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Monday, February 28, 2022

How does the methyl orange indicator works?

Methyl orange (C14H14N3NaO3S) is an organic compound composed of nitrogen, carbon, sulfur hydrogen, oxygen, and sodium. It is an organic dye used as a pH indicator in titrations, because of its unique and diverse color variations at different pH levels.

Methyl Orange is an indicator used in acid-base titration which is known to shift color from red to orange-yellow in the range of pH of 3.1 to 4.4. This is due to the change in electrons and their arrangement when hydrogen ions are added and removed. When methyl orange becomes alkaline, a hydrogen ion is lost from the -NN- bridge between the rings.

The electrons that were once used to bind the hydrogen now neutralize the positive charge on the terminal nitrogen, preventing it from forming a pi bond. At endpoint this indicator turns from red to orange to yellow as the acidity of the solution decreases. If the solution becomes more acidic, the reverse is true.

According to modern benzenoid theory, pH indicators such as methyl orange exist in interchangeable forms, specifically the benzenoid and quinonoid structures. The theory states that one form predominates in one medium. The color of the Quinonoid form of the indicator is deeper than that of the Benzenoid form. Depending on the pH level, methyl orange can exist in either form.
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Why methyl orange changes color at different pH

Methyl Orange is a basic indicator that is employed in acid-base titration. In acidic conditions, it turns red, whereas, in basic conditions, it turns yellow. The indicator color change depends on the presence or loss of an ion. Methyl orange indicator has a working pH range of 3.1 (red) and 4.4 (yellow).

The Quinonoid Theory of indicators states that every acid-base indicator exists in two tautomeric forms, the benzenoid form, and the quinonoid form. The two forms of colors are different. With a change in media, the concentrations of the two forms change.

Both forms have different colors. With a change in medium, the concentrations of the two forms change. Because they have different colors in different mediums, the medium changes as the color changes, giving us a suitable point to consider as a neutralization point.

The quinonoid form of methyl orange is red and is found mostly in acidic solutions, whereas the benzenoid form is yellow and is found primarily in basic solutions.

Below equilibrium is maintained by two forms.

Why methyl orange changes color at different pH

As a result, the methyl orange indicator changes color since one of the above-mentioned structures was previously more dominant, but as the pH of the solution changes, the concentration of the other form increases while the concentration of the previous form decreases.
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Saturday, February 26, 2022

Methyl orange indicator in titration

Compounds that change color when exposed to acidic/basic solutions are known as indicators. Color indicators are widely used to detect pH and can be added to the reaction mixture to determine the titration endpoint/equivalence point.

In chemistry, different types of titration, including acid-base, redox, precipitation, and complexometric, several types of indicators are used. Each one has its pKa, pH range, and produces a particular color at different pH values. The two theories that explain the acid-base indicator are Ostwald's theory and the quinonoid theory.

What is methyl orange?

Methyl orange is an organic compound composed of nitrogen, carbon, sulfur hydrogen, oxygen, and sodium. C14H14N3NaO3S is an organic dye used as a pH indicator in titrations, because of its distinct and diverse color variations at different pH levels.

It is not the same as a universal indicator like litmus paper, since it has a narrow range of sensitivity. This means that it can only be used as an acidity test within the pH range of 3.1 to 4.4. It's also widely used in a variety of industries, including printing, paper, textiles, and food.

Properties of methyl orange:


Molecular Weight/ Molar Mass 327.33 g·mol−1
Formula C14H14N3NaO3S
Density 1.28 g/cm3
Appearance Orange or yellow solid
Melting point > 300 °C
pKa 4.2
pH range 3.1 to 4.4
Color in acid Red
Color in base Yellow


FAQ (Frequently Asked Questions):


How is methyl orange synthesis?

The synthesis of methyl orange involves a four-step exothermic reaction. Sodium nitrite, sulfanilic acid, and dimethylaniline are used to make methyl orange.

Is methyl orange is a natural indicator?

The methyl orange is not a natural indicator; it is an organic compound that is synthesized using sodium nitrate, dimethylaniline, and sulphaniic acid.

Is methyl orange a weak acid or base?

Methyl orange is a weak acid that breaks down into orange neutral molecules when it comes in contact with water. In acidic conditions, the equilibrium is to the left, and the concentration of neutral molecules is too low to observe the orange color.

What color is methyl orange?

Methyl orange is a solid powder that is orange or yellow and is soluble in water and ethanol.

What type of indicator is methyl red?

Methyl red is a pH indicator that is red when the pH is less than 4.4, yellow when the pH is greater than 6.2, and orange in between, with a pKa of 5.1. It is commonly used as an acid-base indicator.

How does the methyl orange indicator work?

Methyl orange color has been observed to change from red to orange-yellow, this is due to a change in the electrons and their arrangements ions are inserted and removed. When methyl orange becomes basic, a hydrogen ion is lost from the -NN- bridge between the rings.

Why methyl orange is used as an indicator?

Because of its clear and distinct color variance at different pH values, methyl orange is an often used pH indicator in titration.

What is the pH range of the methyl orange indicator?

Methyl orange indicator has a working pH range of 3.1 (red) and 4.4 (yellow).

What is the color of the methyl orange indicator in acidic solution?

In an acidic medium, the color of the methyl orange indicator is red.

What color is the methyl orange indicator in a basic solution?

In a basic medium, the color of the methyl orange indicator is yellow.

Methyl orange is a natural indicator of true or false?

False, methyl orange is an artificial indicator that is synthesized in a laboratory. A natural indicator is a compound that changes color when exposed to acidic or basic media, for example, turmeric.

How is the methyl orange indicator prepared in the laboratory from methyl orange powder?

In a volumetric flask, weigh 100 mg of methyl orange and dissolve it in 100.00 mL of 95 % ethanol.

Why methyl orange is a good indicator?

Methyl orange is a commonly used pH indicator because it provides simple and distinct color changes throughout its pH range. It changes color at the pH of a midi-strength acid, it's widely employed in acid titrations. Methyl orange turns red in an acidic environment and yellow in a basic environment.

What happens when methyl orange is added to vinegar?

The methyl orange color changes from red to orange when the acidity of the solution decreases and vice versa as the acidity increases.

What is the pH range of phenolphthalein and methyl orange?

Methyl orange has a pH range of 3.1 to 4.4, it turns red to orange. Phenolphthalein has a pH range of 8.3 to 10.0, it turns colorless to pink.


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Wednesday, February 23, 2022

pH range and color change of indicators used in titration

Compounds that change color when exposed to acidic or basic solutions are known as indicators. Color indicators are widely used to detect pH and can be added to the reaction mixture to determine the titration endpoint or equivalence point.

A variety of indicators are used in different types of titrations, including acid-base, redox, precipitation, and complexometric. Each has its pKa, pH range, and produces a different color at different pH levels.


In chemistry, there are three types of indicators: natural indicators, artificial indicators, and olfactory indicators, while artificial and natural indicators are the two most commonly used forms.

Here are some common indicators are listed in table form along with their pH range, and color change under acidic, basic, and neutral environments.


List of indicators used in acid-base titration:
Name of Indicator Useful pH Range Color Change
Bromocresol Green 3.6 to 5.2 Yellow to blue
Bromocresol Purple 5.2 to 6.8 Yellow to bluish-violet
Bromophenol Blue 2.8 to 4.6 Yellow to bluish-violet
Bromothymol Blue 6.0 to 7.6 Yellow to blue
m-Cresol 1.2 to 2.8 and 7.6 to 9.2 Red to yellow and yellow to violet
Cresol Red 0.2 to 1.8 and 7.2 to 8.8 Red to yellow and yellow to violet-red
Dimethyl Yellow 2.8 to 4.6 Red to yellow
2-4 Dinitrophenol 2.8 to 4.4 Colorless to yellow
Methyl Orange 2.9 to 4.6 Red to yellow
Methyl Red 4.2 to 6.3 Red to yellow
1-Naphtholphthalein 7.3 to 8.7 Pale red to blue
3-Nitrophenol 6.8 to 8.4 Colorless to yellow
4-Nitrophenol 5.0 to 7.0 Colorless to yellow
Phenolphthalein 8.3 to 10.0 Colorless to red/pink
Phenol Red 6.8 to 8.4. Yellow to red
Thymol Blue 1.2 to 2.8 and 8.0 to 9.6 Red to yellow and to violet-blue
Thymolphthalein 8.3 to 10.5 Colorless to blue    

List of common metal indicators used in complexometric titration:

Name of Indicator Useful pH Range Color Change
Calcein - Orange-yellow to yellowish red
Calcon - Purple red to pure blue
Catechol Violet 0.0 to 8.0 Blue/red to yellow
Dithizone - Pink to green
Methyl-thymol Blue 4.0 to 10.0 Red to yellow to blue
Mordant Black II 7.0 to 11.0 Blue to pink
Murexide 6.0 to 13.0 Yellow to reddish-purple to blue-purple
Pyridylazonaphthol - Yellow to Red
Sodium Alizarin Sulphonate 3.7 to 5.2 Bluish-red to yellow
Thoron - Red to yellow
Xylenol orange 6.4 to 10.4 Yellow to orange-red

List of common indicators used in non-aqueous titrations:


Name of Indicator Useful pH Range Color Change
Alkali Blue 6B 9.4 to 14 Red to Blue
Crystal Violet 0.0 to 2.0 Violet (basic), to bluish-green (neutral) to yellowish green (acidic)
1-Naphtholbenzein 8.2 to 10.0 Green (basic) to orange (neutral) to yellow (acidic)
Quinaldine Red 1.0 to 2.2 Magenta to colorless.

List of common indicators used in oxidation and reduction (Redox) titrations:


 
Name of Indicator E0, V Color of oxidized and reduced form
Potassium permanganate (KMnO4) 1.51 V Purple to colorless
Crystal Violet 0.0 to 2.0 Violet (basic), to bluish-green (neutral) to yellowish green (acidic)
1,10-Phenanthroline iron(II) sulfate complex (Ferroin) +1.08 V Red to blue
Ceric ammonium sulphate - Pink to very pale blue
Phenanthroline blue +1.06 V Deep red to light-blue
Methylene blue +0.53 Blue to colorless
Safranin T +0.24 Red-violet to colorless
Barium Diphenylamine-4-Sulphonate +0.84 V Colorless to violet
Indigo carmine +0.29 Blue to colorless

List of common indicators used in adsorption and miscellaneous:

Name of Indicator Useful pH Range Color Change
Amaranth - Orange-red to yellow
Dicblorofluorescein 5 to 8 Precipitate orange to pink
Starch - Colorless to blue
Potassium chromate 6.5 to 10.5 Yellow to reddish brown


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Saturday, February 19, 2022

Preparation of amaranth indicator solution

Learn the procedure for making amaranth 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.

Amaranth (C20H11N2Na3O10S3) is an anionic dye, chemically described as trisodium l-( 4-sulpho-lnaphthylazo)-2-naphthol-3, 6-disulphonate. It can be applied to natural and synthetic fibers, paper leather, and phenol-formaldehyde resins.

Amaranth usually comes as a trisodium salt, its appearance of reddish-brown, dark red to purple powder which is soluble in water. In the chemical and biological sectors, amaranth indicator solution has a wide range of uses. It's also used as a dye in food, wool, cosmetics, and silk, as well as an indicator in hydrazine titrations.

How to prepare amaranth indicator for titration:

  • Weigh accurately 0.1 gm of amaranth and pour it into a 100.00 ml volumetric flask containing 50.00 ml of distilled water and mix it.
  • Once it is dissolved, dilute to 100.00 ml with distilled water.
  • The concentration of the prepared solution is about 2 g/L.

Amaranth has a pKa of strongest acidic is 3.4 and pKa of strongest basic is 1.1. The color changes from orange-red to yellow when used for titration of iodine and iodides with potassium iodate.


References:
  1. Wikipedia contributors. (2021, October 24). Amaranth (dye). In Wikipedia, The Free Encyclopedia.  Available Here:
  2. Law.resource.org. 2022. [online] Available Here:

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Friday, February 18, 2022

Preparation of starch indicator solution

Learn the procedure for making a starch solution for iodometric titration.

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.

Starch (C6H10O5)n is a polysaccharide comprising glucose monomers joined in α 1, 4 linkages. The linear polymer amylose is the most basic type of starch, while amylopectin is the branched form. It is a tasteless, soft white powder that is insoluble in cold water, alcohol, and other solvents.

Starch is the most common indicator for titrations containing iodine. Iodine with starch forms a dark blue complex. In iodimetry, the endpoint corresponds to a sudden color change to blue.

How to prepare starch indicator for titration:

  • Weigh accurately 0.3 gm of starch in 10.00 ml of water with constant stirring.
  • Add enough boiling water to make around 100 ml and boil for a few minutes and then set aside to cool.
  • The concentration of the prepared solution is about 0.3% w/w.

Starch pKa in strongest acidic is 11.3 and in strongest basic -3. In redox titrations starch and iodide are often used since they can absorb the I2 that is released: when an oxidizing agent is present, the solution turns blue; when a reducing agent is present, the blue color fades because of triiodide.


References:
  1. Wikipedia contributors. (2021, December 5). Iodine–starch test. In Wikipedia, The Free Encyclopedia. Available Here:
  2. Britannica, The Editors of Encyclopaedia. "starch". Encyclopedia Britannica, 14 Mar. 2021,  Available Here:


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Preparation of potassium chromate indicator solution

Learn the procedure for making a potassium chromate 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.

Potassium chromate (K2CrO4) also known as tarpachite is an inorganic compound that is yellow orthorhombic or hexagonal crystal at room temperature. Potassium chromate comes in powder form and appears as a yellow compound that is soluble in water and it is insoluble in alcohol and ether. 

K2CrO4 is used as an indicator in the detection of chloride by titration with standard silver nitrate (AgNO3) solution. The potassium chromate indicator method commonly known as Moore (Mohr) technique is a precipitation titration method. A change in color from yellow to reddish-brown indicates the endpoint.

How to prepare potassium chromate indicator for titration:

  • Weigh accurately 05.00 gm of potassium chromate and pour it into a 100.00 ml volumetric flask containing 50.00 ml of distilled water and swirl until it completely dissolved.
  • Once it is dissolved, dilute to 100.00 ml with distilled water.
  • The concentration of the prepared solution is about 50 grams/liter.

Potassium chromate has pKa (Strongest Basic) values of -6.2; its suitable acidity range is pH 6.5 to 10.5, though when there are ammonium salts in solution, the solution acidity pH 6.5 to7.2 is suitable. It is the most commonly used indicator in the determination of chloride by titration with standard silver nitrate solution.

When Cl- or Br- ions coexist, the potassium chromate indicator method can only be used for direct titrations. The iodide ion and the thiocyanate ion cannot be determined with this method.


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Thursday, February 17, 2022

Preparation of methylene blue indicator solution

Learn the procedure for making a methylene blue 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.

Methylene blue (C16H18ClN3S), also known as methylthioninium chloride, is a photoactive phenothiazine dye. It has 3, 7-bis (dimethylamino) phenothiazine-5-ium as the counterion.

Methylene blue is a heterocyclic aromatic chemical compound that occurs as a dark green crystalline powder with a metallic appearance. It is an oxidation-reduction agent which is soluble in water, ethanol, and ethylene glycol. It's useful in a variety of fields, including biology and chemistry.

How to prepare methylene blue indicator for titration:

  • Weigh accurately 15.20 mg of methylene blue and pour it into a 100.00 ml volumetric flask containing 50.00 ml of distilled water and swirl until it completely dissolved.
  • Once it is dissolved, dilute to 100.00 ml with distilled water.
  • The concentration of the prepared solution is about 0.15 g/L.

Methylene blue has pKa values of 2.6, and 11.2. It’s blue when mixed with an oxidizing agent, while turns colorless when mixed with a reducing agent, Methylene blue changes color since it loses electrons in the presence of oxidizing agents. It is widely used as a redox indicator in analytical chemistry. It is also used as an indicator in a variety of chemical reactions.

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Wednesday, February 16, 2022

Preparation of ferroin indicator solution

Learn the procedure for making a 1, 10-phenanthroline ferrous complex indicator.

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.

Ferroin sulfate (C36H24FeN62+) can be prepared by adding phenanthroline to ferrous sulfate in water. Ferroin is a redox indicator, which is a complexation of phenanthroline and iron. The Fe (II) - phenanthroline complex is red in its reduced state and Fe (III) - phenanthroline complex is blue in its oxidized state. In titrimetric analysis, ferroin serves as an indicator of oxidation-reduction reactions.

How to prepare ferroin indicator for titration:

  • Weigh accurately 01.49 gm of 1, 10-phenanthroline, and 0.70 gm of ferrous sulphate, pour it into a 100.00 ml volumetric flask containing 50.00 ml of water, and swirl until it completely dissolved.
  • Once it is dissolved, dilute to 100.00 ml with distilled water.
  • The concentration of the prepared solution is about 17 g/L.
For visualizing oscillatory Belousov–Zhabotinsky reactions, it is a popular indicator in redox titration. When the oxidation potential of the solution is increased from 1.04 to 1.08 volts, ferrous 1,10-phenanthroline, an oxidation-reduction indicator, changes from red to pale blue.



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Preparation of quinaldine red indicator solution

Learn the procedure for making a quinaldine red 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.

Quinaldine red (2-(p-Dimethylaminostyryl) quinoline ethiodide) is a colorimetric phosphate detection reagent that is known to be a cationic fluorescent probe for proteins. C21H23IN2 comes in powder form and appears as a dark green compound with a metallic luster however appears purple when dissolved.

It dissolves sparingly soluble in water and freely soluble in ethanol/methanol. Quinaldine Red is used as a cationic fluorescent probe, dyes, metabolites, and an agent in bleaching.

How to prepare quinaldine red indicator for titration:

  • Weigh accurately 0.1 gm of quinaldine red and pour it into a 100.00 ml volumetric flask containing 50.00 ml of methanol and swirl until it completely dissolved.
  • Once it is dissolved, dilute to 100.00 ml with methanol.
  • The concentration of the prepared solution is about 01 gram/liter.

Quinaldine red has pKa values of 2.63, and its pH range is 1.0 to 2.2. Quinaldine red is an indicator that turns from colorless to red throughout the pH range. It is the most commonly used indicator in non-aqueous titrations, acid-base titrations as well as titration of bases with perchloric acid in glacial acetic acid (CH3COOH).



References:
  1. Wikipedia contributors. (2021, November 8). Quinaldine red. In Wikipedia, The Free Encyclopedia.  Available Here:
  2. Law.resource.org. 2022. [online] Available Here:

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Monday, February 14, 2022

Preparation of crystal violet indicator solution

Learn the procedure for making a crystal violet 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.

Crystal violet (C25H30ClN3) also known as methyl violet, gentian violet, or hexamethyl pararosaniline chloride is a triarylmethane dye used as a histological stain and indicator. It comes in powder form and appears as a dark green compound with a metallic luster however appears purple when dissolved.

Methyl violet is soluble in water, alcohol, chloroform, and insoluble in ether. It can be used to make paints and inks for printing. It can also be used as an acid-base indicator, as well as a colorimetric assay development reagent.

How to prepare crystal violet indicator for titration:

  • Weigh accurately 0.5 gm of crystal violet and pour it into a 100.00 ml volumetric flask containing 50.00 ml of acetic acid and swirl until it completely dissolved.
  • Once it is dissolved, dilute to 100.00 ml with acetic acid.
  • The concentration of the prepared solution is about 05.00 gram/liter.
Crystal violet has pKa values of 9.4. Its pH range is 0.0 to 2.0. In an acidic medium, Crystal violet gives yellowish-green, while in a basic condition, it turns violet color. It is the most commonly used indicator in non-aqueous titrations, as well as also used for acid-base titration.



References:
  1. Wikipedia contributors. (2022, February 13). Crystal violet. In Wikipedia, The Free Encyclopedia. Available Here:
  2. Law.resource.org. 2022. [online] Available Here:
  3. Preparation of Indicator Solutions : Pharmaceutical Guidelines. Available Here:
  4. ‘Recipe for Crystal Violet for the Gram Stain’. ThoughtCo, Available Here:
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Preparation of xylenol orange indicator solution

Learn the procedure for making a xylenol orange 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.

The chemical reagent xylenol orange (C31H32N2O13S) is commonly employed as a tetra-sodium salt as a metal titration indicator. It will appear red in the titration when used for metal titrations and will turn yellow once it reaches its endpoint. It comes in very dark brown to very dark red metallic or crystalline powder which is soluble in water, and ethanol.

Initially, a small quantity of xylenol orange is added to the cobalt solution, forming a complex with some of the Co2+. The color of the xylenol orange changes as the xylenol orange loses the metal ion. The indicator cannot bind the metal ion as strongly as the complexing agent (EDTA) which is used in the titration.

How to prepare xylenol orange indicator for titration:

  • Weigh accurately 0.1 gm of xylenol orange and pour it into a 100.00 ml volumetric flask containing 50.00 ml of distilled water and swirl until it completely dissolved.
  • Once it is dissolved, dilute to 100.00 ml with distilled water and filter if necessary.
  • The concentration of the prepared solution is about 01 gram/liter.

Xylenol orange has pKa values of 2.6, 6.4, 6.5, 10.5, and 12.3. Its pH range is 6.4 to 10.4. In an acidic medium, xylenol orange turns yellow, while in a basic condition, it turns orange-red color. It's a versatile indicator in EDTA titrations in an acidic medium.



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Sunday, February 13, 2022

Preparation of catechol violet indicator solution

Learn the procedure for making a catechol violet 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.

Catechol violet (C19H14O7S) is an azo dye used in complexometric titrations as an indicator. This phthalene dye chelates metals to form blue to blue-violet complexes. When alkaline, it is known to be unstable. At a neutral pH, the stability improves. The color can be yellow when the pH is between 2 and 7.

It comes in dark-red-brown metallic or crystalline powder which is soluble in water, ethylene glycol, monomethyl ether, and ethanol.

How to prepare catechol violet indicator for titration:

  • Weigh accurately 0.1 gm of catechol violet and pour it into a 100.00 ml volumetric flask containing 50.00 ml of distilled water and swirl until it completely dissolved.
  • Once it is dissolved, dilute to 100.00 ml with distilled water.
  • The concentration of the prepared solution is about 01 gram/liter.

Pyrocatechol violet has pKa values of 7.21. Its pH range is 0.0 to 8.0. It is used as a metal indicator and turns from red to violet over the pH range.


References:
  1. Wikipedia contributors. (2022, January 21). Catechol. In Wikipedia, The Free Encyclopedia. Available Here:
  2. Law.resource.org. 2022. [online] Available Here:
  3. Dr John Elfick, j., 2022. Learn how to prepare useful acid-base indicators. Uq.edu.au. Available Here:
  4. Sabnis, R. W. (2008). Handbook of Acid-Base Indicators. Boca Raton, FL: CRC Press.
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Saturday, February 12, 2022

Preparation of eriochrome black T indicator solution

Learn the procedure for making eriochrome black T 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.

Eriochrome Black T/ solochrome black-T (C20H12N3NaO7S) is an azo dye used in complexometric titrations as an indicator. This blue dye also forms a complex with calcium and magnesium ions, turning pink in the process.

Mordant Black II comes in blue powder form which is soluble in water and alcohol, and insoluble in common organic solvents. It is mostly employed as an indicator in the ethylenediaminetetraacetic acid (EDTA) method for determining the hardness of the water.

How to prepare eriochrome black T indicator for titration:

  • Weigh accurately 0.5 gm of eriochrome black-T/solochrome black-T and pour it into a 100.00 ml volumetric flask containing 50.00 ml of ethyl alcohol and swirl until it completely dissolved.
  • Weigh 4.5 gm of hydroxylamine hydrochloride and transfer it to the flask containing the EBT and swirl until it completely dissolved.
  • Once it is dissolved, dilute to 100.00 ml with ethyl alcohol.
  • The concentration of the prepared solution is about 5 g/L.

Eriochrome black T has two pKa values, 6.3 and 11.55. Its ph range is 7.0 to 11.0. It transitions from blue to pink through the pH range and is used as a pH indicator (Metal indicator).

It is blue in its deprotonated state. When it forms a complex with magnesium, calcium, or other metal ions, it turns red. The indicator is added and remains blue because EDTA contains all Ca2+ and Mg2+ ions.



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