Acid-base reactions and the concept of pH are critical concepts in chemistry, environmental sciences and Earth science. First, students will present hypotheses of whether the pH will increase or decrease when calcite or pyrite are dissolved in water. Second, in a facilitated activity, students (in groups) will dissolve pyrite and calcite in water and measure the pH after the minerals dissolve. Third, they will hypothesize what happens to the pH when they mix the pyrite and calcite together (in water). Fourth, they will then test their hypotheses by mixing them and measuring pH. Fifth they will discuss if their results support their hypotheses. Last, they will expand what they learned in the experiments to how minerals can be used in water treatment.