In the equation FeOH^2+ (aq) + HPO^2-4 (aq) ↔ FeOH (HPO4) (s), what does the left side represent?

The left side of the equation represents the reactants in the chemical reaction. In any chemical equation, the reactants are the substances that undergo a change to form new substances, which are known as products. In this case, Fe(OH)₂⁺ (aq) and HPO₄²⁻ (aq) are the reactants that combine to form the product, Fe(OH)(HPO₄) (s).

The aqueous notation (aq) indicates that the reactants are in solution, and their combination results in the formation of a solid product, which is represented by the (s) notation. This solid product indicates a precipitate formed when the two reactants react in solution. Understanding this helps to frame the concept of a chemical reaction, where the left side always details the starting materials that participate in the reaction, leading to the formation of new substances on the right.