I used JCE Classroom Activity #111 in my chemistry classes today. (Subscription to JCE required.) What a great way to help students make the connection between number of ions present, the charges of the ions and the neutral compound formula.
This activity is used as a reinforcement activity following my use of JCE Classroom Activity #113: An Interlocking Building Block Activity in Writing Formulas of Ionic Compounds. It could be used as a stand alone activity to support writing ionic formulas and names.