--- title: "High and low explosives; TNT preparation" subject: "Engineering Chemistry" chapter: 7 key: "semester_2/engineering_chemistry:high-low-explosives-tnt" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/high-low-explosives-tnt site: BCT Engineering --- # High and low explosives; TNT preparation Engineering Chemistry · Chapter 7: Explosives - Asked in: 2073 Magh, 2+3 marks; 2070 Magh, 3+2 marks; 2068 Magh, 2+3 marks (asked 3 times) - 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/high-low-explosives-tnt - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-7 ## Question What are high explosives and low explosives? Write the preparation and uses of TNT. ## Short answer Low explosives deflagrate (burn rapidly) and are used as propellants (e.g., black powder). High explosives detonate with a shock wave, shattering effect, and need a detonator (e.g., TNT). TNT is prepared by stepwise nitration of toluene (from benzene + CH₃Cl/AlCl₃) with HNO₃/H₂SO₄; used in shells, bombs, mining. ## Answer #### Low explosives **Low explosives** burn rapidly (deflagrate) at a speed of a few metres per second to about 400 m/s, and the gas pressure pushes the material forward rather than shattering it. They are used as propellants and for slow blasting. Examples: black powder (gunpowder: KNO₃ + charcoal + S), smokeless powder, fireworks, safety fuse. Uses: firing bullets and shells, rocket propellant, quarrying soft rock, fireworks, safety fuses. #### High explosives **High explosives** detonate: the decomposition travels as a shock wave faster than about 1000 m/s (up to 9000 m/s) and has a strong shattering effect (brisance). They need a detonator to start them. - **Primary (initiating) explosives** are very sensitive and used in detonators: lead azide Pb(N₃)₂, mercury fulminate Hg(ONC)₂. - **Secondary explosives** are less sensitive and need a detonator: TNT, picric acid, RDX, PETN, dynamite, nitroglycerine (GTN). Uses: mining, blasting rocks, demolition, military shells and bombs. #### 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 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. What distinguishes a high explosive? A. It burns slowly at a few m/s B. It never needs a detonator C. It only produces smoke D. It detonates; the decomposition travels as a shock wave faster than about 1000 m/s with strong shattering effect Answer: D. High explosives detonate with brisance and need a detonator to start. (Key point: High explosive behaviour) 3. Which reagent mixture is used to nitrate toluene to make TNT, and what is the role of H2SO4? A. Dilute HNO3 + dilute H2SO4; H2SO4 acts as a reducing agent B. Conc. HNO3 + conc. H2SO4; H2SO4 is a dehydrating agent that helps give NO2+ C. Conc. HNO3 alone; H2SO4 is not needed D. Conc. HCl + conc. H2SO4; H2SO4 supplies the nitro group Answer: B. TNT is made by stepwise nitration of toluene with conc. HNO3 and conc. H2SO4; the sulfuric acid removes water and helps form NO2+. (Key point: Nitrating mixture) 4. Which is a use of TNT? A. Making soap and detergents B. Use as a propellant for slow burning in fireworks C. Filling shells, bombs and mines and for mining and demolition D. Use only as a detonator primary charge Answer: C. TNT is a secondary high explosive used in shells, bombs, mines, mining, quarrying and demolition. (Key point: Uses of TNT) ## Related in Engineering Chemistry - [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 - [High vs plastic explosives; TNT](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ahe-vs-plastic-tnt) — 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 - [Low explosives and uses; glycerol trinitrate](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alow-explosives-gtn) — Engineering Chemistry, chapter 7 - [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 ## Related in other subjects - [High level vs low level languages](https://www.bctengineer.com/question.md?key=semester_1%2Fcomputer_programming%3Ahigh-low-level-languages) — Computer Programming, chapter 1, asked 2× - [Low pass to high pass transformation](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Alowpass-to-highpass-transformation) — Filter Design, chapter 3, asked 2× - [RC low and high pass filters](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Afilter-lpf-hpf-transfer) — Basic Electronics Engineering, chapter 1 - [Ideal low pass and high pass filters](https://www.bctengineer.com/question.md?key=semester_4%2Fsignals_and_systems%3Afrequency-response-lp-hp-filters) — Signals and Systems, chapter 5