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Procedure to Analyze Solubility

Solubility tests can identify different components and substances contained in an unknown compound. Generally, a technician only needs a small amount of the test substance for solubility tests. Solubility analysis also determines whether the substance to be tested is a weak acid, a strong base, a neutral compound or a strong acid. There are several methods and procedures to analyze solubility, depending on the elements contained on the unknown compound.

Water
- Water soluble compounds have several characteristics: they possess not more than four carbons, they have polar groups of nitrogen, oxygen and sulfur, and are frequently water soluble. Low molecular weight or C4 compounds have these qualities, making them highly soluble in water. Those having five or six carbons can either be insoluble or be of borderline solubility. Technically, the greater the branching, the greater the water solubility and the lower the melting and boiling points, in contrast to straight chain substances.
Hydrochloric Acid
- A solution of 5 percent hydrochloric acid readily dissolves amines in a compound, forming hydrochloride salt that is also soluble in aqueous or watery medium. This happens because of a reduction in the base composition of hydrochloric acid, which fails to dissolve some amines belonging to the di- and tri-aryl groups, and other high molecular weight compounds.
Sodium Hydroxide or Sodium Bicarbonate
- Strong acids readily dissolve in a weak base like 5 percent NaHCO3 (sodium bicarbonate). A strong base like NaOH (sodium hydroxide) will react to dissolve both weak and strong acids. Comparing the reaction of the test substance to these two compounds will help determine whether the substance is either a strong acid or a weak one. Generally, carboxylic acids, which are strong acids, are soluble in both NaOH and NaHCO3. Phenols or weak acids only readily dissolve in NaOH.
Concentrated H2SO4/ H3PO4
- Cold, concentrated sulfuric acid (H2SO4) dissolves many compounds quite readily: alcohols, aldehydes, alkenes, alkynes, amides, esters, nitroaromatics and ketones. This occurs because of two factors: sulfuric acid has high ionizing properties and strong acidity. Further testing should be done as a consequence to distinguish the composition of the test substance. Extremely weak bases and inert compounds (alkyl halides, many simple aromatics and alkanes) fail to dissolve in sulfuric acid.
  Phosphoric acid (H3PO4) is a relatively weaker ionizing solvent than sulfuric acid, although it still is able to dissolve aldehydes, alcohols and esters, but not aromatics, alkynes and alkenes.

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