As per literature, a compound is said to be slightly soluble when one part of the compound is soluble in approximately 1,000 to 10,000 parts of the solvent. The compound considered is soluble to the extent - 1 g in 1,000 to 5,000 mL of methanol giving a clear colored solution after filtration to remove undissolved solute.
A substance like potassium carbonate is said to be very soluble in water because many of its crystals have to be added to the water before no more will dissolve. When some of the crystals remain on the base of the container and will not dissolve even after a lapse of time, the solution is said to be saturated.
In contrast, a saturated solution of a substance like calcium hydroxide (slaked lime) is obtained after only a few lumps are added to the water. Calcium hydroxide is, therefore, only slightly soluble in water.
The maximum amount of a solute that can dissolve in a solvent at a specified temperature and pressure is its solubility.
Solubility is often expressed as the mass of solute per volume (g/L) or mass of solute per mass of solvent (g/g), or as the moles of solute per volume (mol/L).
Even for very soluble substances, however, there is usually a limit to how much solute can dissolve in a given quantity of solvent. In general, the solubility of a substance depends on not only the energetic factors we have discussed but also the temperature and, for gases, the pressure.
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