Solubility Rules

The terms soluble and insoluble are relative terms.

soluble soluble insoluble

solute

Solubility:the maximum amount of solute needed to make a

saturated solution, under given conditions.

Basis Solubility Rules1. All ionic compounds containing Group 1 elements,

H+ and ammonium ion are soluble.2. All ionic compounds with Group VII elements

(other than F) and metals are soluble, except those of Ag+, Hg+1, and Pb+2.

3. All acetates and nitrates are soluble.4. All sulfates are soluble except those of Ba+, Sr+2,

Pb+2, Ca+2, Ag+, Hg+1.

5. Carbonates, hydroxides, oxides, sulfides, phosphates, chromates and dichromates are soluble; ONLY when bonded with those in rule 1.

Using the Solubility rules:1. Predict whether a solute will dissolve in water.2. Predict when a ppt will form during a reaction.

NaCl(aq) + KBr(aq)

NaCl (s) Na+ (aq) + Cl- (aq)

KBr (s) K+ (aq) + Br - (aq)

NaBr(aq) + KCl(aq)

Precipitation reactions:The formation of an ionic compound that is not soluble in the current solvent.

Spectator ions - do not participate, remain moving freely in solution.

Indicate if any of the product form a precipitate (ppt).

KOH (aq) + AgNO3 (aq)

Calcium nitrate + sodium carbonate

KNO3 (aq) + AgOH (aq)

Ca(NO3)2 + Na2CO3 CaCO3 + NaNO3

ppt

ppt2

Indicate if any of the product form a precipitate (ppt).

Na2SO4 (aq) + KCl (aq)

Iron (III) chloride + lead (II) nitrate

2 NaCl (aq) + K2SO4 (aq) 2

FeCl3 + Pb(NO3)2 3 2 Fe(NO3)3 + 3 PbCl2 2ppt

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

The complete ionic equation shows all ions in their dissociated form.

Ag+(aq) + NO3

−(aq) + Na+

(aq) + Cl−(aq) → AgCl(s) + Na+

(aq) + NO3−

(aq)

The net ionic equation shows the actual reaction that occurs – no spectators:

Ag+(aq) + Cl−

(aq) → AgCl(s)

Spectator ions

Write the molecular equation and the net ionic equation for the reaction between aqueous lead (II) nitrate and aqueous potassium iodide.

Pb(NO3)2(aq) + 2 KI(aq) → PbI2(s) + 2 KNO3(aq)

Pb2+(aq) + 2 I−

(aq) → PbI2(s)

Spectator ions

K+ NO3−