Practical work 2. Experimental problems on “Sulfur”
In this practical work problems on sulfuric acid, sulfates and sulfides are solved. To identify sulfuric acid BaCl₂ is used: H₂SO₄ + BaCl₂ → BaSO₄↓ + 2HCl, a white precipitate insoluble in acid. With zinc dilute H₂SO₄ gives hydrogen: Zn + H₂SO₄ → ZnSO₄ + H₂; concentrated acid acts as an oxidizing agent and gives SO₂ (poisonous), so this experiment is shown only by the teacher in a fume cupboard. To tell apart three tubes containing CaCl₂, Na₂S and K₂SO₄, use AgNO₃ (white precipitate with CaCl₂), BaCl₂ (white precipitate with K₂SO₄) and a lead salt (black PbS with Na₂S). Acid is never added to Na₂S: poisonous H₂S would escape. To make AlCl₃ from Al₂(SO₄)₃ add BaCl₂: Al₂(SO₄)₃ + 3BaCl₂ → 3BaSO₄↓ + 2AlCl₃, then filter off the precipitate. All work is done in goggles, gloves and an apron, under the teacher’s supervision, in small amounts; barium and lead salts are poisonous, nothing is smelled or tasted, and waste is collected in a special vessel.
“Experiment plan”: for each problem make a table: aim — reagent — expected result — equation — hazard. The teacher (or a video) shows the experiment and you record it. At the end: which reaction gives a poisonous gas, and why is it done only in a fume cupboard?