Laboratory sessions

Laboratory sessions connect the theory of the year with experiment. The list: 1) preparing zinc hydroxide and its reaction with acid and alkali (amphoteric nature): ZnCl₂ + 2NaOH → Zn(OH)₂↓ + 2NaCl; Zn(OH)₂ + 2HCl → ZnCl₂ + 2H₂O; the precipitate dissolves in excess alkali, while copper(II) hydroxide is not amphoteric; 2) building ball-and-stick models of the crystal lattices of KCl, sulfur and iodine; 3) qualitative reactions of HCl, NaCl, NaBr and NaI with AgNO₃ (white, pale yellow, yellow precipitate) and detecting iodine with starch; 4) detecting chloride ions in a soil solution; 5) halogens displacing one another; 6) dissolving iodine in water and in an organic solvent; 7) getting to know samples of sulfur and its natural compounds; 8) detecting the sulfate ion in various solutions with BaCl₂; 9) preparing ammonia from an ammonium salt and studying its properties; 10) getting to know samples of mineral fertilizers. All work is done under the teacher’s guidance, in goggles, gloves and apron, in small amounts; only the teacher works with chlorine or bromine water, ammonia and acids; nothing is smelled or tasted; if a solution spills, rinse with plenty of water and tell the teacher. Benzene causes cancer, so we do not use it here: the teacher chooses the solvent. Only session 2 (models) can also be done at home with simple materials (plasticine, sticks); the samples in sessions 7 and 10 are looked at only at school, when the teacher shows them.