HSC Chemistry 1 Initial Notes

Part IV Chemistry — First Paper 74

Chapter 25 Safe Use of the Laboratory 25.1 Key Concepts & Theoretical Foundations Chemistry is an experimental science, and the laboratory is where theory is tested. Safety is therefore the first competence a chemist must master: it protects the worker, the apparatus and the validity of the result. Hazard classification (GHS) Every chemical is labelled with pictograms of the Globally Harmonised System: corrosive (attacks skin/metal), flammable, toxic, oxidising (feeds fire), explosive, harmful/irritant, health hazard and environmental hazard. The accompanying Material Safety Data Sheet (MSDS) lists properties, handling, storage, first aid and disposal, and must be read before an experiment. The exothermic-dilution rule Dissolving a strong acid in water releases large heat. If water is poured onto concentrated acid, the first drops boil and spit acid. Therefore always add acid to water, slowly and with stirring, so the large heat capacity of water absorbs the heat safely. Storage of reactive substances. Alkali metals (Na, K) are stored under kerosene because they react violently with moisture and air; white phosphorus is stored under water; oxidisers are kept away from fuels; volati

HSC 2027 Science — Teacher’s Guide 76 25.2 Master Reaction & Data Sheet Master Formula Sheet (a) Neutralising spills HCl + NaHCO3 −→NaCl + H2O + CO2 ↑ H2SO4 + 2NaHCO3 −→Na2SO4 + 2H2O + 2CO2 ↑ NaOH + CH3COOH −→CH3COONa + H2O (b) Dangerous mixtures to AVOID NaOCl + 2HCl −→NaCl + Cl2 ↑+H2O (bleach + acid →toxic Cl2) 2Na + 2H2O −→2NaOH + H2 ↑ (violent, flammable H2) (c) Confirmatory tests for common gases H2 : lit splint →squeaky “pop”, O2 : glowing splint relights CO2 : Ca(OH)2 + CO2 −→CaCO3 ↓+H2O, NH3 : moist red litmus →blue Cl2 : bleaches moist litmus, SO2 : turns K2Cr2O7 green H2S : blackens lead-acetate paper, HCl : white fumes with NH3 (d) Concentration relations M = nsolute Vsoln(L), N = M × (n-factor), C1V1 = C2V2, ppm = msolute(mg) Vsoln(L) Drying agents: CaCl2, conc. H2SO4, P2O5, silica gel. 25.3 Tables, Diagrams & Visual Layouts Hazard Example Store Precaution Corrosive H2SO4, NaOH acid cabinet gloves; acid→water Flammable ethanol, ether fireproof, cool no flame/spark Toxic Cl2, HCN ventilated fume hood Oxidiser KMnO4, KNO3 away from fuel no organics nearby Water-reactive Na, K under kerosene keep dry Fire class Fuel Correct extinguisher A wood, paper water, foam B oils, so