Thursday, January 19, 2023

Diazotization Titration: Principle, Types, Applications

Learn the principle, theory, types, and applications of diazotization titration, which involves the conversion of an aromatic amine into diazonium compounds.

Titration is a method of chemical qualitative analysis used to determine the unknown concentration of an analyte. It is also known as titrimetry and volumetric analysis, in which an endpoint is determined by adding a known concentration of titrant to an unknown amount of analyte. Titration can be classified based on its procedures and goals, such as acid-base titration, precipitation titration, complexometric titration, and redox titration.

What is diazotization titration?

In pharmaceutical analysis, diazotization titration is a type of titration that involves the conversion of the primary aromatic amines into particular diazonium compounds. The reaction mechanism for diazotization titration was first discovered in 1853 by Peter Griessin.

According to his reactions, a diazonium compound or salt will be formed when the primary aromatic group reacts with sodium nitrite (NaNO2). Furthermore, the medium of this reaction is acidic.

Principle of diazotization titrations:

The basic principle behind diazotization titration is that, in the presence of an acid, the given sample of a primary aromatic amine will react with sodium nitrite (NaNO2) to yield a diazonium salt (for example, hydrochloric acid).

The chemical reaction of this process is as follows:

R-NH2+ NaNO2+ HCl→ R-N+≡ N-Cl–+ NaCl + H2O

Theory:

You will use sodium nitrite for the direct diazotization method in an acidic medium. it will release HNO2, and by measuring the volume of NaNO2 in the solution, we can easily analyze the number of primary amine groups that have free -NH2 groups.

The chemical reaction of this process is as follows:

NaNO2 + HCl →HONO + NaCl

ArNH2 + HONO + HCl →ArN2Cl + 2H2O

Using the starch paper test or an indicator, you can find the excess NaNO2 that is still present in the solution. Excess sodium nitrite (NaNO2) indicates that the reaction has reached its endpoint. The starch and I2 that are released at the end will react to produce a blue color. It is significant to note that it will only occur when an inorganic acid is present. Therefore, the following chemical reaction occurs to test it with starch iodide paper or solution:

KI + HCl →HI+ KCl

2HI +2HONO→ I2 +2NO +2H2O (excess)

I2 + Solution of paste of starch→ blue color (endpoint)

Types of diazotization titrations:

There are three different types of diazotization titration: direct method, indirect method, and other methods.

Direct Method:

The process consists of treating an amino group with an acidic solution, to yield the diazonium salts of the diazonium compounds. This solution will be stored in ice water to keep the temperature between 0 to 5°C. Then, titrate it with sodium nitrate and observe the endpoint.

Indirect method:

The indirect method of titration applies to insoluble diazonium salts. In this technique, you will need to add the excess nitrous acid into the sample titration solution. You need to titrate it against some other since it is an insoluble diazonium salt.

Other methods:

The other method consists of conversion into diazo oxides, which are typically more stable than diazo compounds.

Factors affecting diazotization titrations:

The following are some of the factors that affect diazotization titration:
  • The acid concentration used in titration
  • Time taken by the reaction
  • The efficiency of the attached diazotized group (rapid or slow)
  • The pH of sodium nitrite
  • Reaction temperature

Application of diazotization titrations:

  • The analysis of sulfonamides is the basic application of diazotization titration in pharmaceuticals.
  • It is used to determine the primary aromatic amine compound.
  • Diazotization titration is also used to determine the chlorophenol, alpha drug, procaine, etc.
  • It is commonly used in the dye and pigment industries.

Commonly asked questions on diazotization titrations are as follows.

What are the conditions required for diazotization titrations?
Maintaining the temperature of the reaction and rate of titration are the conditions required for diazotization titrations.

What indicator is used in diazotization titration?
Starch iodide paper is used as an indicator to indicate the endpoint of a reaction in diazotization titrations.

Why is HCl used in diazotization?
The diazotization reaction is conducted in the presence of excess HCl to avoid azo coupling.

What is the other name for diazotization titration?
Diazotization titration is also known as nitrite titration which is used in the analysis of aromatic compounds containing an amino group in the molecules.

What are the examples of slow and fast diazotized groups?
Nitrogen oxide, carboxylic groups, and sulpha, are examples of slow diazotized groups, and anilide, toluidine, and aminophenol are examples of fast diazotized groups.


Keaywords:
Applications, examples, principle, advantages and disadvantages
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Friday, January 13, 2023

Applications of redox titration

Titration is a common laboratory technique for quantitative chemical analysis, to determine the concentration of a specific analyte/solute by comparing it with the known concentration of a solution in the presence of an indicator. 

Titration is classified into four different types based on goals and processes such as acid-base titration, redox titration, precipitation titration, and complexometric titration.

What is redox titration?

Redox titration is an analytical method to determine the concentration of sample analyte, redox reactions are oxidation-reduction chemical reactions in which the oxidation states of the reactants change. In which a redox indicator solution or potentiometer is used to determine the endpoint.

There are different types of redox titration depending on the titrant used, such as permanganometry, iodometry, bromatometry, iodimetry, cerimetry, and dichrometry, and based on the method are direct titration and back titration.

The reactions involved in redox titration are redox reactions in which electrons are transferred and oxidation states are changed. As a result, redox titrations are a useful way to learn more about the substances we come into contact with.

Concept of oxidation and reduction:

Oxidation:
It could be described as the loss of electrons to an oxidizing agent to produce a more positive or higher oxidation state.

Reduction:
It could be described as gain electrons from a reducing agent to produce a more negative or lower oxidation state.

Applications of redox titration:

Redox titrations have numerous applications in chemistry, industrial analyses, food industries, pharmaceutical preparations, agriculture, environmental analysis, and other fields. Its common example is the titration of sulfite in wine using iodine, as well as that of alcohol, which can be determined based on its oxidation by potassium dichromate (K2Cr2O7).
  • Industrial applications of redox titration:
Evaluation of chlorination of public water sources is one of the most important industrial applications of redox titration. As well as to determine the purity or content analysis of raw materials, oxidation-reduction reactions are also used.
  • Pharmaceutical applications of redox titration:
Redox titration is used in pharmaceutical analysis to measure the concentration of active pharmaceutical ingredients (concentration of iron) in pharmaceutical goods, such as tablets, capsules, and other medicinal products.
  • Applications of redox titration in chemistry:
Redox reaction is most commonly used to identify elements with medium and high concentrations. Many inorganic analytes can be analyzed using redox titrimetry. In inorganic analysis, it is used to determine the water content in a non-aqueous solvent using Karl Fischer reagent as a titrant. As well as dissolved oxygen can be a determination by this method.
  • Applications of redox titration in food:
The food industry makes broad use of an analytical method that enables it to estimate how much of a reactant is present in a sample. Redox titration can be used to measure the concentration of salt, sugar content as well as vitamin C, and E content present in a food product.

Some of the real-life applications and common applications of redox reactions are as follows.
  • It is used to purify metals.
  • It is used in environmental analysis for the determination of dissolved oxygen.
  • Redox reactions are used to manufacture a wide variety of chemicals, including chlorine and caustic soda.
  • Redox Reaction is used in combustion
  • Redox Reaction is used in electrochemistry
  • Redox Reaction is used in photosynthesis applications
  • Redox Reaction is used in photographic Films
  • Redox reactions are used in the electroplating process
  • Oxidation-reduction reactions are used to sanitize water and bleach materials.

Keywords:

Class 11 ncert pdf, medicine,  photosynthesis, pharmacy, potential, electrochemistry, everyday life, chemistry, dentistry, food, metallurgy, public health and environmental analyses.
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Thursday, December 22, 2022

Difference between natural and synthetic indicators

The major difference between natural and synthetic indicators is that natural indicators are those that come from or are made of substances that occur naturally, whereas synthetic indicators are compounds that are manufactured in a lab from artificial substances.

Compounds that change colour when added to acidic or alkaline solutions are called indicators. Indicators are often used to determine pH. Colored indicators can be added to the reaction mixture to determine the endpoint or equivalence point of different titration methods, such as acid-base.

Indicators are either weak acids or weak bases that change colour when the amount of hydrogen ions in a solution or its pH changes. In water, the indicators dissociate slightly to form ions. In chemistry, there are primarily two types of indicators: natural indicators and artificial indicators.

Natural indicators:

Natural indicators are naturally occurring substances that can be used to determine whether a substance is acidic or basic. These naturally occurring indicators are used to identify hydrogen ions (H+) and hydroxyl ions (OH-) in a sample solution.

Examples of natural indicators: 

Turmeric, tomato, litmus, china-rose, clove oil, curry powder, red cabbage, vanilla extract, onion, grape juice, cherries, etc.

 
Natural indicator Color in acid Color in base
Turmeric Yellow Brick red
Beet root Pink Pale yellow
Red cabbage Red Green

Artificial indicators:

Indicators that do not occur naturally but are produced artificially in the laboratory or obtained through a chemical reaction are considered synthetic indicators. These synthetic indicators are used for titration, identifying acids and bases, and determining the pH of various solutions.

Examples of artificial indicators: 

Methyl orange, phenolphthalein, thymol blue, litmus paper, malachite green, etc.
Synthetic indicator Color in acid Color in base
Litmus Red Blue
Phenolphthalein Colorless Pink
Methyl Orange Pink Yellow



Keywords:
Define, 10 examples, methyl orange, litmus paper, class 9, class 10 students 


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Tuesday, November 8, 2022

Preparation of dimethyl yellow indicator solution

Learn the procedure for making a dimethyl yellow indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Most of the time, color indicators are used to measure pH. To find the endpoint or equivalence point of the titration, they are added to the reaction mixture.

Dimethyl yellow (C14H15N3) is an organic compound chemically described as 4-(Dimethylamino)azobenzene, N,N-Dimethyl-4-(phenylazo)aniline, Butter yellow, Methyl yellow. It is used as an acid-base indicator, as well as an indicator for non-aqueous titration which changes from yellow to red through a pH range pH 2.9 to pH 4.00.

Dimethyl yellow comes in the form of a yellow to orange-brown powder that is soluble in alcohol, benzene, chloroform, ether, and petroleum but, insoluble in water.

How to prepare dimethyl yellow indicator mixture for titration:
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Saturday, November 5, 2022

Preparation of calcein indicator solution

Learn the procedure for making a calcein indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Most of the time, color indicators are used to measure pH. To find the endpoint or equivalence point of the titration, they are added to the reaction mixture.

Calcein (C30H26N2O13), which is also called fluorexon or fluorescein complex, is a fluorescent dye with wavelengths of 495 and 515 nm for excitation and emission, respectively. It is used as a complexometric indicator for the titration of calcium ions with EDTA and fluorometric determination of calcium. 

Calcein is a fluorescent metal indicator, chemically described as 2, 7 Bis[bis(carboxymethyl)aminomethyl]fluorescein. Calcein comes in the form of a yellowish-orange powder that is slightly soluble in water.

In acidic conditions, a calcein solution emits a yellowish-green fluorescence, whereas there is no fluorescence in basic conditions. However, under basic conditions, Calcein will emit fluorescence in the presence of metal ions such as Al, Ba, Ca, Cu, Mg, and Zn.

How to prepare calcein indicator mixture for titration:

To make a fine powder that can be used as an indicator, mix 1 gram of calcein with 100 gm of potassium chloride.
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Friday, November 4, 2022

Preparation of calcon indicator solution

Learn the procedure for making a calcon indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Most of the time, color indicators are used to measure pH. To find the endpoint or equivalence point of the titration, they are added to the reaction mixture.

Calcon (C20H13N2NaO5S) is an azo dye chemically described as, 2-Hydroxy-1-(2-hydroxy-1-naphthylazo) naphthalene-4-sulfonic acid sodium salt that is used as an indicator (metal indicator) for complexometric titrations of calcium with ethylenediaminetetraacetic acid (EDTA) in the presence of magnesium.

Calcon comes in the form of a dark, blackish-brown powder that is soluble in water, ethanol, and methanol. It produces a purple color when calcium ions in an alkaline solution are present and a blue color when these ions are absent.

How to prepare calcon indicator for titration:
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Monday, October 31, 2022

Preparation of dithizone indicator solution

Learn the procedure for making a dithizone indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Most of the time, color indicators are used to measure pH. To find the endpoint or equivalence point of the titration, they are added to the reaction mixture.

Dithizone (C13H12N4S) is a sulfur-containing organic compound chemically described as 1,5-diphenylthiocarbazone, which is used as a complexometry/metal indicator. It comes in the form of crystalline black powder which is soluble in ethanol but insoluble in water.

It is a good ligand and can form complexes with several toxic metals, including lead, thallium, and mercury. Additionally, it acts as a chelating agent for toxic metals including lead and mercury.

How to prepare dithizone indicator for titration:

  • Accurately weigh 25 mg of dithizone and pour it into a 100 mL volumetric flask with 50 ml of ethanol.
  • Once it is dissolved, dilute it to 100.00 mL with ethanol.
  • The concentration of the prepared solution is about 01 g/L.

Dithizone has a pKa of 1:4.50;pK2:15 (25°C), When used as an indicator, it produces a pink color in a pH range of 4 to 5 when zinc ions are present, and a green color when these ions are absent.


References:

Wikipedia contributors. (2022, August 9). Dithizone. In Wikipedia, The Free Encyclopedia. Available Here:
Law.resource.org. 2022. [online] Available Here:
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Saturday, October 29, 2022

Preparation of pyridylazo naphthol indicator solution

Learn the procedure for making pyridylazo naphthol indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Most of the time, color indicators are used to measure pH. To find the endpoint or equivalence point of the titration, they are added to the reaction mixture.

Pyridylazonaphthol (C15H11N3O) is an orange-colored dye chemically described as 1-(2-Pyridylazo)-2-naphthol (PAN) which is used as an acid-base/complexometry/metal indicator. It comes in the form of orange powder which is soluble in ethanol but insoluble in water.

When copper ions are present in an acidic solution, it produces a yellow color. However, when these ions are absent, the solution becomes red. It is a useful indicator in complexometric titrations because it may form chelates with metal ions.

How to prepare pyridylazo naphthol indicator for titration:
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Friday, October 28, 2022

Preparation of sodium alizarin sulfonate indicator solution

Learn the procedure for making sodium alizarin sulfonate indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Most of the time, color indicators are used to measure pH. To find the endpoint or equivalence point of the titration, they are added to the reaction mixture.

Sodium alizarin sulfonate is a chemical compound, chemically described as sodium 1,2-dihydroxy-9, 10 anthraquinone-3-sulphonate, used as a metal indicator. It comes in the form of yellow-orange powder which is soluble in water and ethanol.

At a pH of about 4.0, it produces a bluish-red lake with thorium and aluminum ions, However, the solution turns yellow when these ions are absent.

How to prepare sodium alizarin sulfonate indicator for titration:
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Saturday, October 22, 2022

Preparation of alkali blue 6B indicator solution

Learn the procedure for making an alkali blue 6B indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Most of the time, color indicators are used to measure pH. They are added to the reaction mixture to find the endpoint or equivalence point of the titration.

Alkali blue 6B (C37H29N3O3S) is a chemical compound, chemically described as sodium para-rosaline mono sulphonate.

Alkali blue 6B has been used as a pH indicator for the non-aqueous titration method, which changes color from blue to greenish-red and its pH range is 9.4 (Blue) to pH 14.0 (Red). Alkali Blue 6B is a solid that is a dark blue powder. It is soluble in ethanol, but not in water.

How to prepare dichlorofluorescein indicator for titration:
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Preparation of α-Naphtholbenzein indicator solution

Learn the procedure for making 1-Naphtholbenzein indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Most of the time, color indicators are used to measure pH. They are added to the reaction mixture to find the endpoint or equivalence point of the titration.

α-Naphtholphthalein (C28H18O4) is a dye, chemically describes as 4, 4′-(α-Hydroxybenzylidene)di-1-naphthol, p-naphtholbenzein

α-Naphtholbenzein has been used as a pH indicator during the acid-base titration method which changes color from colorless/reddish to greenish blue at pH 7.3–8.7. It changes from green (basic) to orange (neutral) to yellow (acidic) when used as an indicator for non-aqueous titrations.

Naphtholbenzein is a solid that is colorless to slightly reddish or blue-green. It dissolves in ethanol, acetic acid, and acetone, but not in water.

How to prepare dichlorofluorescein indicator for titration?

  • Accurately weigh 0.2 g of 1-Naphtholbenzene and pour it into a 100 ml volumetric flask with 50 ml of acetic acid.
  • Once it is dissolved, dilute it to 100.00 mL with acetic acid.
  • The concentration of the prepared solution is about 2.0 g/L.


References:
  1. Wikipedia contributors. (2022, April 3). Naphtholphthalein. In Wikipedia, The Free Encyclopedia. Available Here:
  2. Law.resource.org. 2022. [online] Available Here:
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Friday, October 21, 2022

Preparation of dichlorofluorescein indicator solution

Learn the procedure for making dichlorofluorescein indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Color indicators are commonly used to measure pH and are added to the reaction mixture to identify the titration endpoint or equivalence point.

Dichlorofluorescein (C20H10Cl2O5) is an organic dye of the fluorescein family, which is chemically described as 2′, 7′-Dichloro-3, 6-fluorandiol.

In Fajan’s method, it is used as an indicator for argentometric titration and as adsoprtion indicator. The color of the titration reaction changes from colorless to pale pink on reaching the equivalence point.

Dichlorofluorescein usually comes in the form of crystalline powder, in the color of orange to red-brown powder, which is soluble in ethanol and methanol but insoluble in water.

How to prepare dichlorofluorescein indicator for titration:

  • Weigh 0.1 gm of dichlorofluorescein accurately and pour it into a 100.00 ml volumetric flask containing 50.00 ml of rectified spirit.
  • Once it is dissolved, dilute it to 100.00 ml with rectified spirit.
  • The concentration of the prepared solution is about 1.0 g/L.


References:
  1. Wikipedia contributors. (2022, June 30). Dichlorofluorescein. In Wikipedia, The Free Encyclopedia. Available Here:
  2. Law.resource.org. 2022. [online] Available Here:
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Thursday, October 20, 2022

Preparation of phenosafranine indicator solution

Learn the procedure for making phenosafranine indicator solution.

The compound that changes color when exposed to acidic or basic solutions is called an indicator. Color indicators are commonly used to measure pH and are added to the reaction mixture to identify the titration endpoint/equivalence point.

Phenosafranine (C18H15ClN4) is a compound or dye, chemically described as 3,7-Diamino-5-phenylphenazinium chloride.

Phenosafranine is a phenylphenazinium bacterial stain for microscopy that is used as an indicator in adsorption and redox titration.

It turns the precipitate red when used in the titration of chloride or bromide with silver nitrate in an acid solution. Once the precipitate is complete, the color of the precipitate changes to blue color.

Phenosafranine usually comes in the form of powder, crystals, or flakes, and its appearance of dark green powder which is soluble in water.

How to prepare phenosafranine indicator for titration:
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Tuesday, October 18, 2022

Why KCl is used for the calibration of conductivity meter

Potassium chloride, often known as KCl, is the most commonly used solution for calibrating conductivity meters due to its high stability and solubility.

If you want reliable and repeatable results from the conductivity meter, calibration using pre-prepared standard solutions is essential. The most common calibration solution is potassium chloride (KCl). Calibration of a conductivity meter is an important maintenance task. Regular calibration produces consistent and reliable readings.

Electrical conductivity (EC) is the measure of the ion concentration present in the sample. The ability of a substance to transmit electric current in a certain area is known as conductivity. Siemens (S) is the unit of measurement for electrical conductivity, and scientific instruments commonly show measured units as MilliSiemens per centimeter mS/cm or MicroSiemens per cm μS/cm.

Because of its solubility and stability, KCl is the solution most often used in the process of calibrating the conductivity meter. Conductivity standard solutions are made up of a KCl: Water ratio. The mixing ratio is determined by the desired ion concentration level of the standard solution.

Molarity/Concentration of KCl

Standard conductivity

0.001 M

147 µS/cm ±10% at 25°C

0.01 M

1.413 mS/cm ±10% at 25°C

0.1 M

12.88 mS/cm ±10% at 25°C



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