The document summarizes a study on the influence of problem-based learning (PBL) and worksheets on student achievement in learning about buffer solutions in chemistry. The study found that: 1) Students who learned about buffer solutions using PBL and worksheets performed better on post-tests compared to students who learned via conventional teaching methods. 2) PBL with worksheets was more effective at improving students' cognitive skills like application and analysis of buffer solution concepts. 3) Students in the PBL group achieved a 77.93% improvement in learning outcomes, higher than the 63.85% improvement of students in the conventional teaching group.