Addresses AP® Chemistry Big Idea 1 and Learning Objective 1.19. Determine the identity of 2 unknown Group I metal carbonates using gravimetric analysis. Can be taught using either a guided or an inquiry activity. In the guided activity, students precipitate the carbonates with excess calcium ions. After drying, the mass and moles of the resulting calcium carbonate are determined. From that data, they calculate the formula mass of the unknown Group I metal carbonate and identify the Group I metal.