Applications of non-aqueous titration

Using non-aqueous titration, the concentration of an unknown acid or base in a non-aqueous solution can be determined. It can also be used to identify the equivalence point of a non-aqueous solution reaction between an acid and a base.

Non-aqueous titration is a type of titration in which the analyte is dissolved purely in a non-aqueous solvent (does not contain a water molecule). Acid or base is used as a titrant to perform this titration. In a weakly acidic or basic medium, aqueous solvents quickly accept or donate protons. For this reason, the titration method needs to use non-aqueous solvents to get accurate and precise endpoints. The use of non-aqueous titrations in pharmaceutical assays is one of the most common applications for this technique.

Analysis of non-aqueous titration is based on the Bronsted-Lowry theory, in which the following are two of the most important reasons that the non-aqueous titration theory satisfies:

• Suitable for titrations of weak acid and base
• An appropriate solvent medium is used to dissolve organic compounds

Hence, non-aqueous solvents such as acetones and alcohols replace water in titrations since they do not compete with other analytes for proton donation or acceptance.

In the non-aqueous titration of a particular analyte, four types of solvents are commonly used.

1. Aprotic solvents-(Chloroform and benzene)
2. Protophilic solvents-(Acetic and acid sulphuric acid)
3. Protogenic solvents-(Amines liquid and ammonia)
4. Amphiprotic solvents-(Acetic acid and alcohols)

Here is an example of a reaction for which water is not a suitable solvent:

R-NH2 + H+ ⇌ R-NH3+

When carried out in an aqueous solvent it is completed by the following reaction:

H2O + H+ ⇌H3O+

A weak base or acid can be the organic solvent. The titration is conducted in the presence of a strong acid or base. The strong acid/base is employed to titrate the weak acid or base sample.

Applications of non-aqueous titration:

• Non-aqueous titration has a wide range of applications, especially in the field of medicine. Some applications of non-aqueous titration are mentioned below.
• Assay and composition analysis of pharmaceutical products is one of the most important applications of non-aqueous titration.
• It is used to know the purity of assays.
• It is employed to determine the concentration expressions.
• A mixture of primary, secondary, and tertiary amines is determined using a non-aqueous titration method.
• Non-aqueous titrations are used to measure the concentration of a certain analyte.
• Non-aqueous titrations can be used to determine the identity of hydrophobic drugs such as diuretics, phenobarbitone, tetracyclines, and steroids, etc,
• It is also used to determine the composition of antitubercular drugs and adrenergic drugs.

Crystal violet, methyl red, naphtholbenzein, quinaldine red, and thymol blue, are some examples of indicators that can be employed in the titration of non-aqueous solutions.

People also ask

Which titration is used in non-aqueous titration?

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Keywords:

Acidimetric, titrant, principle, curve, procedure, advantages, Arrhenius Concept, Lewis, Bronsted theory, amine, ketone, chemistry, pharmacy, classes 10, 11, and 12, and students, etc.

Mohr’s method indicator

Chromate ions (CrO42-) are typically used as the indicator in Mohr’s titration, which argentometrically determines the bromide, chloride, and cyanide ions by giving a red-brown color at the endpoint.

Precipitation titration is a type of titration that involves the formation of a precipitate during the titration process. Based on the application type and endpoint detection technique precipitation titration is classified into three methods, Mohr, Volhard, and Fajan's method.

Precipitation titration is based on chemical reactions that yield ionic compounds of limited solubility. Silver nitrate (AgNO3) is often considered the most important precipitating reagent. Titration methods that are based on the use of silver nitrate are commonly referred to as argentometric methods.

Which indicator is used in the Mohr method?

Potassium chromate can be used as an indicator for the argentometric detection of chloride, bromide, and cyanide ions that react with silver ions to produce a brick-red silver chromate precipitate in the region of the equivalence point.

When determining the concentration of chloride ions in a solution containing a silver nitrate standard, the Mohr method employs the use of chromate ions as indicators. Once all the chloride has precipitated as white silver chloride, the first excess of titrant will form a silver chromate precipitate, indicating that the process has reached its endpoint.

The following are the reactions:

Ag+ Cl- ↔ AgCl(s)

2Ag + CrO42-↔ Ag2CrO4 (s)

The amount of chloride in an unknown sample can be calculated by knowing the stoichiometry and moles consumed at the endpoint. The test determines the concentration of chloride in a solid sample.

List of indicators:

Method	Name of indicator	Endpoint color
Mohr's titration	Potassium chromate (K2CrO4)	Red-silver chromate
Volhard’s titration	Ferric ion (Fe3+)	Red-brown
Fajan’s titration	Dye Dichlorofluorescein (C20H10Cl2O5)	Green suspension turn pink

Commonly asked questions on the Mohr’s indicator are as follows.

Why is potassium chromate used as an indicator in the Mohr method?

The silver ions react with chromate ions when the potassium chromate (K2CrO4) is used as an indicator after the chloride ion has been extinction and when the solubility product of silver chromate is exceeded, a reddish-brown precipitate starts to form.

What solution is used in the Mohr method?

The Mohr method is a kind of precipitation titration in which the concentration of chloride ions in a given solution is measured by titrating it with a solution of silver nitrate.

What is used as a standard solution in Mohr’s method of titration?

The silver nitrate (AgNO3) solution is used as a standard in the titration of Mohr’s method.

What is the color in Mohr's method?

In Mohr's method, once all the chloride ions have interacted, red silver chromate is formed.

Why is it called Mohr's method?

German chemist Karl Friedrich Mohr was given the method. Thus, this process is known as Mohr's method. It is a method of direct titration.

Keywords:

Titrant, principle, medium, acid, analysis, ferric acetate, volumetric, compound, potassium thiocyanate (KSCN), potassium chloride (KCl), sodium chloride(NaCl) chemistry, class, and students, etc.

Conditions and requirements for the precipitation titration

A volumetric analysis in which a precipitate is formed, or when the analyte and titrant react to form a precipitate throughout titration, is known as precipitation titration. The process of titration known as "precipitation titration" helps in the formation of precipitate during the method of titration.

Volhard's, Mohr's, and Fajan's methods are three types that can be used to perform precipitation titrations. In the process of precipitation titration, the titrant reacts with the analyte to form a substance that is insoluble. 

This process continues until the last drop of the analyte has been consumed. Precipitation Titration is used to determine the presence of salt, halide ions, chloride, bromide, iodide, halogen, metal ions, etc.

What conditions are necessary for precipitation titration?

• It should only involve a single suitable stoichiometry reaction.
• It must be an extremely quick reaction.
• At the endpoint, it must display the change in the reactant’s concentration.

What are the requirements for precipitation titration?

• It has fast precipitation
• It is necessary that the precipitate be practically insoluble
• There should be no change in the oxidation state
• During titration, it is essential that the equivalence point can be identified.
• The formation of the precipitate is stoichiometric
• The results of the titration should not be distorted appreciably by adsorption.

Keywords:

NaCl, curve, acid-base, argentometric, chloride ions, steps, class, student, reaction, chemistry, chemical reaction, and NaOH, etc.

Factors affecting precipitation titration

Precipitation titration is a type of titration that includes the formation of precipitate during the titration technique. In the process of precipitation titration, the titrant reacts with the analyte to form a precipitate, which is an insoluble substance. This process will continue till the last amount of analyte is consumed. Using silver ions, it can estimate the concentration of chloride.

Precipitation titration refers to volumetric methods which work on the following principle.

Amount of added precipitating reagent = quantity of substance being precipitated

For example: Ag+ (aq) + Cl–(aq) → AgCl(s).

Precipitation titrations help to determine the concentration of salt in food, and beverages and to analyze drugs and halide ions in a sample solution.

Factors Affecting the Precipitation Titrations:

• Solvent nature:

The polarity has directly proportional to the precipitate formation. If the solvent has more polarity, it will improve the precipitation; For example, the formation of precipitate will be increased by the presence of water.

• Reactants concentration:

The concentration of reactants present in a solution is directly proportional to the precipitation reactions that take place. Concentrated solutions form precipitates that are easily soluble, while diluted solutions produce precipitates that are unstable.

• Order of adding reagents:

The order of adding reagents is significant in the precipitate's formation. As several compounds need pretreatment with an alkali or an acid before the precipitating agent is added, and other compounds need to be treated with an alkali or an acid after the precipitating agent has been added.

• The pH of the solution:

Precipitation titrations are directly proportional to the solution's pH. In contrast with basic solutions, acidic solutions enhance the precipitate formation.

• Low solubility product formation throughout the titration:

The endpoint in the precipitation titrations decreases as a result of the formation of the low solubility product during precipitation. Therefore, it can be overcome by modifying the pH of the solution.

• Temperature:

The precipitation formation has a relationship that is directly proportional to temperature. As the temperature rises, the capacity for the formation of precipitates also improves.

• Concentration and nature of foreign substances:

The concentration of foreign chemicals in precipitation products reduces the product's stability. The ability of foreign compounds to form coprecipitation is then taken into account. By keeping the temperature at an ideal level during the titration, you will avoid the problems associated with this condition.

Keywords:

NaCl, curve, argentometric, chloride ions, Volhard’s, Fajan’s, Mohr’s, halide, class, student, reaction, chemistry, analyte, titrant, chemical reaction, NaOH.

Requirements of metal ion indicator

Complexometric titration, also known as chelatometry, is a kind of titration (volumetric technique) that employs a colored compound for the determination of a chemical reaction endpoint. It is the most effective technique that can be used in the pharmaceutical sector and other fields to identify the amount of a certain type of metal ion that is present in a sample solution.

For titrations of metal cations with EDTA, it is necessary the use a complexometric indicator like eriochrome black T, calcein, murexide, fast sulphon black, etc. to detect when the equivalence point/endpoint has been achieved.

The endpoint has been obtained when there is a color change, which indicates that the indicator has been displaced from the metal cations in the solution (often by EDTA). Thus, the free indicator (rather than the metal complex) serves as the endpoint indicator. In complexometric titrations, organic dyes are the most commonly used indicators.

Requirement for metal ion indicator:

A successful EDTA titration depends on an accurate estimation of the endpoint at which the reaction will stop. The following characteristics must be present in a metal ion indicator to be suitable for use in the visual detection of endpoints:

1. The color reaction should occur before the endpoint, which occurs when almost all of the metal ions have complexed with EDTA.
2. The indicator needs to have a color response that is specific or selective.
3. The color must have an intensity that is high enough to allow the use of a minimum indicator.
4. The indicator must be stable in the titration medium, and on storage.
5. It should be easily available in the market with a sufficiently high purity level.
6. The color change of the indicator should occur at a near equivalence point, and it should be particularly sensitive to metal ions.
7. The color contrast between the indicator and metal-indicator complex should be easily observable.
8. The Metal-indicator complex should be stable enough to make a clear color change, but less stable than the Metal-EDTA complex.
9. The change in equilibrium from the metal-indicator complex to the metal-EDTA complex must be rapid.
10. In the pH range where the proposed titration is to be done, all of the above conditions must be met.

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Theory of metal ion indicator

Complexometric titration, or chelatometry, is a type of titration (volumetric technique) that uses a colored compound to identify the endpoint of a chemical reaction. This is the most efficient method for determining the amount of a specific type of metal ion in a solution.

Complexometric titrations are used in analytical chemistry for determining the presence of different metal ions in sample solutions. Generally, the endpoint of the complexometric titration is determined using an indicator that changes color, such as eriochrome black T, murexide, fast sulphon black, calcein, etc.

Explain the theory of the metal ion indicator:

In complexometric titrations, organic dyes are the most commonly used indicators. These dyes work by forming a colored complex with the metal ion that is being titrated. During the reaction, the indicator is replaced by EDTA, which forms a more stable complex with the metal, and when the reaction is finished, the color changes.

The following reaction can be used to illustrate the use of a metal ion indicator in an EDTA titration:

M-In + EDTA M-EDTA + In

This reaction will take place, only if the m-EDTA complex is more stable than the m-In complex.

M + In M-In

The equation describing the stability of the metal indicator complex KIn be given here.

  [M-In]

KIn =   ________

 [M] [In]

Since the change in color of the indicator is also affected by the concentration of hydrogen ions, it is convenient to define a conditional indicator constant K’In, which fluctuates with pH.

K' In be more than 104, and the ratio of the conditional formation constant of the metal-EDTA K’ MY to K’In must be of the order 104 to offer a good endpoint. This will ensure that the error is minimal.

The strength of the metal-indicator complex in comparison to the metal-EDTA complex determines how accurate the end point of the indicator is. After the equivalence point, the color will change if the metal-indicator complex is too strong. But, if the metal-indicator complex is not strong enough, you will not reach the equivalence point until the endpoint is reached.

The majority of metallochromic indicators are also weak acids. This results, for example, in a pH dependence of the conditional formation constant for the metal-indicator complex.

As a result, the conditional formation constant for the metal–indicator complex relies on the pH of the titrant. This allows some control over the titration error of an indicator, as the strength of a metal–indicator complex can be altered by adjusting the pH at which the titration is performed. However, since the indicator is a weak acid, pH also affects the color of the uncomplexed indicator.

References:

• Complexometric titration with EDTA, Part III,lscollege, Available Here:
• ‘Complexation Titration’. Chemistry LibreTexts, 23 Nov. 2014, Available Here:
• ‘Complexometric Indicator’. Wikipedia, 12 Aug. 2022. Wikipedia, Available Here:
• ‘Colours of Transition Metal Ions’. Unacademy, Available Here: 

Keywords:

Principle, EDTA titration curve, titrand, metallochromic indicators, metal-ligand complexes ph of buffer solution, , acid-base, types of metal ion indicator, blue, red, hardness of water, electrode, selectivity, Calmagite, PAN, masking and damasking agents, example, properties, name, role, redox.

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Applications of complexometric titrations

Indicators of complexometric titration

Requirements of metal ion indicator

Metal ion indicator in complexometric titration

Metal ion indicator in complexometric titration

Titration is a laboratory technique used to estimate the concentration of an unknown analyte. It is classified into four types based on their goals and procedures: acid-base, complexometric, precipitation, and redox titration.

Complexometric titration, also known as chelatometry, is a volumetric analytical method that detects the endpoint of a chemical reaction by using a colored complex. It is the most precise way to find out how much of a certain metal ion is in a sample solution.

The EDTA reacts with the metal ions in the sample to form complexes, which can then be measured using standard acids. It is possible to identify metal ions in a sample by determining the endpoint of the titration. There are two ways to observe the complexometric titration endpoint: the visual method and the instrumental method. The several types of complexometric titration include a direct, back, replacement, and indirect titration.

Table of Contents: What is metal ion indicator? Example of a metal ion indicator Application of metal ion indicators Is eriochrome black T a metal ion indicator? Role of metal ion indicators How do you identify colored metal ions? Transition Metal Colors in Aqueous Solution

What is a metal ion indicator?

A metal ion indicator is a substance used in analytical chemistry that changes color when it binds to metal ions in a solution. Metal ion indicators are usually polyprotic complexing agents that are used to indicate the endpoint in the titration.

Generally, an indicator is a substance that can be added to the reaction mixture to show the equivalence or endpoint point of the titration. In different pH solutions, an acid-base indicator changes color to tell us when an acidic solution has turned into a basic solution. An indicator for redox titration will change color either when all of the reactants have been used up or when there is still excess titrant remaining.

A metal ion indicator would also require a color change to indicate the presence of metal ions. For example, ferrous (Fe2+) ions form a complex with ferricyanide to produce Prussian blue. The ferricyanide can be employed as an indicator in a reaction that generates ferrous ions. When ferrous ions are formed, the solution turns blue; when they are used up, the solution becomes colorless.

What is an example of a metal ion indicator?

A good example of a metal ion indicator is xylenol orange, which is an organic reagent that is used as an indicator in cobalt titration. It turns red when it forms a complex with metal ions such as Co2+.

Some other examples include eriochrome black T(for aluminum, cadmium, zinc, calcium, and magnesium), hematoxylin (for copper), murexide (calcium ions) and calcein (for calcium).

What is the application of metal ion indicators?

• The major application of metal ion indicator is that it is used to precisely determine the endpoint of a complexometric titration.
• In the pharmaceutical sector, it is commonly used to determine the metal concentration of a drug product.
• It is also utilized in the process of determining the total hardness present in water.

Is eriochrome black T a metal ion indicator?

Yes, EBT is a metal ion indicator for complexometric titrations. It forms a colored complex with calcium (Ca), magnesium (Mg), and other metal ions when it is protonated.

What is the role of metal ion indicators in complexometric titration?

In complexometric titrations, commonly used indicators are the organic dyes. These dyes do their work by forming a colored complex with the metal ion that is being titrated. During the reaction, EDTA replaces the indicator to form a more stable complex with the metal. When the reaction happens, the color changes.

How do you identify colored metal ions?

In chemistry, an analytical procedure known as the flame test is used to detect the presence of certain elements, most prominently metal ions, based on properties characteristic to each element.

What color are metal ions?

The following lists the colors of common transition metal ions in an aqueous solution.

Transition Metal Ion	Colour
Ferrous ion Iron (Fe2+)	Olive green
Cobalt (Co2+)	Pink
Ferric ion (Fe3+)	Yellow
Manganese Mn2+	Pale Pink
Dichromate (Cr2O72-)	Yellow
Chromium (Cr2+)	Blue-violet
Titanium (Ti3+)	Purple
Titanium (Ti2+)	Pale brown
Zinc (Zn2+)	Colorless
Vanadium (V4+)	Blue-grey

Keywords:

EDTA titration curve, metallochromic indicators, ph of buffer solution, types of metal ion indicator, hardness of water, electrode, selectivity, almagite, PAN, masking and damasking agents.

References:

• ‘Complexation Titration’. Chemistry LibreTexts, 23 Nov. 2014, Available Here:
• ‘Complexometric Indicator’. Wikipedia, 12 Aug. 2022. Wikipedia, Available Here:
• ‘Colours of Transition Metal Ions’. Unacademy, Available Here: 
• Rattenbury em. Complexometric titrations. In: introductory titrimetric and gravimetric analysis. Elsevier; 1966:130-139.

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Applications of complexometric titrations

Indicators of complexometric titration

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Requirements of metal ion indicator

Indicators of complexometric titration

Complexometric titrations are specifically used to determine mixtures of different metal ions in solution. Typically, the endpoint of the complexometric titration is determined using a color-changing indicator such as eriochrome black T, calcein, etc.

Titration is a unique laboratory method for determining the concentration of an unknown analyte. Depending on the goals and procedures of the titration, it can be divided into four different types: acid-base, complexometric, precipitation, and redox titration.

Table of Contents: What is complexometric titration? What is a complexometric indicator? Example of complexometric indicator List of complexometric indicators

What is complexometric titration?

Complexometric titration, commonly known as chelatometry, is a volumetric analytical technique that uses a colored complex to detect the endpoint of a chemical reaction. It is the best way to find out how much of a certain type of metal ion is in a solution.

The metal ions in the sample react with the EDTA to form complexes, which can then be measured with standard acid. By measuring the endpoint of the titration, it is possible to the determination of the metal ions in the sample. Direct titration, back titration, replacement titration, and indirect titration are the types of complexometric titration.

The detection of endpoint in complexometric titration can be observed by two methods visual method or instrumental method.

Visual method:

Because of its precision and cost-effectiveness, it is the most used method. The techniques listed below are examples of the visual methods used to determine the endpoint of complexometric titrations.

• PM indicators or Metallochromic
• pH indicators
• Redox indicators

Instrumental method:

When using visual methods to find endpoints, there is a possibility that one will make a human error or be inaccurate. Consequently, some instrumental techniques are used in the determination of an endpoint.

• Photometry
• Potentiometry
• Miscellaneous methods

What is a complexometric indicator?

Complexometric indicators are water-soluble organic compounds that are also called pM indicators or metallochromic indicators. A complexometric indicator is an ionochromic dye that changes color in the presence of certain metal ions. It forms a weak complex with the ions in solution; its color is very different as compared to the form existing outside the complex.

Complexometric indicators are used in analytical chemistry to indicate the endpoint, it happens when all the metal ions in the solution are sequestered by a chelating agent(most usually EDTA). These indicators are also known as metallochromic indicators.

Example of complexometric indicator:

One of the most notable examples of a complexometric indicator is the Eriochrome Black T indicator. The indicator Eriochrome Black T is capable of displaying a wine-red color when bound to metal ions and a blue color when free from metal ions.

In an EDTA titration, the preferred blue endpoint is obtained when enough EDTA is added and the metal ions bound to the indicator are chelated by EDTA, leaving the free indicator molecule. When rare earth metals are present, Eriochrome Black T is employed to detect their presence. Therefore, a blue endpoint is obtained when it is used as an indicator in EDTA titrations.

List of indicators used in complexometric titration:

When determining metal ions by using reactions that form complexes, we always need a complexometric indicator to show us when the reaction is done.

Here are some common indicators used in complexometric titration are some of the names are,

• Eriochrome Black T or Solochrome Black T (Ethylenediaminetetraacetic acid):

Use: Aluminum, cadmium, zinc, calcium and magnesium, and other rare earth metals detection
Appearance: Brownish black powder

• Thymolphthalein complexone:

Use: Calcium (Ca), strontium (Sr) and Barium (Ba) detection
Appearance: White to off white

• Xylenol orange:

Use: Gallium, indium, scandium, and zinc/cobalt titrations 
Appearance: Red brown to dark brown

• Hematoxylin:

Use: Bismuth, copper and zirconium detection
Appearance: Light to dark-brown

• Ammonium purpurate or Murexide:

Use:Calcium ions detection
Appearance: Dark red to purple powder

• Bromopyrogallol red:

Use: Chelometric titrations 
Appearance: Brownish red color

• Calcein (fluorescent metal indicator):

Use: Calcium detection
Appearance: Yellow to orange brown crystalline

• Calmagite:

Use: Calcium and magnesium detection
Appearance: Brownish black

• Dithizone:

Use: Mercury and lead detection
Appearance: Black

• Murexide:

Use: Calcium copper, nickel, cobalt, and thorium detection
Appearance:Dark Red to Purple

• Patton-Reeder Indicator (Calconcarboxylic acid):

Use: Calcium with magnesium detection
Appearance: Dark purple to black powder

• Curcumin:

Use: Boron detection
Appearance: Yellow

• Fast Sulphon Black:

Use: Copper detection
Appearance: Grey to Black Solid

The following are some frequently asked questions about complexometric titration indicators:

Which indicators are used in complexometric titration?

Eriochrome black T, fast sulphon black, murexide, calcein, and eriochrome red B, etc. are the indicators used in the complexometric titration.

Which type of indicator is EDTA?

EDTA (ethylenediaminetetraacetic acid) is a type of complexometric indicator composed of two amino groups and four Lewis bases (carboxyl groups).

Why buffer solution used in EDTA titration?

Because it resists pH changes, a buffer solution is employed in EDTA titration. since all reactions involving metal ions and EDTA are pH-dependent.

What is a pM indicator?

It is a dye that acts as a chelating agent. This makes a dye-metal complex that looks different from the original dye and is less stable than the corresponding chelate-metal complex.

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