--- title: "High and plastic explosives; nitrocellulose, TNT [partly illegible]" subject: "Engineering Chemistry" chapter: 7 key: "semester_2/engineering_chemistry:nitrocellulose-tnt" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/nitrocellulose-tnt site: BCT Engineering --- # High and plastic explosives; nitrocellulose, TNT [partly illegible] Engineering Chemistry · Chapter 7: Explosives - Asked in: 2071 Magh - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/nitrocellulose-tnt - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-7 ## Question [?] high explosive and plastic explosive with examples. (a) [Nit]rocellulose and (b) TNT. ## Short answer High explosives detonate with shattering effect; primary (lead azide) initiate, secondary (TNT, RDX) are main charges. Plastic explosives (C-4, Semtex) are mouldable mixtures of high explosive and plasticiser. Nitrocellulose is prepared by nitrating cellulose with HNO₃/H₂SO₄; used in smokeless powder and cordite. TNT is made by stepwise nitration of toluene; used in shells, bombs, and mining. ## Answer **Reading:** the question is "Define/Differentiate high explosive and plastic explosive with examples. Give the preparation of (a) nitrocellulose and (b) TNT." #### High explosive **High explosives** detonate: the decomposition travels through the material as a shock wave at more than about 1000 m/s (up to about 9000 m/s) and has a strong shattering effect (brisance). - **Primary (initiating) explosives** are very sensitive and explode with a small spark or shock; they are used in detonators: lead azide Pb(N₃)₂, mercury fulminate Hg(ONC)₂. - **Secondary explosives** are less sensitive and need a detonator to set them off: TNT, picric acid, RDX, PETN, dynamite, nitroglycerine (GTN). Uses: mining, blasting rocks, demolition, military shells and bombs. #### Plastic explosive **Plastic explosives** are high explosives (such as RDX or PETN) mixed with a plasticiser (oil, wax, polymer) to form a putty-like mass that can be moulded by hand into any shape. They are safe to handle, stable, waterproof, and need a detonator. Examples: C-4 (about 91% RDX), Semtex, PE-4. #### (a) Nitrocellulose (guncotton) **Preparation:** cellulose (cotton) is nitrated with a mixture of conc. HNO₃ and conc. H₂SO₄ at about 30–40 °C for a few hours, then washed free of acid and dried. ```text [C₆H₇O₂(OH)₃]n + 3n HNO₃ --H₂SO₄--> [C₆H₇O₂(ONO₂)₃]n + 3n H₂O ``` **Properties:** white fibrous solid that looks like cotton; insoluble in water; burns rapidly and cleanly without ash; explodes when detonated or struck. The highly nitrated form (guncotton, ~13% N) is a high explosive; the less nitrated form (pyroxylin) is soluble in ether–alcohol. **Uses:** smokeless powder and cordite (with nitroglycerine), blasting gelatin, celluloid, lacquers and artificial leather, photographic film. #### (b) 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. What distinguishes a high explosive? A. It burns slowly at a few m/s B. It never needs a detonator C. It detonates; the decomposition travels as a shock wave faster than about 1000 m/s with strong shattering effect D. It only produces smoke Answer: C. High explosives detonate with brisance and need a detonator to start. (Key point: High explosive behaviour) 2. What is a plastic explosive? A. A high explosive (RDX/PETN) mixed with a plasticiser to form a putty-like mass that can be hand-moulded B. A low explosive made from plastics C. A liquid explosive absorbed in kieselguhr D. A primary explosive used in detonators Answer: A. Plastic explosives such as C-4 and Semtex are RDX/PETN with oil, wax or polymer, safe and mouldable. (Key point: Plastic explosive) 3. How is nitrocellulose prepared? A. Cotton is burnt in air B. Cotton is treated with dilute NaOH C. Cotton is reacted with CH3Cl and AlCl3 D. Cellulose (cotton) is nitrated with conc. HNO3 and conc. H2SO4 at about 30-40 C, then washed and dried Answer: D. Cellulose -OH groups are nitrated to -ONO2 using the nitrating mixture at 30-40 C. (Key point: Nitrocellulose prep) 4. 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 alone; H2SO4 is not needed C. Conc. HCl + conc. H2SO4; H2SO4 supplies the nitro group D. Conc. HNO3 + conc. H2SO4; H2SO4 is a dehydrating agent that helps give NO2+ Answer: D. TNT is made by stepwise nitration of toluene with conc. HNO3 and conc. H2SO4; the sulfuric acid removes water and helps form NO2+. 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