Insoluble salts are primarily prepared using the precipitation method, also known as a double decomposition reaction. This involves mixing two soluble salts in aqueous solution. These soluble salts react, forming a new insoluble salt that precipitates out of the solution, leaving a soluble salt behind. The insoluble salt can then be separated through filtration.
The Precipitation Method: A Step-by-Step Guide
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Choosing Reactants: Select two soluble salts that, when reacted, will produce your desired insoluble salt as one of the products. Solubility rules are crucial for this step. You can find comprehensive tables of solubility rules online or in chemistry textbooks.
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Mixing Solutions: Carefully mix the aqueous solutions of the two soluble salts. The reaction will occur spontaneously upon mixing. You will observe the formation of a solid precipitate.
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Filtration: Separate the solid precipitate (your insoluble salt) from the remaining soluble salt solution by filtration. Use filter paper to capture the solid, allowing the liquid to pass through.
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Washing and Drying: Wash the collected solid on the filter paper with distilled water to remove any residual soluble salts. Then, dry the solid to obtain your pure insoluble salt.
Examples:
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Preparing Lead(II) iodide (PbI₂): Mix solutions of lead(II) nitrate (Pb(NO₃)₂) and potassium iodide (KI). Lead(II) iodide is the insoluble precipitate. The soluble byproduct is potassium nitrate (KNO₃).
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Preparing Silver Chloride (AgCl): Mix solutions of silver nitrate (AgNO₃) and sodium chloride (NaCl). Silver chloride is the insoluble precipitate, and sodium nitrate (NaNO₃) remains dissolved.
Other Considerations:
While the precipitation method is the most common, other methods might be used depending on the specific salt. However, the precipitation method offers a straightforward and effective way to synthesize various insoluble salts in a laboratory setting.
Several resources confirm this method, including TutorChase, Study.com, SaveMyExams, and the Royal Society of Chemistry (rsc.org). These sources consistently highlight precipitation as the primary method for preparing insoluble salts.
