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

# Low explosives and uses; glycerol trinitrate

Engineering Chemistry · Chapter 7: Explosives

- Asked in: 2068 Bhadra, 2+3 marks
- Video: [Types of explosives, TNT, Collodion cotton, Nitroglycerine, Ammonium nitrate, Low and High explosive](https://www.youtube.com/watch?v=Phtz7WN91rU) — Mine eng
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/low-explosives-gtn
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-7

## Question

What are low explosives? Write their uses. Give the preparation and applications of glycerol trinitrate.

## Short answer

Low explosives deflagrate, producing a pushing effect; used as propellants in guns, rockets, fireworks, and for gentle blasting. GTN is prepared by nitrating glycerol with HNO₃/H₂SO₄ below 15°C. It is used in dynamite, gelignite, cordite, blasting, and as a vasodilator for angina.

## Answer

#### 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. 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 burn rapidly (deflagrate) and gas pressure pushes material forward rather than shattering it
   D. They shatter rock by brisance
   Answer: C. Low explosives deflagrate at a few m/s to about 400 m/s, giving a propelling effect. (Key point: Low explosive behaviour)

2. For what are low explosives mainly used?
   A. Shattering hard rock in demolition
   B. Filling detonators
   C. Making dyes
   D. As propellants (bullets, rockets), fireworks, safety fuses and slow blasting of soft rock
   Answer: D. Their gentle pushing action suits propellants and soft-rock blasting. (Key point: Low explosive uses)

3. How is glycerol trinitrate prepared?
   A. By nitrating glycerol with a mixture of conc. HNO3 and conc. H2SO4
   B. By oxidising glycerol with KMnO4
   C. By heating glycerol with dilute HNO3 alone
   D. By reacting glycerol with HCl
   Answer: A. Glycerol is nitrated with conc. HNO3 and conc. H2SO4 (3 -OH groups become -ONO2). (Key point: Reagents for GTN)

4. Which is a use of glycerol trinitrate?
   A. Making dynamite and gelignite, and in dilute form a medicine for angina
   B. Making polythene
   C. Use as a food preservative
   D. Use as a fertiliser
   Answer: A. 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

- [Primary and low explosives; glycerol trinitrate](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aprimary-low-explosives-gtn) — 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×
- [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
- [Explosive characteristics; TNT preparation and uses](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aexplosive-characteristics-tnt) — Engineering Chemistry, chapter 7