chemistry

Patent Blue V

Patent Blue V 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 Patent Blue V rather than just read about it. In short: Patent Blue V, also called Food Blue 5, Sulphan Blue, Acid Blue 3, L-Blau 3, C-Blau 20, Patentblau V, Sky Blue, or C.I. 42051, is a sky blue synthetic triphenylmethane dye used as a food coloring. As a food additive, it has E number E131.

Key takeaways

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

Reference excerpt

Patent Blue V, also called Food Blue 5, Sulphan Blue, Acid Blue 3, L-Blau 3, C-Blau 20, Patentblau V, Sky Blue, or C.I. 42051, is a sky blue synthetic triphenylmethane dye used as a food coloring. As a food additive, it has E number E131. It is a sodium or calcium salt of [4-(α-(4-diethylaminophenyl)-5-hydroxy- 2,4-disulfophenylmethylidene)-2,5-cyclohexadien-1-ylidene] diethylammonium hydroxide inner salt.

Use as dye

It is not widely used, but in Europe it can be found in Scotch eggs, certain jelly sweets, blue Curaçao, and certain gelatin desserts, among others. An important advantage is the very deep color it produces even at low concentration; a disadvantage is that it fades fairly quickly when exposed to light. In medicine, Patent Blue V is used in lymphangiography and sentinel node biopsy as a dye to color lymph vessels. It is also used in dental disclosing tablets as a stain to show dental plaque on teeth. The color of the dye is pH-dependent. In aqueous solution, its color will vary from a deep blue in alkaline or weakly acidic medium to a yellow–orange in stronger acidic conditions. It is useful as a pH indicator for the range 0.8–3.0. The structure is also redox-sensitive, changing from a reduced yellow form to an oxidized red form in solution. The reduction potential of around 0.77 volts is similar to that of other triphenylmethane dyes. It is usable as a reversible redox indicator in some analytical methods. Because of its pH-dependent color, Patent Blue V was included in chemistry sets from Salter Science in the 1970s and 80s under the name Sky Blue.

Regulation Patent Blue V is banned as a food dye in Australia, Canada, and US, because health officials in these countries suspect that it may cause allergic reactions, with symptoms ranging from itching and nettle rash to nausea, hypotension, and in rare cases anaphylactic shock; it is therefore not recommended in those countries for children.

References

Illustrations

Worked examples

Example 1 — a first encounter with Patent Blue V

Start with the simplest possible case. Write down what Patent Blue V 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 Patent Blue V 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 Patent Blue V 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 Patent Blue V

In research: Patent Blue V 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 Patent Blue V 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: Patent Blue V is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acid dyes, Anilines, Benzenesulfonic acids, so understanding it makes those chapters shorter.
In everyday life: Look for Patent Blue V 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 Patent Blue V in 20 minutes

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

Frequently asked questions

What is Patent Blue V in simple terms?

Why does Patent Blue V 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 Patent Blue V?

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 Patent Blue V.