--- title: "Low and high explosives; GTN preparation" subject: "Engineering Chemistry" chapter: 7 key: "semester_2/engineering_chemistry:high-low-gtn" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/high-low-gtn site: BCT Engineering --- # Low and high explosives; GTN preparation Engineering Chemistry · Chapter 7: Explosives - Asked in: 2072 Magh, 2+3 marks; 2069 Poush, 3+2 marks (asked 2 times) - Video: [Lec-40_Preparation and uses of explosives | Chemistry I | First Year Engineering](https://www.youtube.com/watch?v=TEl1VnSeOHk) — FIRST YEAR ENGINEERING_LJIET - 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-gtn - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-7 ## Question Give an account of low and high explosives. Write the preparation and applications of GTN. ## Short answer Low explosives deflagrate, used as propellants. High explosives detonate (>1000 m/s) with shattering effect, needing a detonator. GTN (nitroglycerine) is made by nitrating glycerol with HNO₃/H₂SO₄ below 15°C; used in dynamite, cordite, blasting, and as a vasodilator. ## 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 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, as higher temperatures can cause 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. - Dilute form is 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. What distinguishes a high explosive? A. It burns slowly at a few m/s B. It detonates; the decomposition travels as a shock wave faster than about 1000 m/s with strong shattering effect C. It never needs a detonator D. It only produces smoke Answer: B. High explosives detonate with brisance and need a detonator to start. (Key point: High 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 - [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× - [Explosive characteristics; GTN and TNT; applications](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aexplosive-characteristics-gtn-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 vs plastic explosives; TNT](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ahe-vs-plastic-tnt) — Engineering Chemistry, chapter 7 - [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 - [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 ## Related in other subjects - [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× - [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× - [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