator in analysis.

A self-indicator is a chemical compound that itself indicates the endpoint of the titration. The discussion above leads us to the conclusion that KMnO4 is a self-indicator.


Frequently Asked Question (FAQ):

Why is potassium dichromate not a self-indicator?

Since potassium dichromate (k2cr2o7) acts as an oxidizing agent only in acidic conditions, it cannot be used as a self-indicator since its reduction product blocks itself during visual detection at the end of the reaction.

In which titration is KMnO4 used as a self-indicator?

KMnO4 is used as a self-indicator in redox titration to detect the endpoint. Redox titration is performed to identify the oxidizing or reducing agents in a solution. In redox titration, either the reducing or oxidizing agent will be employed as the titrant against the other agent.

Is permanganate a self-indicator?

Yes, permanganate is a self-indicator. Solutions of KMnO4 are dark purple. When employed as a titrant, once the endpoint is reached and the KMnO4- is in excess, the solution has a permanent pink color when employed as a titrant (provided that the solution is initially colorless). KMnO4 serves as its self indicator as a result.

Why is KMnO4 strong oxidizing agent?

KMnO4 is a strong oxidizing agent since the main metal atom (Mn) in KMnO4 is in an extremely high +7 oxidation state, meaning it has lost all of its valence electrons. As a result, KMnO4 is a potent oxidizing agent.


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Monday, May 23, 2022

Redox titration: Principle, Types, Indicators, Applications, and Advantages

Learn about the principle, types, and applications of redox titration, which is a type of titration based on a redox reaction between analyte and titrant.  

Titration is a type of quantitative chemical analysis used to determine an analyte's unknown concentration. It is also known as titrimetry referring to volumetric analysis because volume measurement is important in titration. The titrant is added from a burette until the reaction is complete, and an indicator is usually employed to signify the equivalence point or endpoint.

 Titration consists of four types based on the different procedures and goals such as including acid-base, complexometric, precipitation, and redox titration.

What is redox titration explain with example?

A redox titration is called oxidation-reduction titration it is an oxidation-reduction process that takes place between an oxidizing and a reducing agent. In this type of titration, a chemical reaction occurs with the transfer of electrons to the reactant ions of aqueous solutions. 
Principle and types of redox titration

In the oxidation-reduction titration process, an oxidizing compound is titrated with the standard solution of the reducing agent, or a reducing compound is titrated with a standard solution of an oxidizing agent.

It is used for the analysis of organic solutes and generally evaluating chlorination. In an oxidation-reduction (redox) titration, generally, a potentiometer or redox indicator solution is used. 

Treating an iodine solution with a reducing agent to form iodide while using a starch indicator to aid determine the endpoint of the titration is the most common example of redox titration.
 

What is the principle of redox titration?

The principle involved in oxidation-reduction (Redox titration) is that the oxidation process involves the loss of electrons while the reduction process involves the gain of electrons.

Oxidant + ne ↔ Reductant

The following are the key characteristics of redox reactions which consist of both oxidation and reduction reactions.

Oxidation reaction:
The following are examples of how a solute can be oxidation reaction:
Oxygen atom addition
  • Hydrogen atom removal
  • Electron donation or loss
  • An overall enhance in the substance's oxidation state
Reduction reaction:
The following are examples of how a solute can be reduction reaction:
  • Hydrogen atom addition
  • Oxygen atom removal
  • Accepting electrons
  • Reduction in the oxidation state of the analyte

Redox titration curve:

It is important to understand the shape of the redox titration curve to evaluate it. The titration curve of a complexometric titration or an acid-base titration explains how the concentration of H3O+ or Mn+ varies as titrant is added. In redox titrations, it is more suitable to monitor the potential of the titration reaction rather than the concentration of a species.  

Indicators used in redox titration:

Potassium permanganate, iodine, ceric ammonium sulphate, phenanthroline blue, methylene blue, ferrous ions in dichromate solution, 1, 10 phenanthroline monohydrate, 2,2’-bipyridine, 5,6-dimethyl phenanthroline, and safrannin-T. Etc. are the commonly used redox indicators. 

The endpoint of redox titrations can be determined in a variety of ways such as self indicators, external Indicators, redox indicators, and instrumental techniques, etc. 

The redox indicators are indicators that exhibit a reversible change of color between oxidized and reduced forms and undergo a specified color change at a specific potential. These are indicators are weak reductants or oxidizers that have different colors in their reduced and oxidized forms. 

The color changes take place within a specific redox potential transition range, which must include the redox potential at the equivalence point in the redox titration to be performed.

If using an oxidizing volumetric solution, the indicator's redox potential should be greater than the potential of the solution, and when using a reducing volumetric solution, it should be lower.

Types of redox titration:

There are different types of redox titration based on the titrant used they are bromatometry, iodometry or iodimetry, cerimetry, permanganometry, and dichrometry, etc., and based on the method they are classified as direct titration, and back titration.

Iodometric titration:

The iodometric titration is a process for determining the concentration of an oxidizing agent in a sample solution. It is a type of redox titration that uses sodium thiosulphate, as a reducing agent to titrate iodine. A starch solution is used as an indicator in an iodometric titration because it can absorb the iodine (I2) that is released.

Iodimetric titration:

When an analyte that is a reducing agent is directly titrated with a standard iodine solution, the method is called iodimetry.

Bromatometry titration:

Bromatometry is the process that involves titration by oxidation using potassium bromate. It is a type of redox titration that is used to determine the bromination of a chemical indicator.

Cerimetric titration:

Cerimetry is a method of volumetric chemical analysis that can be used for analyses of nonstoichiometric levels that either oxidize Fe2+ or reduce Fe3+. It is a type of redox titration in which the endpoint is determined by a color change in the iron (II)–1, 10-phenanthroline complex (ferroin).

Permanganometric titration:

It is a type of redox titration in which the permanganate is used to determine the amount of analyte present in unknown samples solution. Permanganometry provides the detection and quantification of different chemical species, including manganese (II), iron (II), oxalate, nitrite, and hydrogen peroxide, etc.

Dichrometry titration:

It is a qualitative analysis in chemistry it involves the use of potassium dichromate (K2Cr2O7) which is used to determine the amount of solute in the sample.  

Applications of redox titration:

Redox titration is a quantitative chemical analysis method with a variety of applications, some of which are listed below.
  • Redox titration applied in the pharmaceutical field
  • It is used in public health and environmental analyses
  • It is used in the food industry
  • Applications of redox titration in different industries for research
  • Applications of redox titration in chemistry
  • Redox titration also used in the real-life applications
  • Redox reaction used in electrochemistry
  • The theory and practical taught in schools and colleges

Advantages of redox titration:

  • It's usually inexpensive and requires little equipment which is generally available in the lab
  • It does not need particular or expensive chemicals
  • Does not require high expertise, has a simple operating procedure
  • The analysis can be automated, with very precise results
  • Provides quick results

Disadvantages of redox titration:

  • It is a destructive technique that frequently consumes large amounts of the substance being analyzed
  • It requires reactions to take place in a liquid phase
  • It produces large volumes of chemical waste


Commonly asked questions on redox titration are as follows.

What are the factors affecting redox titrations?
The concentration of reactant, completeness of the reaction, temperature, and pH are the major factors that affect redox titration.

What are apparatus needed for titration?
Apparatus used to perform titration consist burette, stand, conical flask, pipette, funnel, beaker, volumetric flask, burette and wash bottle, etc., as well as some instruments such as pH meter, conductivity meter, colorimeter, Karl-Fischer titrator, and potentiometer, etc., are also used for different methods of titration.

What is the importance of the redox reaction?
A wide range of inorganic analytes can be analyzed using redox titration Oxidation-reduction reactions are extremely important not just in chemistry, biochemistry, and industrial processes, but also in geology and biology.
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