According to Wikipedia, in Europe the semantic distinction between the rational science of chimia and the occult alchimia arose in the early 18th century. So it seems like there was a need to separate these terms with the advancement of scientific practices and the term chemistry (with the Arabic article "al-" dropped) came to refer to the scientific practice while alchemy came to refer to the older non-scientific practice.
Turkish language in 19th century followed a different path by shifting the meaning of a completely different esoteric practice, sīmiya1 (letter magic), to be used in place of esoteric/old chemistry and by keeping the word kīmiya as the scientific/modern chemistry.
I am wondering if similar semantic changes/shifts happened in Arabic and Farsi languages, but could not find any information since I do not speak/read these languages and the online sources I found regarding the etymology of the word mostly focus on European languages.
1 "Sīmiya" (derived from Ancient Greek sema σήμα: "sign", "symbol") is etymologically unrelated to "kīmiya" (either derived from the ancient Egyptian khem/khm, meaning "blackness" or derived from the Greek χημεία, meaning "cast together").