7.3 Preparation of Salts
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14. Outline the general guidelines for the solubility of common salts in water.
| Salt Group | Solubility Rule |
|---|---|
| Sodium, Potassium, Ammonium | All are soluble |
| Nitrates | All are soluble |
| Chlorides | All are soluble except silver chloride (AgCl) and lead(II) chloride (PbCl2) |
| Sulfates | All are soluble except barium sulfate (BaSO4), calcium sulfate (CaSO4), and lead(II) sulfate (PbSO2) |
| Carbonates | All are insoluble except sodium, potassium, and ammonium carbonates |
| Hydroxides | All are insoluble except sodium, potassium, ammonium, and calcium hydroxide (partially soluble) |
15. How do you prepare a clean, dry sample of an insoluble salt from two soluble starting materials?
By precipitation.
Mix the two soluble salt solutions together to form a precipitate. Filter the mixture to isolate the insoluble residue. Wash the residue thoroughly with distilled water to remove spectator ions, then leave the filter paper in a warm setting to dry.
Mix the two soluble salt solutions together to form a precipitate. Filter the mixture to isolate the insoluble residue. Wash the residue thoroughly with distilled water to remove spectator ions, then leave the filter paper in a warm setting to dry.
16. How do you prepare a soluble salt by reacting an acid with an insoluble substance?
Add the excess insoluble reactant (metal, metal oxide, or carbonate) directly into the warm acid until no more dissolves. Filter the solution to remove unreacted solids. Heat the filtrate until saturated, then allow it to cool slowly to cause crystallization. Filter the crystal structures, wash with dynamic chilled distilled water, and pat dry.
17. Why is an excess of the insoluble substance added when preparing soluble salts?
To ensure that all of the acid reactant is fully consumed, preventing the final crystal yield from being contaminated with unreacted acid solutions.
18. How do you prepare a soluble salt when starting with a soluble base/alkali?
By performing an acid-base titration. Use an indicator to locate the precise neutralization endpoint volume. Repeat the procedure without using the colored chemical indicator using the exact volume matched, then evaporate and crystallize the salt solution cleanly.