What is the theory behind solubility test to identify particular ions? 

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jerichorayel eNotes educator| Certified Educator

Solubility is defined as the property of any substance (solid, liquid, or gas) to dissolve in any solvent in order to form a homogenous solution of the solute in the solvent. 

Generally, we use the solubility test in order to determine the characteristic of the unknown substance. The first rule is the term "like dissolves like" where in polar or ionic substances most likely will be dissolved in polar solvents such as water. Non-polar solutes on the other hand can be dissolved in non-polar solvents such as hexane. 

Now, to determine the particular ions to be dissolved, there are some methods that are usually imposed.

  • Some ions when dissolved give color in the solution. This can be a parameter in determination of possible ion contents. 
  • There is list for the water solubility test available in the internet to specify what type of compounds can be dissolved by water. For example, carbonates of all metals are insoluble in water except the carbonates of Na+, K+ and NH4+.
  • Addition of sof certain reagent to precipitate the unknown ions. Examples of which are solutions of NaOH, NH3. AgNO3 and H2SO4.