The Overheated Nitrocellulose Sample
A school laboratory stores an old bottle of nitrocellulose (cellulose nitrate) with a nitrogen content of about 13.4 %. A technician notices the bottle feels warm to the touch and there is a faint smell of nitrogen oxides. The bottle is stored in a wooden cupboard next to bottles of concentrated nitric acid, ethanol and sodium hydroxide pellets. The cupboard has no ventilation. The technician asks you whether to move the bottle, open it, or leave it alone until the teacher arrives in 30 minutes. A fire extinguisher rated for electrical fires only is mounted on the wall.
1. Assess the immediate hazard and recommend the safest action for the next 30 minutes.
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High-nitrogen nitrocellulose (above roughly 12.6 % N) is unstable and can self-heat and spontaneously ignite; the warmth and NOx smell are warning signs of decomposition, not a harmless odour. Do not open or move the bottle unnecessarily - friction or shock can trigger ignition. Clear the area, keep people away, and call the teacher or a responsible adult immediately. The cupboard is unventilated and contains an oxidiser (HNO3) and a flammable solvent (ethanol), so a fire could spread quickly. The CO2/electrical extinguisher is not ideal for a nitrate fire, but the priority is evacuation and alerting staff, not firefighting. Record the incident and arrange for the material to be disposed of by a qualified waste contractor.
2. Explain chemically why the nitrogen content matters, and how a lower-nitrogen grade would behave differently.
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Nitrocellulose is cellulose with some hydroxyl groups converted to nitrate esters (–ONO2). The degree of substitution determines nitrogen content. More nitrate groups means more oxidiser built into the same molecule, more strain energy and less thermal stability. A grade with about 11–12 % N (used in lacquers and celluloid) is much less sensitive and can be handled and stored more safely, though it still burns vigorously. The 13.4 % material is closer to the guncotton range and must be kept wet with water or alcohol and stored cool, in small quantities, away from acids and flammables.
3. The teacher proposes storing the bottle next to the NaOH pellets because 'bases neutralise acids'. Evaluate this reasoning.
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The reasoning confuses two different hazards. NaOH does neutralise nitric acid, but the problem here is decomposition of the nitrate ester itself, not free acid. Alkali can hydrolyse nitrate esters and generate heat, and mixing an unstable energetic material with a strong base adds a reaction pathway rather than removing one. The correct storage is: small quantity, kept wetted, cool, away from oxidisers, acids, bases and flammables, in a labelled, ventilated cabinet. The 'neutralise the acid' argument is a plausible-sounding but incorrect judgement call.