Practical work 3: experimental problems on metals
Practical work 3 solves three kinds of problems on metals. The first: identify NaOH, CaCO₃, Al₂(SO₄)₃ and FeCl₃ in four numbered test tubes. Plan: CaCO₃ is a white powder insoluble in water; FeCl₃ is a yellow-brown solution; the other two (NaOH and Al₂(SO₄)₃) are separated with phenolphthalein (NaOH turns crimson) or by adding them to each other: Al₂(SO₄)₃ + 6NaOH → 2Al(OH)₃↓ + 3Na₂SO₄, and the precipitate dissolves in excess NaOH. Confirmation: FeCl₃ + 3NaOH → Fe(OH)₃↓ + 3NaCl (brown precipitate). The second: make CuO from a soluble copper salt, for example CuSO₄ + 2NaOH → Cu(OH)₂↓ + Na₂SO₄, then Cu(OH)₂ → CuO + H₂O (on heating). The third: prepare ZnCl₂ in several ways: Zn + 2HCl → ZnCl₂ + H₂↑; ZnO + 2HCl → ZnCl₂ + H₂O; Zn(OH)₂ + 2HCl → ZnCl₂ + 2H₂O; ZnCO₃ + 2HCl → ZnCl₂ + H₂O + CO₂↑; Zn + CuCl₂ → ZnCl₂ + Cu. Every experiment is planned first and done only after the teacher's permission, in goggles and gloves, with small amounts of reagents; when heating, point the mouth of the test tube away from yourself and others; if acid or alkali gets on you, rinse with plenty of water and tell the teacher. The report has, for each experiment, the plan, observation, equation and conclusion.
Fill in the report table: “Problem”, “Plan”, “Observation”, “Equation (molecular / net ionic)”, “Conclusion”. Write the plan in your notebook and work only after the teacher approves it; do not work with reagents at home.