---
title: "Primary and low explosives; glycerol trinitrate"
subject: "Engineering Chemistry"
chapter: 7
key: "semester_2/engineering_chemistry:primary-low-explosives-gtn"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/primary-low-explosives-gtn
site: BCT Engineering
---

# Primary and low explosives; glycerol trinitrate

Engineering Chemistry · Chapter 7: Explosives

- Asked in: 2072 Asoj, 2+3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/primary-low-explosives-gtn
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-7

## Question

What are primary and low explosives? Give the preparation and uses of glycerol trinitrate.

## Short answer

Primary explosives (e.g., lead azide) are extremely sensitive and used in detonators. Low explosives (e.g., black powder) deflagrate, producing a propelling effect for guns, rockets, and gentle blasting. GTN is made by nitrating glycerol with HNO₃/H₂SO₄ below 15°C; it is used in dynamite, cordite, blasting, and as a vasodilator.

## Answer

#### Primary explosives
Primary (initiating) explosives are extremely sensitive to heat, shock and friction and detonate even with a small spark. They are used in detonators and primers to start the explosion of secondary explosives. Examples: lead azide Pb(N₃)₂, mercury fulminate Hg(ONC)₂, lead styphnate.

#### Low explosives
**Low explosives** burn rapidly (deflagrate) instead of detonating; the burning front travels at a few metres per second up to about 400 m/s. The gases produced give a pushing (propelling) effect rather than a shattering one. They are used as propellants and for gentle blasting.
Examples: black powder (gunpowder: KNO₃ + charcoal + S) and smokeless powder. Uses: firing bullets and shells, rocket propellants, quarrying soft rock, fireworks and safety fuses.

#### Preparation of glycerol trinitrate (GTN, nitroglycerine, TNG)
GTN is made by nitrating glycerol with a mixture of conc. HNO₃ and conc. H₂SO₄ (the sulfuric acid absorbs the water formed). The temperature is kept below 10–15 °C by cooling, because higher temperatures can cause an explosion.

```text
CH₂OH                      CH₂ONO₂
|                          |
CHOH  + 3HNO₃ --H₂SO₄-->   CHONO₂  + 3H₂O
|                          |
CH₂OH                      CH₂ONO₂
```
The oily layer of GTN is separated, washed with water and sodium carbonate solution, and dried. It is a colourless to pale yellow oily liquid, very sensitive to shock, and explodes violently:
4C₃H₅(ONO₂)₃ → 12CO₂ + 10H₂O + 6N₂ + O₂

#### Uses
- Making dynamite (absorbed in kieselguhr), blasting gelatin and gelignite.
- Component of smokeless propellants such as cordite.
- Blasting in mining and tunnelling.
- In dilute form, a medicine (vasodilator) for angina.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why are primary explosives used in detonators?
   A. They are extremely sensitive and start the explosion of secondary explosives
   B. They are insensitive
   C. They burn slowly
   D. They are propellants
   Answer: A. Lead azide and mercury fulminate detonate with a small spark. (Key point: Primary explosive use)

2. How do low explosives act?
   A. They detonate with a shock wave above 1000 m/s
   B. They explode only with a detonator
   C. They shatter rock by brisance
   D. They burn rapidly (deflagrate) and gas pressure pushes material forward rather than shattering it
   Answer: D. Low explosives deflagrate at a few m/s to about 400 m/s, giving a propelling effect. (Key point: Low explosive behaviour)

3. Why is the nitration of glycerol kept below about 10-15 C by cooling?
   A. Higher temperatures can cause the product to explode
   B. The reaction does not occur above 15 C
   C. To increase the water produced
   D. To make glycerol solid
   Answer: A. GTN is very shock- and heat-sensitive, so cooling prevents a violent explosion during preparation. (Key point: Temperature control)

4. Which is a use of glycerol trinitrate?
   A. Making polythene
   B. Use as a food preservative
   C. Making dynamite and gelignite, and in dilute form a medicine for angina
   D. Use as a fertiliser
   Answer: C. GTN is absorbed in kieselguhr for dynamite, used in cordite and blasting, and a dilute form is a vasodilator for angina. (Key point: Uses of GTN)

## Related in Engineering Chemistry

- [Low explosives and uses; glycerol trinitrate](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alow-explosives-gtn) — Engineering Chemistry, chapter 7
- [Primary and low explosives; TNT and TNG](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aprimary-low-tnt-tng) — Engineering Chemistry, chapter 7
- [High and low explosives; TNT preparation](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ahigh-low-explosives-tnt) — Engineering Chemistry, chapter 7, asked 3×
- [Low and high explosives; GTN preparation](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ahigh-low-gtn) — Engineering Chemistry, chapter 7, asked 2×