Teach students about chemical formulas, balanced chemical equations, and mole ratios with this unique “continuous variation” demonstration. Mix two solutions in various proportions and measure the volume of precipitate that forms in each mixture. Why do different ratios of liquids produce different amounts of precipitate? Which ratio will give the most precipitate? There's a simple answer but a powerful lesson—the maximum amount of precipitate will form when the ratio of the two solutions corresponds to the optimum mole ratio for the reactants. Chemicals are provided for two series of reactions, copper(II) chloride with trisodium phosphate and iron(III) nitrate with sodium hydroxide. Bright colorful solutions produce contrasting color precipitates that stand out and are easy to see. Teacher Demonstration Notes included. Enough materials are included to perform the demonstration seven times.
Concepts: Stoichiometry, mole ratio, double replacement reaction, solubility rules.
Time Required: 30 minutes
Chemicals Provided: Copper(II) chloride solution, iron(III) nitrate solution, sodium hydroxide solution, trisodium phosphate solution.
Flinn Catalog/Reference Manual Page 405
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