16. Salts

Solubility of 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.
  

Next: Ammonia