This paper presents an analysis of the scientific reasoning of a dyad of secondary school students about the phenomenon of dissolution of gases in water as they work on this in a simulated laboratory experiment. A web-based virtual laboratory was developed to provide learners with the opportunity to examine the influence of physical factors on gas solubility in water. An evaluation process involving 180 students revealed that the concepts connected to the dissolution of gas in water caused problems for the students even after having experimented with the virtual laboratory. To investigate the nature of learners' reasoning about the visualised events, 13 video-recorded groups of learners were analysed. This study follows the reasoning of one group that displayed a possibly productive way of solving the problem. The results address the students' general difficulty of discovering something that they are conceptually unprepared for within the virtual laboratory. The analysis shows how the students eventually found a way out of their dilemma by making an analogy with other dissolving processes. In effect, the analysis elucidates some of the analytical work that had to be done by the participants when collaboratively negotiating a shared meaning of a scientific concept in concord with a given task and set of instructional materials. Implications for design might be to provide the learning material with explicit hints that enable students to connect to specific phenomena related to the one investigated concept. The findings show the usefulness of video analytic research, informed by CA and ethnomethodology. This analytical framework can support design processes and provide useful information, which might identify hurdles to learning a scientific concept by simulated events and pathways to overcome these hurdles.