Predicting Solubility with Solubility Rules

1
Predicting Solubility with Solubility Rules

• Solubility and solution concentrations are
  usually expressed in units of mol/L
• Different compounds have different solubility
• Generally if a solute has a solubility of greater
  than 0.1 M in a particular solvent, it is
  classified as soluble in that solvent
• If it is less than 0.1 M, then the solute is
  insoluble (forms a precipitate) in that solvent
• Through experimentation, a set of qualitative
  solubility rules have been determined

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Solubility Rules
Rule No. Rule statement summary
1 Hydrogen, ammonium and group l ions form soluble compounds with all negative ions
1
2 Acetate and nitrate ions form soluble compounds with all positive ions
2
All compounds soluble
Ions of group l (Li, Na, K, etc.), NH4 and
H
All compounds soluble
CH3COO-, NO3-
3
3 Sulfide ions form soluble compounds only with ions listed in rule 1 and with group ll cations
3
3
4 Chloride, bromide and iodide ions form compounds that have low solubility with silver, lead (ll), mercury (l) copper (l) and thallium positive ions only
4
S-2 with Mg2, Ca2, Sr2, Ba2, Ra2 and ions
in group l
Soluble compounds
S-2 with all other positive ions
Forms precipitates
Forms precipitates
Cl-, Br- and I- with Ag, Pb2, Cu1, Tl
4
5 Sulfate ions forms compounds that have low solubility with calcium, strontium, barium, radim and lead (ll) positive ions Sulfate ions forms compounds that have low solubility with calcium, strontium, barium, radim and lead (ll) positive ions
5
6 Hydroxide ion form compounds that are soluble with those listed in rule 1 and strontium, barium, radium and thallium Hydroxide ion form compounds that are soluble with those listed in rule 1 and strontium, barium, radium and thallium
6
6
SO42- with Ca2, Sr2, Ba2, Ra2, Pb2
Forms precipitates
OH- with Sr2, Ba2, Ra2, Tl and ions in rule 1
Soluble compounds
OH- with all other positive ions
Forms precipitates
5
7 Phosphate, carbonate and sulfite ions form compounds that have low solubility with all positive ions except those listed in rule 1 Phosphate, carbonate and sulfite ions form compounds that have low solubility with all positive ions except those listed in rule 1
7
7

• PO4-3, CO3-2, SO3-2 with positive
• ions in rule 1

Soluble compounds
PO4-3, CO3-2, SO3-2 with all other positive ions
Forms precipitates