A Level Chemistry OCR Practice Exam

What is the function of spectator ions in a solution?

1. They change the pH

2. They drive the reaction forward

3. They balance the charge

4. They remain unchanged during the reaction

The correct answer is: They remain unchanged during the reaction

Spectator ions are ions that do not participate directly in the chemical reaction but are present in the solution. Their primary role is to maintain electrical neutrality in the solution, balancing the charge without undergoing any chemical change. Because they remain unchanged during the reaction, they can be found in the same form on both the reactant and product sides of a reaction equation. For instance, in a precipitation reaction, the barium ions and nitrate ions in solution may dissociate and recombine, while the sodium ions and chloride ions remain as spectator ions, maintaining total charge balance. Their presence allows the reaction to proceed without altering the overall number of ions or the solution's composition apart from the formation of the precipitate. This function distinguishes spectator ions from other species in the reaction that actively participate in the formation of products or changes in the solution’s properties, which is why they are characterized as "spectators."