Theory
Nitrogen is the most abundant gas in the atmosphere, making up about 78% of the air by volume. As the element at the head of Group 15, it shows a remarkable range of oxidation states, from -3 in ammonia to +5 in nitric acid and the nitrate ion. This lab studies the descriptive chemistry of nitrogen and its common compounds.
1. Oxidation states of nitrogen
Nitrogen displays every whole-number oxidation state from -3 to +5. Key examples: ammonia (NH₃) and the ammonium ion (NH₄⁺) at -3; nitrogen gas (N₂) at 0; nitrous oxide (N₂O) at +1; nitric oxide (NO) at +2; the nitrite ion (NO₂⁻) at +3; nitrogen dioxide (NO₂) at +4; and the nitrate ion (NO₃⁻) and nitric acid (HNO₃) at +5.
2. Ammonia and the ammonium ion
Ammonia is a weak base: it accepts a proton to form the ammonium ion (NH₄⁺). Warming any ammonium salt with sodium hydroxide releases ammonia gas, recognised by its sharp smell and by turning damp red litmus paper blue. This is the standard confirmatory test for the ammonium ion.
3. The nitrogen oxoacids
Nitrous acid (HNO₂) is a weak acid in which nitrogen is +3; it is unstable and used cold, for example in diazotization. Nitric acid (HNO₃) is a strong acid in which nitrogen is +5; concentrated nitric acid is also a powerful oxidizing agent that attacks most metals, releasing nitrogen oxides rather than hydrogen.
4. Tests for nitrate and nitrite
The classic confirmatory test for the nitrate ion is the brown ring test: a solution of iron(II) sulfate is added to the sample, then concentrated sulfuric acid is poured carefully down the side of the tube. A brown ring forms at the junction of the two layers, due to the complex [Fe(H₂O)₅NO]²⁺. The nitrite ion gives a positive brown ring test without needing concentrated acid, and also decolourises acidified potassium permanganate.
5. The nitrogen cycle context
These interconversions are the laboratory counterpart of the nitrogen cycle, in which nitrogen moves between N₂, ammonia and ammonium, nitrite, and nitrate through fixation, nitrification, and denitrification.
Apparatus and Reagents
The equipment and reagents a real nitrogen-chemistry experiment uses. In this simulation they are modelled for you, but the observations correspond to what each test would actually show.
- Test tubes, test-tube rack, and a Bunsen burner for gentle warming.
- Red and blue litmus paper for detecting evolved ammonia.
- Ammonium chloride (NH₄Cl) and other ammonium salts.
- Sodium hydroxide (NaOH) solution for the ammonium test.
- Dilute and concentrated nitric acid (HNO₃); dilute nitrous acid (HNO₂), used cold.
- Iron(II) sulfate (FeSO₄) solution and concentrated sulfuric acid for the brown ring test.
- Sodium nitrate (NaNO₃) and sodium nitrite (NaNO₂) as sources of the two ions.
- Acidified potassium permanganate (KMnO₄) for distinguishing nitrite from nitrate.
Instructions
This is a predict-and-check lab. In each tab you decide the answer yourself first, enter or choose it, and only then does the simulation confirm the correct result so you can compare. Record every result in your worksheet.
Simulation — The Nitrogen Bench
| Species | Your value | Correct |
|---|---|---|
| No rows yet — choose a species, predict, and check. | ||
Team Questions
Work these out with your team, type each answer, and check it.
Example Lab Report
A worked example showing the expected format and the predict-and-check workflow.
Nitrogen Chemistry
Chemistry | Section: [Your Section] | Date: [Date]
Lab Members: [Names of all members present]
Objective — To assign the oxidation state of nitrogen in its common species, to carry out and interpret the identification tests for the ammonium, nitrite, and nitrate ions, and to predict the products of key reactions of nitrogen compounds, comparing every prediction with the simulation.
Part A — Oxidation States (worked example)
In the nitrate ion, NO₃⁻, each oxygen is -2, giving -6 total for three oxygens. The overall charge is -1, so nitrogen must be +5 (since +5 - 6 = -1). In ammonia, NH₃, each hydrogen is +1, giving +3 total, and the molecule is neutral, so nitrogen is -3. Both predictions matched the simulation.
Part B — Identification Tests (worked example)
Warming ammonium chloride with sodium hydroxide released a colourless, sharp-smelling gas that turned damp red litmus blue, confirming the ammonium ion. For the nitrate sample, adding iron(II) sulfate followed by concentrated sulfuric acid produced a brown ring at the junction of the layers, the positive brown ring test. Acidified permanganate was decolourised by the nitrite sample but not by the nitrate sample, distinguishing the two.
Part C — Reactions and Products (worked example)
Concentrated nitric acid with copper gave the brown gas nitrogen dioxide, while dilute nitric acid with copper gave colourless nitric oxide that browned in air. Heating ammonium chloride caused sublimation, with ammonia and hydrogen chloride recombining on the cooler glass. Each predicted product matched the simulation.
Discussion and Conclusion — Every prediction agreed with the simulation. Nitrogen ranged from -3 in ammonia to +5 in nitrate and nitric acid; the ammonium, nitrite, and nitrate ions were each confirmed by their characteristic tests; and the reactions of nitric acid and ammonium salts followed from nitrogen's oxidation states and the oxidizing power of nitric acid.
Practice Quiz
For extra practice on this topic, use the interactive Nitrogen Chemistry quiz in the Quizzes section of the site.