The reaction of a ketone and an aldehyde in aqueous Na[subscript 2]CO[subscript 2] is described. This experiment is performed in the absence of strong bases or organic solvents and offers the opportunity for students to observe the critical role that reaction temperature and base strength have in determining the product of the base-mediated addition of a ketone to an aldehyde. When the reaction takes place at room temperature, the aldol addition product is produced. But, when the reaction is heated to 50 [degree]C, the aldol condensation product is isolated. Both reactions use the same quantities of reagents. The reaction temperature is the factor that determines which product is formed. When NaOH is used in place of Na[subscript 2]CO[subscript 2], the aldol condensation product is isolated regardless of temperature. (Contains 1 figure/scheme.)