The net ionic equation is:
6 OH⁻(aq) + 6 H⁺(aq) ⇒ 6 H₂O (l)
Explanation:
First it is convenient to determine the cation and the anion in each compound. Cations are the positive ions of a compound and are usually metals. Anions are the negative ions of a compound and are nonmetals.For that it is important to recognize polyatomic ions in a reaction. Polyatomic ions are charged molecules that bind so strongly that they cannot disassociate during chemical reactions. In other words, polyatomic ions are groups of two or more atoms that are chemically linked. These have a specific load and do not separate into individual components. Polyatomic ions can have both positive and negative charges. Some of the most common polyatomic ions are CO₃²⁻, NO₃⁻, NO₂⁻, SO₄²⁻, SO₃²⁻, ClO₃⁻, PO₄³⁻ and OH⁻.
Then you must make sure that the initial equation is completely balanced. To balance an equation, you must add coefficients in front of the compounds to match the amount of atoms of each element on both sides of the equation.
In this case, the final balanced equation after balancing is:
3 Ca(OH)₂(aq) + 2 H₃PO₄(aq) ⇒ 6 H₂O(l) + Ca₃(PO₄)₂(s)
When a species or compound dissociates, it separates into its positive (cation) and negative (anion) components. These will be the components that are balanced at the end for the net ionic equation.
Given that strong acids such as H₃PO₄ and strong bases such as Ca(OH)₂ are completely dissociated, in addition to everything previously mentioned related to polyatomic ions, the net ionic equation will be:
3 Ca⁺² (aq) + 6 OH⁻(aq) + 6 H⁺(aq) + 2 PO₄⁻³(aq) ⇒ 6 H₂O (l)+3 Ca⁺² (aq) + 2 PO₄⁻³ (aq)
In this case it was taken into account that the coefficients located in front of each molecule indicate the amount of each molecule for the reaction and that the subscripts next to each atom or ion is the number of atoms or ions in the equation. By multiplying the coefficient mentioned by the subscript, you get the amount of each element or ion present in the reaction.
The spectator ions are those that are present on both sides of the reaction and are not changed by the reaction, that is, they are present in exactly the same amount on both sides of the equation. In this way, they can be canceled from both sides of the reaction. The spectator ions in this case are PO₄³⁻(aq) and Ca²⁺(aq).
This leaves you with the net ionic equation:
6 OH⁻(aq) + 6 H⁺(aq) ⇒ 6 H₂O (l)
