Solubility Rules
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1SOLUBILITY RULES
A SUMMARY OF SOLUBILITIES
RULE
EXCEPTIONS
1. Nitrates and acetates are generally
No common ones. Silver acetate, mercurous acetate,
soluble.
and lead acetate are moderately soluble.
2. compounds of the alkali metals and the
No common ones.
ammonium ion are generally soluble.
1+
2+
2+
3. Chlorides, bromides, and iodides are
The halides of Ag
, Hg
, and Pb
; also HgI
, BiOCl,
2
2
generally soluble.
and SbOCl.
4. Sulfates are generally soluble.
PbSO
, SrSO
, and BaSO
are insoluble.
4
4
4
CaSO
, Hg
SO
, and Ag
SO
are moderately soluble.
4
2
4
2
4
The corresponding bisulfates are more soluble.
5. Carbonates, chromates, phosphates,
Those of the alkali metals and ammonium ion are
and sulfites are generally insoluble.
soluble. Many acid phosphates are soluble, i.e.,
Mg(H
PO
)
and Ca(H
PO
)
.
2
4
2
2
4
2
6. Sulfides are generally insoluble.
Those of the alkali metals and ammonium ion are
soluble. The alkaline earth metals are soluble. Cr
S
2
3
and Al
S
decompose and precipitate as hydroxides.
2
3
7. Hydroxides are generally insoluble.
Those of the alkali metals and ammonium ion are
soluble. The hydroxides of Ba, Sr, and Ca are
moderately soluble, i.e., Ca(OH)
@20°C = 0.02M
2
(Consider theses strong electrolytes in water.) The
hydroxide of Mg is only very lightly soluble, i.e.
Mg(OH)
@20°C = 0.0002M (Consider this an
2
insoluble substance.)
8. Almost all ionic compounds containing
-
-
-
-
-
NO
, ClO
, ClO
, ClO
, and ClO
are
2
4
3
2
soluble.
9. All inorganic acids are soluble.
Solubility of organic acids is variable.
SOLUTIONS MADE FROM THE ABOVE SPECIES, WHEN SOLUBLE, ARE FOUND
TO EXIST AS CHARGED PARTICLES AND THUS CONDUCT ELECTRIC CURRENT.
SUMMARY OF STRONG AND WEAK ELECTROLYTES
RULE
EXCEPTIONS
1. Most acids are weak electrolytes
Common strong acids (strong electrolytes) are HCl,
HBr, HI, HNO
, H
SO
, HClO
, and HClO
3
2
4
3
4
2. Most bases are weak electrolytes
Strong base hydroxides (strong electrolytes) are
those of Li, Na, K, Rb, Ca, Sr, and Ba.
3. Most soluble salts are strong
Important weakly ionized salts are HgCl
, Hg(CN)
,
2
2
electrolytes.
CdCl
, CdBr
, CdI
, and Pb(C
H
O
)
.
2
2
2
2
3
2
2
WHEN A SPECIES IS LISTED AS A STRONG ELECTROLYTE, WRITE IT IN IONIZED
FORM IN AQUEOUS SOLUTIONS. WEAK ELECTROLYTES ARE WRITTEN IN
MOLECULAR FORM IN AQUEOUS SOLUTIONS.
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