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Iodometric Titration: Principle, Example, Advantages, and How Does it Work

Why do we standardize a solution?

Titration, often referred to as titrimetry, is a volumetric analysis used to measure the analyte concentration in a sample solution. In which the two steps performed are called standardization and titration.

Standardization is the process of calculating the exact concentration of the prepared solution. Titration is the process of calculating an unknown sample concentration. Standardization is often done in the form of titrations.

It consists of a burette filled with titrant and a pipette that is used to pour the titrand into the conical flask where the reaction takes place.

Until the reaction is complete, i.e., the chemical equivalence point or endpoint, a titrant of a known concentration is applied. To indicate the endpoint, a chemical compound called an indicator is used.

Why do we standardize a solution?

It is required to standardize the solution/reagent before starting an experiment since it allows us to obtain accurate measurements during the experiment; On the other hand, the exact concentration of the solution may differ.

You can also reduce the deviation of instrumental and random human errors by standardizing the solution.

As a result, it's necessary to standardize and measure the actual concentration right at the start of the titration.

Example of standardization in chemistry:

Standardization of sodium hydroxide (NaOH) using potassium hydrogen phthalate (C8H5KO4) or oxalic acid dihydrate (C2H2O4). In which KHP/oxalic acid solution is used as a primary standard.

If you prepare the 0.1N NaOH solution, however, its actual concentration is not actual 0.1N therefore we need to standardize it to determine its exact concentration.

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How and where should NaOH solution be stored?

Sodium hydroxide also known as caustic soda belongs to the category of inorganic compounds is highly soluble in water. It is a corrosive white crystalline solid that freely absorbs moisture from air until dissolved. Its molecular formula is NaOH, molar mass is 39.997 g/mol, and density is 2.13 g/cm³.

In industrial, NaOH is a commonly used as strong base. It is used to make sodium salts and detergents, as well as for pH control and organic synthesis. It is usually handled in bulk as an aqueous solution because solutions are cheap and easy to handle.

Table of Contents:

How to store sodium hydroxide?
What happens when NaOH is left in an open container?
Where should NaOH solution be stored?
Why standardized NaOH should be kept in a stoppered bottle?
Why is a plastic bottle generally preferred to a glass bottle to store NaOH?
How long can you store NaOH solution?
Can we store NaOH in aluminum container?
Why does glass not react with acid?

How to store sodium hydroxide?

Most sodium hydroxide is packaged in plastic containers which is made from high-density polyethylene (HDPE). To avoid water and/or CO2 adsorption, solid form of NaOH should be stored in airtight containers with limited atmospheric exposure. When not in use, make sure the container is tightly sealed and airtight. When not in use, make sure the container is tightly sealed and airtight.

What happens when NaOH is left in an open container?

Sodium hydroxide pellets absorb water from the air so rapidly that they melt if exposed in the open, hence it need to be covered.

Where should NaOH solution be stored?

Plastic containers should be used to store sodium hydroxide stock solutions, glass containers should be avoided. To avoid the formation of carbonate in volumetric NaOH solutions, they should be kept away from air.

Why standardized NaOH should be kept in a stoppered bottle?

When atmospheric carbon dioxide comes into contact with the stored NaOH, it reacts to form carbonic acid, therefore, the base concentration decreases. To avoid contact with ambient carbon dioxide, NaOH should be stored in a closed bottle.

Why is a plastic bottle generally preferred to a glass bottle to store NaOH?

The fact that Na2CO3 is also a component of glass is one reason for this. As a result, the Sodium carbonate formed in the air by the reaction of NaOH and CO2 can initiate crystallization on the Na2CO3 in the glass, thus creating a bonding between stopper and bottle.

The given reaction is that NaOH reacts with CO2 to form Na2CO3, and if a glass stopper is used, it will be tightly stuck. By the reaction

2NaOH (aq) + CO2 (g) -> Na2CO3(s) + H2O (l).

There are Teflon sleeves for standardized conical glass stoppers as well as conical plastic stoppers, which prevent this.

How long can you store NaOH solution?

When stored correctly in a dark, cool environment, sodium hydroxide solution has a shelf life of approximately 30 days.

Can we store NaOH in aluminum container?

NaOH cannot be stored in a vessel made with aluminum (Al) or zinc (Zn), because hydrogen gas is produced (redox reaction occurs) when sodium hydroxide reacts with aluminum from sodium metalluminate. In the reaction between sodium hydroxide and metals, hydrogen atoms undergo reduction.

Why does glass not react with acid?

Because glass has a very robust and stable atomic structure, it is unaffected by acid. Due to its strong chemical bonds, the most common material in glass, silicon dioxide, is a particularly non-reactive substance, making glass very resistant to most acids. Glass is resistant to most acids, however is susceptible to attack by alkaline substances, particularly the concentration of OH- ions which gives a pH greater than 09.00.

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Iodometric Titration: Principle, Example, Advantages, and How Does it Work

Why do we need to standardize NaOH solution?

In chemistry, the process of determining the precise concentration (molarity) of a solution is known as standardization. One of the most important preconditions for reliable and transparent titration determination is the so-called titer standardization/determination of the volumetric solution used for the titration.

In the titration procedure, the titrant is usually added to a known quantity of analyte (the unknown solution) from a burette until the reaction is complete. The concentration of the unknown can be determined by knowing the volume of titrant added. An indicator is often used to indicate the endpoint, or equivalence point, of the reaction.

Why is there a need to standardize the NaOH solution?

To find out the exact concentration (molarity/normality) of the prepared NaOH solution, it needs to be standardized. Unfortunately, sodium hydroxide is not a good primary standard. Since solid NaOH is highly hygroscopic, it cannot be weighed precisely. It absorbs carbon dioxide (CO2) from the air, forming sodium carbonate and lowering the amount of NaOH.

So we'll need to determine the exact concentration of the prepared NaOH solution that has the approximate concentration. The concentration of NaOH can be determined precisely by titrating a potassium hydrogen phthalate (KHP) sample of known mass with the prepared NaOH solution.

What does it mean to standardize a NaOH solution?

Standardization is the process of finding the exact concentration (molarity) of a solution. The molarity of a sodium hydroxide solution will be measured in the first standardization by titrating a sample of KHP with the NaOH.

Why is the standardization of NaOH necessary?

Because sodium hydroxide is hygroscopic, it absorbs moisture from the air quickly, changing its concentration.

Why standardized NaOH should be kept in a stoppered bottle?

As atmospheric carbon dioxide reacts with the stored NaOH to form carbonic acid when it comes into contact with it. As a result, the concentration of the base decreases. Therefore, sodium hydroxide must be kept in a closed bottle to avoid interaction with atmospheric carbon dioxide.

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Iodometric Titration: Principle, Example, Advantages, and How Does it Work

Learn about the principle of iodometric titration, reaction, indicators, examples, advantages, and how the iodometric titration works.

Titration, often known as titrimetry, is a volumetric analysis used to measure analyte concentration in a sample solution. It consists of a burette filled with titrant and a pipette used to introduce the titrand into the conical flask where the reaction occurs.

A titrant of known concentration is added until the reaction is complete i.e. the chemical equivalence point. A titrant of known concentration is applied, until the reaction is complete, i.e. the chemical equivalence or endpoint. Titration is mainly classified into four types: acid and base, redox, complexometric, and precipitation titration.

Table of Contents:

What is redox titration?
What is iodometric titration?
Principle of iodometric titration
Reaction involved in iodometric titration
Examples of iodometric titration
How does iodometric titration work?
Indicator is used in iodometric titration
Advantages of iodometric titration

What is redox titration?

Redox titration is a type of titration; it is an oxidation-reduction reaction that occurs between an oxidizing and a reducing agent. There are several types of redox titration, including bromatometry, cerimetry, iodometry, iodimetry, permanganometry, and dichrometry are classified as direct titration, and back titration.

It is a laboratory method used to determine the concentration of a sample analyte by causing a redox reaction between the titrant and the analyte. A potentiometer or a redox indicator may be required for this type of titration.

What is iodometric titration?

Iodometry, known as iodometric titration, is a type of redox titration in which a solute (oxidizing agent) is added to excess iodide to obtain iodine, and the amount of iodine produced is determined by titration with a sodium thiosulfate solution.

It's an indirect titration in which starch indicator is used to determine the endpoint. At the end of the experiment, the blue color of the starch-iodine complex will fade.

What is the principle of iodometric titration?

Iodometric titration works on the principle of determining the concentration of an oxidizing agent in a sample solution. Iodometry involves the indirect titration of iodine liberated by reaction with the analyte.

In which starch solution is used as an indicator as it can absorb the I2 that is released. When titrated with a standardized sodium thiosulphate (Na2S2O3) solution, absorption causes the color to change from bright yellow to dark blue. This indicates the endpoint of the titration.

Reaction involved in iodometric titration:

The reaction between iodine and the thiosulfate ion is as follows.

Examples of iodometric titration:

To standardize the sodium thiosulfate (Na2S2O3) using potassium dichromate (K2Cr2O7)
Iodometric estimation of Cu (II) (Copper (II) oxide ) using sodium thiosulfate solution
Estimation of vitamin C by the iodometric method

How does iodometric titration work?

To use this iodometric titration procedure will require using a material that has oxidizing properties. This oxidizing property indicates that it has the ability to remove electrons that are owned by other compounds.

This oxidizing substance is later dissolved in the solvent and then the solution is acidified. We can use sulfuric acid (H2SO4), hydrochloric acid (HCl), or acetic acid (CH3COOH) to acidify the solution. Following that, add chlorine and allow the mixture to settle in a dark room for a few minutes.

The iodide will then be released as a result of this procedure and then titrated with a standardized solution of sodium thiosulfate (Na2S2O3). As the solution becomes yellow and becomes more dilute, this solution of sodium thiosulfate will act as a reducing agent. The starch indicator will then be added and will be titrated until the color of the solution becomes clear.

Indicator is used in iodometric titration:

In an iodometric titration, starch is commonly used as an indicator since it can absorb the I2 that is released. It causes the absorption color to change from dark blue to pale yellow when the solution is titrated with a standardized thiosulfate solution. Due to the formation of a starch-iodine complex, the endpoint in iodometric titration is the disappearance deep blue-black color.

Advantages of iodometric titration:

Iodometry can be used to determine the concentration of both reducing and oxidizing agents.
It has the ability to precisely determine the concentration of the analyte.
It allows you to visually detect reactivity at equilibrium point(s).
The presence of iodine in starch causes a visible blue color change that occurs simultaneously, which is one of the two most important criteria for titration.
It requires only a small amount of chemicals or substances.

Frequently Asked Questions (FAQ):

Why is KI used in iodometric titration?

Because iodide will oxidize iodine in the presence of an oxidizing agent, KI (potassium iodide) is employed in iodometric titrations.

Why excess of KI is used in iodometric titration?

Excess KI is added to help in the solubilization of free iodine, which is insoluble in water under normal conditions.

What do you mean by iodometric and iodimetric titration?

Iodometry and iodimetry both are common volumetric analysis titration methods. Iodometric titration is an indirect titration method used to quantify oxidizing agents, whereas iodometric titration is a direct titration method used to quantify reducing agents.

References:

Wikipedia contributors. (2022, February 3). Iodometry. In Wikipedia, The Free Encyclopedia. Available Here:
Hyprowira, and PT Hyprowira Adhitama. Iodometric Titration Functions and How It Works. Available Here:
‘Iodometric Determination of Cu in Brass’. Chemistry LibreTexts, 18 Jan. 2017, Available Here:

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What is end point in iodometric titration?

Iodometry, also known as iodometric titration, is a volumetric chemical analysis method based on a redox titration in which the presence or disappearance of elementary iodine is used to determine the endpoint of the titration. It is a type of titration in which the Iodide solution is titrated with an oxidizing agent. The oxidation of iodide to iodine is the basis of iodometry.

End point of iodometric titration:

A starch solution is used as an indicator in an iodometric titration as it can absorb the I2 that is released. This absorption causes the color to change from deep blue to pale yellow when the solution is titrated with a standardized thiosulfate solution. This indicates the endpoint of the iodometric titration.

It is a technique for determining the amount of oxidizing chemicals in a solution. The concentration of the oxidizing agent is measured by titration of iodine with thiosulfate in which starch is used as an indicator. The detection of the endpoint is based on the formation of the blue starch complex.

The following is the chemical reaction:

I2+Na2S2O3→2NaI+Na2S2O4

The reduction of iodine shows by this principle.

Due to thiosulphate decomposition, iodometric titrations are performed in a weak-acidic medium. Because iodine disproportionates at basic pH, iodimetric titrations are carried out in neutral or moderately alkaline (pH 8.0) or weakly acidic solutions.

Frequently Asked Question (FAQ):

Why the endpoint in iodometric titration is colorless?

Starch is a branched molecule in which iodine (I2) is trapped; therefore, gives it a blue color. However, at the end of the titration, when all of the iodine (I2) has transformed into iodide (I-) ions (after the thiosulphate ion has reduced it), there is no more iodine (I2) to be trapped in starch, so the blue color fades.

Is starch solution an indicator?

To detect the presence of iodine, a starch solution is commonly used as an indicator. A deep-blue starch–iodine complex is formed when starch and iodine are present together.

Why iodometric titrations are done in dark?

Because light accelerates a side reaction in which atmospheric oxygen oxidizes iodide ions to iodine, the reaction mixture should be kept in the dark before titration.

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Why starch is added towards the end of iodometric titration?

Starch is added near the endpoint of an iodine titration when the iodine concentration is low, as the starch-iodide combination is not highly soluble in water. This keeps I2-related errors from remaining adsorbed on the complex and going undetected.

Iodometry is one of the most significant redox titration methods. Many organic and inorganic compounds react immediately, quickly, and quantitatively with iodine.

Iodometry is a volumetric analysis that can be used to determine the amount of both reducing and oxidizing substances, through direct iodine titration or by titration of iodine with sodium thiosulfate (Na2S2O3).

Why is a starch added at the end of the reaction of iodometric titration and not in the initial stage?

When the iodine solution is lower, starch is added at the end. The trapped molecules of iodine do not react with Na S O, the endpoint is diffuse. If the starch was added earlier in the titration, an iodine-starch complex would develop, resulting in a reddish-brown endpoint.

Starch and iodine produce a deep blue complex, adding just a few drops of reducing agent will transform the solution from nearly black to clear. This is considerably easier to observe than the fading yellow color of the iodine alone.

The color change becomes noticeable only at the equivalence point, which is why we don't add the starch earlier. Iodine color fades more slowly on its own, giving a better idea of whether we are close to (pale yellow) or far from the equivalence point (red).

It means we can titrate more rapidly without the starch if we know we're not close there yet, and then adding the starch near the end makes it simpler to observe if any unreacted iodine remains.

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How does iodometric back titration work?

Back titration is a titration in which a known excess of standard reagent is added to the solution and the excess is titrated instead of the original sample. Back titration is used when direct titration is not possible due to the slow reaction between analyte and titrant.

Titrate an iodine solution with a thiosulfate solution or another compound that will be reduced by iodine in direct iodometric titration. Alternatively, we can use an iodide (I) solution that has been oxidized by a stronger oxidant than iodine.

Back titration involves allowing excess iodine to react with the analyte, such as acetone, and then determining the excess amount of iodine used by titration with thiosulfate. Because we know how many moles of iodine we've added and how many haven't reacted, determining how many moles have reacted and, ultimately, determining how many analytes were present is simple.

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Purpose of back titration

Complexometric titration is a volumetric analysis in which the endpoint of the analysis or titration is identified by the formation of a colored complex. It is classified as direct titration, back titration, replacement titration, and alkalimetric titration of metals.

A back titration is a titration method, also called an indirect titration, that uses an excess amount of a known concentration of a substance to determine the concentration of an unknown. A chemical reaction occurs between these compounds. Since the quantity of compound with known concentration is already known, a back titration can be used to quantify the amount of the compound that has reacted with the unknown compound.

Purpose of back titration:

Back titration is intended to resolve some of the problems that can arise when using direct or forward titration. The following are some of the possible reasons for developing a back titration technique:

Impurities in the analyte may cause problems with direct titration.
In a direct or forward titration, the analyte reacts slowly with the titrant.
When the acid or base is an insoluble salt, such as calcium carbonate, it is used.
When one of the reactants, such as ammonia, is volatile.
Back titration can be used to analyze a solution with an unknown concentration using weak acid-weak base reactions.
When the molar concentration of an excess reactant is known, however, the strength or concentration of an analyte must be determined, and a back titration is used. In acid-base titrations, back titration is also commonly used: When the acid or base is an insoluble salt (e.g., calcium carbonate).

What is the significance of back titration in chemistry?

When the endpoint of the reverse titration is easier to identify compared to the endpoint of the regular titration, such as in precipitation reactions, back titration is useful. Back titrations are also effective when the interaction between the solute and the titrant is very slow, or when the analyte is in an insoluble solid.

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Monday, April 4, 2022

Why is back titration used for insoluble salts?

Back titration (Indirect titration) is a type of complexometric titration used for analyzing substances that are either insoluble or partially soluble in water. Two steps are usually followed in a back titration: measuring the amount consumed by the analyte and calculating the excess quantity.

The solid can be made to react with an excess of acid in these conditions. Because excess is used, the reaction can be quite rapid. After the reaction is completed, titration with alkali can be used to detect how much acid is remaining. The composition/purity of the original solid can be determined based on the volume and concentration of alkali used.

In this example, a mixture of calcium oxide (CaO) and silicon dioxide (SiO2) is analyzed to estimate the % by mass of calcium oxide present. As calcium oxide reacts with acids, but silicon dioxide does not, the method can be used.

Back titration is used when the endpoint is easier to see than with a normal titration, which is applied to several precipitation reactions.When the interaction between the analyte and the titrant is very slow, or when the analyte is in a non-soluble solid, back titrations are also useful.

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Thursday, March 31, 2022

When and why is back titration used?

Back titration or indirect titration is a type of complexometric titration in which a known excess of standard reagent is introduced to the solution and the excess is titrated instead of the original sample.

Back titration is a titration performs in reverse. In a back titration, two steps are commonly followed: measuring the amount consumed by the analyte and calculating the excess quantity.

Why is back titration used?

When the endpoint of the reverse titration is easier to identify than the endpoint of the regular titration, such as in precipitation reactions, back titration is useful. Back titrations are also effective when the interaction between the analyte and the titrant is very slow, or when the analyte is in a non-soluble solid.

Table of Contents:

Why is back titration used?
When do we use back titration?
Why is back titration used in EDTA?
What is back titration of aspirin?
Why is back titration used for CaCO3?
Where is back titration used?
Why is back titration more accurate?
What is the example of back titration?

When do we use back titration?

Back titration is performed when the molar concentration of an excess reactant is known, but we need to determine the concentration of an analyte.
When the analyte and titrant reaction is slow or when the analyte is in an insoluble solid
When determining the endpoint of a normal titration is difficult, such as weak acid and weak base titration.
It is used when the acid or base is a salt that is insoluble, such as calcium carbonate.
Back titration is most typically used when determining the endpoint of a regular titration is difficult.
When one of the reactants is volatile, such as ammonia.

Why is back titration used in EDTA?

Titrations with EDTA can be done in different ways, including direct, back (indirect), displacement, and masking. Using normal titration procedures isn't always possible. Back titration is a technique that can be used in such instances.

Generally, we used two reagents in back titration: one that reacts with the original sample and the other that reacts with the first reagent. In this method, the excess of EDTA is added to the metal ion solution, which is then titrated with a known concentration of a second metal ion.

With EDTA, the second metal ion must form a weaker complex than the solute ion. As a result, the second metal does not displace the solute ion from its complex with EDTA.

Why do we use back titration in the analysis of aspirin?

For direct titrations, several reactions are slow or have an unfavorable equilibrium. Aspirin is a weak acid with a slow hydrolysis rate; i.e., each molecule of aspirin reacts with 2 hydroxide ions. To overcome this problem, we use back titration in the analysis of aspirin.

In which, an HCl (Hydrochloric acid) titration is used to determine the amount of unreacted base when a known excess amount of base is introduced to the sample solution. This type of reaction occurs at a rapid rate, resulting in an abrupt and easily seen end-point.

Why is back titration used to determine calcium carbonate?

Because calcium carbonate (CaCO3) is insoluble in water and cannot be directly titrated, determining its concentration requires a back titration. Back titration is done when the primary standard is not soluble in water and the direct titration is not possible.

Where is back titration used?

When the molar concentration of an excess reactant is known, but the strength or concentration of an analyte must be determined, back titration is performed. In acid-base titrations, back titration is commonly used: When the acid or base is an insoluble salt (for example calcium carbonate).

Why is back titration more accurate?

In a direct titration, a standard titrant is added to the analyte until the endpoint is reached. In a back titration, an excess of standard titrant is added to the analyte, and the excess titrant is titrated to determine how much is in excess, this makes it a more accurate method.

What is the example of back titration in analytical chemistry?

Determination of acetylsalicylic acid in aspirin and determination of calcium carbonate (CaCO3) is an example of back titration that performs in the lab.

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