We present the results of a study designed to provide insight into interactive simulation use during guided-inquiry activities in chemistry classes. The PhET Interactive Simulations project at the University of Colorado develops interactive simulations that utilize implicit--rather than explicit--scaffolding to support student learning through exploration and experimentation. In the study, 80 students in a General Chemistry class were given ten minutes to explore the PhET simulation "Molecule Polarity" in self-selected groups, with no instructions on how to interact with the simulation. Using mouse click data, audio recordings and clicker question responses, we investigated: students' ability to use the simulation by analyzing the extent to which they explored the simulation, the discussions students engaged in during simulation use, and student perceptions of simulation use. We found effective simulation use, with the 22 groups exploring an average of 18 of the 23 available features in "Molecule Polarity." Sixty-four percent of student utterances were part of on-topic (polarity) discussion segments, with most off-topic discussions being intermittent and brief. Students largely found the simulation useful for their learning and experienced either brief or no frustration during sim exploration. These results indicate that students in large classes can use interactive simulations designed with implicit scaffolding through exploration, and can do so without frustration overwhelming the perception of value brought by the simulation use. This work suggests that implicitly scaffolded interactive simulations can provide environments that support guided-inquiry learning and channel students into productive inquiry while minimizing the need for explicit guidance.