chemistry

Scarlet GN

Scarlet GN is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Scarlet GN rather than just read about it. In short: Scarlet GN, or C.I. Food Red 2, FD&C Red No. 4, or C.I. 14815 is a red azo dye once used as a food dye.

Key takeaways

Scarlet GN belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Scarlet GN to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Scarlet GN from memory before moving on to harder problems.

Reference excerpt

Scarlet GN, or C.I. Food Red 2, FD&C Red No. 4, or C.I. 14815 is a red azo dye once used as a food dye. As a food additive, it has the E number E125. It is usually used as a disodium salt.

Preparation To synthesize Food Red 2, 2,4-dimethylaniline-6-sulfonic acid is diazotized with sodium nitrite and hydrochloric acid Diazotization. The resulting diazonium salt is reacted with 5-hydroxynaphthalene-1-sulfonic acid via azo coupling.

Use Originally, Food Red 2 was used as a food colorant. Under the designation E 125, Food Red 2 was approved as a food colorant in the EU by Directive 62/2645/EEC until the end of 1976. Food Red 2 is mainly used as a colorant in cosmetics (shampoos, bubble bath, liquid soaps). It is approved in the EU by Regulation (EC) No. 1223/2009. The colorant is also approved for cosmetics in South Africa, Turkey, and Thailand, whereas in Japan and the USA it may not be used in food, pharmaceuticals, or cosmetics. In the United States, it is not permitted for use in food or ingested drugs and may only be used in externally applied drugs and cosmetics, due to potential carcinogenic effects from ingesting it. An exception was added in 1965 to allow its use in the coloring of maraschino cherries, which were considered mainly decorative and not a foodstuff. This exception was repealed and the dye banned in the US on September 22, 1976 due to mounting safety concerns. In the European Union, it is not permitted as a food additive.

References

Illustrations

Worked examples

Example 1 — a first encounter with Scarlet GN

Start with the simplest possible case. Write down what Scarlet GN claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Scarlet GN before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Scarlet GN ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Scarlet GN

In research: Scarlet GN appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Scarlet GN in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Scarlet GN is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acid dyes, Azo dyes, Food colorings, so understanding it makes those chapters shorter.
In everyday life: Look for Scarlet GN outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Scarlet GN in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Scarlet GN means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Scarlet GN out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Scarlet GN in simple terms?

Scarlet GN, or C.I. Food Red 2, FD&C Red No. 4, or C.I. 14815 is a red azo dye once used as a food dye.

Why does Scarlet GN matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Scarlet GN?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Scarlet GN.