1. Chapter 9 Aqueous Solutions
Predicting Solubilities

2. Solubility Chemists express solubility (S) as:
mass of solute dissolved per 100 mL of water or
moles of solute per litre of solution

3. Solubility Generally, it is agreed that:
if solute has S > 0.1 mol/L, it is classified as SOLUBLE.
if solute has S < 0.01 mol/L, it is classified as INSOLUBLE.
if solute has S between 0.1 mol/L and mol/L, it is classified as PARTLY or SLIGHTLY SOLUBLE.
for our purposes, if S < 0.1 mol/L, it is classified as INSOLUBLE.

4. Solubility Rules …are determined experimentally.
…can be used as a guideline to predict solubility.
Use the solubility table on periodic table handout from class

5. Table 1: Solubility of Ionic Compounds at SATP
ANION
Cl-, Br-, I-
S2-
OH-
SO42-
CO32- PO43- SO32-
C2H3O2-
NO3-
ClO3- C A T
High Solubility
> 0.1 mol/L
(at SATP)
most
Group 1, NH4+,
Group 2
Sr2+, Ba2+, Tl+
Group 1, NH4+
all I O N
Low Solubility
< 0.1 mol/L
Ag+ Pb2+, Tl+, Hg22+ Cu+
Ag+ Pb2+ Ca2+ Ba2+
Sr2+
Ag+
none
Ca2+

6. Solubility Rules- Others?
See p334 Table 9.1
(5 rules, higher number takes priority)
See p336 Language Link !

7. Solubility Examples Is the compound Soluble (S) or Insoluble (I)?
PbCl2
KNO3
Li2CO3
Ans I S

8. Solubility Factors
Many, but not all ionic compounds, are soluble in water.
Why not all?
There are several factors:
1. Ion Charge
Compounds with higher ion charge tend to be insoluble because when the charge is inc., the force that holds ions together is inc.
e.g PO43- has large ion charge and is insoluble

9. Solubility Factors
2. Ion Size - When atoms gain e-, ion size is larger e.g. Cl + e-  Cl- (non-metals) - When atoms lose e-, ion size is smaller e.g. Na  Na+ + e- (metals)
larger
smaller

10. Solubility Factors 2. Ion Size - continued
Small ions bond more closely than large ions
∴cmpds with small ions are less soluble
If you compare ions in the same family in the periodic table, as you go down the family, ion size inc
∴ solubility inc.

11. Homework Textbook Read p330-331, 334 Do p335 #1-3 p336 #1-6
(See answers on p367)
BLM 9-1 and 9-4
(See answers on website)