In addition to a using a citation manager like Zotero to generate single citations for resources, you can also use citation generators in individual databases. This is very helpful when you are looking for something quick, on the fly, and not working with many resources. However, not all citation generators are able to convert into the ACS Style, or some do not offer a citation generator at all.
Zotero bib is an online citation generator that generates individual citations one at a time for individual articles free of charge. You can plug in the DOI, URL, or ISBN of a resource to generate the citation. They also have the ACS style in their offered list. Make sure you are selecting the proper citation format before using the generator.