Thursday, July 21, 2022

How to remove air bubbles from burette tip

Titration, also known as titrimetry, is a method used to determine the concentration of an unknown solution by comparing it to the concentration of a known solution in the presence of an indicator. Titration is a quantitative as well as volumetric technique. To carry out the titration, you will need different apparatus, such as a pipette, burette, conical flask, volumetric flask, beaker, etc.

Before performing the titration experiment, ensure that the titration apparatus or glassware are properly rinsed with deionized water to remove any sample residue. Before taking the initial reading of the burette, make sure the tip is clean and dry. Once your burette is conditioned and filled without any air bubbles or leakage, take an initial volume reading.

How do you remove air bubbles from the burette tip?

By draining some volume of titrant into a beaker, we eliminate air bubbles that may be present at the tip of the burette as well as the stopcock. If the bubbles persist, you can try forcing the titrant through the burette tip at a higher rate. Then grasp the burette and slightly jerk it down when the stopcock is open.

How does an air bubble affect titration?

If an air bubble is present during the titration, the volume reading may be inaccurate. Throughout the titration, the amount of air released from the tip will be counted along with the amount of titrant that has already left the burette.

This indicates that the volume of solution delivered through the tip will not equal the volume determined by taking the final burette reading and subtracting it from the initial reading.

Why are air bubbles in the burette tip a possible source of error in a titration experiment? How do you remove air bubbles from the burette tip?

Burets measure how much volume of liquid is released through the tip. During the titration, the amount of air released from the tip will be counted along with the volume of the titrant that has already left the burette.

This means that the volume of liquid delivered through the tip will not be the amount calculated by subtracting the final burette reading from the initial burette reading. This cause error in calculations and therefore it is considered a possible source of error in a titration experiment.

The following are different ways to remove air bubbles.
  • When you quickly open the burette valve, the air bubble is often removed from the tip.
  • If you gently tapping the tip of the burette while the titrant is flowing, the air bubble may remove.
  • Use a squeeze bulb on the top of the burette to push the liquid out through the tip while the burette valve is open.

Why do bubbles of air rise up through water?

Bubbles are gases, which have a lower density than liquid water. They get pushed up to the surface because they are less dense and rise up as they are lighter than around them.

What will happen if we don't remove the air bubbles from the nozzle of a burette?

While doing the titration if we do not remove the air bubble from the nozzle of the burette, we will get inaccurate results. The process of titration is the one that is used in the analysis. Because the presence of air bubbles results in causes errors in volume readings.




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Wednesday, July 20, 2022

Why does the burette need to be rinsed before titration?

After washing the burette with water, we have to rinse it with titrant so that the results of experiments or titrations are more accurate. It is required to rinse the burette with water after washing because if the burette is used without adequate cleaning and washing, the results of some studies using the burette may be inaccurate and the readings due to the presence of water droplets values may vary.

Titration, or titrimetry, is a quantitative and volumetric method for determining the concentration of an unknown solution using the concentration of a known solution in the presence of an indicator. A burette, pipette, conical flask, volumetric flask, beaker, etc. are required for conducting the titration.

Why is it important to rinse the burette with the titrant before beginning the titration?

It is significant to rinse the burette with distilled water to remove contaminants. In addition, it should be rinsed with a titrant to remove any possible traces of distilled water, to ensure that the solution in the burette is not diluted.

Why do you need to rinse the burette with a base before you completely fill it with NaOH?

The purpose of the burette is to measure the volume precisely. The accuracy of the titration determines its accuracy. The accuracy of a titration is directly proportional to precision.

If the burette had an acidic chemical residue, it would neutralize a portion of the sodium hydroxide solution that you are using to measure. This will lead you to believe that there was more acid in our sample than it actually was.

The rinsing with base ensures that none of your NaOH is unintentionally neutralized by unwanted chemical residue in the burette, which would change the concentration of a prepared solution of NaOH which may give a calculation error.

Why is it important to rinse the burette of an auto titrator before analysis?

If the burette hasn't dried completely before we use it, any trace of water that's still inside will dilute our titrant, resulting in a change in the concentration of the solution.



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Friday, July 15, 2022

What is complexometric titration in chemistry?

Titration, also known as titrimetry and volumetric analysis, is a chemical qualitative analysis technique that is used to determine the unknown concentration of an identified analyte. In the process of titration, an analyte and a titrant are used. To find the endpoint of titration for analysis, a known concentration of titrant is added to an unknown quantity of analyte. 

When the endpoint is reached, the moles of titrant and analyte will be identical. Titration can be divided according to its processes and goals, acid-base titration, complexometric titration, precipitation titration, redox titration, etc.

What is complexometric titration?

Complexometric titration also called chelatometry used to determine the metal ions n a solution. It is a type of volumetric titration wherein the colored complex is used to determine the endpoint of the titration. In this kind of titration, an indicator is used that can cause a clear change in color in the titration, which shows the endpoint of the titration.

In complexometric titrations, a metal-ligand complexation reaction is used. It is based on the formation of a complex between the analyte and the titrant. It is a common method to titrate metal ions in a solution using the chelating agent EDTA.

One example of complexometric titration is the process of determining the hardness of water by titrating it with EDTA while using eriochrome black-T as the indicator. For complexometric titrations in analytical chemistry, EDTA (Ethylenediaminetetraacetic acid) is one of the most often employed chelating agents.

What is the principle of complexometric titration?

The principle behind complexometric titrations is the transformation of a simple ion into a complete ion to determine the endpoint using a metal indicator and the displacement of water from the solvation sphere of the metal ions by ligands.

When EBT binds to metal ions, it turns a wine-red color. Though, when it is not bound to metal ions, it remains blue. While EDTA is colorless regardless of whether it is coupled or not to a metal ion.

What are the indicators used in complexometric titration?

Complexometric indicators are the indicators used in complexometric titrations. When particular metal ions are present, the color of these indicators changes significantly. These are also referred to as metallochromic indicators or PM indicators.

These indicators are water-soluble organic molecules. Some complexometric indicators are Eriochrome Black T, calcein, fast sulphon black, hematoxylin, Curcumin, etc.

Examples of indicators that turn pink when calcium or magnesium is present are Calmagite and Eriochrome Black-T. A complexometric EDTA titration using either Calmagite or EBT as the indicator reaches its endpoint when the color changes from pink to blue.

What is the classification of complexometric titration?

Ethylene diamine tetra acetic acid (EDTA) can be used as a chelating titrant in several ways. Consequently, EDTA titrations can be performed in a variety of ways, as follows.

Direct titration:

Direct titration is the most practical and easy method of EDTA isometric titration. It is similar to the acid-base titration technique. To provide a sample with metals, the EDTA solution is added to the titration standard. This sample is then titrated until the endpoint is reached. Direct complexometric titration can be used to identify a variety of metals including zinc, copper, aluminum, barium, lead, mercury, bismuth, chromium, etc.

Back titration:

Because we are titrating for the excess amount of EDTA, this is known as back titration. An excess of EDTA standard solution is added to the metal solution. The excess EDTA is then back titrated with the solution of the second metal ion.

Replacement titration:

Substitution titration is used when direct titration or back titration fails to produce sharp endpoints. The metal–EDTA complex receives this analyte; the metal present in the analyte displaces another metal from the metal-EDTA complex.

Indirect titration:

Certain anions react with metal cations to form a precipitate. EDTA does not affect these anions. Consequently, indirect titration with EDTA can be employed to analyze these substances. Indirect titration can be used to determine barium ions.


Key terms used in complexometric titrations:

  • 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.
  • Buffer: A solution consisting of an acid and its conjugate base is used to control the pH of a solution.
  • pH: A measure of the hydrogen ion concentration is equal to - log [H+].
  • Complex: a substance composed of two or more components capable of independent existence.
  • Metal chelate: a species that is simultaneously bound to two or more sites on a ligand.
  • Complexing agent or ligand: molecules and/or anions with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond.
  • Chelation: the process involved in the formation of a chelate.
  • Chelating agents: organic molecules containing two or more donor groups that combine with metal to form a complex are having a ring structure.


Frequently Asked Question (FAQ):


What are the methods of endpoint detection in complexometric titration?

In a complexometric titration, there are two ways to identify the endpoint: visual technique and instrumental techniques.

Why eriochrome black t is used in complexometric titration?

In complexometric titrations, the eriochrome black T is used as an indicator because it forms a colored complex in its protonated form with calcium, magnesium, or other metal ions. In the process, its color shifts from blue to pink and red.

What is the role of buffer solution is used in EDTA titration?

All reactions between metal ions and EDTA are pH-dependent, so a buffer solution is used because it is resistant to pH changes. Ammonium chloride and ammonia buffer (NH4Cl + NH4OH buffer) buffer solution of pH 10 is used in EDTA titration to determine the hardness of the water.



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Saturday, July 9, 2022

What is acid base titration in chemistry?

Titration is also known as titrimetry is a quantitative and volumetric method for determining the concentration of an unknown solution using the concentration of a known solution in the presence of an indicator.

To determine the concentration of an analyte in a solution, it is necessary to slowly add a volume of titrant (typically with a burette) until the color of the indicator changes to indicate a chemical reaction.

In quantitative chemical analysis, there are four types of titrations in terms of their purposes and methods, such as acid-base titration, redox titrations, precipitation titrations, and complexometric titrations.

What is acid-base titration?

As you know, there are a lot of different compounds, both organic and inorganic. With the help of titration, you can determine their acidic or basic properties.

An acid-base titration is a quantitative analysis technique for determining the concentration of an acid or base by neutralizing it with a standard solution of acid or base of known concentration (Molarity).

Acid-base titrations involve neutralizing acids and a base therefore is also known as neutralization titration. It depends on the analyte's chemical interaction with a standard reagent.

Three different theories have been proposed to characterize acids and bases Arrhenius theory, Bronsted-Lowry theory, and the Lewis theory of acids and bases.

What is the principle of acid-base titration?

The acid-base titration principle is based on the neutralizing reaction that occurs between acid and base.
ACID + BASE ⇒ SALT + WATER

Strong/ weak acids or bases are used in acid-base titrations. It is used to determine how much acid or base there is. It is also used to determine the strength of an unknown acid or base. It determines the pKa of an unknown acid or pKb of an unknown base. 

Not every reaction can be called a titration. Consequently, a reaction can be considered a titration under certain conditions. 

The conditions are listed below:
  • The reaction must quickly.
  • A stoichiometric reaction should take place.
  • The change in free energy during the reaction must be sufficiently large.
  • There should be a method to determine the completion of the result.

What is an example of acid-base titration?

One example of an acid-base titration is the standardization of a NaOH solution usingCH3COOH, where sodium hydroxide is used as the strong base and is added to the burette, and acetic acid is used as the weak acid and is added to the conical flask. Acetic acid dissociation rises when a strong base is introduced to a weak acid.

What is the classification of acid-base titration?

Acid-base titrations are classified into four categories such as strong acid and strong base, weak acid and a strong base, weak base and strong acid, and weak acid and weak base.

Strong acid-strong base titration:
Example: Titration of hydrochloric acid (HCl) which is a strong acid and sodium hydroxide (NaOH) which is a strong base.

Weak acid and a strong base titration:
Example: Titration of acetic acid (CH3COOH) which is a weak acid and sodium hydroxide (NaOH) which is a strong base.

Weak base and strong acid:
Example: Titration of ammonia (NH3) which is a weak base and hydrochloric acid (HCl) which is a strong acid.

Weak acid and weak base:
Example: Weak acid includes formic Acid (HCOOH), Acetic Acid (CH3OOH), etc, and the weak base includes Ammonium Hydroxide (NH4OH), Ammonia (NH3)

What are indicators in acid base titration?

Acid-base indicators are weak acid or weak base that changes color as the concentration of hydrogen (H+) or hydroxide (OH-) ions in an aqueous solution changes. However, unlike other acids, the acid and base form the indicator have unique colors.

Indicators are often used in applications that require pH changes, such as titrations, pH tests, and science presentations because the color of the indicator depends on the pH of the solution.

The pH range of an indicator, which is dependent on the acid strength of the indicator, is its most important characteristic. The range of pH values over which an indicator changes color from its acid form to its base form is known as the indicator's pH range.

It extends from the highest pH, where only the acid form is visible, to the lowest pH, where only the basic form is visible. The indicator is insensitive to pH changes outside its range because it does not change color at these pH values.

Phenolphthalein and methyl orange are the two most common indicators used in the acid-base titration. Litmus is probably the best-known pH indicator. Common acid-base indicators include methyl red, thymol blue, bromocresol green, phenol red, etc.

What is the equivalence point in an acid-base titration?

The equivalence point is the point in a titration where the amount of titrant added is just enough to make the analyte solution completely neutral. In an acid-base titration, the equivalence point, moles of base = moles of acid, and the solution only contains salt and water. The endpoint of a reaction is the moment at which the reaction is completed.

It is essential to remember that endpoints and equivalence points may not be the same. As the equivalence point is determined by the stoichiometry of the reaction, whereas the endpoint is just the change in color of the indicator. 

Usually, the endpoint can be determined only after the addition of a slight excess amount of the titrant. If the endpoint is different from the equivalence point, then it amounts to an error in the experiment.


Key terms used in acid-base titrations:

  • 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.
  • Buffer
A solution consisting of an acid and its conjugate base is used to control the pH of a solution.
  • pH
A measure of the hydrogen ion concentration is equal to - log [H+].
  • pKa
The pKa value describes the acidity of a certain molecule. The strength of an acid is determined by how tightly a proton is retained by a Bronsted acid.


Frequently Asked Questions (FAQ):


What is the titration curve in chemistry?

The plot of the pH of the analyte solution vs the volume of titrant applied added as the titration progresses.

Why is acid-base titration important?

The main purpose of a strong acid-strong base titration is to determine the concentration of an acid solution by titrating it with a solution of known concentration, or vice versa until neutralization occurs. Therefore, the reaction between a strong acid base and a strong base will produce water and salt.

What are the steps of acid-base titration?

The steps of acid-base titration are: selection of titrant and the titrate, selection of normality of titrate, select the amount of liquid you wish to pipette, selection of indicator, note the endpoint when solution changes color, and calculate the normality of the titrant using the final reading.

Which indicator is used in acid-base titration?

Common acid-base indicators include methyl red, thymol blue, bromocresol green, phenol red, etc. Phenolphthalein and methyl orange are the two most common indicators used in the acid-base titration. 

Litmus is probably the best-known pH indicator. Phenolphthalein is chosen because of its pH-dependent color change between 8.3 and 10. It shows pink in basic solutions and colorless in acidic ones.

Why is NaOH used in titration?

In a titration, sodium hydroxide is used if the unknown sample solution is acidic, as bases are utilized to neutralize acids.


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References:
  • Wikipedia contributors. "Acid–base titration." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 7 May. 2022.
  • GH Jeffery, J Bassett, J Mendham, RD Denney, Vogel's Textbook of Quantitative Chemical Analysis, 5th ed, 1989, Wiley, NY.


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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.


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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.




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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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