Practical work 2: experimental problems on alkali metals and calcium
In practical work 2 you first make a plan for each problem: which reagent detects which ion and what is observed. For example, four numbered test tubes hold NaCl, Na₂SO₄, Na₂CO₃ and NaOH solutions: phenolphthalein turns NaOH and Na₂CO₃ crimson; adding acid to those two, gas shows Na₂CO₃ (CO₃²⁻ + 2H⁺ → H₂O + CO₂↑); of the other two, BaCl₂ gives white BaSO₄ with Na₂SO₄ (Ba²⁺ + SO₄²⁻ → BaSO₄↓) and AgNO₃ gives white AgCl with NaCl. KOH and Ca(OH)₂ solutions are separated with CO₂ or Na₂CO₃: Ca(OH)₂ turns cloudy (CaCO₃↓), KOH does not. For the chain Ca(OH)₂ → CaCO₃ → Ca(HCO₃)₂ → CaCO₃ → CaCl₂: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O; CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂; Ca(HCO₃)₂ → CaCO₃↓ + CO₂ + H₂O (on heating); CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑. Write every equation in molecular, full ionic and net ionic form. All experiments are done with the teacher, in goggles and gloves, with small amounts of reagents; if alkali or acid gets on you, rinse at once with plenty of water and tell the teacher. Barium salts are poisonous, so never put them near the mouth.
Report: for each problem make a table with columns “Problem”, “Plan”, “Observation”, “Equation (molecular / full ionic / net ionic)”, “Conclusion”. Write the plan in your notebook first; the experiment is done only after the teacher approves it. Working with reagents at home is forbidden.