Dissolution and Precipitation Notes

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Glossary

Dissolution: The process of a solute dissolving in a solvent to form a solution.
Precipitation: The process where a solid forms and separates from a solution.
Ionisation: The process by which an atom or molecule gains or loses electrons to form ions.
Dissociation: The process by which an ionic compound separates into its individual ions when it dissolves in a solvent.
Cation: A positively charged atom (i.e. has lost an electron)
Anion: A negatively charged atom (i.e. has gained an electron)

Dissolution

Dissolution is the process of a solute dissolving in a solvent to form a solution.
In our case, dissolution usually happens with a salt.

Salt (+ water) -> Cation + Anion

The water is left out of the product because dissolving is not a chemical reaction, it is a physical change.

E.g.

$$NaC{l}_{(s)}\to N{a}_{(aq)}^{+}+C{l}_{(aq)}^{-}$$ $$MgC{l}_{2(s)}\to M{g}_{(aq)}^{2+}+2C{l}_{(aq)}^{-}$$

That’s right, you still have to balance the equation.

Precipitation

In a precipitation reaction, tow soluble salts react to form an insoluble salt and a soluble salt. The insoluble salt is called the precipitate.
A solubility table is used to predict which salts will form a precipitate and which will not.

My favourite solubility table (where X means insoluble):

Another solubility table:

To solve a precipitation reaction, first swap ions to get products, then apply solubility rules and balance the equation. The order to swap ions is: AB + CD -> AD + CB.

Example
Lithium Carbonate + Calcium Nitrate -> Lithium Nitrate + Calcium Carbonate
$L{i}_{2}C{O}_{3(aq)}+Ca(N{O}_3{)}_{2(aq)}\to LiN{O}_{3(aq)}+CaC{O}_{3(s)}$
Note that the precipitate has been placed last in the equation, but it can be placed as the first product if desired (like in many textbooks).