The Foundations of Chemistry

TABLE 4-8 Solubility Guidelines for Common Ionic Compounds in Water

Generally Soluble Exceptions

Na
, K
, NH 4
compounds No common exceptions

fluorides (F) Insoluble: MgF 2 , CaF 2 , SrF 2 , BaF 2 , PbF 2
chlorides (Cl) Insoluble: AgCl, Hg 2 Cl 2
Soluble in hot water: PbCl 2
bromides (Br) Insoluble: AgBr, Hg 2 Br 2 , PbBr 2
Moderately soluble: HgBr 2
iodides (I) Insoluble: many heavy-metal iodides

sulfates (SO 42 ) Insoluble: BaSO 4 , PbSO 4 , HgSO 4
Moderately soluble: CaSO 4 , SrSO 4 , Ag 2 SO 4

nitrates (NO 3 ), nitrites (NO 2 ) Moderately soluble: AgNO 2
chlorates (ClO 3 ), Moderately soluble: KClO 4
perchlorates (ClO 4 )
acetates (CH 3 COO) Moderately soluble: AgCH 3 COO

Generally Insoluble Exceptions

sulfides (S^2 ) Soluble: those of NH 4
, Na
, K
, Mg^2
, Ca^2

oxides (O^2 ), hydroxides (OH) Soluble: Li 2 O, LiOH, Na 2 O, NaOH, K 2 O, KOH,
BaO, Ba(OH) 2
Moderately soluble: CaO, Ca(OH) 2 , SrO,
Sr(OH) 2

carbonates (CO 32 ), phosphates Soluble: those of NH 4
, Na
, K

(PO 43 ), arsenates (AsO 43 )

*Dissolves with evolution of heat and formation of hydroxides.

TABLE 4-9 Bonding, Solubility, Electrolyte Characteristics, and Predominant Forms of Solutes in Contact with Water

Acids Bases Salts

Strong Weak Strong Insoluble Weak Soluble Insoluble

acids acids bases bases bases salts salts

Examples HCl CH 3 COOH NaOH Mg(OH) 2 NH 3 KCl, NaNO 3 , BaSO 4 , AgCl,
HNO 3 HF Ca(OH) 2 Al(OH) 3 CH 3 NH 2 NH 4 Br Ca 3 (PO 4 ) 2
Pure compound ionic Molecular Molecular Ionic Ionic Molecular Ionic Ionic
or molecular?
Water-soluble or Soluble Soluble Soluble Insoluble Soluble† Soluble Insoluble
insoluble?

100% ionized or Yes No Yes (footnote‡)No Yes§ (footnote‡)
dissociated in dilute
aqueous solution?
Written in ionic Separate Molecules Separate Complete Molecules Separate ions Complete
equations as ions ions formulas formulas

*Most common inorganic acids and the low-molecular-weight organic acids (XCOOH) are water-soluble.
†The low-molecular-weight amines are water-soluble.
‡The very small concentrationsof “insoluble” metal hydroxides and insoluble salts in saturated aqueous solutions are nearly completely dissociated.
§There are a few exceptions. A few soluble salts are molecular (and not ionic) compounds.