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.
Posted by No comments:
Labels: , ,

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).


People also ask:
Posted by No comments:
Labels: , , ,

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?
  • When KMnO4 is reduced with oxalic acid the Decolourisation?
  • 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?
Posted by No comments:
Labels: , , ,

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?
Posted by No comments:
Labels: , ,

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.


People also ask:
  • What is the endpoint in KMnO4 standardization?
  • What is the endpoint of titration KMnO4 vs oxalic acid?
  • 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…..
Posted by No comments:
Labels: , , ,

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.
Posted by No comments:
Labels: , , ,

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.


You may also like this
Posted by No comments:
Labels: , , ,

Tuesday, June 28, 2022

What happens if too much indicator is added to a titration?

Compounds that change color when added to acidic or alkaline solutions are called indicators. Most of the time, colored indicators are used to determine the pH, and they can also be added to the reaction mixture to find out where the endpoint or equivalence point is for the different types of titration.

The indicator is selected based on the pH range that falls within the pH change of the reaction. In acid-base, redox, precipitation, and complexometric titration, different types of indicators are used. Each one has a pKa, a pH range. In chemistry, there are three types of indicators: natural indicators, artificial indicators, and olfactory indicators.

Why is it necessary to use a few drops of the indicator?

It is important to use no more than 2/3 drops of indicator solution since the indicator itself is a weak acid. Hence, we use only a few drops, as adding more can change the pH of the solution, and it can consume the titrant, which interferes with the actual reading of the analysis. 

Therefore, ideally, we would only need one or two drops, as this would give us an accurate color change at the equivalence or endpoint of the reaction.

Indicators are weak acids or bases that are usually made from plant pigments and have unique colors in their ionized and non-ionized states. These colors are related to the pH of the solution being analyzed. 

Phenolphthalein, methyl orange, phenol red, thymol blue, starch, eriochrome black-T, and potassium chromate are some of the examples of indicators.


People also ask:

What happens if too much indicator is added to a titration? (Does it affect the end point, is so why and how?)
Why is it important to use no more than 2/3 drops of indicator solution?
Why is it necessary to use few drop of the indicator?
What happens if you add too much phenolphthalein indicator?
Why is it important not to add too much indicator to the solution?
Why do we use two or three drops of indicator?
Why doesn't the indicator affect the titration results?
Posted by No comments:
Labels: ,

Monday, June 27, 2022

What happens if you use the wrong indicator in a titration?

Compounds that change color at a certain pH level are called acid-base indicators. Usually, they are weak acids or bases, their color changes in color correspond to the protonation or deprotonation of the indicator itself.

An indicator is a Bronsted-Lowry conjugate acid-base pair in which the acid is a different color than the base. During titration, the endpoint is when the indicator changes color.

In titration, the equivalence point is when the amount of acid and base is just enough to cause complete consumption of the acid and the base.

What happens if you use the wrong indicator?

Using the wrong indicator for any type of titration can result in relatively large errors. As we know indicator works within the specific pH range, if we use an incorrect indicator can result in titrant consumption that is either extremely low or very high, making it impossible to determine the exact molarity or normality of the titrand (Sample solution).

A suitable indicator for a titration will change color over a narrow pH range and have a distinct color at low pH and a different, distinct color at high pH.

For example,
We cannot use phenolphthalein as an indicator for titrating strong acids and weak bases, since phenolphthalein changes color between pH 8.1 - 10, which is slightly below 7. Phenolphthalein is a basic indicator that can only distinguish changes in the range of basic pH.

People also ask:

Does any indicator affect titration?
Why is it important to use the same indicator in a titration?
Would a different indicator be better in this titration Why?
What is indicator error in titration?
What would happen if you forgot to add phenolphthalein to your reaction mixture?
Why doesn't the indicator affect the titration results?
Posted by No comments:
Labels: ,

Saturday, June 11, 2022

Which indicator is used in the titration of the weak acid-weak base?

Question:-

Which indicator is used in the titration of the weak acid-weak base?
The options are...
  • A. Phenolphthalein
  • B. Methyl orange
  • C. Bromothymol blue
  • D. No indicator is suitable

The correct answer is D: No indicator is suitable for this titration since it requires a vertical portion of the curve over two pH units.


Explanation:

The vertical component of the titration curve when titrating a weak acid with a weak base is so short that it's difficult to find an indicator that will change colors in this small region, therefore a pH meter could be used to determine the endpoint.
Posted by No comments:
Labels: , ,

Which indicator is used in the titration of a weak acid and strong base?

Question:-

Which indicator is used in the titration of a weak acid and strong base?
The option are...
  • A. Methyl orange
  • B. Phenolphthalein
  • C. Bromothymol blue
  • D. Thymolphthalein

The correct answer is B: Phenolphthalein indicator is suitable in the titration of a weak acid and strong base titration as it changes sharply at the equivalence point.


Explanation:

The pH value at the weak acid-strong base equivalence point will be on the basic side. The pH range of phenolphthalein (8-10) also falls within this basic range, making it suited for titration.

Phenolphthalein is a weak organic acid that turns pink from colorless when the concentration of OH- ions increases, indicating the endpoint.
Posted by No comments:
Labels: , ,

Which indicator is used in the titration of strong acid and weak base?

Question:-

Which indicator is used in the titration of strong acid and weak base?
The options are...
  • A. Phenolphthalein
  • B. Bromothymol blue
  • C. Thymol blue
  • D. Methyl orange


The correct answer is D: Methyl orange indicator suitable in the strong acid weak base titration.

Explanation:

The equivalence point for titration of a strong acid and a weak base is less than 07.00; therefore the methyl orange is a suitable chemical indicator that changes sharply at the endpoint.

Methyl orange has a pKa of 3.47, and a pH range of 3.1 to 4.4, it turns red in acidic medium and yellow in basic conditions. At the beginning of this type of titration, the pH is high, so the solution appears yellow.

When acid is added, the solution becomes more acidic, and the methyl orange turns red which is the endpoint of the reaction. When a strong acid reacts to a weak base, pH will change gradually making an acidic solution with a pH of less than 07.00.

This is why an indicator that changes its basic color to an acidic color is an excellent choice for this titration. The titration of hydrochloric acid and ammonia is an example of strong acid and weak base.
Posted by No comments:
Labels: , ,

Which indicator is used in the titration of strong acid and a strong base?

Question:-

Which indicator is used in the titration of strong acid and a strong base?
The option are...
  • A. Phenolphthalein
  • B. Methyl orange
  • C. Phenol red
  • D. Thymol blue

The correct answer is A: Phenolphthalein indicator suitable in the titration of strong acid and strong base.

Explanation:

Equivalence or stoichiometric point for titrations between strong bases and weak acids is above pH 07.00, therefore the phenolphthalein indicator is used to perform a titration of a strong acid-strong base as it changes color between pH 8.3 and pH 10.00. It gives pink color to the basic solutions and is colorless in acidic ones.

Due to the high strength of the base, this pH change would occur within a fraction of a drop of actual neutralization in the case of a titration between a strong acid and a strong base.

A titration of hydrochloric acid (HCl) and sodium hydroxide (NaOH) is an example of strong acid and strong base.
Posted by No comments:
Labels: , ,

Thursday, June 9, 2022

Why is phenolphthalein used as an indicator in weak acid vs strong base titration?

Phenolphthalein is an organic compound with the formula C20H14O4. It belongs to the phthalene family and is a weak acid that can lose H+ ions in water. It comes in the form of fine crystalline, yellowish white to light orange powder. It is used as a component of the universal indicator, along with bromothymol blue, thymol blue, and methyl red.

The pKa of phenolphthalein is 9.3, and the pH range is 8.20 to 10.00. Over a range of acidic pH, the molecule has no color. At pH 8.2, it starts to turn pink, and at pH 10.00 and above, it turns a bright magenta color.

Why is phenolphthalein used in weak acid strong base titration?

Generally, phenolphthalein is used as an indicator in acid-base titration, particularly for the titration of strong bases-weak acids and strong acid-strong base titration. Depending on the acid and the base, the equivalence point (stoichiometric point) for the titrations between strong bases and weak acids is somewhere above pH 7.

Phenolphthalein indicator changes color around a pH of 8 to 10, which is right in the range of the equivalence point of these titrations, making them useful. It shows pink in basic solutions and colorless in an acidic medium.

Therefore, phenolphthalein is used as an indicator for titration of a weak acid and strong base such as acetic acid (CH3COOH) and sodium hydroxide (NaOH).
Posted by No comments:
Labels: , ,

Why phenolphthalein is used as indicator in titration?

A titration is a technique for determining the concentration of an unknown sample solution using a solution of known concentration. Generally, the titrant from a burette is added to an unknown quantity of the analyte, which pours into the conical flask until the reaction is complete. An indicator is often used to indicate the endpoint or equivalence point.

What is a phenolphthalein indicator?

Phenolphthalein, (C20H14O4), an organic compound of the phthalene family, is a weak acid, which can lose H+ ions in solution. It is a thin, crystalline, and yellowish-white to light orange powder.

Phenolphthalein has a pKa of 9.3 and 8.20 to 10.00 is the pH range for the phenolphthalein indicator. The molecule is colourless over an acidic pH range, beginning to turn pink at pH 8.2 and becoming vivid magenta at pH 10.00 and above.

The most common application of phenolphthalein is as an indicator in acid-base titrations. It, along with thymol blue, bromothymol blue, and methyl red, is used as a component of the universal indicator.

Why is phenolphthalein used as an indicator in titration?

Phenolphthalein is used as an indicator in acid-base titration because it changes color between 8.3 and 10 pH, is economical, readily available, easily soluble, and has an endpoint that is very recognizable from either direction.

The pH of the equivalence point for an acid-base titration determines which indicator to use. Choose an indicator that changes colour at or near the equivalence point (Stoichiometric point). At this point, the titration curve will be steep, and we will get a sharp endpoint of the reaction.

When the pH rises above 07.00, phenolphthalein changes color. As a result, it works well as an indicator for the titration of strong acids and bases. It can also be used to titrate weak acids and strong bases with equivalence point above pH 07.00.

Because the equivalence point is below pH 07.00, it is not a good choice for titrations between a strong acid and a weak base. In this case, methyl orange is more suitable.

Frequently Asked Question (FAQ):

How can phenolphthalein change color?

Phenolphthalein is an indicator that changes colour depending on whether it meets an acid or a base. The phenolphthalein ion is pink, and the phenolphthalein molecule is colorless. When a base is introduced to phenolphthalein, the molecule ⇌ ions equilibrium shifts to the right, resulting in increased ionisation as the H+ ions are removed.

Which indicator is used for weak acid and a strong base?

Since the phenolphthalein indicator changes rapidly at the equivalence point, it is a good choice for weak acid and strong base titrations.

Phenolphthalein is which type of indicator?

Phenolphthalein is a synthetic pH indicator used in acid-base titration. It is a colorless, weak acid that is most commonly used in titration as an indicator to indicate the endpoint of the titration. Because this molecule dissociates to produce pink color when dissolved in water, the formation of pink color indicates the endpoint of the reaction.

You may also like this
Posted by No comments:
Labels: , ,
Subscribe to: Posts (Atom)