The Solubility Rules
Introduction
What are solubility rules?
The solubility rules tell us whether a salt is soluble or insoluble.
- When a salt is added to a solvent (usually water), it can undergo different changes.
- The salt may dissolve completely OR
- The salt will not dissolve (a precipitate)
- These rules help us predict
Solubility Rules
Full Solubility Rules Table
| Soluble | Except When Combined With |
|---|---|
| All group 1 cations and | None |
| None | |
| Insoluble | Except When Combined With |
| All group 1 cations and | |
| All group 1, 2, and | |
| All group 1, | |
| All group 1, |
Soluble
| Soluble | Except When Combined With |
|---|---|
| All group 1 cations and | None |
| None | |
Contradicting Rules
If two rules contradict each other, the preceding rule is the one that is obsolete.
- All group 1 metal ions and ammonium ions are ALWAYS soluble.
- All nitrate salts are ALWAYS soluble.
- Salts containing chlorine ions, bromide ions, and iodine ions are soluble EXCEPT when combined with silver, lead, or mercury.
- Salts containing sulfate ions are soluble EXCEPT when combined with calcium, bariume, lead, or mercury sulfate.
Insoluble
| Insoluble | Except When Combined With |
|---|---|
| All group 1 cations and | |
| All group 1, 2, and | |
| All group 1, | |
| All group 1, |
Contradicting Rules
If two rules contradict each other, the preceding rule is the one that is obsolete.
- Carbonates and phosphates are ALWAYS insoluble. However, the contradicting rule of group 1 and ammonium being always soluble means that ==it can be soluble== under those circumstances.
- Sulphites are insoluble EXCEPT when combined with group 1, 2, and ammonium ions.
- Oxides are insoluble EXCEPT when combined with group 1, ammonium, barium, and calcium ions.
- The same applies with hydroxides.
Learning Solubility Rules
- Learning the solubility rules is not an easy task. It requires a commitment to memory and remembering these rules in long-term memory.
- Some tips you could use are …
- Knowing that lots of ions have the same exceptions.
- Creating acronyms for the rules, such as using “AABC” to remember hydroxides are insoluble with ammonium, all group 1, barium, and calcium.
Applying The Solubility Rules
- The solubility rules is applied when two ionic solutions create a chemical reaction, and the products require its solubility to be predicted.
- When these two ionic solutions react, it will either dissolve or make a precipitate (insoluble salt).
Example 1: Potassium Chloride and Silver Nitrate
Potassium Chloride and Silver Nitrate Equation
- In order to apply the solubility rules, you must look at the products first.
- We know that potassium is in our first product (
), which is a group 1 metal ion. This means that it is always soluble, meaning it will NOT be a precipitate. - However, silver chloride will not be soluble due to the solubility rules.
- We know that potassium is in our first product (