The aim of this study was to investigate the effect of Problem-Based Learning (PBL) on undergraduate students' learning about solutions and their physical properties, and on their scientific processing skills. The quasi experimental study was carried out through non-equivalent control and comparison groups pre-post test design. The data were collected through both quantitative and qualitative means. The sample group of the study was 84 freshmen who took the General Chemistry-II course, in two separate classrooms from the Department of Primary Science Education at a school of education in a state university established in the eastern Anatolia region of Turkey, during the spring semester in the 2010 academic year. The study was implemented over five weeks. Quantitative data were collected through an academic achievement test, a scientific processing skill test, and specific scales developed for PBL. In addition, qualitative data were collected through interviews. Pre-test data was analyzed by independent samples t-test, post-test data was analyzed through ANCOVA (Analysis of Covariance). Qualitative data was analysed in a descriptive manner and presented in tables. The findings of the study revealed that PBL is more effective than conventional instruction in improving students' learning and scientific processing skills. In addition, it was also revealed that PBL increased students' levels of accessing and using knowledge, working in a group and cooperating, autonomous learning and problem solving skills. However, it was also revealed that PBL has disadvantages, such as difficulties in assessing the skills gained through PBL, students' difficulties in getting used to the PBL, difficulty in setting up heterogenous groups and overcoming problems encountered during establishment of cooperation in the groups, dealing with competition between the students, and limited time. (Contains 19 tables.)