Definition and meaning of Insoluble Compound in chemistry.
Solubility is actually a sliding scale rather than an absolute yes or no property. Chemists usually call a compound insoluble if less than 0.1 grams dissolves in 100 milliliters of water. For an ionic compound, this insolubility depends entirely on a battle between two competing energy forces.
The first force is lattice energy, which holds the solid ionic crystal tightly together. The second force is hydration energy, which is released when water molecules surround the broken ions. An ionic compound becomes insoluble when its lattice energy is much stronger than its hydration energy.
The liquid water molecules simply cannot pull with enough force to break the solid crystal apart. Students can predict whether a compound will dissolve by memorizing a standard set of solubility rules. Chemists can also measure this physical property exactly using a number called the solubility product constant.
This constant is written as Ksp in standard textbooks and reference tables. A very tiny Ksp value always indicates a highly insoluble or sparingly soluble salt.
ExampleBarium sulfate is a classic example of a highly insoluble ionic compound in water. If you mix dissolved barium ions and sulfate ions together, they instantly form a thick white solid. This extreme low solubility makes barium sulfate very useful in the modern medical field. Doctors give patients a thick barium sulfate drink before taking an X-ray of their stomach. The heavy barium atoms coat the digestive tract to block X-rays and create a clear picture. Because it is completely insoluble, the toxic barium safely passes through the body without entering the blood.
Is any chemical compound completely 100 percent insoluble?
No. Every chemical compound dissolves to some tiny, measurable extent in a liquid. The word insoluble just means the dissolved amount is too small to matter for practical chemistry purposes.
How can you quickly predict if a compound is insoluble?
Students usually memorize a simple list of solubility rules for common ionic compounds. For example, most salts containing sodium or nitrate will dissolve, but most carbonates or sulfides will not.
Why do two clear liquids sometimes make an insoluble compound when mixed?
The mixed liquids might contain different floating ions that strongly attract each other. When these specific ions crash together, they form a new solid crystal that falls out of the solution.
