[ELI5] Chemical Precipitation


[ELI5] Chemical Precipitation

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Some salts are more soluble in water than others. If a reaction occurs which creates a low-soluble salt, it will “precipitate” into a solid which will fall out of solution and sit on the bottom of the container.

The classic case is silver chloride (AgCl) which has very low solubility in water.

In one container, you can dissolve silver nitrate (AgNO3) in water. The silver cations and nitrate ions will separate… each one surrounded by water molecules.

In another container, you can dissolve sodium chloride (NaCl) in water. The sodium cations and chloride anions separate… each one surrounded by water molecules.

Now, if you mix the above two containers, it won’t stay dissolved. Every time silver and chloride come together, they will form a solid that does not redissolve and it will “fall out of solution” or precipitate. The remaining sodium and nitrate ions will remain dissolved in the water.

A reaction of two (or more) substances that are soluble in a solution occurs. A product of the reaction isn’t soluble and precipitates out as a solid, either floating or sinking to the bottom depending on density.