In an action research study, 66 students from Year 11 in an Australian school were shown the colour of methyl violet indicator in some hydrochloric acid solutions, and then in an acetic acid solution. The intent was to create a cognitive conflict, resolution of which would lead to an understanding of the concept weak acid. Student learning emanating from the demonstration was evaluated by written answers to the following: 'Describe the demonstration', 'What was the aim of the demonstration?', 'Explain the observations', and 'What do you think you have learned?' Some students were also interviewed. Learning outcomes were disappointing, not because of failure to resolve the intended conflict, but because of failure to attend to the key features of the demonstration and failure to realize a conflict. Some interesting cases of unintended, and undesirable, learning occurred. The role of the teacher was a focus of this study, and recommendations to improve the conduct of cognitive conflict demonstrations were implemented in follow-up years, and improved learning outcomes resulted.