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Solubility is the process of a solute dissolving in a solvent. Water is the universal solvent, meaning it can dissolve most substances. Of course, the golden rule of solubility is “like dissolves like,” meaning that polar solvents will dissolve polar solutes and nonpolar solvents will dissolve nonpolar solutes. Sometimes, water does not dissolve a substance as much as another solvent can.

When trying to determine if a precipitate will form from two aqueous solutions, how exactly can we do that? Well the simple answer to this question is to memorize the solubility rules that follow. Why memorize these long boring rules? Solubility is an important part of chemistry. Say you want to find the equilibrium concentrations of a certain reaction. Since solids and liquids are not a part of the equilibrium expression, a large error will occur in your calculations if you cannot tell what is a solid and what is not. So this is one of the basic essentials you need to know. Therefore, remember these well. It will only do you good.

Soluble Substances With Some Exceptions

All 1A cations and substances containing the ammonium ion (NH4+) – Always soluble

Nitrates (NO3) – Always soluble

Chlorates (ClO3) – Always soluble

Perchlorates (ClO4) – Always soluble

Sulfates (SO42-) – Always soluble, with the exceptions of when it is combined with the cations Ca2+, Sr2+, Ba2+, Hg22+, Pb2+, or Ag+

Acetates (C2H3O2) – Always soluble

Chlorides (Cl) – Always soluble, with the exceptions of when it is combined with the cations Hg22+, Pb2+, or Ag+

Bromides (Br) – Always soluble, with the exceptions of when it is combined with the cations Hg22+, Pb2+, or Ag+

Iodides (I) – Always soluble, with the exceptions of when it is combined with the cations Hg22+, Pb2+, or Ag+

Fluorides (F) – Always soluble, with the exceptions of when it is combined with the cations Ca2+, Ba2+, Mg2+, Sr2+, or Pb2+

Insoluble Substances With Some Exceptions

Carbonates (CO32-) – Always insoluble, with the exceptions of when it is combined with a 1A cation or the ammonium ion (NH4+)

Oxides (O2-) – Always insoluble, with the exceptions of when it is combined with a 1A cation or the ammonium ion (NH4+)

Phosphates (PO43-) – Always insoluble, with the exceptions of when it is combined with a 1A cation or the ammonium ion (NH4+)

Hydroxides (OH) – Always insoluble, with the exceptions of when it is combined with a 1A cation, the ammonium ion (NH4+), Ba2+, Sr2+, or Ca2+

Sulfides (S2-) – Always insoluble, with the exceptions of when it is combined with a 1A cation, a 2A cation, or the ammonium ion (NH4+)

And those are your solubility rules. When trying to remember which of the hydroxides are soluble, it is simply remembering all the strong bases or vise versa. Now that you know these rules, it will be much easier to proceed with the rest of solubility and precipitation reactions. Have fun.

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