How to explain the uses of ammonia and nitric acid

Ammonia and nitric acid are two of the most useful nitrogen chemicals in industry, and they are closely connected, one is made from the other, and together they make a very common fertiliser. In the exam, “uses” questions look easy but lose marks when students give vague answers like “used in factories”. A full-mark answer names specific uses and, where it can, the substance being made. This topic lives in manufactured substances in industry, right next to the Haber Process.

Where they come from, in one line each

You do not need the full manufacturing detail to answer a uses question, but a single sentence of context helps. Ammonia is manufactured by the Haber Process, combining nitrogen and hydrogen over an iron catalyst:

N₂ + 3H₂ ⇌ 2NH₃

Nitric acid is then manufactured industrially by oxidising ammonia. So the chain runs: air and natural gas give ammonia, and ammonia gives nitric acid. Knowing that chain makes the uses easier to remember, because so many of them come back to nitrogen for plants.

The uses of ammonia

Ammonia’s uses are worth learning as a short list:

• Making fertilisers. This is the biggest use by far. Ammonia is reacted with acids to make ammonium salts, ammonium nitrate, ammonium sulphate and urea, which supply the nitrogen that crops need for healthy growth.
• Making nitric acid. A large share of ammonia is oxidised to make nitric acid, which then has its own set of uses.
• Household cleaning agents. Ammonia solution is alkaline and dissolves grease, so it appears in some window and floor cleaners.
• Other manufacturing. Ammonia is used to make nylon and other nitrogen-containing products.

If a question asks you to test for ammonia in the lab, remember it is the only common alkaline gas: it turns moist red litmus paper blue, which is the standard laboratory test for ammonia.

The uses of nitric acid

Nitric acid is a strong acid, and its uses split into two groups:

• Making fertilisers. Neutralised with ammonia, it makes ammonium nitrate, one of the most widely used nitrogen fertilisers.
• Making explosives. Nitric acid is used to manufacture explosives such as TNT and nitroglycerine, and it is also used in making dyes and plastics.

So both chemicals point back to fertilisers, and nitric acid adds explosives, dyes and plastics on top.

The reaction that links them

The single most useful equation here is the neutralisation of ammonia by nitric acid, because it makes ammonium nitrate, a substance that appears in both lists:

NH₃ + HNO₃ → NH₄NO₃

Ammonia is alkaline and nitric acid is acidic, so this is an acid-alkali neutralisation. Ammonium nitrate is an excellent fertiliser because it is rich in nitrogen from both the ammonium ion and the nitrate ion, and it is very soluble in water so plants can take it up easily. If you can write this equation and explain why ammonium nitrate is nitrogen-rich, you have the sharpest point in the whole topic.

A worked “explain” example

Question: Explain why ammonium nitrate is used as a fertiliser. A good answer says: ammonium nitrate contains a high percentage of nitrogen, supplied by both the ammonium ion and the nitrate ion; nitrogen is an essential element for plant growth; and ammonium nitrate is soluble in water, so it dissolves in the soil and is absorbed by the roots. That is three clear reasons, each worth a mark, rather than one vague sentence.

One trap to avoid

A frequent slip is confusing ammonia with the ammonium ion. Ammonia is the gas NH₃, which is alkaline; the ammonium ion, NH₄⁺, is what forms when ammonia reacts with an acid and appears in salts like ammonium nitrate. In your answers, use “ammonia” for the gas and “ammonium” only for the salts and the ion. A neat extra fact examiners like: warming any ammonium salt with an alkali releases ammonia gas, which you can identify because it turns moist red litmus paper blue, the same test again, now used in reverse to confirm a salt contains the ammonium ion.

How to structure your exam answer

1. If asked, give the one-line origin: ammonia from the Haber Process, nitric acid from ammonia.
2. List the uses of ammonia, fertilisers first, then nitric acid and cleaning.
3. List the uses of nitric acid, fertilisers, explosives, dyes and plastics.
4. Write the linking equation, NH₃ + HNO₃ → NH₄NO₃, and name the product.
5. If asked, explain why ammonium nitrate is a good fertiliser: nitrogen-rich and soluble.

Answered in that order, a uses question becomes quick, specific marks. Topics like this reward precise vocabulary over guesswork, and precise vocabulary is exactly what a teacher can tighten with you. Our online one-to-one lessons run in English from RM50 an hour, with a paid one-hour trial; see how it works for what a lesson covers.