Chemical Equations Involving Ions

Guided Instructional Activity                          Unit 6: Chemical Reactions and Stoichiometry
GIA 6-3: Ionic Equations                                                                             NAME:_________________

In reactions involving aqueous ionic compounds, the dissolved ionic compounds break into their respective ions and float around in the solution independent of each other but in the ratio according to their chemical formula.  For example, the following balanced equation: Na₂SO₄(aq) + Pb(NO₃)₂(aq) à 2NaNO₃(aq) + PbSO₄(s) would actually have Na₂SO₄(aq) exist as Na⁺ and SO₄^2- ions floating around separately but in a 2 Na⁺ : 1 SO₄^2- ratio.  When aqueous ionic equations are written out with the ions separated the equation is called the “Total Ionic Equation.”  For example note how the (aq) compounds are split up

     2Na⁺(aq) + SO₄^2-(aq) + Pb²⁺(aq) + 2NO₃^- (aq) à 2Na⁺(aq) + 2NO₃^- (aq) + PbSO₄(s)

Notice that PbSO₄(s) is not split up into ions.  Can you think why this is the case?

In the total ionic equation, notice that there are two ions that are exactly in the same state and with the same charge on both sides of the arrow.  These are the Na⁺(aq) and NO₃^-(aq) ions.  Since these ions don’t change in the course of the reaction, they are called “spectator ions.”  In the “Net Ionic Equation” the spectator ions are removed and only the components of the rxn that change remain.  Ex:  SO₄^2-(aq) + Pb²⁺(aq) à PbSO₄(s)

Exercise:  For the following reactions, balance the equations, write the total ionic equation, circle the spectator ions and write the net ionic equation.

1.      KBr(aq) +     F₂(g) à     KF(aq) +     Br₂(l)

2.      Zn(s) +     HCl(aq) à     ZnCl₂(aq) +     H₂(g)

3.      FeCl₃(aq) +     Na₂CO₃(aq) à     Fe₂(CO₃)₃(s) +     NaCl(aq)

4.      CaCl₂(aq) +     Na₃PO₄(aq) à     NaCl(aq) +     Ca₃(PO₄)₂(s)

5.      Al(s) +    CuCl₂(aq) à     AlCl₃(aq) +     Cu(s)

Questions:

1. What types of reactions have net ionic equations?
2. List the ions that were consistently spectator ions.  Looking at your solubility table (the red sheet), what do you notice about these ions?
3. Look back at your balanced net ionic equations.  Check to see that they are still balanced in terms of number and types of atoms.  Also notice that they are balanced in terms of charge!  Formulate a rule for identifying whether a net ionic equation is balanced or not.