🔬 Industrial Preparation of Methyl Orange

Methyl orange is a widely‑used azo dye and pH indicator.

Photo: Industrial methyl orange reactor unit (via OpenPR). Credit: OpenPR.

1. What Is Methyl Orange?

A yellow to orange powder, methyl orange turns red in acid (pH ≤ 3.1) and yellow in alkaline (pH ≥ 4.4), making it ideal for titrations 2.

2. Industrial Process Overview

Step A: Diazotization

p‑Sulfanilic acid reacts with NaNO₂ in HCl at below 5 °C to form the diazonium salt 3.

Step B: Coupling

The diazonium salt couples with N,N‑dimethylaniline in acidic medium, then NaOH is added to form the sodium salt, yielding methyl orange crystals 4.

Step C: Isolation & Purification

Crystals are filtered, washed with brine, ethanol, ether, and dried. This gives a pure dye for industrial use 5.

3. Industrial Equipment & Conditions

Industrial scale uses large, cooled reactors, agitators, filtering units, and crystallizers. Raw materials are high‑grade acids and reagents 6.

4. Safety & Quality Control

Diazonium salts can be hazardous if dry — processes keep them wet. Temperature and pH are strictly monitored for quality and yield 7.

5. Applications

• Acid‑base titrations in labs.
• Textile dyeing and quality control.
• Research tool in analytical chemistry.

🎯 Quick Facts Table

Property	Value
Formula	C₁₄H₁₄N₃NaO₃S
pH transition	3.1 (red) → 4.4 (yellow)
Density	1.28 g/cm³
Solubility	5 g/L at 20 °C

6. Industrial vs Lab Process

Lab uses small flasks and test tubes, larger quantities, simpler isolation. Industrial uses large reactors, crystallizers, and automated purification for scale and cost efficiency.

🧩 Quiz Game: Score Your Knowledge!

1. What temperature is needed for diazotization?

2. The color change range of methyl orange is?

Score: 0/2

7. Embedding Videos & Images

Use the YouTube iframe embed code and always write original context around it to stay AdSense‑compliant.

8. Summary

Industrial preparation of methyl orange follows diazotization → coupling → purification. Monitoring of pH and temperature ensures high purity yield for lab and textile use.

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🖋️ Written by Er. Rajeev's Stemfact.in.

🧪 Free Chemistry PDF: Download 4 MCQs on Methyl Orange with answers. Useful for Class 10 & Olympiad practice.

Sample Question:

Which of the following describes the color change of methyl orange in base?

• A) Red
• B) Orange
• C) Yellow ✅
• D) Colorless

📥 Download Methyl Orange MCQs PDF

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Color Change by Indicators in Various Acids and Bases

Color Change by Indicators in Acids and Bases (Natural & Synthetic)

Indicators are substances that help us detect whether a solution is acidic or basic. They show color or smell changes depending on the nature (pH) of the solution. Some indicators are synthetic like litmus or phenolphthalein, and some are natural like hibiscus, red cabbage, onion, or vanilla.

1. Litmus

Solution	Litmus Color
Acid (e.g. HCl)	Red
Base (e.g. NaOH)	Blue

2. Methyl Orange

Solution	Methyl Orange Color
Acid (e.g. H₂SO₄)	Red
Base (e.g. KOH)	Yellow

3. Phenolphthalein

Solution	Phenolphthalein Color
Acid (e.g. CH₃COOH)	Colorless
Base (e.g. NH₄OH)	Pink

4. Universal Indicator

pH Range	Color
1–3	Red
4–6	Orange/Yellow
8–11	Blue
12–14	Purple

5. Red Cabbage

Solution	Red Cabbage Color
Acid (e.g. Vinegar)	Red/Pink
Base (e.g. Baking Soda)	Green/Blue

6. Hibiscus Flower Extract

Solution	Hibiscus Color
Acidic	Red
Basic	Green

7. Onion (Smell Indicator)

Solution	Smell Change
Acid	No change in smell
Base	Smell disappears

8. Vanilla Extract (Smell Indicator)

Solution	Smell Change
Acid	Smell retained
Base	Smell disappears

Natural indicators are eco-friendly and can be prepared at home using kitchen materials.

Knowing the pH Scale