I’ve just spotted a bug in biblatex-chem, and a fix is on the way to CTAN. It looks like changes in the biblatex core have made the comma after journal titles when using the chem-rsc style disappear. This was working earlier: I’ve retested an old version and it is not due to anything I’ve done.
On another matter, I’ve been asked to look at turning page ranges into single pages in biblatex-chem. I need to add the appropriate functions to biblatex, so there may be a delay (I have lots on at the moment). It is definitely on my list to do. Why do this? Well, some journals insist on first-page only, but in a database both pages will be present. So the code needs to handle things. There should be another update once I sort this: a few days.