Do 90% of all German Chemistry graduates start a PhD?
According to the German Chemical Society, apparently 90% of master's recipients in chemistry do start doctoral studies afterwards.

Partly this is because PhD "admission" is largely not an admissions process at all in Germany. Individual faculty members who receive grants can hire master's recipients as "Wissenschaftliche Mitarbeiter" (literally "scientific worker," but "research assistant" is a better translation). They can do this without recourse to going through a department-level admissions process, and can skip outside advertising altogether if they have an internal candidate they can appoint instead. And, since many students follow the rule of "Was der Bauer nicht kennt, isst er nicht"—"What the farmer doesn't know, he doesn't eat"), many students do their entire education at one school.

So yes, it's much easier to get a PhD position if you're already in Germany.