Saturday, March 5, 2022

What is the color of methyl orange and phenolphthalein?

An indicator is a substance that changes color when exposed to acidic or basic conditions. To determine the endpoints of acid-base titration, we employ phenolphthalein and methyl orange as indicators.

The selection of a certain indicator for titration is decided based on a plot known as the pH curve, which is typical of a specific reaction. The dissociation of the H+ ion from the indicator causes a pH indicator's colour to change. In the flask, the indicator is always added to the reactant.

What is the color of phenolphthalein and methyl orange in the acidic and basic and neutral medium?

  • Methyl orange produces a red color in acidic solutions, whereas yellow color in basic solutions.
  • Phenolphthalein is colorless in acidic solutions, whereas process pink color in basic solutions. 
Color change of phenolphthalein:
Color of phenolphthalein in acid Colourless
Color of phenolphthalein in base Pink
Color of phenolphthalein in neutral Colourless

Color change of methyl orange:

Colour of methyl orange in acid Red
Colour of methyl orange in base Yellow
Colour of methyl orange in neutral Yellow

In an acid-base titration, different types of indicators are used; however, depending on the pH range, phenolphthalein and methyl orange are the most commonly used indicators. Phenolphthalein has a pH range of 8.3 to 10.0, while that of methyl orange is 3.1 to 4.4.


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Friday, March 4, 2022

Methyl red indicator in titration

The compound which changes color when exposed to the acidic or basic solution is called an indicator. Color indicators are widely used to detect pH and can be added to reaction mixtures to determine titration endpoints or equivalence points.

In chemistry, several types of indicators are used in various forms of titration, including acid-base, precipitation, redox, and complexometric. Each one has its pKa and pH range and generates a distinct hue at various pH levels. Ostwald's idea and the quinonoid theory are the two theories that explain the acid-base indicator.

What is methyl red?

Methyl red (2-(N, N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid), the indicator dye also known as C.I. Acid Red 2, becomes red in acidic solutions. It is an azo compound that differs from methyl orange in that the sulphonic acid function has been substituted with a carboxylic acid function.

Methyl red (C15H15N3O2) is a weak acid that dissociates in water to form red neutral molecules. It's an azo dye that's used as a pH indicator and comes in the form of a dark red crystalline powder. It turns red below pH 4.4, yellow above pH 6.2, and orange in the middle, with a pKa of 5.1.

Prperties of methyl red:

 
Formula of Methyl red  pKa of Methyl red pH range of methyl red  Color in acidic medium Color in basic medium
C15H15N3O2 5.1 4.4 to 6.2 Red Yellow

How does methyl-red work as an indicator?

The acid-base indicators are weak acids or bases that come in both ionized and non-ionized forms and have a variety of colors. The degree of dissociation is controlled by the pKa value of the analyte. The two forms are equivalent when the pH equals the pKa. One variant predominates above or below this. We select compounds with the suitable pKa and consequently pH for the color change, that provide good, distinctive color contrast.

The pH-dependent color change of methyl red is caused by a structural change. The unprotonated form on the left is a simple diazo dye, due to the extended conjugation, it appears yellow. When the dimethylamino group is protonated at pH's less than 4.0 to 6.0 the predominant structural form is the quinone diimine form on the right.

What is the color of methyl red in the acidic medium?

The color of methyl red in an acidic medium is red.

What is the color of methyl red in the basic medium?

Methyl red has a yellow color in an alkaline medium and neutral solution.

What titration is methyl red used for?

Methyl red is suitable for the titration of a strong acid with a strong base; Due to its low pH range, it is good for acid titration.

Can methyl red be used for NaOH titration with HCl?

Yes, we can use methyl red, phenolphthalein, or methyl orange as indicators in the titration of a strong base with strong acid.

Why was methyl red used as an indicator rather than phenolphthalein?

If the endpoint of the compounds that have in between pH 4.0 to 6.2, methyl red indicator used in that titration which turns red to yellow, Whereas phenolphthalein is used for pH 8.2 to 10.0, which turns from colorless to pink.
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Difference between methyl red and methyl orange

The major difference between them is that the methyl orange has a pH range of 3.1 (red) and 4.4 (yellow), while methyl red has a pH range of 4.4 (red) to 6.2 (yellow), they will both show a change in pH level at different points on the scale.

Methyl red and methyl orange both are used as an indicator in an acid-base titration, they both serve the same purpose, although the pH ranges are different.

What is methyl orange?

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

Methyl orange is a weak acid that breaks down into orange neutral molecules when it comes in contact with water. Since it has a narrow range of sensitivity, it is not the same as a universal indicator like litmus paper. This implies that it can only be used to determine acidity in the pH range of 3.1 to 4.4.

What is methyl red?

Methyl red (C15H15N3O2), commonly known as C.I. Acid Red 2, is an indicator dye that becomes red in acidic solutions. It is an azo molecule with a structure that differs from methyl orange (Orange 3) in that the function of the sulphonic acid has been substituted by a carboxylic acid function.

Methyl red is a weak acid that dissociates in water to form red neutral molecules. It's an azo dye that comes in the form of a dark red crystalline powder that's used as a pH indicator. It's red at pH under 4.4, yellow at pH above 6.2, and orange in the middle, having a pKa of 5.1.

Difference between methyl red and methyl orange indicator:

  • Methyl orange comes in the form of orange or yellow solid, while methyl red comes in the form of a dark red crystalline powder.
  • Methyl orange is soluble in water (5 g/L) and ethanol (0.03 g/100 ml), while methyl red is soluble in ethanol (1mg/mL) and practically insoluble in water.
  • Methyl orange indicator has a pH range of 3.1 and 4.4, while methyl red indicator has a pH range of 4.4 to 6.2.
  • Methyl orange turns red below pH 3.1 and yellow above pH 4.4, while methyl red turns red below pH 4.4 and yellow above pH 6.2.
  • Methyl orange has a pKa of 3.47 in water at 25 °C, while methyl red has a pKa of 5.1.
  • Methyl orange is suitable for strong acid-weak base titration, while Methyl red is good for titration of strong acid (Analyte) with a strong base.
  • The melting point of methyl orange is about > 300 °C, while the melting point of methyl red is 179–182 °C.
  • The molar mass of methyl orange is 327.33 g·mol−1, while the molar mass of methyl red is 269.304 g·mol−1.
  • The density of methyl orange is 1.28 g/cm3, while the density of methyl red is 0.791 g/cm3.

Frequently Asked Question (FAQ):

Are methyl red and methyl orange the same?

Methyl red and methyl orange is not the same thing, however, they are both used for the same thing (pH indicator) in different pH ranges.

What does it mean when methyl red turns orange?

The orange color is considered negative in the methyl red test, as there is less acid production in it.
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Thursday, March 3, 2022

Why is methyl orange used in titration?

In chemistry, methyl orange is often used as a pH indicator because it provides easy and clear color changes across its pH range. It's broadly used in acid titrations since it changes color at the pH of a midi-strength acid.

Methyl orange turns red in an acidic environment (pH is less than 4.4), while in a basic environment (pH is greater than 6.2), it turns yellow, with a pKa of 5.1. It is normally used as an acid-base indicator.

Why is a methyl orange indicator used in titration?

Methyl orange is used in titrations with acidic solutions, because it has such a narrow range, allowing it to be used as an indicator. Its clear and vivid color change makes it a more suitable indicator for titration experiments. Generally, drops of titrant can be added to the analyte until the desired color is reached, indicating the end of the titration.

For laboratory practicals, preparation and use of methyl orange indicator is quite easy. If you want to find the equivalence point between a known titrant and an analyte, you can use an indicator.

Most mineral acids can be titrated with it, but not organic acids. It can be used to titrate an acid with a moderately weak base like sodium carbonate (Na2CO3). When used in titrations of strong acid and weak base, methyl orange is quite accurate, as its equivalence point is below pH 7.0.


Frequently Asked Question (FAQ):


Methyl orange indicator is used in which titration?

Generally Methyl orange is suitable for strong acid-weak base titration since it will change sharply at the equivalence point.

When should you use the methyl orange indicator?

Methyl orange indicator is used when the equivalence point of the acid-base titration is around at pH range of 3 to 5. It turns red in an acidic medium, while it turns yellow in basic conditions.

Why is methyl orange and phenolphthalein not a suitable indicator for complexometric titration?

Methyl orange and phenolphthalein is not suitable indicator for complexometric titration, because they both are acid-base indicator that reacts to pH, whereas complexometric titration works on different principle in which the formation of a colored complex is used to indicate the endpoint.
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Wednesday, March 2, 2022

Why is methyl orange a suitable indicator for titrating weak base and strong acid?

Because it changes from a basic to an acidic color, methyl orange is a suitable chemical indicator in strong acid weak base titration.

The equivalence point of a strong acid vs weak base is about pH 3.5 and 6.5. As a result, an indicator that changes color within this range is required. For this, methyl orange is the most suitable indicator, because it sharply changes color in that region, therefore the endpoint and equivalence point should be the same.

Why is methyl orange a suitable indicator for titrating weak base and strong acid?

Methyl orange (C14H14N3NaO3S) is a synthetic indicator commonly used as a pH indicator since it provides simple and distinct color changes throughout its pH range. It has a pH range of 3.1 to 4.4 and the color of the methyl orange indicator in an acidic medium is red, while yellow in a basic medium.

In titration, methyl orange is a widely employed indicator. As it turns red below pH 3.3 and yellow above pH 4.4, consequently, it is a helpful indicator for discriminating between strong/weak acids.

Acid-base reactions generally involve attempting to achieve pH 7.0 – a neutral solution. However, methyl orange turns yellow at pH 4.4 and above, making it unsuitable to represent the endpoint of the neutralization reaction. Alternatives such as phenolphthalein are becoming more popular.

Frequently Asked Question (FAQ):


Can we use methyl orange for strong acid strong base titration?

Methyl orange is not commonly used in strong acid-strong base titrations, because of its changes in color in the pH range of 3 to 5. A pH of roughly 7.00 is obtained by titrating a strong acid and a strong base. As a result, phenolphthalein is a suitable indication.

For which titration would methyl orange be a suitable indicator?

Methyl orange is a good chemical indicator in strong acid weak base titration as it changes its basic color to acidic color.

Which indicator is used in the titration of Na2CO3 against HCl?

The sodium carbonate content of a sample is determined using methyl orange as an indicator in a titration against standard hydrochloric acid.
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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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