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Ore Processing | Fire Assaying |
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Silt and clay in water are removed by coagulation with a flocculant. When this activity is used to model the collection of precious metals by the lead, the silt and clay particles represent the gold and silver atoms, while the flocculant represents the lead as it falls through the molten sample.
In the activity, the calcium oxide (lime, CaO) reacts with the water to make the solution basic as shown by the following reaction: CaO + H2O = Ca++ + 2OH-. The ammonium aluminum sulfate (ammonium alum, shortened to be just aluminum sulfate because the ammonium ion does not take part in the reaction) then reacts with the hydroxide to form the gelatinous hydroxide: Al(NH4)(SO4)2 in water yields aluminum ion in solution: Al+3 + NH4+ + 2SO4-2 . The aluminum ion reacts with the hydroxide: Al+3 + 3OH- = Al(OH)3, a gelatinous precipitate.
Skills: Observing, Recording, Investigating, Modeling
Time: 40 minutes
Audience: Teachers and students, grades 5 - 8.
Objective: To experiment with chemical and physical ways to clarify water.
Safety: Wear chemical splash goggles.
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Key Concepts |
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