5.7: Predicting Solubility Trends
The solubility of many simple ionic compounds can be predicted by applying the set of rules shown below.
- Salts of the alkali metal ions and the ammonium ion, Li + , Na + , K + , and NH 4 + are almost always soluble .
- Virtually all metal nitrates and metal acetates are soluble.
- Metal halides are generally soluble , except for salts of Ag + , Pb 2 + , Cu + and Hg + .
- Metal sulfates are generally soluble , except for salts of Ba 2 + , Pb 2 + and Ca 2 + .
- With exception of the alkali metal ions and ammonium ( Rule 1 ), the following salts are generally insoluble : metal carbonates (CO 3 2 - ), metal phosphates (PO 4 3 - ) and metal chromates (CrO 4 2 - ).
- Metal hydroxides and metal sulfides are generally insoluble , except for those covered by Rule 1 and Ca 2 + , Sr 2 + and Ba 2 + .
Applying these rules to the reaction between lead nitrate and potassium iodide, the reactants are both soluble (Rule 1 and Rule 2). In the products, potassium nitrate will be soluble (Rule 2) and lead iodide will be insoluble , based on Rule 3.
Mixing each of the following salt solutions results in the formation of a precipate. In each case, identify the insoluble salt.
- NaCl + Pb(NO 3 ) 2
- Fe(C 2 H 3 O 2 ) 3 + KOH
- Ca(NO 3 ) 2 + K 2 SO 4
- Li 2 S + CuSO 4
- Co(C 2 H 3 O 2 ) 2 + LiOH
For each of the ionic compounds given below, determine whether or not the compound will be soluble in water, according to the trends given above.
- AgNO 3 ☐ soluble ☐ insoluble
- MgCl 2 ☐ soluble ☐ insoluble
- Na 2 SO 4 ☐ soluble ☐ insoluble
- AgCl ☐ soluble ☐ insoluble
- Ba(NO 3 ) 2 ☐ soluble ☐ insoluble
- PbI 2 ☐ soluble ☐ insoluble
- Mg(NO 3 ) 2 ☐ soluble ☐ insoluble
- BaSO 4 ☐ soluble ☐ insoluble
- FeCl 3 ☐ soluble ☐ insoluble
- Pb(CH 3 COO) 2 ☐ soluble ☐ insoluble