chemistry

Red fuming nitric acid

Red fuming nitric acid 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 Red fuming nitric acid rather than just read about it. In short: Red fuming nitric acid (RFNA) is a strong and storage-stable oxidizer. It consists of nitric acid (HNO3), dinitrogen tetroxide (N2O4) and a small amount of water.

Key takeaways

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

Reference excerpt

Red fuming nitric acid (RFNA) is a strong and storage-stable oxidizer. It consists of nitric acid (HNO3), dinitrogen tetroxide (N2O4) and a small amount of water. The color of red fuming nitric acid is due to the dinitrogen tetroxide, which breaks down partially to form the reddish-brown nitrogen dioxide. The nitrogen dioxide dissolves until the liquid is saturated, and produces toxic fumes with a suffocating odor. RFNA increases the flammability of combustible materials and is highly exothermic when reacting with water. It is commonly used in bipropellant rockets as the oxidizer. It can also be a component of a monopropellant; with substances like amine nitrates dissolved in it, it can be used as the sole fuel in a rocket. This is inefficient and it is not normally used this way. Since nitrogen dioxide is a product of decomposition of nitric acid, its addition stabilizes nitric acid in accordance with Le Chatelier's principle. Addition of dinitrogen tetroxide also increases oxidizing power and lowers the freezing point. It is usually used with an inhibitor because nitric acid attacks most container materials. There are many inhibitors to use, with various, sometimes secret, substances, including hydrogen fluoride. Hydrogen fluoride for instance will passivate the container metal with a thin layer of metal fluoride, making it nearly impervious to the nitric acid. Any combination of RFNA with inhibitor is called inhibited RFNA, or IRFNA. Inhibited RFNA was the oxidizer of the world's most-launched light orbital rocket, the Kosmos-3M. In former-Soviet countries, inhibited RFNA is known as Mélange. During World War II, the German military used RFNA in some rockets. The mixtures used were called S-Stoff (96% nitric acid with 4% ferric chloride as an ignition catalyst) and SV-Stoff (94% nitric acid with 6% dinitrogen tetroxide) and nicknamed Salbei (sage). Other uses for RFNA include fertilizers, dye intermediates, explosives, and pharmaceutical acidifiers. It can also be used as a laboratory reagent in photoengraving and metal etching.

Compositions IRFNA IIIa: 83.4% HNO3, 14% NO2, 2% H2O, 0.6% HF IRFNA IV HDA: 54.3% HNO3, 44% NO2, 1% H2O, 0.7% HF S-Stoff: 96% HNO3, 4% FeCl3 SV-Stoff: 94% HNO3, 6% N2O4 AK20: 80% HNO3, 20% N2O4 AK20F: 80% HNO3, 20% N2O4, fluorine-based inhibitor AK20I: 80% HNO3, 20% N2O4, iodine-based inhibitor AK20K: 80% HNO3, 20% N2O4, potassium-based inhibitor AK27I: 73% HNO3, 27% N2O4, iodine-based inhibitor AK27P: 73% HNO3, 27% N2O4, phosphorus-based inhibitor

Corrosion Hydrofluoric acid content of IRFNA When RFNA is used as an oxidizer for rocket fuels, it usually has a HF content of about 0.6%. The HF forms a metal fluoride layer on the surface of the storage vessels, inhibiting corrosion. Water content of RFNA To test the water content, a sample of 80% HNO3, 8–20% NO2, and the rest H2O depending on the varied amount of NO2 in the sample. When the RFNA contained HF, there was an average H2O% between 2.4% and 4.2%. When the RFNA did not contain HF, there was an average H2O% between 0.1% and 5.0%. When the metal impurities from corrosion were taken into account, the H2O% increased, and the H2O% was between 2.2% and 8.8% Corrosion of metals in RFNA Stainless steel, aluminium alloys, iron alloys, chrome plates, tin, gold and tantalum were tested to see how RFNA affected the corrosion rates of each. Experiments were performed using 16% and 6.5% RFNA samples and the different substances listed above. Many different stainless steels showed resistance to corrosion. Aluminium alloys did not endure as well as stainless steels especially in high temperature, but the corrosion rates were not high enough to prohibit the use of this with RFNA. Tin, gold and tantalum showed high corrosion resistance similar to that of stainless steel. These materials are better though because at high temperatures the corrosion rates did not increase much. Corrosion rates at elevated temperatures increase in the presence of phosphoric acid. Sulfuric acid decreased corrosion rates.

Illustrations

Worked examples

Example 1 — a first encounter with Red fuming nitric acid

Start with the simplest possible case. Write down what Red fuming nitric acid 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 Red fuming nitric acid 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 Red fuming nitric acid 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 Red fuming nitric acid

In research: Red fuming nitric acid 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 Red fuming nitric acid 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: Red fuming nitric acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Oxidizing acids, Rocket oxidizers, so understanding it makes those chapters shorter.
In everyday life: Look for Red fuming nitric acid 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 Red fuming nitric acid in 20 minutes

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

Frequently asked questions

What is Red fuming nitric acid in simple terms?

Red fuming nitric acid (RFNA) is a strong and storage-stable oxidizer. It consists of nitric acid (HNO3), dinitrogen tetroxide (N2O4) and a small amount of water.

Why does Red fuming nitric acid 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 Red fuming nitric acid?

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 Red fuming nitric acid.