Solubility Rules

Precipitation Reactions

If you’re not part of the solution

You’re part of the precipitate

Types of reactions

• Single Replacement

• Double Replacement

• Synthesis

• Decomposition

• Combustion

• NEW-Precipitation

Precipitation Reaction

• Reaction where two soluble salts react to form an insoluble salt.

• Reaction looks like a double replacement reaction.

Solubility Rules

• Some ions always form water soluble compounds.

• Other ions always form water insoluble compounds

• The rest are sometimes water soluble and sometimes insoluble

Always Soluble

• The following ions are always soluble, no matter what the other ion is.– Group IA (Li, Na…)

– Ammonium (NH4+)

– Nitrates (NO3-)

– Chlorates (ClO3-)

– Acetates (C2H3O2-)

Almost always soluble

• Halides (Cl, Br…)– Except for fluorides

– Except for silver, mercury(I) and lead

• Sulfates– Except for barium, calcium, lead,

mercury(I)

Mostly insoluble

• Hydroxide (OH-)– Except for barium, strontium and

calcium (these ARE soluble along with the always soluble ions)

• Sulfides, carbonates, chromates, and phosphates.

Soluble salts

• Soluble salts are broken into their ions when in solution.

• This means that if two soluble salts are mixed and only soluble salts can be produced, THERE WILL BE NO REACTION

What this means…

• For precipitation reactions, the insoluble salts are the ones to look for.

• When looking for a possible precipitate, cross out any ions that are always soluble

Example

• AgNO3(aq) + NaCl(aq)-> ?

– (aq) means the salts are both soluble.– Cross out the always soluble ions– Can the remaining ions be combined to make

an insoluble salt?– AgCl is insoluble– So there is a reaction.

Halides are mostly soluble except for silver, lead, and mercury

Another example

• LiNO3(aq) + FeCl(aq)-> ?

– Again, both are dissolved in water– Cross out the always soluble– The iron(I) nitrate will be soluble and lithium

chloride will be soluble.– Since no insoluble salt can be formed, NO

REACTION

Yet another

• CuSO4(aq) + BaCl2(aq)-> ?• Cross out the always soluble• Oops, nothing is always soluble.• Look for anything that is mostly insoluble.• Look for anything that can cause it to be

insoluble• There will be a reaction• The precipitate will be barium sulfate

Sulfates are mostly soluble except for barium, lead, mercury and calcium