---
title: "High vs plastic explosives; TNT"
subject: "Engineering Chemistry"
chapter: 7
key: "semester_2/engineering_chemistry:he-vs-plastic-tnt"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/he-vs-plastic-tnt
site: BCT Engineering
---

# High vs plastic explosives; TNT

Engineering Chemistry · Chapter 7: Explosives

- Asked in: 2075 Baisakh, 2.5+2.5 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/he-vs-plastic-tnt
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-7

## Question

Write the points of difference between high explosives and plastic explosives. Mention the preparation and applications of TNT.

## Short answer

High explosives are solid/liquid, cannot be moulded; plastic explosives are putty-like, mouldable mixtures of RDX/PETN and plasticizer. TNT is prepared by stepwise nitration of toluene with HNO₃/H₂SO₄; used in ammunition, mining, demolition.

## Answer

#### High explosives vs plastic explosives
| Basis | High explosive | Plastic explosive |
|---|---|---|
| Physical state | Solid (crystalline/powder) or liquid | Soft, putty-like, dough-like mass |
| Moulding | Cannot be moulded | Can be moulded by hand into any shape |
| Composition | Single compound or mixture (TNT, PETN) | High explosive (RDX/PETN) + plasticiser |
| Handling | Cast or pressed into containers | Safe and easy to shape and fix on objects |
| Water resistance | Varies | Generally waterproof |
| Examples | TNT, picric acid, dynamite | C-4, Semtex |

#### Preparation of TNT (2,4,6-trinitrotoluene)
TNT is made by the stepwise nitration of toluene with a mixture of conc. HNO₃ and conc. H₂SO₄ (H₂SO₄ is a dehydrating agent, giving NO₂⁺). Toluene itself is obtained from benzene by Friedel–Crafts methylation (benzene + CH₃Cl, anhydrous AlCl₃).

```text
C₆H₆ + CH₃Cl --AlCl₃--> C₆H₅CH₃ + HCl            (toluene)
C₆H₅CH₃ --HNO₃/H₂SO₄, 30°C-->  mononitrotoluene
        --HNO₃/H₂SO₄, 60°C-->  dinitrotoluene
        --HNO₃/oleum, 100-110°C--> 2,4,6-trinitrotoluene
```
```text
Structure of TNT (ring carbons C1 to C6)
           CH₃
            |
       .----C1---.
 O₂N--C2         C6--NO₂
       |         |
       C3        C5
       '---C4----'
            |
           NO₂
```
The product is washed with water and dilute sodium carbonate and recrystallised from alcohol. It is a pale yellow crystalline solid, m.p. 81 °C.
Decomposition: 2C₇H₅N₃O₆ → 3N₂ + 5H₂O + 7CO + 7C

#### Uses
- Filling for shells, bombs, grenades, torpedoes and mines.
- Mining, quarrying and demolition (alone or as amatol/ammonal mixtures).
- Raw material for other explosives and dyes.

## Check yourself

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

1. How does a plastic explosive differ from an ordinary high explosive?
   A. It is a soft, putty-like mass that can be moulded by hand
   B. It cannot be moulded
   C. It is always a liquid
   D. It is a primary explosive
   Answer: A. Plastic explosives are RDX/PETN with a plasticiser, easy to shape. (Key point: Moulding difference)

2. What is a plastic explosive made of?
   A. Black powder and wax
   B. TNT only
   C. Kieselguhr and nitroglycerine
   D. A high explosive (RDX/PETN) plus a plasticiser
   Answer: D. RDX/PETN mixed with oil, wax or polymer. (Key point: Composition)

3. How is TNT formed from toluene?
   A. In one step at 0 C
   B. In three stages of nitration at rising temperatures (about 30, 60, then 100-110 C)
   C. By reducing toluene with H2 and then adding HNO3 once
   D. By oxidising toluene with KMnO4
   Answer: B. Nitration goes through mono-, di- and finally trinitrotoluene, with higher temperature and oleum for the last stage. (Key point: Stepwise nitration)

4. Which is a use of TNT?
   A. Filling shells, bombs and mines and for mining and demolition
   B. Making soap and detergents
   C. Use as a propellant for slow burning in fireworks
   D. Use only as a detonator primary charge
   Answer: A. TNT is a secondary high explosive used in shells, bombs, mines, mining, quarrying and demolition. (Key point: Uses of TNT)

## Related in Engineering Chemistry

- [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×
- [High and plastic explosives; nitrocellulose, TNT [partly illegible]](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Anitrocellulose-tnt) — Engineering Chemistry, chapter 7
- [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×
- [Plastic explosive; TNT preparation; detonator](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aplastic-explosive-tnt) — 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
- [Explosive characteristics; TNT preparation](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atnt-characteristics) — Engineering Chemistry, chapter 7