Methyl Orange

Methyl Orange is an azo dye which is soluble in water. It is an organic compound composed of carbon, hydrogen, nitrogen, sodium, oxygen and sulphur. Methyl Orange doesn’t react permanently with acids or bases. Its effective pH value ranges from pH 3.1 to pH 4.4. Methyl orange is not similar to litmus paper because methyl orange has a very low range compared to litmus. Methyl orange doesn’t have a full spectrum of colors.

What is Methyl Orange?

Methyl Orange is a chemical indicator that identifies whether a substance is basic or acidic. It is abbreviated as MeO. Methyl orange, a popular indicator is used for titration. During titration, it gives different colors at different pH values. Methyl orange is a weak base.

It is found in yellow color in the unionized form. It turns pinkish red in color When the medium turns acidic. It is used in labs and industries as a pH indicator.

Structure of Methyl Orange

The structure of methyl orange consists of a central azo group (―N=N―), which is the characteristic feature of azo dyes. This azo group connects two aromatic rings: a benzene ring and a naphthalene ring. One of the nitrogen atoms in the azo group is protonated and carries a positive charge when the indicator is in its acidic form. The other nitrogen atom is connected to a sodium atom and a sulfonate group, which contribute to the water solubility of methyl orange. The structure of Methyl Orange is shown below:

Methyl Orange

Chemical Formula of Methyl Orange

Chemical Formula of Methyl Orange is C₁₄H₁₄N₃NaO₃S

IUPAC Name of Methyl Orange

IUPAC Name of Methyl Orange is Sodium 4-{(4-(dimethylamino)phenyl) diazenyl)}benzene-1-sulphonate

Methyl Orange pH Range

Methyl orange is used as an indicator because of its various pH ranges. The pH range of methyl orange is 3.1 to 4.4

General Properties of Methyl Orange

Methyl Orange has some important properties. These properties are given below in the box.

Colour	Orange or yellow
Appearance	Orange crystalline powder
Odor	Odorless
Molar Mass	327.33 g.mol-1
Density	1.28 g/cm³
Melting Point	300°C
Storage condition	Store +5°C to +30°C
Flash point	37°C
Solubility	Soluble in water

Preparation of Methyl Orange

Methyl Orange is generally found in powdered form. To make a solution of methyl orange we have to dissolve 0.1g of methyl orange powder in per 100cc of distilled water. However, the methyl orange solution which is for indicator is more sensitive and hence prepared by dissolving only 0.02 gram of methyl orange in 100cc of water

Preparation of Methyl Orange with Sulphanilic Acid

To produce methyl orange from sulfanilic acid and N, N -dimethylaniline, a reaction named diazonium coupling reaction was used. Diazonium coupling reaction is a typical reaction for treating an aliphatic amine to yield a carbocation.

At first, in presence of HCl, sulphanilic acid and sodium nitrate react and Then the prepared diazotized sulfanilic acid is treated with N, N-dimethyl aniline to get the desired product that is methyl orange.

Preparation of methyl orange from sulfanilic acid is can be understood from the chemical reactions below:

Methyl Orange Indicator

Water soluble azo dye, methyl orange, is popularly known as pH indicator which is generally used in the titration. It is used in titration because of its colour variations at different pH levels. Methyl Orange is not much strong indicator like litmus. Methyl orange makes only a narrow spectrum in colour band . In acid solution, methyl orange turns into red colour and in base solution, methyl orange turns into yellow colour.

Colour Change of Methyl Orange

Generally methyl orange is found in orange colour. But when methyl orange is used as an indicator of acid solution, it becomes red from yellow/orange colour. Similarly, when it is used in base solution, methyl orange becomes yellow. This is the property of Color change of methyl orange.

Methyl Orange in Acid

In a Acidic medium, methyl orange turns red from orange.

It is popularly used in acid titration because it changes colour at the pKa of a mid-strength acid. Methyl orange is not similar to a universal indicator litmus, because it does not have a complete spectrum of colour transition, however it does have a sharp end point. When Methyl Orange comes into contact with water then it breaks down into orange neutral molecules. Methyl Orange is a weak acid.

Methyl Orange in Base

By the various pH levels of methyl orange, we use it as an indicator. In base solution, Methyl orange turns into yellow colour from orange colour.

Difference between Phenolphthalein and Methyl Orange

Methyl Orange and phenolphthalein are two indicators apart from litmus paper which is used in identification of acid and base. The difference between the methyl orange and phenolphthalein are described below:

Parameters	Methyl Orange	Phenolphthalein
In Acidic medium	Methyl orange turns red from orange.	Phenolphthalein remains colourless in Acidic conditions.
In Alkaline condition	Methyl orange turns into yellow colour.	Phenolphthalein turns into pink colour.
pH value	The pH value of Methyl Orange ranges from 3.1 to 4.4	The pH value of phenolphthalein ranges from 8.2 to 10.0
pKa	The pKa of methyl orange is 3.5	The pKa of phenolphthalein is 9.4

Applications of Methyl Orange

The uses and applications of Methyl Orange are given below:

• Methyl orange is used as an important indicator for titration. It acts similar to Litmus.
• We will get colour variations at different levels of pH value by using methyl orange.
• It is used as a dye.

Conclusion

As an indicator for titration, Methyl Orange has a significant importance. It turns red from orange in Acidic conditions and turns yellow in alkaline conditions. As an indicator, methyl orange is used in laboratories as well as in industries. It has some harmful effects too.

Frequently Asked Questions on Methyl Orange

What is the Original Colour of Methyl Orange?

The original colour of methyl orange is orange colour.

What is the Nature of Methyl Orange?

The nature of methyl orange is acidic.

What is Methyl Orange best used for?

Methyl orange is best used for pH indicator for titration. It is used in laboratories as well as industries.

Is Methyl Orange toxic?

Methyl orange can be toxic or fatal if it is swallowed. It can cause Nausea, vomiting, diarrhoea etc.

Is Methyl Orange Soluble in Water?

Yes, methyl orange is soluble in water.

How to Prepare Methyl Orange from Sulfanilic Acid?

To produce methyl orange from sulfanilic acid and N, N -dimethylaniline, a reaction named diazonium coupling reaction is used. In presence of HCl, sulfanilic acid and sodium nitrate react and Then the prepared diazotized sulfanilic acid is treated with N, N-dimethyl aniline to get the desired product that is methyl orange.

What is Chemical Formula of Methyl Orange?

The chemical name of Methyl Orange is C₁₄H₁₄N₃NaO₃S.

Which Colour Methyl Orange gives in Acid and Base?

Methyl orange is found in orange colour. In acid, methyl orange turns into red and in base solution and turns into yellow colour in base

What is the difference between Phenolphthalein and Methyl Orange?

The difference between the methyl orange and phenolphthalein are described below

• pH value of Methyl Orange ranges from 3.1 to 4.4 while that of phenolphthalein ranges from 8.2 to 10
• In Acidic Solution, Methyl Orange becomes red coloured while phenolphthalein is colourless
• In basic solution, Methyl Orange becomes yellow coloured while phenolphthalein is pink
• pKa of Methyl Orange is 3.5 while that of phenolphthalein is 9.4