chemistry

Methyl yellow

Methyl yellow 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 Methyl yellow rather than just read about it. In short: Methyl yellow, or C.I. 11020, is an organic compound with the formula C6H5N2C6H4N(CH3)2. It is an azo dye derived from dimethylaniline.

Key takeaways

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

Reference excerpt

Methyl yellow, or C.I. 11020, is an organic compound with the formula C6H5N2C6H4N(CH3)2. It is an azo dye derived from dimethylaniline. It is a yellow solid. According to X-ray crystallography, the C14N3 core of the molecule is planar. It is used as a dye for plastics and may be used as a pH indicator.

In aqueous solution at low pH, methyl yellow appears red. Between pH 2.9 and 4.0, methyl yellow undergoes a transition, to become yellow above pH 4.0.

Safety It is a possible carcinogen. As "butter yellow", the agent had been used as a food additive in butter and margarine before its toxicity was recognized.

History Butter yellow was synthesized by Peter Griess in the 1860s at the Royal College of Chemistry in London. The dye was used to dye butter in Germany and other parts of the world during the latter half of the 19th century and the beginning of the 20th before being phased out in the 1930s and 40s. It was in the 1930s that research led by Riojun Kinosita showed the link between several azo dyes and cancer, linking butter yellow to liver cancer in rats after two to three months exposure. In 1939, the International Congress for Cancer Research issued a recommendation for the banning of cancer-causing food dyes (including butter yellow) from food production. In 2014, dried tofu products such as dougan (豆乾) from Taiwan were found to have been adulterated with methyl yellow which was used as a coloring agent.

See also Structurally similar compounds:

Chrysophenine Methyl red Solvent Yellow 56 Methyl orange

References

Illustrations

Worked examples

Example 1 — a first encounter with Methyl yellow

Start with the simplest possible case. Write down what Methyl yellow 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 Methyl yellow 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 Methyl yellow 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 Methyl yellow

In research: Methyl yellow 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 Methyl yellow 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: Methyl yellow is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anilines, Azo dyes, Dimethylamino compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Methyl yellow 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 Methyl yellow in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Methyl yellow 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 Methyl yellow out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Methyl yellow in simple terms?

Methyl yellow, or C.I. 11020, is an organic compound with the formula C6H5N2C6H4N(CH3)2. It is an azo dye derived from dimethylaniline.

Why does Methyl yellow 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 Methyl yellow?

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 Methyl yellow.