Ask students to provide the observations. After a few minutes there will be considerable heated debate. See if you can then develop two charts such that the students find their results compatible with one or the other. The discussion can lead to ways in which scientists work out their differences. In this experiment all students receive what appear to be identical groups of chemicals.
Some students tend to disregard their observations and adopt the majority opinion.
This experiment can help to build a student's confidence in the reliability of their observations. Go to Top Makeup ans. 1-3 see presentation questions. All three students have different results. The tubes have not simply been mixed up because precipitates are observed in one that are not even present in the other.