This paper describes 11th grade students’ understanding about the concept of precipitation reaction as the final part of the learning of solubility and solubility product chapter. Precipitation reaction is an important reaction in industry, pharmacy, and daily life. In the learning process, students are asked to predict the formation of precipitation based on their understanding of solubility and solubility product concept. Thirty eleventh grade students in one of the best senior high school in Padang were chosen as the subject of this study. Classroom learning process was observed and recorded. Data of students’ understanding were collected through a set of essay problems which was validated through expert judgment, and then integrated in students’ end-of-chapter test. Through qualitative analysis, this study revealed some mistakes and misconceptions that students have regarding the application of precipitation reaction concept, and possible sources of them. Recommendations for improving
the quality of learning this concept in the future are provided at the end of the paper.