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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.


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…..

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.


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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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?


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?


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.


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.


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.


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.


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).


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.

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Wednesday, June 8, 2022

How to find first and second equivalence points

Titration is a method for determining the concentration of an analyte using a solution of known concentration (Titrant). The acid-base titration is a quantitative technique for determining the concentration of acid/base through neutralization. Typically, an indicator is used to detect the endpoint of the titration, which causes the solution's color to change.

The equivalence point (also known as the stoichiometric point) of a chemical reaction is the point where chemically equivalent amounts of reactants are mixed. According to the chemical process, the equivalence point for an acid-base reaction is where the moles of acid and moles of base neutralize each other.

The first equivalence point occurs when the first hydrogen ion H+ from the initial volume of acid is neutralized by the titrant base.
H2A + OH- H2O+HA-
At the first equivalence point, one mole of acid reacts with one mole of a base.

The second equivalence point is the point in a titration at which both hydrogen ions H+ from the initial volume of acid have been neutralized by the titrant base.
H2A+2OH2H2O+A2+
At the second equivalence point, one mole of acid reacts with two moles of a base.

The titration curve is shown in the diagram below.

How to find first and second equivalence points

The volumes of strong base necessary to reach the first and second equivalence points are almost identical. The only difference between each equivalence point is the height of the steep rise.


What is the first equivalence point in titration?

Titration is a technique for determining the concentration of an unknown analyte (Titrand) using a known concentration solution (Titrant). The acid-base titration is a type of quantitative method for determining acid or base concentrations by neutralizing with a known concentration of acid or base. Generally, an indicator is used to detect the endpoint of the titration, which changes the color of the solution.

The point in the titration at which the amount of titrant added is sufficient to neutralize the analyte solution is referred to as the equivalence point. At the equivalence point, the number of moles of the acid is equal to the number of moles of the product, resulting in the formation of a salt product and water.

The equivalence point, or stoichiometric point, is the point where adding enough base to neutralize the acid to form a salt. At the equivalence point, there are an equal amount of moles of acid and base.

First equivalence point in titration:

The first equivalence point is the point of the titration in which the first hydrogen ion H+ from the initial volume of acid is neutralized by the base employed as the titrant.
H2A + OH- →H2O+HA-
At the first equivalence point, one mole of acid reacts with one mole of the base.

An example of the first equivalence point in titration:

Titration of diprotic acids such as sulfuric acid (H2SO4) and carbonic acid (H2CO3). In water, a diprotic acid dissociates in two stages.

From the beginning to the first equivalence point, the equations for acid-base reactions between a diprotic acid, H2X, and NaOH base.

All H+ ions from the first dissociation have reacted with NaOH base at the first equivalence point, and all H+ ions from both reactions have reacted at the second equivalence point. Diprotic acid titration curves have two equivalence points due to the successive dissociations,

Why is the pH of the first equivalence point, of a titration of polyprotic acid?

The first equivalence point in the titration of phosphoric acid (H3PO4) with sodium hydroxide (NaOH) has a pH of around 05.
For example:
H3PO4 is a weak triprotic acid. (pKa 1 is 2.16, pKa 2 is 7.16, and pKa 3 is 12.3).
The first equivalent point is: H3PO4 + NaOH → NaH2PO4 + H2O
The pH of the resultant solution is calculated as follows: 
pH = (pKa1 + pKa2)/2 = 4.66


Tuesday, June 7, 2022

Difference between equivalence point and half equivalence point

Titration is a method for determining the unknown concentration of an analyte (Titrand) using a solution of known concentration (Titrant). The titrant is typically added to a known amount of the analyte using a burette until the reaction is completed. Often, a visual indicator is used to indicate the end-point of a reaction. Since the volume of the titrant is already known, the concentration of the analyte can be easily determined using the titration formula.


What is half equivalence point?

The half equivalence point is the midway point between the equivalence point and the starting point in a titration. It is also known as the midpoint of titration. At this moment, the pH of the analyte solution is equal to the dissociation constant, or pKa, of the acid employed in the titration. The half equivalence point happens at one-half the volume of the first equivalence point.

If there are several equivalence points in the titration, the same number of half equivalence points exists. For example, the second-half equivalence point occurs between the first and second equivalence points. Because, at the half equivalence point, the pKa of the acid is equal to the pH of the solution, determining the half equivalence point is rather simple.

What is the equivalence point?

The equivalency point is also known as a stoichiometric point, it is the point in the titration process where the chemical reaction in the titration mixture ends. In a titration, the equivalence point is the actual point of the desired chemical reaction in the reaction mixture.

Typically, titrations are used to determine the concentration of a substance in a sample solution. The equivalence point can be determined by the pH change, color change, precipitation formation, temperature change, conductivity change, etc..

Difference between equivalence point and half equivalence point:

The major difference between the half equivalence point and equivalence point is that the half equivalence point is the midpoint between the beginning point and equivalence point of a particular titration, whereas the equivalence point is the point where the chemical reaction between titrant and titrand ends.

Frequently Asked Question (FAQ): 

What does the half equivalence point mean?

The half equivalence point is where exactly half of the acid in the buffer solution has reacted with the titrant.

Are there two equivalence points with diprotic acid?

Yes, the number of equivalence points on a titration curve for a polyprotic acid corresponds to the number of acidic protons in the acid. Since a diprotic acid is titrated using two acidic protons, the titration curve contains two equivalence points.

Why is the pH equal to the pKa at the half equivalence point?

At the half-equivalence point, half of the acid is neutralized; therefore the amount of salt produced is half that of the acid; the concentrations of salt and acid are equal. Now, this solution is a buffer solution, and when the Henderson-Hasselbalch equation is used, the log value becomes zero.


Endpoint and equivalence point in chemistry

In analytical chemistry, we use titration to determine acids, bases, reductants, oxidants, metal ions, and a variety of other species. Throughout the process of titration a chemical reaction occurs. In this case, an analyte reacts with a titrant, which is a standard reagent filled in the burette.

As a reference material in titrimetric methods, we sometimes use a primary standard, which is a highly pure and stable solution. To findout the endpoint of the reaction, we use an indicator. However, this is not the point at which the chemical process ends. The equivalence point is the actual point.

What is an endpoint?

Endpoint refers to the point in the titration process where the color of the indicator changes. For example, when Eriochrome Black T (EBT) is used as an indication in complexometric titration, the color changes from wine red to blue at the endpoint.

What is an equivalence point?

The point in the titration process where the chemical reaction in the titration mixture ends is called the equivalence point. It is also known as a stoichiometric point in titration. pH change, color change, precipitation formation, temperature change, and conductivity change are all methods for establishing the equivalence point.

How does the equivalence point differ from the endpoint and which comes first during titration?

There are two important stages, known as the endpoint and equivalence point, that are reached during the process. In a titration, an equivalence point is a point where the added titrant is chemically equivalent to the sample analyte. The endpoint, on the other hand, is the point where the solution changes color.

The major difference between equivalence and endpoint is that the equivalency point is the point at which a chemical reaction comes to an end, whereas the endpoint is the point at which color changes. The equivalence point comes before the endpoint.

What is the difference between endpoint and stoichiometric point?

The equivalence point is the common name for the stoichiometric point, and the differences between them have already been described above.

Why does the endpoint occur after the equivalence point?

Because a chemical reaction always occurs before a color change, the endpoint appears soon after the chemical reaction reaches the equivalence point. The color changes at the point where the pH of the titration solution becomes basic. Therefore, the endpoint can be determined following the complete neutralization at the equivalence point.

What is the midpoint of titration?

It is a point at which precisely enough acid/base has been introduced to neutralize one-half of the acid/base that was initially present and occurs halfway to the equivalence point.

In other words, the point at which half of the analyte is neutralized by the added titrant is referred midpoint of titration.

Is it possible for the endpoint and equivalence point to be the same?

Although endpoints are often referred to as equivalence points, the two terms are not the same. Since the difference between an equivalent point and an endpoint is minimal, they can be regarded as identical for laboratory purposes.

What is the pH at the endpoint of a titration?

The pH at the endpoint of a titration involving a strong acid and a strong base will be 07.00, pH > 07.00 when a weak acid is titrated with a strong base, and pH<7 when a weak base is titrated with a strong acid.

Is the endpoint always after the equivalence point?

The endpoint of the titration comes is either almost or after the equivalence point and the equivalence point of the titration comes either almost with the endpoint or before the endpoint.


Saturday, June 4, 2022

What is equivalence point in chemistry?

Titration is an analytical chemistry technique used to determine the concentration of unknown sample solutions using solutions of known concentration. In the titration technique, the solution of known concentration is known as the titrant which is filled in the burette and the solution of unknown concentration is known as the analyte which is poured into a conical flask.

Endpoint and equivalence point are two different important stages that occur in the titration process. Numerous students mistakenly believe that the equivalence point and the endpoint of the titration are the same, although they are not. The endpoint is the moment at which an indicator changes the color of the solution. More often than not, the color change takes place after the equivalence point has been reached.

Define equivalence point in titration:

“It is a point in a titration, at which amount of titrant added is just sufficient to neutralize the analyte solution completely”

Equivalence point in titration?

The equivalence point of a chemical reaction is the point at which the number of moles of substance contained in the sample is stoichiometrically equal to the amount of titrant added. The minimum amount of titrant is required to completely neutralize or react with the analyte. In the titration of a diprotic acid, there exist many equivalence points that are multiples of the initial equivalence point.
equivalence point

It is also known as the stoichiometric point since it is the point at which moles of acids equal the amount of base needed to neutralize them. The equivalence point comes either closer to an endpoint or before an endpoint. This gives the point where the reaction ends.

Note that this does not mean that the ratio of acids and bases is equal to 1:1. The ratio is determined by the acid-base chemical equation in its balanced form. This does not necessarily mean that the acid-base ratio is 1:1. The ratio is calculated by the chemically balanced acid-base equation. The ratio is estimated by the balanced acid-base chemical equation.

Example of equivalence point:

Consider the sodium hydroxide (NaOH) and hydrochloric acid (HCl) titration as an example of an acid-base reaction. One mole of NaOH and one mole of HCl react chemically to form salt and water.
HCl + NaOH → NaCl + H2O

During titration, a prepared solution of NaOH is added gradually to a sample solution containing HCl and an appropriate indicator. The sodium hydroxide begins to react with the hydrochloric acid of the sample. When enough sodium hydroxide has been added to the sample to react with all of the hydrochloric acid, the equivalence point has been reached.

Methods of determining the equivalence point:

There is a different method that used to determine the equivalence point is as follows.
  • Color change
  • pH indicator
  • Precipitation
  • Conductance
  • Isothermal colorimetry
  • Thermometric titrimetry
  • Spectroscopy

What is half equivalence point?

The halfway between the equivalence point and the starting point in a titration is known as the half equivalence point. In an acid-base titration, the half-equivalence point is where the concentration of an added base equals half of the initial acid concentration. The half-equivalence point is also known as the midpoint of titration. The half equivalence point is fairly simple to determine as the pKa of the acid is equal to the pH of the solution at this point.

Why do diprotic acids have two equivalence points?

This is due to the two ionizing hydrogen’s in the acid do not dissociate from the acid at the same time. Protons are usually donated in steps by diprotic acids. As a result, the acid will have two acid dissociation constants, the second of which will be lower than the first.

What species are present at the equivalence point?

Only neutral ions (the cation from the strong base and the anion from the strong acid) and water are present in the solution at the equivalence point. Salt and water are present at the point of equivalence in acid-base titrations.
 

Frequently Asked Question (FAQ):

Why is the point in the titration when neutralization occurs called the equivalence point?

Because this is the point in a titration where the relative amounts of each component in the chemical reaction are precisely defined by the coefficients in the balanced chemical equation, it's called the equivalence point.

Is the equivalence point always 7?

In a strong acid-strong base titration, the equivalence point always occurs at pH=7. It is greater than 7 for a weak acid-strong base, and less than 7 for a strong acid-weak base because only the conjugate acid is present and it’s around about 7 for the weak acid-weak base.

Why is the pH at the equivalence point not always equal to 7 in a neutralization titration? When would it be 7?

Titration is a process in which an acid and a base react to neutralize each other. However, not all of the salts that formed are neutral. When a strong acid with a weak base, will give is a slightly acidic salt, likewise, a weak acid with a strong base gives a slightly basic salt.

Consider the reaction of acetic acid (acetic acid), a weak acid, with a strong base, such as sodium hydroxide (NaOH).

A salt, sodium acetate (C2H3NaO2), and water (H2O) are generated during the neutralization reaction. As a base, the acetate ion reacts with water to produce CH3COOH and OH- CH3COO- + H2O → CH3COOH + OH- The reaction of the acetate ion raises the pH of the solution from 7-8. The pH of the solution is increases from 7.0 by this acetate ion reaction. Because the conjugate base of a strong acid is strong and weak to dissociate water, the pH for strong acid strong base titrations is 7.


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References:
  • Wikipedia contributors. "Equivalence point." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 10 Dec. 2021.
  • Vogel, A.I.; J. Mendham (2000). Vogel's Textbook of Quantitative Chemical Analysis (6th ed.).