Writing ionic equations in chemistry

1. How to write ionic
equations
SOLUBILITY LAB

2. How does a salt dissolve in water?
 The reactant (left side of the equation) is a solid salt such as calcium chloride
CaCl2
 The products (right side of the equation) are ions, now separated from each other
because they are dissolved in water.
Ca2+ and 2 Cl-
Make sure you show the correct charges on the ions!
When a compound dissolves,
you get a homogeneous
mixture

3. Write the chemical equation for the
dissolution
CaCl2 (s) → Ca2+
(aq) + 2 Cl-
(aq)
 (s) means that the compound is in solid form.
 (aq) means that the ions are dissolved in water (aqueous form)
 Make sure the equation is balanced! There are 2 Cl ions in the formula on
the left, so there must be 2 ions on the right.

4. What about polyatomic ions?
 Polyatomics need to stay together.
 Start by reviewing the chart on p. 149. You will be using several of these ions!
Potassium nitrate
 Nitrate is a polyatomic, so use the formula NO3
-. Do not write N and O as separate
ions!
KNO3 (s) → K+
(aq) + NO3
-
(aq)

5. Precipitation reactions
 In this week’s experiment you will be looking for combinations of ions that are not
soluble, so they will result in solids that don’t dissolve in water.
 Example: silver chloride is not soluble, so if a silver solution and chloride solution
were mixed, a solid would form:
Ag+
(aq) + Cl-
(aq) → AgCl (s)
 Do you see that this is the reverse of a dissolution equation?
 The solid would be called a precipitate in this reaction.

6. Beautiful chemistry!
 Check out this video with an up-close (and slightly weird in the case of copper)
view of precipitation reactions
 https://www.youtube.com/watch?v=BGUfC3UUBkI