16. Salts
Solubility of Salts
Precipitation - To form insoluble salt
Titration - Only for salts of K+, Na+ and NH4+.
Acid + Insoluble Base/Carbonate/Metal - Only for soluble salts
- All Group I and ammonium compounds are soluble.
- All nitrates are soluble.
- All chlorides are soluble, except AgCl, PbCl2
- All sulfates are soluble, except PbSO4, CaSO4, BaSO4
- All carbonates are insoluble, except Group I carbonates and ammonium carbonate
- All oxides and hydroxides of metals are insoluble, except Group I and ammonium compounds and Ca(OH)2 is slightly soluble.
Precipitation - To form insoluble salt
- Mix the two aqueous solutions of the reactants together.
- Filter the mixture to collect the residue (precipitate).
- Wash the precipitate with distilled water and dry with filter paper.
Titration - Only for salts of K+, Na+ and NH4+.
- Fill a burette with acid. Record the initial reading as V1 cm3.
- Pipette 25 cm3 of alkali and transfer solution into a conical flask.
- Add 2 drops of a suitable pH indicator.
- Add the acid from the burette into the conical flask until a colour change is seen. This indicates the end point.
- Record the final reading as V2 cm3.
- Repeat steps 1 and 2 without adding the pH indicator.
- Add (V2 – V1) cm3 of acid into the alkali.
- Heat the solution till saturated.
- Cool the saturated solution for crystals to form.
- Filter to collect the crystals as residue.
- Wash the crystals with cold distilled water.
- Dry with filter paper.
Acid + Insoluble Base/Carbonate/Metal - Only for soluble salts
- Add excess insoluble base/carbonate/metal to warm acid, with stirring, till no more solid can dissolve.
- Filter to remove excess insoluble base/carbonate/metal.
- Evaporate the filtrate to saturation.
- Cool the saturated solution for crystals to form.
- Filter the crystals, wash with cold distilled water and dry with filter paper.