Can ketones form hemiacetals?
No, ketones do not form hemiacetals.
At one time, the term "hemiacetal" included both hemiacetals and hemiketals.
But the IUPAC has re-instituted the term "hemiketal" as a subclass of hemiacetals
Technically, an aldehyde forms a hemiacetal, and a ketone forms a hemiketal. You can remember this by realizing that both terms contain "ket".